Northeast Fisheries Science Center Reference Document 03-09
Stock
Assessment of Summer Flounder for 2003
by Mark Terceiro
National Marine Fisheries Serv., Woods Hole Lab., 166 Water St., Woods
Hole, MA 02543
Print
publication date August 2003;
web version posted August 7, 2003
Citation: Terceiro, M. 2003. Stock assessment of summer flounder for 2003. Northeast Fish. Sci. Cent. Ref. Doc.
03-09; 179 p.
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SUMMARY
This assessment of the summer flounder (Paralichthys
dentatus) stock along the Atlantic coast (Maine to North Carolina)
is an update through 2002/2003 of commercial and recreational fishery
catch data, research survey indices of abundance, and the analyses
of the data. For 2002, commercial and recreational fishery quotas
were 6,612 mt and 4,408 mt, respectively, for a total of 11,020 mt.
The reported commercial landings used in this assessment for 2002
were 6,407 mt, while estimated recreational landings were 3,610 mt,
for a 2002 landings total of 10,017 mt.
An analytical assessment (virtual population analysis,
VPA) of commercial and recreational total catch at age (landings plus
discards) was conducted. Indices of recruitment and stock abundance
were developed from Northeast Fisheries Science Center winter, spring
and autumn, Massachusetts spring and autumn, Rhode Island annual, Connecticut
spring and autumn, New Jersey annual, and Delaware annual trawl survey
data. Recruitment indices were also developed from young-of-year surveys
conducted by the states of North Carolina, Virginia, and Maryland.
The stock assessment indicates that the summer flounder
stock is not overfished and overfishing is not occurring relative to
the current biological
reference points. The fishing mortality rate has declined from 1.32 in
1994 to 0.23 in 2002, below the overfishing definition reference point
(Fthreshold = Ftarget = Fmax = 0.26).
There is an 80% chance that the 2002 F was between 0.21 and 0.28. The
estimate of F for 2002 may understate the actual fishing mortality; retrospective
analysis shows that the current assessment method tends to underestimate
recent fishing mortality rates (e.g., by about 40% over the last three
years). Total stock biomass has increased substantially since 1989, and
on January 1, 2003 was estimated to be 56,100 mt, 5% above the biomass
threshold of 53,200 mt. There is an 80% chance that total stock biomass
in 2003 was between 51,000 and 63,000 mt.
Spawning stock biomass (SSB; Age 0+) declined 72% from 1983 to 1989
(18,800 mt to 5,200 mt), but has increased eight-fold, with improved
recruitment and decreased fishing mortality, to 42,200 mt in 2002. Retrospective
analysis shows a tendency to slightly overestimate the SSB in the most
recent years. The arithmetic average recruitment from 1982 to 2002 is
40 million fish at age 0, with a median of 35 million fish. The 2002
year class is currently estimated to be about average at 38 million fish.
There is no consistent retrospective pattern in the estimation of the
abundance of age 0 fish over the last three years. If the landings for
2003 do not exceed the Total Allowable Landings (TAL) and the proportion
of catch discarded does not increase, the TAL in 2004 would need to be
12,790 mt (28.2 million lbs) to meet the target F rate of Fmax =
0.26 with 50% probability.
INTRODUCTION
The Stock Assessment Workshop (SAW) Southern Demersal Working Group met
on June 9, 2003 to assess the status of summer flounder. The following
scientists and managers participated in the meeting:
Paul Caruso -- MADMF
Sarah McLaughlin -- NOAA Fisheries NERO
Chris Moore -- MAFMC
Paul Nitschke -- NOAA Fisheries NEFSC
David Simpson -- CTDEP
Mark Terceiro (Chair) -- NOAA Fisheries NEFSC
Although they were unable to attend the meeting, Najih Lazar of the
RIDFW, Anne Mooney of the NYDEC, Don Byrne of the NJFGW, Stew Michels
of the DEDFW, Steve Doctor of the MDDNR, Chris Bonzak of the Virginia
Institute of Marine Science (VIMS), Rob O'Reilly of the VMRC, and Carter
Watterson of the NCDMF provided research survey and/or fisheries catch
data that were used in the assessment.
The following terms of reference were addressed for summer flounder:
1. Characterize the commercial and recreational catch including landings
and discards.
2. Estimate fishing mortality, spawning stock biomass, and total stock biomass
for the current year and characterize the uncertainty of those estimates.
3. Where appropriate, estimate a TAC and/or TAL based on stock status and target
mortality rate for the year following the terminal assessment year.
4. Provide short term projections (2-3 years) of stock status based on the
target fishing mortality rate.
For assessment purposes, the previous definition of Wilk et al.
(1980) of a unit stock extending from Cape Hatteras north to New England
has been accepted in this and previous assessments (e.g., NEFSC 2002).
The joint Mid-Atlantic Fishery Management Council (MAFMC) Atlantic States
Marine Fisheries Commission (ASMFC) Fishery Management Plan (FMP) for
summer flounder has as a management unit all summer flounder from the
southern border of North Carolina, northeast to the U.S.-Canadian border.
A recent summer flounder genetics study, which revealed no population
subdivision at Cape Hatteras (Jones and Quattro, 1999), is consistent
with the definition of the management unit. A recent consideration of
summer flounder stock structure incorporating new tagging data concluded
that evidence supported the existence of stocks north and south of Cape
Hatteras, with the stock north of Cape Hatteras possibly composed of two
distinct spawning aggregations, off New Jersey and Virginia-North Carolina
(Kraus and Musick, 2003). The conclusions of Kraus and Musick (2003) are
consistent with the current assessment stock unit.
Amendment 1 to the FMP in 1990 established the overfishing definition
for summer flounder as the fishing mortality rate equal to Fmax,
initially estimated as 0.23 (NEFC 1990). Amendment 2 in1992 set
target fishing mortality rates for summer flounder for 1993-1995 (F =
0.53) and 1996 and beyond (Fmax = 0.23). Major regulations
enacted under Amendment 2 to meet those fishing mortality rate targets
included: 1) an annual fishery landings quota, with 60% allocated to the
commercial fishery and 40% to the recreational fishery, based on the historical
(1980-1989) division of landings, with the commercial allocation further
distributed among the states based on their share of commercial landings
during 1980-1989; 2) commercial minimum landed fish size limit at 13 in
(33 cm), as established in the original FMP; 3) a minimum mesh size of
5.5 in (140 mm) diamond or 6.0 in (152 mm) square for commercial vessels
using otter trawls that possess 100 lb (45 kg) or more of summer flounder,
with exemptions for the flynet fishery and vessels fishing in an exempted
area off southern New England (the Northeast Exemption Area) during 1
November to 30 April; 4) permit requirements for the sale and purchase
of summer flounder; and 5) annually adjustable regulations for the recreational
fishery, including seasons, a 14 in (36 cm) minimum landed fish size,
and possession limits.
Amendment 3 to the FMP revised the western boundary of the Northeast
Exemption Area to 72°30'W (west of Hudson Canyon), increased the large
mesh net possession threshold to 200 lbs during 1 November to 30 April,
and stipulated that only 100 lbs could be retained before using a large
mesh net during 1 May to 31 October. Amendment 4 adjusted Connecticut's
commercial landings of summer flounder and revised the state-specific
shares of the commercial quota accordingly. Amendment 5 allowed states
to transfer or combine the commercial quota. Amendment 6 allowed multiple
nets on board commercial fishing vessels if properly stowed, and changed
the deadline for publication of overall catch limits and annual commercial
management measures to 15 October and the recreational management measures
to 15 February.
The results of previous assessments indicated that summer flounder abundance
was not increasing as rapidly as projected when Amendment 2 regulations
were implemented. In anticipation of the need to drastically reduce fishery
quotas in 1996 to meet the management target of Fmax , the
MAFMC and ASMFC modified the fishing mortality rate reduction schedule
in 1995 to allow for more stable landings from year to year while slowing
the rate of stock rebuilding. Amendment 7 to the FMP set target fishing
mortality rates of 0.41 for 1996 and 0.30 for 1997, with a target of Fmax
= 0.23 for 1998 and beyond. Total landings were to be capped at 8,400
mt (18.51 million lbs) in 1996-1997, unless a higher quota in those years
provided a realized F of 0.23.
Amendment 12 in 1999 defined overfishing for summer flounder to occur
when the fishing mortality rate exceeds the threshold fishing mortality
rate of FMSY. Since FMSY could not be reliably estimated
for summer flounder, Fmax = 0.24 was used as a proxy for FMSY,
and was also defined as the target fishing mortality rate. The stock was
defined to be overfished when the total stock biomass falls below the
minimum biomass threshold of one-half of the biomass target, BMSY.
Because BMSY could not be reliably estimated, the biomass target
was defined as the product of total biomass per recruit and contemporary
(1982-1996) median recruitment, estimated to be 153,350 mt (338 million
lbs), with the biomass threshold defined as 76,650 mt (169 million lbs).
In the 1999 stock assessment (Terceiro 1999), these reference points were
updated using estimates of median recruitment (1982-1998) and mean weights
at age (1997-1998), providing a biomass target of 106,444 mt (235 million
lbs) and biomass threshold of 53,222 mt (118 million lbs). The Terceiro
(1999) reference points were retained in the 2000 and 2001 stock assessments
(NEFSC 2000, MAFMC 2001a) because of the stability of the input data.
