Northeast Fisheries Science Center Reference Document 05-05
Effectiveness of a square-mesh escape panel
in reducing finfish
bycatch in a small-mesh
used in the longfin
inshore squid (Loligo
National Marine Fisheries Serv., Woods Hole Lab., 166 Water St., Woods
Hole, MA 02543
Web version posted June 14, 2005
Hendrickson L. 2005. Effectiveness of a square-mesh escape panel in reducing finfish bycatch
in a small-mesh bottom trawl used in the longfin inshore squid (Loligo pealeii) fishery. US Dep
Commer, Northeast Fish Sci Cent Ref Doc. 05-05; 37 p.
Information Quality Act Compliance: In accordance with section 515 of Public Law 106-554, the Northeast Fisheries Science Center completed both technical and policy reviews for this report. These predissemination reviews are on file at the NEFSC Editorial Office.
A small-mesh bottom trawl fishery for Loligo pealeii (longfin inshore squid) occurs throughout the year on the continental shelf
of the east coast of the United States. During winter, the fishery
is concentrated in the offshore waters of the Mid-Atlantic Bight and
Southern New England. Several types of high-opening bottom trawls
are used in the fishery, but all are comprised of small-mesh, diamond
A minimum mesh size regulation (50 CFR § 648.23) has
been in effect since May 2, 1996 for
vessels which possess L. pealeii. The regulation states that a
minimum mesh size of 4.76 cm (1 7/8 in.) diamond mesh (inside stretched
mesh) may be used "throughout the codend for at least 150 continuous
meshes forward of the terminus of the net, or for codends with less than
150 meshes, the minimum mesh size codend shall be a minimum of one-third
of the net measured from the terminus of the codend to the head rope.".
In addition, a codend cover or strengthener may be used provided that
the effective mesh opening of the cover is at least 11.43 cm (4.5 in.)
diamond mesh (inside stretched mesh) along the top 50% of the net surface.
The codend cover may not constrict the effective mesh opening in the
top 50% of the net to less than 48 mm. Vessel operators fishing for Illex during
the months of June through September, seaward of a line which approximates
the 50 fathom isobath, are exempt from the minimum mesh size regulation.
As a result of the small codend mesh size used in the L. pealeii fishery,
a large portion of the biomass encountered by the net is retained. Consequently,
the potential for bycatch is high for species which co-occur with L.
pealeii. One such species is scup (Stenotomus chrysops), for
which high discard rates of sublegal-sized individuals (<22.86 cm
or 9 in. TL), during winter and spring, have been identified as a major
source of fishing mortality on the heavily-exploited scup stock (NEFSC
2000). Scup and L. pealeii are both schooling species that are
distributed primarily between Cape Cod, MA and Cape Hatteras, NC. Research
bottom trawl surveys conducted by the Northeast Fisheries Science Center
(NEFSC), during 1992-2003, indicate that both species are distributed
offshore during the winter (Figure 1) then migrate inshore during the
spring (Figure 2).
In an effort to reduce discarding of juvenile scup in trawl fisheries,
two Gear Restricted Areas (GRAs) have been in effect since December
27, 2000 (50 CFR § 648.122). Fishing with a codend mesh size smaller
than 11.43 cm diamond mesh,throughout the codend and for at least
75 continuous meshes forward of the terminus of the net, is prohibited
in the Northern GRA (NGRA) during November 1 through December 31 and
in the Southern GRA (SGRA) during January 1 through March 15 (Figure
3). In 2005, the SGRA was moved westward by 3 minutes. Vessels fishing
with a codend mesh size of less than 114.3 mm are subject to scup trip
limits of 226.8 kg (500 lbs) during November 1 to April 30 and 45.4 kg
(100 lbs) during May 1 to October 1. Effective January 2, 2003 (68 FR
68), such vessels were prohibited from fishing within the GRAs unless
they possessed a Scup GRA Exemption Program Authorization, carried a
NMFS-certified observer onboard, and fished with "a specially modified
trawl net. A requirement of the modified trawl net included an escapement
extension consisting of a minimum of 45 meshes of 14.0 cm (5.5 in.) square-mesh
positioned behind the body of the net and in front of the codend.
In the subject study, the parallel haul method is used to evaluate
the effectiveness of a square-mesh escape panel installed in a L.
pealeii bottom trawl, similar to that required by the 2003 GRA regulations,
in reducing the bycatch of scup in offshore waters during the winter.