Concurrent with the development of the 2001 assessment, the MAFMC and
ASMFC convened the ASMFC Summer Flounder Overfishing Definition Review
Committee to review the reference points. The work of the Committee was
reviewed by the MAFMC Scientific and Statistical Committee (SSC) in August
2001. The SSC recommended that the FMSY proxy of Fmax
= 0.26 remain for 2002, and endorsed the recommendation of SARC 31 (NEFSC
2000) which stated that "...the use of Fmax as a proxy for
FMSY should be reconsidered as more information on the dynamics
of growth in relation to biomass and the shape of the stock recruitment
function become available (MAFMC 2001b).
The most recent previous stock assessment completed in 2002 (SARC 35;
NEFSC 2002) found that the summer flounder stock was overfished and overfishing
was occurring relative to the current biological reference points. The
fishing mortality rate had declined from 1.32 in 1994 to 0.27 in 2001,
marginally above the overfishing definition reference point (Fthreshold
= Ftarget = Fmax = 0.26). Total stock biomass in
2001 was estimated to be 42,900 mt, 19% below the biomass threshold (53,200
mt). In the review of the 2002 stock assessment, SARC 35 concluded that
updating the biological reference points was not warranted at that time
(NEFSC 2002).
FISHERY DATA
Commercial Fishery Landings
Total U.S. commercial landings of summer flounder from
Maine to North Carolina peaked in 1979 at nearly 18,000 mt (40 million
lbs, Table 1). The reported landings in 2002 of 6,407
mt (about 14.1 million lbs) were about 3% under the 2002 quota of 6,612
mt (14.6 million lbs). Since 1980, 70% of the commercial landings of summer
flounder have come from the Exclusive Economic Zone (EEZ; greater than
3 miles from shore). The percentage of landings attributable to the EEZ
was lowest in 1983 and 1990 at 63% and was highest in 1989 at 77%. Large
variability in summer flounder landings exist among the states, over time,
and the percent of total summer flounder landings taken from the EEZ has
varied widely among the states.
Northeast Region (Maine to Virginia)
Annual commercial landings data for summer flounder in years prior to
1994 were obtained from trip-level detailed landings records contained
in master data files maintained by the NEFSC (the weighout system; 1963-1993)
and from summary reports of the Bureau of Commercial Fisheries and its
predecessor the U.S. Fish Commission (1940-1962). Beginning in 1994, landings
estimates were derived from mandatory dealer reports under the current
NMFS Northeast Region (NER) summer flounder quota monitoring system.
Prior to 1994, summer flounder commercial landings were
allocated to NEFSC 3-digit statistical area according to interview data
(Burns et al. 1983). During 1994-2002, dealer landings were allocated
to statistical area using fishing Vessel Trip Reports (VTR data) according
to the general procedures developed by Wigley et al. (1997), in
which a matched set of dealer and VTR data is used as a sample to characterize
the statistical area distribution of monthly state landings. A comparison
of the distribution of landings by state and month as indicated by the
dealer, VTR, and matched set data for 1994-2002 is presented in Tables
2-10. Since the implementation of the annual commercial landings quota
in 1993, the commercial landings have become concentrated during the first
calender quarter of the year, with 46% of the landings taken during the
first quarter in 2002 (Table 10).
The distribution of Northeast Region (ME to VA) 1992-2002
landings by three-digit statistical area is presented in Table
11. Areas 537-539 (Southern New England), areas 611-616 (New York
Bight), areas 621, 622, 625, and 626 (Delmarva region), and areas 631
and 632 (Norfolk Canyon area) have generally accounted for over 80% of
the NER commercial landings. A summary of length and age sampling of summer
flounder landings collected by the NEFSC commercial fishery port agent
system in the NER is presented in Table 12. For
comparability with the manner in which length frequency sampling in the
recreational fishery has been evaluated, sampling intensity is expressed
in terms of metric tons of landings (mt) per 100 fish lengths measured.
The sampling is proportionally stratified by market category (jumbo, large,
medium, small, and unclassified), with the sampling distribution generally
reflecting the distribution of commercial landings by market category.
Overall sampling intensity has improved markedly since 1995, from 165
mt per 100 lengths to 30-60 mt per 100 lengths, and temporal and geographic
coverage has generally improved as well (Tables 13-21).
The age composition of the NER commercial landings for 1994-2002 was
generally estimated semiannually by market category and (usually) 1-digit
statistical area (e.g., area 5 or area 6), using standard NEFSC procedures
(market category length frequency samples converted to mean weights by
length-weight relationships; mean weights in turn divided into landings
to calculate numbers landed by market category; market category numbers
at length apportioned to age by application of age-length keys, on semiannual
area basis). For 2000-2002, sampling was generally sufficient to make
quarterly estimates of the age composition in area 6 (in some cases, by
division) for the large and medium market categories.
The distribution of 1994-2002 length frequency samples
by market category, 1- and 2-digit statistical area (division), and calendar
quarter is presented in Tables 13-21. NER landed numbers at age were raised
to total NER (general canvas) commercial landings when necessary by assuming
that landings not accounted for in the weighout/mandatory reporting system
had the same age composition as that sampled, as follows: calculate proportion
at age by weight; apply proportions at age by weight to total NER commercial
landings to derive total NER commercial catch at age by weight; divide
by mean weights at age to derive total NER commercial landed numbers at
age. The proportion of large and jumbo market category fish in the NER
landings has increased since 1996, while the proportion of small market
category landings has become very low. The mean size of fish landed in
the NER commercial fishery has been increasing since 1993, and was 0.9-1.0
kg (2.0-2.2 lbs) during 2000-2002, typical of an age 3 summer flounder
(Tables 22-23).
North Carolina
The North Carolina winter trawl fishery accounts for
about 99% of summer flounder commercial landings in North Carolina. A
separate landings at age matrix for this component of the commercial fishery
was developed from North Carolina Division of Marine Fisheries (NCDMF)
length and age frequency sampling data. The NCDMF program samples about
10% of the winter trawl fishery landings annually, at a mean (2000-2002)
rate of between 6 and 8 mt of landings per 100 lengths measured (Table
24). All length frequency data used in construction of the North Carolina
winter trawl fishery landings at age matrix were collected in the NCDMF
program; age-length keys from NEFSC commercial data and NEFSC spring survey
data (1982-1987) and NCDMF commercial fishery data (1988-2002) were combined
by appropriate statistical area and semiannual period to resolve lengths
to age. Fishery regulations in North Carolina also changed between 1987
and 1988, with increases in both the minimum mesh size of the codend and
minimum landed fish size taking effect. It is not clear whether the change
in regulations or the change in keys, or some combination, is responsible
for the decreases in the numbers of age-0 and age-1 fish estimated in
the North Carolina commercial fishery landings since 1987. Landed numbers
at age and mean weights at age from this fishery are shown in Tables
25-26.
Commercial Fishery Discards
In a previous assessment, analysis of variance of fishery observer data
for summer flounder was used to identify stratification variables for
an expansion procedure to estimate total landings and discards from the
observer data kept and discard rates (weight per day fished) in the commercial
fishery. Initial models included year, quarter, fisheries statistical
division (2-digit area), area (divisions north and south of Delaware Bay),
and tonnage class as main effects. Quarter and division consistently emerged
as significant main effects without significant interaction with the year
(NEFSC 1993). The estimation procedure expands transformation bias-corrected
geometric mean catch (landings and discards) rates in year, quarter, and
division strata by total days fished (days fished on trips landing any
summer flounder by any mobile gear, including fish trawls and scallop
dredges) to derive fishery landings and discards. The use of fishery effort
as the multiplier (raising factor) allows estimation of landings from
the fishery observer data for comparison with dealer reported landings,
to help judge the potential accuracy of the procedure and/or sample data.
For strata with no fishery observer sampling, catch rates from adjacent
or comparable strata were substituted as appropriate (except for Division
51, which generally has very low catch rates and negligible catch). Estimates
of discard were stratified by 2 gear types (scallop dredges; trawls) for
years when data were adequate (1992 and later years). Estimates at length
and age were stratified by gear only for 1994-2000 and 2002, again due
to sample size considerations. Only 11 fish were sampled from the sea
scallop dredge fishery 2001, and so the scallop dredge discards were assumed
to have the same length and age composition as the trawl fishery discards
in 2001.
While estimates of catch rates from the NER fishery
observer data were used in this assessment to estimate total discards,
catch rate information is also reported in the VTR data. A comparison
of discard to total catch ratios for the fishery observer and VTR data
sets for trawl and scallop dredge gear indicates similar discard rates
from the two data sources. Overall fishery observer and VTR discard to
total catch ratios for 1994-2002 were generally within 10% of each other;
2001 was an exception, with an overall discard to total catch ratio of
49% in the fishery observer data and 29% in the VTR data. Discard rates
of summer flounder in the scallop dredge fishery were much higher than
in the trawl fishery (Tables 27-28).
The change in mid-1994 from the interview/weighout data reporting system
to the VTR/mandatory dealer report system required a change in the estimation
of effort (days fished) to estimate total discards. An initial examination
of days fished and catch per unit effort (CPUE; landings per day fished)
for cod conducted at SAW 24 (NEFSC 1997a) compared these quantities as
reported in the full weighout and VTR data sets (DeLong et al.,
1997). This comparison indicated a shift to a higher frequency of short
trips (trips with one or two days fished reported), and to a mode at a
lower rate of CPUE. It was not clear at SAW 24 if these changes were due
to the change in reporting system (units reported not comparable), or
real changes in the fishery, and so effort data reported by the VTR system
were not used quantitatively in the SAW 24 assessments. In the SAW 25
assessment for summer flounder (NEFSC 1997b), a slightly different comparison
was made. The port agent interview data for 1991-93 and merged dealer/VTR
data for 1994-1996 (the matched set data), which under each system serve
as the "sample" to characterize the total commercial landings, were compared
in relative terms (percent frequency). For summer flounder, the percent
frequency of short trips (lower number of days fished per trip) increased
during 1991-1996, but not to the degree observed for cod, and the mode
of CPUE rates for summer flounder increased in spite of lower effort per
trip. For the summer flounder fishery, these may reflect actual changes
in the fishery, due to increased restrictions on allowable landings per
trip (trip landings limits might lead to shorter trips) and stock size
increases (higher CPUE). As for cod, however, the influence of each of
these changes (reporting system, management changes, stock size changes)
has not been quantified. Total days fished in the summer
flounder fishery were comparable between 1989-1993 period and 1994 (Tables
29-37; WO DF and WO/VTR DF). With increasing restrictions on the fishery
in 1995-2002 (lower landings quota, higher stock size, and thus increasing
impact of trips limits and closures), total days fished declined relative
to the early 1990s (Tables 38-53). Questions will
remain about the accuracy of the VTR data . However, because the effort
measure is critical to the estimation of discards for summer flounder,
the VTR data were used as the best data source to estimate summer flounder
fishery days fished for 1994-2002.
Two adjustments were made to the dealer/VTR matched data subset days
fished estimates to fully account for summer flounder fishery effort during
1994-2002. First, the landings to days fished relationship in the matched
set was assumed to be the same for unmatched trips, and so the days fished
total in each discard estimation stratum (2-digit area and quarter) was
raised by the dealer to matched set landings ratio. This step in the estimation
accounted for days fished associated with trips landing summer flounder,
and provided an estimate of discard for trips landing summer flounder
(Tables 36-53, variable OB EST DISC 1).
Given the restrictions on the fishery however, there is fishing activity
which results in summer flounder discard, but no landings, especially
in the scallop dredge fishery. The days fished associated with these trips
was accounted for by raising strata discard estimates by the ratio of
the total days fished on trips catching any summer flounder (trips with
landings and discard, plus trips with discard only) to the days fished
on trips landing summer flounder (trips with landings and discard) (Tables
36-53, variable NO KEPT RATIO), for VTR trips reporting discard of any
species (DeLong et al. 1997). For this step , it is necessary to
assume that the discard rate (as indicated by the fishery observer data,
which includes trips with discard but no landings, and which is used in
previous estimation procedure steps) is the same for trips with only discards
as for trips with both landings and discards.
Discard estimates for 1989-2002 are summarized in Tables 29-53 (variable
OB EST DISC MT). Discards as a proportion of the fishery observer data
estimated landings (OB EST LAND MT) were highest in 2001 (53%), and lowest
in 1995 and 1996 (5 and 7%). Estimates of landings from observer data
ranged from +35% (1996) to -69% (2001) of the reported landings in the
fisheries, with discards ranging from 41% (1990) to 6% (1995) of the reported
landings. Total discards estimated for 2000, 2001, and 2002 were 18%,
16%, and 9% of the reported landings. Scallop dredge fishery discard to
landed ratios are much higher than trawl fishery ratios, purportedly because
of closures and trip limits. Although the scallop dredge landings of summer
flounder are less than 5% of the total, the discards of summer flounder
are of the same order of magnitude as in the trawl fishery.
These discard estimates were based only on the days
fished data for ports in the NER during 1989-1996, and so it was necessary
to raise the discard estimate to account for discarding occurring outside
the NER reporting system (i.e., NER state reporting systems such as Connecticut
and Virginia, and North Carolina). To determine the proper raising factor,
landings accounted for by the NER reporting system (which result from
the fishing effort on which the fishery observer discard estimate is based)
were compared with total NER landings, plus that portion of North Carolina
landings from the EEZ (it is assumed that only the North Carolina fishery
in the EEZ would experience significant discard, as mesh regulations in
state waters have resulted in very low discards in state waters since
implementation of the regulation in 1989; R. Monaghan, NCDMF; personal
communication, June 30, 1997). As a result of this exercise, the total
discard estimates were raised by 11 to 38% for the 1989-1996 period. Since
1996, all states' landings and are included in the NER dealer reporting
system, so no raising is necessary to account for missing landings. As
recommended by SAW 16 (NEFSC 1993), a commercial fishery discard mortality
rate of 80% was assumed to develop the final estimate of discard mortality
(Table 54).
Existing fishery observer data were used to develop estimates of commercial
fishery discard for 1989-2002. However, adequate data (e.g., interviewed
trip data, survey data) are not available to develop summer flounder discard
estimates for 1982-1988. Discard numbers were assumed to be very small
relative to landings during 1982-1988 (because of the lack of a minimum
size limit in the EEZ), but to have increased since 1989 with the implementation
of fishery regulations under the FMP. It was recognized that not accounting
directly for commercial fishery discards in 1982-1988 would result in
an underestimation of fishing mortality and population sizes in these
years.
NEFSC fishery observer length frequency samples were converted to sample
numbers at age and sample weight at age frequencies by application of
NEFSC survey length-weight relationships and fishery observer, commercial
fishery, and survey age-length keys. Sample weight proportions at age
were next applied to the raised fishery discard estimates to derive fishery
total discard weight at age. Fishery discard weights at age were then
divided by fishery observer mean weights at age to derive fishery discard
numbers at age. Classification to age for 1989-1993 was done by semiannual
(quarters 1 and 2 pooled, quarters 3 and 4 pooled) periods using NEFSC
fishery observer age-length keys, except for 1989, when first period lengths
were aged using combined commercial landings (quarters 1 and 2) and NEFSC
spring survey age-length keys. For 1994-2002, only NEFSC winter, spring,
and fall survey age-length keys were used, since fishery observer age-length
keys were not yet available and commercial landings age-length keys contained
an insufficient number of small summer flounder (<40 cm = 16 inches)
that comprise most of the discards. Fishery observer
sampling intensity is summarized in Table 54. Estimates of discarded numbers
at age, mean length and mean weight at age are summarized in Tables
55-57.
The reason for discarding in the trawl and scallop dredge fisheries
has been changing over time. During 1989 to 1995, the minimum size regulation
was recorded as the reason for discarding summer flounder in over 90%
of the observed trawl and scallop dredge tows. In 1999, the minimum size
regulation was provided as the reason for discarding in 61% of the observed
trawl tows, with quota or trip limits given as the discard reason in 26%
of the observed tows, and high-grading in 11% of the observed tows. In
the scallop fishery in 1999, quota or trip limits was given as the discard
reason in over 90% of the observed tows. During 2000-2002, minimum size
regulations were identified as the discard reason in 40-45% of the observed
trawl tows, quota or trip limits in 25-30% of the tows, and high grading
in 3-8%. In the scallop fishery during 2000-2002, quota or trip limits
was given as the discard reason for over 99% of the observed tows. As
a result of the increasing impact of trip limits, fishery closures, and
high grading as reasons for discarding, the age structure of the summer
flounder discards has also changed, with a higher proportion of older
fish being discarded (Table 55).
Recreational Fishery Landings
Summary landings statistics for the summer flounder
recreational fishery (catch type A+B1) as estimated by the National Marine
Fisheries Service (NMFS) Marine Recreational Fishery Statistics Survey
(MRFSS) are presented in Tables 58-59. Recreational
fishery landings decreased 39% by number and 32% by weight from 2001 to
2002, as the fishery landed 82% (3,610 mt, 8.0 million lbs) of the 4,408
mt (9.7 million lbs) harvest limit established for 2002.
Length frequency sampling intensity for the recreational
fishery for summer flounder was calculated by MRFSS subregions (North
- Maine to Connecticut; Mid - New York to Virginia; South - North Carolina)
on a metric tons of landings per hundred lengths measured basis (Burns
et al. In Doubleday and Rivard, 1983). For 2002, aggregate sampling
intensity averaged 112 mt of landings per 100 fish measured (Table
60).
MRFSS sample length frequency data, NEFSC commercial age-length data,
and NEFSC survey age-length data were examined in terms of number of fish
measured/aged on various temporal and geographical bases. Correspondences
were made between MRFSS intercept date (quarter), commercial quarter,
and survey season (spring and summer/fall), and between MRFSS subregion,
commercial statistical areas, and survey depth strata to integrate data
from the different sources. Based on the number, size range, and distribution
of lengths and ages, a semiannual (quarters 1 and 2; quarters 3 and 4),
subregional basis of aggregation was adopted for matching of commercial
and survey age-length keys with recreational length frequency distributions
to convert lengths to ages.
The recreational landings historically have been dominated
by relatively young fish. Over the 1982-1996 period, age 1 fish accounted
for over 50% of the landings by number; summer flounder of ages 0 to 4
accounted for over 99% of landings by number. No fish from the recreational
landings were determined to be older than age 7. With increases in the
minimum size during 1997-2001 (to 14.5 in [37 cm] in 1997, 15 in [38 cm]
in 1998-1999, generally 15.5 in [39 cm] in 2000, and various state minimum
sizes from 15.5 [38 cm] to 17.5 in [44 cm] in 2001-2002) and reductions
in fishing mortality, the age composition of the recreational landings
now includes mainly fish at ages 2 and 3. The number of summer flounder
of ages 4 and older landed by the recreational fishery in 2002 (16% of
the landings by number) was the highest in the time series (Table
61).