The bycatch of other finfish species, as well as L. pealeii catch,
was also quantified during the study.
Two Loligo fishing vessels of similar size,
horsepower and gear configuration (Table 1), the F/V Sea Breeze and
F/V Iron Horse, were chartered by the Northeast Fisheries Science
Center (NEFSC) to conduct a parallel haul study. Both vessels fished
with identical high-opening, two-seam "rope trawl" nets manufactured
by Superior Trawl in Davisville, Rhode Island. Identical, detachable
codends manufactured specifically for the study were laced onto the body
of each net with a rope woven through plastic rings. One vessel fished
the control codend while the other vessel fished the experimental codend
on a parallel course with the two vessels located as close as possible
throughout each tow. The control codend was constructed of 165 by 180
meshes of 6 cm (2 3/8 in.) diamond mesh nylon twine (inside stretched-mesh
measurement). The codend cover was constructed of 50 by 60 meshes of
15.24 cm (6 in.) diamond mesh polyethylene twine (between the knots).
The only difference between the control codend (Net C) and experimental
codend (Net E) was a square-mesh escape panel installed in Net E between
the codend and the extension (Figure 4).
The square-mesh escape panel was constructed with green, 4 mm Euro webbing
hung square and was 45 meshes deep with a bar length of 8 cm (inside
stretched-mesh measurement of 14.61 cm). The panel was constructed of
green webbing to provide visual contrast between it and the adjacent
white webbing to which it was attached. A hanging ratio of 33% was used
to attach the panel to the codend and net extension (to hold the twine
open 66%). The panel was installed 50 meshes forward of the codend terminus.
The square-mesh panel was outfitted with ten gore lines to reduce any
strain on the net. Inside stretched mesh measurements of ten randomly
selected panel meshes were taken before and after the study to determine
whether knot slippage had occurred.
Sampling was conducted in the Mid-Atlantic
Bight at nineteen stations located inside and outside the SGRA (Figure
Stations 9 and 15 were omitted from the analyses because they were associated
with major gear problems that may have affected the catch rates. Stations
were selected according to depth, without regard for their location in
relation to the SGRA, with the objective of sampling across the depth
range of scup and Loligo habitats. Sampling was conducted during
the day (0700-1700 hrs) when Loligo are located near the seabed
(Brodziak and Hendrickson 1999; Roper and Young 1975). Assignments of
vessel net type (experimental net versus control net) and towing location
(seaward versus shoreward of the other vessel) were chosen at random
during the first tow of each day via a coin toss. Thereafter, towing
location was alternated and net assignments were either E-C-C-E-E or
The same towing protocol was implemented aboard both
vessels and all tows made by each vessel were conducted by the same individual
to further ensure consistent setting and haulback of the gear. A 3:1
scope ratio was used during all tows and amounts of warp payout and haulback
were reported by radio at 50-fm. intervals from one vessel captain to
the other to synchronize the timing of net touchdown, liftoff, and haulback.
According to the NEFSC Observer Program Database, 85% of the tows conducted
during the 1995 to 2003 winter Loligo fisheries were conducted
at 3.0 to 3.3 nmi.∙ hr-1 and averaged 3.2 nmi.∙ hr-1 (knots).
Similarly, the study incorporated a standardized towing speed of 3.2
nmi.∙ hr-1. Based on Vessel Trip Report (VTR) data,
the average tow duration during 97% of the Loligo trips conducted
in winter, during 1997 to 2003, ranged from one to four hours, with a
mode of three hours. A one-hour tow duration was used during the study
to maximize the number of tows conducted per day and still remain within
the range of commercial tow durations. Tow duration was monitored with
a stopwatch and was defined as the time between net touchdown and lift-off
which were determined from the headline sensor screen display that showed
the trawl location in real-time. Actual bottom contact time was identified
post-hoc based on data collected by an inclinometer attached to the footrope
by two chains which allowed it to swing up and down but not side-to-side.
During each tow, the angle of the inclinometer was recorded at one-second
intervals and the resulting data were plotted against tow time to determine
when the net was fishing on the bottom. Sampling was suspended when the
inclinometer data indicated that the net was not fishing on the bottom
for extended periods of time due to sea state. Tow distance was computed
as the actual tow duration multiplied by the average speed over ground.