Limited MRFSS length sampling for larger fish resulted in a high degree
of variability in mean length for older fish, especially at ages 5 and
older. Attempts to estimate length-weight relationships from the MRFSS
biological sampling data provided unsatisfactory results. As a result,
quarterly length (mm) to weight (g) relationships from Lux and Porter
(1966) were used to calculate annual mean weights at age from the estimated
age-length frequency distribution of the landings.
Recreational Fishery Discards
MRFSS catch estimates were aggregated on a subregional
basis for calculation of the proportion of live discard (catch type B2)
to total catch (catch types A+B1+B2) in the recreational fishery for summer
flounder. Examination of catch data in this manner shows that the live
discard has varied from about 18% (1985) to about 81% (1999, 2001-2002)
of the total catch (Table 62).
To account for all removals from the summer flounder stock by the recreational
fishery, some assumptions about the biological characteristics and hooking
mortality rate of the recreational live discard needed to be made, because
biological samples are not routinely taken of MRFSS catch type B2 fish.
In previous assessments, data available from New York Department of Environmental
Conservation (NYDEC) surveys (1988-92) of New York party boats suggested
the following: 1) nearly all (>95%) of the fish released alive from
boats were below the minimum regulated size (during 1988-92, 14 in [36
cm] in New York state waters); 2) nearly all of these fish were age 0
and age 1 summer flounder; and 3) age 0 and 1 summer flounder occurred
in approximately the same proportions in the live discard as in the landings.
It was therefore assumed that all B2 catch would be of lengths below regulated
size limits, and be either age 0 or age 1 in all three subregions during
1982-1996. Catch type B2 was allocated on a semi-annual, subregional basis
in the same ratio as the annual age 0 to age 1 proportion observed in
the landings during 1982-1996. Mean weights at age were assumed to be
the same as in the landings during 1982-1996.
The minimum landed size in federal and most state
waters increased to 14.5 in (37 cm) in 1997, to 15.0 in (38 cm) in 1998-1999,
and to 15.5 in (39 cm) in 2000. Applying the same logic used to allocate
the 1982-1996 recreational released catch to size and age categories during
1997-2000 implied that the recreational fishery released catch included
fish of ages 2 and 3. Investigation of data from the CTDEP Volunteer Angler
Survey (VAS) for 1997-1999 and from the American Littoral Society (ALS)
for 1999, and comparing the length frequency of released fish in these
programs with the MRFSS data on the length frequency of landed fish below
the minimum size, indicated this assumption was valid for 1997-1999 (MAFMC
2001a). The CTDEP VAS and ALS data, along with data from the NYDEC Party
Boat Survey (PBS) was used to validate this assumption for 2000. For 1997-2000
all B2 catch was assumed to be of lengths below regulated size limits,
and therefore comprised of ages 0 to 3. Catch type B2 was allocated on
a sub-regional basis in the same ratio as the annual age 0 to age 3 proportions
observed in the landings at lengths less than 37 cm in 1997, 38 cm in
1998-1999, and 39 cm in 2000 (Table 63).
In 2001, many states adopted different combinations of minimum size
and possession limits to meet management requirements. As a result, minimum
sizes for summer flounder ranged from 15.5 in (39 cm) in Federal, VA,
and NC waters, 16 in (41 cm) in NJ, 16.5 in (42 cm) in MA, 17 in (43 cm)
in MD and NY, to 17.5 in (44 cm) in CT, RI, and DE. Examination of data
provided by MD sport fishing clubs, the CTDEP VAS, the ALS, and the NYDEC
PBS indicated that the assumption that fish released are those smaller
than the minimum size remained valid for 2001, and so catch type B2 was
characterized by the same proportion at length as the landed catch less
than the minimum size in the respective states. The differential minimum
sizes by state continued in 2002. For 2002, increased samples of the recreational
fishery discards by the CT VAS and NYDEC PBS allowed direct characterization
the length frequencies of the discards for these states (Table 63).
Studies conducted to estimate hooking mortality for striped bass and
black sea bass suggest a hooking mortality rate of 8% for striped bass
(Diodati and Richards 1996) and 5% for black sea bass (Bugley and Shepherd,
1991). Work by the states of Washington and Oregon with Pacific halibut
(a potentially much larger flatfish species, but otherwise morphologically
similar to summer flounder) found "average hooking mortality...between
eight and 24 percent" (IPHC, 1988). An unpublished tagging study by the
NYDEC (Weber MS 1984) on survival of released sublegal summer flounder
caught by hook-and-line suggested a total, non-fishing mortality rate
of 53%, which included hooking plus tagging mortality as well as deaths
by natural causes (i.e., predation, disease, senescence). Assuming deaths
by natural causes to be about 18%, (an instantaneous rate of 0.20), an
annual hooking plus tagging mortality rate of about 35% can be derived
from the NYDEC results. In the SARC 25 (NEFSC 1997b) and earlier assessments
of summer flounder, a 25% hooking mortality rate was assumed for summer
flounder released alive by anglers.
However, two recent investigations of summer flounder recreational fishery
release mortality suggest that a lower release mortality rate is more
appropriate. Lucy and Holton (1998) used field trials and tank experiments
to investigate the release mortality rate for summer flounder in Virginia,
and found rates ranging from 6% (field trials) to 11% (tank experiments).
Malchoff and Lucy (1998) used field cages to hold fish angled in New York
and Virginia during 1997 and 1998, and found a mean short term mortality
rate of 14% across all trials. Given the results of these release mortality
studies conducted specifically for summer flounder, a 10% release mortality
rate was adopted in the Terceiro (1999) stock assessment and has been
retained in all subsequent assessments (NEFSC 2000, MAFMC 2001a, NEFSC
2002).
Ten percent of the total B2 catch at age is added
to estimates of summer flounder landings at age to provide estimates of
summer flounder recreational fishery discard at age (Table 63), total
recreational fishery catch at age in numbers (Table
64) and mean weights at age (Table 65). In 2002,
the number of fish discarded and assumed dead in the recreational fishery
(Table 63: 1.3 million fish, 676 mt) was 41% by number and 19% by weight
of the total landed (Table 61: 3.2 million fish; Table 60: 3,610 mt) in
the recreational fishery.
Total Catch Composition
NER commercial fishery landings and
discards at age, North Carolina winter trawl fishery landings and discards
at age, and MRFSS recreational fishery landings and discards at age totals
were summed to provide a total fishery catch at age matrix for 1982-2002
(Table 66; Figure 1). The percentage
of age-3 and older fish in the total catch in numbers has increased during
the last decade from only 4% in 1993 to 41% in 2002. Overall mean lengths
and weights at age in the total catch were calculated as weighted means
(by number in the catch at age) of the respective mean values at age from
the NER commercial (Maine to Virginia), North Carolina commercial, and
recreational (Maine to North Carolina) fisheries (Tables
67-68; Figure 2). The recreational fishery component
of the total summer flounder catch has generally increased since 1995
(Table 69; Figure 3).
BIOLOGICAL
DATA
Aging
Work performed for the SAW 22 assessment (NEFSC 1996b) indicated a major
expansion in the size range of 1-year old summer flounder collected during
the 1995 and 1996 NEFSC winter bottom trawl surveys, and brought to light
differences between ages determined by NEFSC and NCDMF fishery biology
staffs. Age structure (scale) exchanges were performed after the SAW 22
assessment to explore these differences. The results of the first two
exchanges, which were reported at SAW 22 (NEFSC 1996b), indicated low
levels of agreement between age readers at the NEFSC and NC DMF (31 and
46%). In 1996, research was conducted to determine inter-annular distances
and to back-calculate mean length at age from scale samples collected
on all NEFSC bottom trawl surveys (winter, spring and fall) for comparison
with NCDMF samples. While mean length at age remained relatively constant
from year to year, inter-annular distances increased sharply in the samples
from the 1995-1996 winter surveys, and increased to a lesser degree in
samples from other 1995-1996 surveys. As a result, further exchanges were
suspended pending the resolution of an apparent aging problem.
Age samples from the winter 1997 bottom trawl survey, aged utilizing
both scales and otoliths by only by one reader, indicated a similar pattern
as the previous two winter surveys (i.e., several large age 1 individuals),
and some disagreement between scale and otolith ages obtained from the
same fish. Because of these problems, a team of five experienced NEFSC
readers was formed to re-examine the scales aged from the winter survey.
After examining several hundred scales, the team determined that re-aging
all samples from 1995-1997 would be appropriate, including all winter,
spring, and fall samples from the NEFSC and MA DMF bottom trawl surveys
and all samples from the commercial fishery. The age determination criteria
remained the same as those developed at the 1990 summer flounder workshop
(Almeida et al. 1992) and described in the aging manual utilized
by NEFSC staff (Dery 1997). Only those fish for which a 100% agreement
of all group members was attained were included in the revised database,
however. The data from the re-aged database were used in analyses in the
SAW 25 assessment (NEFSC 1997b).
A third summer flounder aging workshop was held at the NEFSC in February,
1999, to continue the exchange of age structures and review of aging protocols
for summer flounder (Bolz et al. 2000). Participants at this workshop
concluded that the majority of aging disagreements in recent NEFSC-NCDMF
exchanges arose from the interpretation of marginal scale increments due
to highly variable timing of annulus formation, and from the interpretation
of first year growth patterns and first annulus selection. The workshop
recommended regular samples exchanges between NEFSC and NCDMF, and further
analyses of first year growth. An exchange of NEFSC and NCDMF aging structures
for summer flounder will again be conducted in 2003. Recently, Sipe and
Chittenden (2001) concluded that sectioned otoliths were the best structure
for aging summer flounder over the age range from 0 to 10 years. Since
2001, both scales and otoliths have routinely been collected in all NEFSC
trawl surveys for fish larger than 60 cm, and studies are underway to
determine the best structure to use for aging these large summer flounder.
Maturity
The maturity schedule for summer flounder used in the 1990 SAW 11 and
subsequent stock assessments through 1999 was developed by the SAW 11
Working Group using NEFSC Fall Survey maturity data for 1978-1989 and
mean lengths at age from the NEFSC fall survey (G. Shepherd, NEFSC, personal
communication, July 1, 1990; NEFC 1990; Terceiro 1999). The SAW 11 work
indicated that the median length at maturity (50th percentile,
L50) was 25.7 cm for male summer flounder, 27.6 cm for female
summer flounder, and 25.9 cm for the sexes combined. Under the aging convention
used in the SAW 11 and subsequent assessments (Smith et al. 1981,
Almeida et al. 1992, Szedlmayer and Able 1992, Bolz et al.
2000), the median age of maturity (50th percentile, A50)
for summer flounder was determined to be 1.0 years for males and 1.5 years
for females. Combined maturities indicated that at peak spawning time
in the autumn, that 38% of age-0 fish are mature, 72% of age-1 fish are
mature, 90% of age-2 fish are mature, 97% of age-3 fish are mature, 99%
of age-4 fish are mature, and 100% of age-5 and older fish are mature.
The maturities for age-3 and older were rounded to 100% in the SAW 11
and subsequent assessments.
In the series of summer flounder assessments, it has been noted that
the NEFSC maturity schedules have been based on simple gross morphological
examination of the gonads and therefore may not accurately reflect (i.e.,
may overestimate) the true spawning potential of the summer flounder stock
(especially for age-0 and age-1 fish). It should also be noted, however,
that spawning stock biomass (SSB) estimates based on age-2 and older fish
show the same long term trends in SSB as estimates which include age 0
and 1 fish in the spawning stock. A research recommendation that the true
spawning contribution of young summer flounder to the SSB be investigated
has been included in summer flounder stock assessments since 1993 (NEFSC
1993). In light of the completion of a URI study to address this research
recommendation, the maturity data for summer flounder for 1982-1998 were
examined in the 2000 assessment (NEFSC 2000) to determine if changes in
the maturity schedule were warranted.
The research at the University of Rhode Island (URI) by Drs. Jennifer
Specker and Rebecca Rand Merson (hereafter referred to collectively as
the "URI 1999" study) attempted to address the issue of the true contribution
of young summer flounder to the spawning stock. The URI 1999 study examined
the histological and biochemical characteristics of female summer flounder
oocytes (1) to determine if age-0 and age-1 female summer flounder produce
viable eggs, and (2) to develop an improved guide for classifying the
maturity of summer flounder collected in NEFSC surveys (Specker et
al. 1999, Merson et al. 2000, Merson et al. In review).
The URI 1999 study examined 333 female summer flounder (321 aged fish)
sampled during the NEFSC Winter 1997 Bottom Trawl Survey (February 1997)
and 227 female summer flounder (210 aged fish) sampled during the NEFSC
Autumn 1997 Bottom Trawl Survey (September 1997) using radioimmunoassays
to quantify the biochemical cell components characteristic of mature fish.
The NEFSC and URI 1999 maturity determinations disagreed for 13% of
the 531 aged fish, with most (10%) of the disagreement due to NEFSC mature
fish classified as immature by the URI 1999 histological and biochemical
criteria. The URI 1999 criteria indicated that 15% of the age-0 fish were
mature, 82% of the age-1 fish were mature, 97% of the age-2 fish were
mature, and 100% of the age 3 and older fish were mature. When the proportions
of fish mature at length and age were estimated by probit analysis, median
length at maturity (50th percentile, L50) was estimated
to be 34.7 cm for female summer flounder, with the following proportions
mature at age: age-0: 30%, age-1: 68%, age-2: 92%, age-3: 98%, and age-4:
100%. Median age of maturity (50th percentile, A50)
was estimated to be about 0.5 years.
SARC 31 (NEFSC 2000) considered 5 options for the summer flounder maturity
schedule for the 2000 stock assessment:
1) No change, use the maturity schedule for combined sexes as in the
SAW 11 and subsequent assessments (rounded to 0.38, 0.72, 0.90, 1.00,
1.00, and 1.00 as in the SAW 25 and Terceiro (1999) assessment analyses).
2) Consider only age-2 and older fish of both sexes in the SSB.
3) Knife edged, age-1 and older maturity for both sexes. This would eliminate
age-0 fish of both sexes from the SSB, and assume that the proportions mature
at age-1 "round" to 100%.
4) NEFSC 1982-1989, 1990-1998 for both sexes, assuming a 1:1 sex ratio in deriving
a combined schedule.
5) NEFSC 1982-1989, 1990-1998 for males, URI 1999 for females, assuming a 1:1
sex ratio in deriving a combined schedule.
The 5 options produce the following maturity schedules for both sexes
combined:
| Option |
|
|
Age |
|
|
|
| |
0 |
1 |
2 |
3 |
4 |
5+ |
| 1 |
0.38 |
0.72 |
0.90 |
1.00 |
1.00 |
1.00 |
| 2 |
0.00 |
0.00 |
0.90 |
1.00 |
1.00 |
1.00 |
| 3 |
0.00 |
1.00 |
1.00 |
1.00 |
1.00 |
1.00 |
| 4 |
0.45, 0.45 |
0.88, 0.82 |
0.97, 0.93 |
1.00, 0.98 |
1.00, 0.99 |
1.00, 1.00 |
| 5 |
0.29, 0.31 |
0.74, 0.76 |
0.95, 0.94 |
0.99, 0.98 |
1.00, 1.00 |
1.00, 1.00 |
SARC 31 concluded that some contribution to spawning from ages 0 and
1 should be included, eliminating options 2 and 3. The differences among
remaining options 1, 4, and 5 were considered to be relatively minor,
and so the SAW 11 schedule (Option 1) was retained for the subsequent
(MAFMC 2001a, NEFSC 2002) and current assessments. SARC 31 recommended
that more biochemical and histological work should be done for additional
years to determine if the results of the URI 1999 study will be applicable
over the full VPA time series. SARC 31 also noted the need for research
to explore whether the viability of eggs produced by young, first time
spawning summer flounder is comparable to the viability of eggs produced
by older, repeat spawning summer flounder.
RESEARCH
SURVEY INDICES
NEFSC spring
Long-term trends in summer flounder
abundance were derived from a stratified random bottom trawl survey conducted
in spring by NEFSC between Cape Hatteras and Nova Scotia since 1968 (Clark
1979). NEFSC spring survey indices suggest that total stock biomass last
peaked during 1976-1977, and the 2003 index (2.42 kg/tow) was at a new
historical high, about 20% above the peak 1976 value of 2.00 kg/tow (Table
70, Figure 4). Age composition data from the
NEFSC spring surveys indicate a substantial reduction in the number of
ages in the stock between 1976-1990 (Table 71).
Between 1976-1981, fish of ages 5-8 were captured regularly in the survey,
with the oldest individuals aged 8-10 years. Between 1982-1986, fish aged
5 and older were only occasionally observed in the survey, and by 1986,
the oldest fish observed in the survey were age 5. In 1990 and 1991, only
three age groups were observed in the survey catch, and there was an indication
that the 1988 year class was very weak. Since 1991, the survey age composition
has expanded significantly. There is strong evidence in the 1998-2002
NEFSC spring surveys of increasing abundance of age-3 and older fish,
due to increased survival of the 1994 and subsequent year classes. Mean
lengths at age in the NEFSC spring survey are presented in Table
72.
NEFSC Autumn
Summer flounder are frequently caught
in the NEFSC autumn survey at stations in inshore strata (< 27 meters
= 15 fathoms = 90 feet) and at offshore stations in the 27-55 meter depth
zone (15-30 fathoms, 90-180 feet) at about the same level as in the spring
survey (Table 70). Furthermore, the autumn survey catches age-0 summer
flounder in abundance, providing an index of summer flounder recruitment
(Table 73, Figure 5). Autumn
survey indices suggest improved recruitment since the late 1980s, and
an increase in abundance of age-2 and older fish since 1995. The NEFSC
autumn surveys indicate that the 1995 year class was the most abundant
in recent years, and that subsequent, weaker year classes are experiencing
increased survival (Table 73). Mean lengths at age in the NEFSC autumn
survey are presented in Table 74.
NEFSC Winter
A new series of NEFSC winter trawl surveys was initiated in February
1992 to provide improved abundance indices for flatfish, including summer
flounder. The surveys target flatfish when they are concentrated offshore
during the winter. A modified 36 Yankee trawl is used that differs from
the standard trawl employed during the spring and autumn surveys in that
long trawl sweeps (wires) are added before the trawl doors to better herd
fish to the mouth of the net, and the large rollers used on the standard
gear are absent with only a chain "tickler" and small spacing "cookies"
are present on the footrope.
The design and conduct of the winter survey (timing, strata sampled,
and the use of the modified 36 Yankee trawl gear) has resulted in greater
catchability of summer flounder compared to the other surveys. Most fish
area captured in survey strata 61-76 (27-110 meters; 15-60 fathoms) off
the Delmarva and North Carolina coasts . Other concentrations of fish
are found in strata 1-12, south of the New York and Rhode Island coasts,
in slightly deeper waters. Significant numbers of large summer flounder
are often taken along the southern flank of Georges Bank (strata 13-18).
Indices of summer flounder abundance from the winter
survey indicate stable stock size during 1992-1995, with catch per tow
values ranging from 10.9 in 1995 to 13.6 in 1993 (Tables
70 and 75). For 1996, the winter survey index
increased by 290% over 1995, from 10.9 to 31.2 fish per tow. The largest
increases in 1996 occurred in the Mid-Atlantic Bight region (offshore
strata 61-76), where increases up to an order of magnitude occurred in
several strata, with the largest increases in strata 61, 62, and 63 off
the northern coast of North Carolina. Most of the increased catch in 1996
consisted of age-1 summer flounder from the 1995 year class. In 1997,
the index dropped to 10.3 fish per tow, due to the lower numbers of age-1
(1996 year class) fish caught. Since 1998, the Winter trawl survey indices
have increased, with the Winter 2003 survey number and weight per tow
indices the highest in the time series (Tables 70 and 75, Figure 4). As
with the other two NEFSC surveys, there is strong evidence in recent winter
surveys of increased abundance of age-3 and older fish relative to earlier
years in the time series (Table 76). Mean lengths
at age in the NEFSC winter survey are presented in Table
77.
Massachusetts DMF
Spring and fall bottom trawl surveys conducted by
the Massachusetts Division of Marine Fisheries (MADMF) show a decline
in abundance in numbers of summer flounder from high levels in 1986 to
record lows in 1990 (MADMF fall survey), and 1991 (MADMF spring survey).
In 1994, the MADMF survey indices increased to values last observed during
1982-1986, but then declined substantially in 1995, although the indices
remain higher than the levels observed in the late 1980s. Since 1996,
both the MADMF spring and fall indices have increased to record high levels
(Tables 78-79, Figure 6). The
MADMF also captures a small number of age-0 summer flounder in a seine
survey of estuaries, and these data constitute an index of recruitment
(Table 80, Figure 7).
Connecticut DEP
Spring and fall bottom trawl surveys
are conducted by the Connecticut Department of Environmental Protection
(CTDEP). The CTDEP surveys show a decline in abundance in numbers of summer
flounder from high levels in 1986 to record lows in 1989. The CTDEP surveys
indicate recovery since 1989, and evidence of increased abundance at ages
2 and older since 1995. The 2002 spring and autumn indices were the highest
in the respective time series (Tables 81-82, Figure
8). An index of recruitment from the autumn series is available (Table
82, Figure 5).
Rhode Island DFW
Standardized bottom trawl surveys have been conducted
since 1979 during the spring and fall months in Narragansett Bay and state
waters of Rhode Island Sound by the Rhode Island Department of Fish and
Wildlife (RIDFW). Indices of abundance at age for summer flounder have
been developed from the autumn survey data using NEFSC autumn survey age-length
keys. Survey indices show that the 1984-1987, 1999, 2000, and 2002 year
classes are all strong. The autumn survey reached a time series high in
2002 (Table 83, Figure 6). An abundance index has
also been developed from a set of fixed stations sampled monthly during
1990-2002. Age-1 indices from this series indicate that strong year classes
recruited to the stock in 1996, 1999, 2000, and 2002, with age 2+ abundance
peaking in 2000 (Table 84). Recruitment indices
are available from both the autumn (Figure 7) and monthly fixed station
surveys.
New Jersey BMF
The New Jersey Bureau of Marine Fisheries (NJBMF)
has conducted a standardized bottom trawl survey since 1988. Indices of
abundance for summer flounder incorporate data collected from April through
October. The NJBMF survey mean number per tow indices and frequency distributions
were converted to age using the corresponding annual NEFSC combined spring
and fall survey age-length keys. Indices of the 1995 year class at age-0
and at older ages in subsequent years indicate that this cohort is the
strongest in the time series. Indices of the 1996-2001 year classes are
below average, while the 2002 year class is average. The NJBMF survey
indices reached a peak in 2002 (Table 85, Figure
8). Age 0 recruitment indices are available from the NJBMF survey
(Figure 5).
Delaware DFW
The Delaware Division of Fish and Wildlife (DEDFW)
has conducted a standardized bottom trawl survey with a 16 foot headrope
trawl since 1980, and with a 30 foot headrope trawl since 1991. Recruitment
indices (age 0 fish; one index from the Delaware estuary proper for 1980
and later, one from the inland bays for 1986 and later) have been developed
from the 16 foot trawl survey data. Indices for age-0 to age-4 and older
summer flounder have been compiled from the 30 foot headrope survey. The
indices use data collected from June through October (arithmetic mean
number per tow), with age 0 summer flounder separated from older fish
by visual inspection of the length frequency. The 16 foot headrope survey
indices suggest poor recruitment in 1988 and 1993, improved recruitment
in 1994-1995, and above average recruitment in 2000 (Tables
86-87, Figure 7). The 30 foot headrope survey indices suggest stable
stock sizes over the 1991-2001 time series, with strong recruitment in
1991, 1994, 1995, and 2000. The 2002 index from the 30 foot survey was
a time series low, presumably reflecting decreased availability to the
survey, rather than a true decrease in abundance (Table
88, Figure 8).
Maryland DNR
The Maryland Department of Natural
Resources (MDDNR) has conducted a standardized trawl survey in the seaside
bays and estuaries around Ocean City, MD since 1972. Samples collected
during May to October with a 16 foot bottom trawl have been used to develop
a recruitment index for summer flounder for the period 1972-2002. This
index suggests that weakest year class in the time series recruited to
the stock in 1988, and the strongest in 1972, 1983, 1986, and 1994. The
2000 and 2001 indices were about average, while the 2002 index was below
average (Table 89, Figure 9).
Virginia Institute of Marine Science
The Virginia Institute of Marine Science (VIMS) conducts
a juvenile fish survey using trawl gear in Virginia rivers and the mainstem
of Chesapeake Bay. The time series for the rivers began in 1979. With
the Bay included, the series is available only since 1988, but many more
stations are included. Trends in the two time series are very similar.
An index of recruitment developed from the rivers only series suggests
weak year classes recruited to the stock in 1987 and 1999, with strong
year classes recruiting during 1980-1984, and 1990. Recruitment indices
since 1990 have been below average (Table 90, Figure
9).
North Carolina DMF
The NCDMF has conducted a stratified random trawl
survey using two 30 foot headrope nets with 3/4" mesh codend in Pamlico
Sound since 1987. An index of recruitment developed from these data suggests
weak year classes recruited to the stock in 1988 and 2000, with strong
year classes in 1987, 1992, and 1996, 2001, and 2002 (Table
91, Figure 9). The survey normally takes place in mid-June, but in
1999 was delayed until mid-July. The 1999 index is therefore inconsistent
with the other indices in the time series, and the 1999 value was excluded
from the VPA calibration in the SARC 31 assessment (NEFSC 2000).
ESTIMATES
OF MORTALITY AND STOCK SIZE
Natural Mortality Rate
The instantaneous natural mortality rate (M) for summer flounder was
assumed to be 0.2 in all analyses, although alternative estimates of M
were considered in the SAW 20 assessment (NEFSC 1996a). In the SAW 20
work, estimates were derived with the methods described by: 1) Pauly (1980)
using growth parameters derived from NCDMF age-length data and a mean
annual bottom temperature (17.5oC) from NC coastal waters;
2) Hoenig (1983) using a maximum age for summer flounder of 15 years;
and 3) consideration of age structure expected in unexploited populations
(5% rule, 3/M rule, e.g., Anthony 1982). SAW 20 (NEFSC 1996a) concluded
that M = 0.2 was a reasonable value given the mean (0.23) and range (0.15-0.28)
obtained from the various analyses, and this value for M has been used
in all subsequent assessments.
ASPIC Model
The non-equilibrium surplus production model incorporating covariates
(ASPIC; Prager 1994, 1995) can be used to estimate maximum sustainable
yield (MSY) and other biological reference points. An ASPIC analysis applied
to summer flounder using various state and federal agency survey biomass
indices (the 1998 analysis) was previously reviewed by the NEFMC Overfishing
Review Panel (Applegate et al. 1998). Based on total weighted mean
squared error (MSE), the NEFSC spring and autumn biomass indices gave
the best fit to the data in that analysis. However, the Overfishing Review
Panel concluded that biological reference points estimated in the 1998
analysis for summer flounder were unreliable, due to the short time series
of reliable catch estimates and lack of dynamic range in the input data
(Applegate et al. 1998).
An ASPIC analysis using projected catch and NEFSC survey biomass indices
through 1999 was reviewed in the 1999 assessment (Terceiro 1999). Model
results were examined for sensitivity by employing a Monte Carlo search
routine and by initializing over a broad range the values of MSY (10,000
to 50,000 mt) and the intrinsic rate of increase (r : 0.12 to 1.25). The
ratio of initial to current biomass (B1 ratio) was assigned a starting
value of 0.50. Overall, the 1999 ASPIC model results for summer flounder
were not well defined and suggested the possibility of numerous local
minima in the sums of squared errors (SSE) response surface. The Monte
Carlo search algorithm was employed in an attempt to provide a better
search of the SSE response surface, and the this generated a range of
estimates of MSY from 19,000 mt to 58,000 mt and of r from 0.49 to 1.08.
Due to the number of iterations needed to reach convergence (>25) and
the probable number of local minima, these results also appeared to be
unreliable. Thus, biological reference points for summer flounder estimated
by the 1999 ASPIC analysis were not considered to be robust, and the ASPIC
analysis has not been repeated in the assessment.
Virtual population analysis
Fishing mortality rates in 2002 and stock sizes in
2003 were estimated using the ADAPT method for calibration of the VPA
(Parrack 1986, Gavaris 1988, Conser and Powers 1990) as implemented in
the NOAA Fisheries Toolbox (NFT) version 2.1 VPA. As recommended by the
MAFMC S&S Committee during the review of the Terceiro (1999) assessment
and by the National Research Council review of the summer flounder assessment
(NRC 2000), ages 0-6 were included in the analysis as true ages, with
ages 7 and older combined as a plus group. An instantaneous natural mortality
rate of M = 0.2 was assumed for all ages in all years. Maturities at age
for all years were 38% for age-0, 72% for age-1, 90% for age-2, and 100%
for ages 3 and older. Stock sizes in 2003 were directly estimated for
ages 1-6, while the age 7+ group was calculated from Fs estimated in 2002.
Fishing mortality on the oldest true age (6) in the years prior to the
terminal year was estimated from back-calculated stock sizes for ages
3-6. Fishing mortality on the age 7+ group was assumed equal to the fishing
mortality for age 6. Winter, spring, and mid-year (e.g., RIDFW monthly
fixed station, DEDFW, and NJBMF) survey indices and all survey recruitment
(age-0) indices were compared to population numbers of the same age at
the beginning of the same year. The recruitment indices available from
the research surveys are summarized in Table 92.
Fall survey indices were compared to population numbers one year older
at the beginning of the next year. Tuning indices were unweighted.
A number of exploratory VPA runs using different combinations of research
survey tuning indices were used to examine the sensitivity of the summer
flounder VPA. The inclusion of each survey index was considered based
on a pre-calibration correlation analysis among all indices, a post-calibration
correlation analysis among the indices and resulting VPA estimates of
stock size, and an examination of the VPA diagnostics (including the partial
variance accounted for by each index, patterns in residuals, and the mean
squared residual (MSR) of the calibrated solution). Survey indices with
trends that did not reasonably match corresponding patterns in abundance
as estimated by other indices and/or the VPA (as evidenced by poor correlation,
high partial variance in tuning diagnostics, or patterns in residuals)
were eliminated from the VPA tuning configuration.
The final run (run F03_1) included the same set of
indices (n=41) in terms of source and age range as used in the 2002 SARC
35 assessment (NEFSC 2002). In addition to a run including all available
indices (F03_ALL) and the run chosen as final (F03_1), the results from
two other runs were also considered (Table 93).
The NEFSC survey indices generally had the lowest partial variances within
the VPA and demonstrated similar rank order of stock sizes at age (significant
correlation among indices at age), but sometimes indicated patterns in
stock size dissimilar to those in the state surveys. Therefore runs were
also examined that contrasted the VPA solutions provided by NEFSC (F03_NEC)
versus state survey (F03_STATE) series. Run F03_NEC had the smallest MSR
of the six runs considered (about 12% smaller than final run F03_2), but
due in part to fewer degrees of freedom, provided less precise (by about
50%) 2003 stock size estimates. Run F03_STATE had the largest MSR (Table
93). The output for the final 2003 assessment VPA (run F03_1) is presented
in Table 94.
The annual partial recruitment of age-1 fish decreased from near 0.50
during the first half of the VPA time series to less than 0.30 since 1994,
and to about 0.20 during 2000-2002; the partial recruitment of age-2 fish
has decreased from 1.00 in 1993 to about 0.80 during 2000-2002 (Table
94). These decreases in partial recruitment at age are in line with expectations
given recent changes in commercial and recreational fishery regulations.
For these reasons, summer flounder are currently considered to be fully
recruited to the fisheries at age 3, and fully recruited fishing mortality
is expressed as the unweighted average of fishing mortality at age for
ages 3 to 5.
Fishing mortality calculated from the average of the
currently fully recruited ages (3-5) has been high, varying between 0.94
and 2.15 during 1982-1997 (55%-82% exploitation), far in excess of the
revised FMP Amendment 12 overfishing definition, Fthreshold
= Ftarget = Fmax = 0.26 (21% exploitation). Fishing
mortality has declined substantially since 1997 and was estimated to be
0.23 (18% exploitation) in 2002, the lowest observed in the 21-year VPA
time series (Figure 10).
Summer flounder spawn in the late autumn and early
winter (peak spawning on November 1), and age 0 fish recruit to the fishery
during the autumn after they are spawned. For example, summer flounder
spawned in autumn 1987 (from the November 1, 1987 spawning stock biomass)
recruit to the fishery in autumn 1988, and appear in VPA tables as age
0 fish in 1988. This assessment indicates that the 1982 and 1983 year
classes were the largest of the VPA series, at 74 and 80 million fish,
respectively. The 1988 year class was the smallest of the series, at only
13 million fish. The 2002 year class is estimated at 38 million fish,
above the time series median of 35 million (Table 94, Figures
11-12).
Total stock biomass has increased substantially since
1989, and at the beginning of 2003 total stock biomass was estimated to
be 56,100 mt. Spawning stock biomass (SSB; Age 0+) declined 72% between
1983 and 1989 (18,800 mt to 5,200 mt), but has increased eight-fold, with
improved recruitment and decreased fishing mortality, to 42,200 mt in
2002 (Table 94, Figures 11-12). In general, the abundance of summer flounder
age 2 and older has increased substantially since the early 1990s. The
age structure of the spawning stock has thus also expanded, with 80% at
ages 2 and older, and 19% at ages 5 and older. Under equilibrium conditions
at Fmax, about 85% of the spawning stock biomass would be expected
to be ages 2 and older, with 50% at ages 5 and older (Figure
13).
A bootstrap procedure (Efron 1982) was used to evaluate the precision
of the final VPA estimates with respect to random variation in tuning
data (survey abundance indices). The procedure does not reflect uncertainty
in the catch-at-age data. Five hundred bootstrap iterations were used
to generate distributions of the 2002 fishing mortality rate and the 2003
total stock biomass. Histogram plots of the distribution of the terminal
year VPA estimates visually indicate the amount of variability. The cumulative
probability can be used to evaluate the risk of making a management decision
based on the estimated value. For fishing mortality, the cumulative plot
indicates the probability that the fishing mortality rate in 2002 was
greater than a given level when measurement errors are considered (e.g.,
some target fishing mortality rate). For stock biomass, the cumulative
plot indicates the probability that biomass at the beginning of 2003 was
less than a given level (e.g., some desired minimum stock biomass).
The precision and bias of the 2002
fishing mortality rates, 1 January 2003 stock sizes, 1 November 2002 spawning
stock biomass, 2002 mean stock biomass, and 1 January 2003 total stock
biomass estimates are presented in Table 95. Bias was less than 10% for
all parameters estimated. The bootstrap estimate of the 2003 total stock
biomass was relatively precise, with a corrected CV of 9%. The bootstrap
mean (56,717 mt) was slightly higher than the VPA point estimate (56,088
mt). The bootstrap results suggest a high probability (>90%) that total
stock biomass in 2003 was at least 50,600 mt, reflecting only variability
in survey observations (Table 95, Figure
14).
The corrected coefficients of variation for the Fs in 2002 on individual
ages were 23% for age 0, 19% for age 1, 15% for age 2, 16% for age 3,
21% for age 4, 31% for age 5, 13% for age 6, and 13% for ages 7 and older.
The distribution of bootstrap Fs was not strongly skewed, resulting in
the bootstrap mean F for 2002 (0. 2392) being slightly higher than the
point estimate from the VPA (0.2310). There is a 80% chance that F in
2002 was between about 0.21 and 0.28, given variability in survey observations
(Table 95, Figure 14).
Retrospective analysis of the summer
flounder VPA was carried out for terminal catch years 1998-2001. This
"internal" retrospective analysis indicates a pattern of underestimation
of fully recruited F (ages 3-5) for 1999-2001, continuing the pattern
observed in the last three assessments (NEFSC 2000, MAFMC 2001a, NEFSC
2002). Fishing mortality was underestimated by 51% for 1999 (0.41 versus
0.84), by 40% for 2000 (0.60 versus 0.36), and by 20% for 2000 (0.35 versus
0.28), relative to the current VPA estimates. Spawning stock biomass has
been generally been overestimated in recent years, ranging from 20% for
1999 and 2000 to 7% for 2001, relative to the current VPA estimates. There
is no consistent retrospective pattern in the estimation of the abundance
of age 0 fish over the last three years (Table 96,
Figure 15). Comparison with previous assessments
("historical retrospective") shows a tendency to substantially underestimate
fully-recruited fishing mortality (ages 2-4, for comparability across
assessments) and slightly overestimate the SSB (ages 0-7+) from the the
mid-1990s through 2000 (Figure 16). The 2002 (NEFSC
2002) and 2003 assessments provide the most consistent sequential estimates
of fishing mortality and SSB since the 1996 and 1997 assessments.
BIOLOGICAL
REFERENCE POINTS
The calculation of biological reference points based
on yield per recruit for summer flounder using the Thompson and Bell (1934)
model was detailed in the 1990 SAW 11 assessment (NEFC 1990). The 1990
analysis estimated Fmax = 0.23. In the 1997 SAW 25 assessment
(NEFSC 1997b), an updated yield per recruit analysis reflecting the partial
recruitment pattern and mean weights at age for 1995-1996 estimated that
Fmax = 0.24. The analysis in the Terceiro (1999) assessment,
reflecting partial recruitment and mean weights at age for 1997-1998,
estimated that Fmax = 0.263 (Figure 17).
The Overfishing Definition Review Panel (Applegate
et al. 1998) recommended that the MAFMC base MSY proxy reference
points on yield per recruit analysis, and this recommendation was adopted
in formulating the FMP Amendment 12 reference points (see Introduction),
based on the 1999 assessment (Terceiro 1999). The 1999 assessment yield
per recruit analysis indicated that Fthreshold = Ftarget=
Fmax = 0.263, yield per recruit (YPR) at Fmax was
0.55219 kg/recruit, and January 1 biomass per recruit (BPR) at Fmax was
2.8127 kg/recruit. The median number of summer flounder recruits estimated
from the 1999 VPA for the 1982-1998 period was 37.844 million fish. Based
on this recruitment, maximum sustainable yield (MSY) was estimated to
be 20,897 mt (46 million lbs) at a biomass (BMSY) of 106,444
mt (235 million lbs). The biomass threshold, one-half BMSY,
was therefore estimated to be 53,222 mt (118 million lbs; Figure
18). The Terceiro (1999) reference points were retained in the 2000
and 2001 stock assessments (NEFSC 2000, MAFMC 2001a) because of the stability
of the input data. In the review of the 2002 stock assessment, SARC 35
concluded that updating these reference points was not warranted (NEFSC
2002), and therefore the reference points were not updated in this assessment
either.
PROJECTIONS
Stochastic projections were made to provide forecasts of stock size
and catches in 2003-2005 consistent with target reference points established
in the FMP. The projections assume that recent patterns of discarding
will continue over the time span of the projections. Different patterns
that could develop in the future due to additional trip and bag limits
and fishery closures have not been evaluated. The partial recruitment
pattern (including discards) used in the projections was estimated as
the geometric mean of F at age for 2000-2002, reflecting recent conditions
in the fisheries. Mean weights at age were estimated as the geometric
means of 2000-2002 values. Separate mean weight at age vectors were developed
for the January 1 biomass, landings, and discards.
One hundred projections were made for each of the
500 bootstrapped realizations of 2003 stock sizes from the final 2003
VPA, using algorithms and software described by Brodziak and Rago (MS
1994) as implemented in the NFT AGEPRO version 3.01. Recruitment during
2003-2004 was generated randomly from a cumulative density function of
the VPA recruitment series for 1982-2002 (median recruitment = 35.368
million fish). Other input parameters were as in Table
97; uncertainty in partial recruitment patterns, discard rates, or
components other than survey variability was not considered.
If landings in 2003 are 10,570 mt (23.3 million lbs)
and discards are 1,100 mt (2.4 million lbs), the forecast estimates a
median (50% probability) F in 2003 = 0.25 and a median total stock biomass
on January 1, 2004 of 63,600 mt, above the biomass threshold of ½ BMSY
= 53,200 mt. Landings of 12,790 mt (28.2 million lbs) and discards of
1,300 mt (2.9 million lbs) in 2004 provide a median F in 2004 = 0.26 and
a median total stock biomass level on January 1, 2005 of 70,500 mt. Landings
of 14,500 mt (32.0 million lbs) and discards of 1,400 mt (3.1 million
lbs) in 2005 provide a median F in 2005 = 0.26 and a median total stock
biomass level on January 1, 2006 of 75,800 mt (Table 97, Figures
18-19).
CONCLUSIONS
Assessment results
The summer flounder stock is not overfished and overfishing is not occurring
relative to the current biological reference points. The fishing mortality
rate has declined from 1.32 in 1994 to 0.23 in 2002, below the overfishing
definition reference point (Fthreshold = Ftarget
= Fmax = 0.26). There is an 80% chance that the 2002 F was
between 0.21 and 0.28. The estimate of F for 2002 may understate the actual
fishing mortality; retrospective analysis shows that the current assessment
method tends to underestimate recent fishing mortality rates (e.g., by
about 40% over the last three years).
Total stock biomass has increased substantially since 1989, and on January
1, 2003 was estimated to be 56,100 mt, 5% above the biomass threshold
(53,200 mt). There is an 80% chance that total stock biomass in 2003 was
between 51,000 and 63,000 mt. Spawning stock biomass (SSB; Age 0+) declined
72% from 1983 to 1989 (18,800 mt to 5,200 mt), but has increased eight-fold,
with improved recruitment and decreased fishing mortality, to 42,200 mt
in 2002. Retrospective analysis shows a tendency to slightly overestimate
the SSB in the most recent years. The age structure of the spawning stock
has expanded, with 80% at ages 2 and older, and 19% at ages 5 and older.
Under equilibrium conditions at Fmax, about 85% of the spawning
stock biomass would be expected to be ages 2 and older, with 50% at ages
5 and older.
The arithmetic average recruitment from 1982 to 2002 is 40 million fish
at age 0, with a median of 35 million fish. The 2002 year class is currently
estimated to be about average at 38 million fish. There is no consistent
retrospective pattern in the estimation of the abundance of age 0 fish
over the last three years.
If the landings for 2003 do not exceed the TAL and the proportion of
catch discarded does not increase, the total allowable landings (TAL)
in 2004 would need to be 12,790 mt (28.2 million lbs) to meet the target
F rate of Fmax = 0.26 with 50% probability. As noted above,
retrospective analysis suggests that the assessment tends to underestimate
fishing mortality rates in the most recent years.
Research Recommendations
The following major data and analytic needs for future assessments were
identified in the SARC 35 review of the 2002 assessment (NEFSC 2002) and
in the preparation of the 2003 assessment:
1) Expand the NEFSC fishery observer program for summer flounder, with
special emphasis on a) comprehensive areal and temporal coverage, b)
adequate length and age sampling, and c) continued sampling after commercial
fishery areal and seasonal quotas are reached and fisheries are limited
or closed, and d) sampling of summer flounder discard in the scallop
dredge fishery. Maintaining adequate observer coverage will be especially
important in order to monitor a) the effects of implementation of gear
and closed/exempted area regulations, both in terms of the response of
the stock and the fishermen, b) potential continuing changes in "directivity" in
the summer flounder fishery, as a results of changes in stock levels
and regulations, and c) discards of summer flounder in the commercial
fishery once quota levels have been attained and the summer flounder
fishery is closed or restricted by trip limits.
2) Evaluate the amount of observer data needed to reliably estimate
discards of summer flounder in all components of the fishery
3) Conduct further research to better determine the discard mortality
rate of recreational and commercial fishery summer flounder discards.
4) Develop a program to annually sample the length and age frequency
of summer flounder discards from the recreational fishery.
5) RIDFW monthly fixed station survey length frequencies are currently
converted to age using length cut-offs points. Investigate the utility
of applying the appropriate NEFSC or MADMF age-length keys to convert
the RIDFW monthly fixed station survey lengths to age.
6) Explore the possibility of weighting survey indices used in VPA calibration
by the areal coverage (e.g., in square kilometers) of the respective
seasonal surveys.
7) Explore the sensitivity of the VPA calibration to the addition of
1 and/or a small constant to values of survey series with "true zeros."
8) Statistically analyze changes in mean weights at age in the catch
and NEFSC surveys. Determine if using mean weights at age in the survey
are more appropriate for estimating the BMSY proxy. Explore
the sensitivity of the mean weights of the catch and partial recruitment
pattern from a longer time series (1997 to 2001) to the re-estimated
BMSY proxy. ) As the NEFSC fall survey age structure expands,
investigate the use of survey mean weights at age for stock weights at
age in yield per recruit, VPA, and projection analyses.
9) Monitor changes in life history (growth and maturity) as the stock
rebuilds.
10) Evaluate use of a forward calculating age-structured model for comparison
with VPA. Forward models would facilitate use of expanding age/sex structure
and allow inclusion of historical data. If sex-specific assessments are
explored, the implications on YPR should also be investigated.
11) Explore the sensitivity of the VPA results to separating the summer
flounder stock into multiple components.
12) Evaluate trends in the regional components of the NEFSC surveys
and contrast with the state surveys that potentially index components
of the stock.
13) Use NEFSC fishery observer age-length keys for 1994 and later years
(as they become available) to supplement NEFSC survey data in aging the
commercial fishery discard.
Major sources of assessment uncertainty
The SARC 35 review of the 2002 assessment (NEFSC 2002) identified the
following major sources of uncertainty:
1) The landings from the commercial fisheries used in this assessment
assume no under reporting of summer flounder landings. Therefore, reported
landings from the commercial fisheries should be considered minimal estimates.
2) The recreational fishery landings and discards used in the assessment
are estimates developed from the Marine Recreational Fishery Statistics
Survey (MRFSS). While the estimates of summer flounder catch are considered
to be among the most reliable produced by the MRFSS, they are subject
to possible error. The proportional standard error (PSE) of estimates
of summer flounder total landings in numbers has averaged 7%, ranging
from 26% in 1982 to 3% in 1996, during 1982-2002.
3) The intensity of fishery observer sampling of the commercial scallop
dredge fishery (outside of exempted area fisheries) was particularly
low in 2001. This level of observer coverage likely was insufficient
to accurately characterize summer flounder discards.
4) The length and age composition of the recreational discards are based
on data from a limited geographic area (Long Island, New York, 1988-1992;
Connecticut, 1997-2001, New York party boats 2000-2001, ALS releases
focused in New York and New Jersey, 1999-2001). Sampling of recreational
fishery discards on a annual, synoptic basis is needed.
ACKNOWLEDGMENTS
Special thanks to Jay Burnett and the staff of the NOAA Fisheries NEFSC
Population Biology Branch for their timely preparation of the 2002/2003
summer flounder ages used in this year's assessment.
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