Average wingspread, doorspread and headrope height were computed for
the period of time that the trawl fished on the bottom. Catch rates were
standardized for the volume of water sampled (m3) during each
tow, computed as the product of average wingspread, average headrope
height and tow distance. Standardized catch rates were scaled by 106 and
log-transformed prior to statistical analysis.
A paired-comparisons t-test, conducted in SAS (SAS Institute
Inc. 1985), was used to determine whether the mean differences in standardized
catch rates between Net C and Net E (loss in terms of number and weight
per m3) were significant for scup, L. pealeii and black
sea bass. The GLM procedure in SAS was used to evaluate whether standardized
catch rates of L. pealeii, scup and black sea bass in Net C were
dependent on water depth, surface temperature or bottom temperature.
Selectivity parameters and the relative fishing intensity of Net E were
estimated for scup, black sea bass, and L. pealeii using the SELECT
model (Share Each LEngth's Catch Total) developed by Millar (1992).
The SELECT model uses a conditional likelihood approach where the proportion
of catch in each length category, in the experimental net, is modeled
as a function of the logistic curve parameters a and b and
the relative fishing intensity (p) of a gear type such that:
Maximum likelihood parameter estimates were obtained by fitting the
SELECT model to catch at length data (binned at 1 cm intervals), with
the use of SOLVER, in an Excel spreadsheet program developed by Tokai
(1997). The analysis only included data from stations where a particular
species was caught in both nets and for consecutive length bins where
the total catches were greater than zero.
Data from NEFSC research bottom trawl surveys conducted in the winter
(February) and spring (March), during 1992-2003, were used to assess
the general spatial overlap between the seasonal distributions of L.
pealeii and either scup or black sea bass and to assess the co-occurrence
of L. pealeii and each of the two species in relation to water
depth. The stratified random survey design and sampling protocols are
described in Azarovitz (1981). Co-occurrence was defined as the percentage
of the combined catch (number per tow) of scup and L. pealeii that
was comprised of scup. The percentage of scup from such tows was binned
into quartiles (0.1-25%; 26-50%, 51-75% and 76-99.9% scup) to assess
the degree of co-occurrence within the depth range of the winter L.
Ten stations were sampled inside and nine stations were sampled outside
of the SGRA at depths of 83 to 155 m (Table 2, Figure
5). VTR data for
1997-2003 indicated that a large majority (89%) of the L. pealeii landings
in the winter directed fishery (January through March) occurred at depths
of 102 m to 183 m. Within this depth range, the percentage of L. pealeii landings
was 6% higher after implementation of the SGRA (93% in 2001-2003) than
before (87% in 1997-2000, Figure 6). The 6% increase in landings was
attributable to a 10% decrease in landings from depths of 102 m to 137
m combined with a 16% increase in landings from depths of 138 m to 183
m. An additional 5% of the landings occurred at depths less than 102
m. All of the stations sampled during the study were located within the
depth range of the winter L. pealeii fishery and most stations
(84%) were located within the 102 m to 183 m depth range (Figure
Catches in the control net (Net C) reflect the selectivity of one type
of net used in the winter L. pealeii fishery. L. pealeii was
caught in Net C at every station, at depths between 83 and 155 m, and
comprised 22% of the combined weight of all species caught during the
study. Bycatch (kg) in Net C consisted of 40 species but was dominated
(89%) by three species (Table 3): spiny dogfish (36%), scup (34%), and
black sea bass (19%). L. pealeii co-occurred most frequently withsummer
flounder (95%), butterfish (95%), silver hake (89%) and spiny dogfish
(84%). Black sea bass and scup co-occurred less frequently with L.
pealeii, at 79% and 63% of the nineteen stations, respectively. Most
(94%) of the nominal L. pealeii catch (kg) in Net C occurred at
depths of 129 m to 155 m and the remaining 6% occurred at depths of 83
m to 117 m (Table 3). Conversely, most of the scup catch (96%) occurred
at depths of 83 m to 117 m and the remaining 4% occurred at depths of
129 to 155 m. Most (66%) of the black sea bass catch occurred at depths
of 129 m to 155 m, but 34% of the catch also occurred at depths of 83
m to 117 m.
The study results suggested that, during the winter of 2004, scup and L.
pealeii co-occurred primarily at depths of 83 m to 129 m, with
smaller amounts of scup catch at depths of 129 m to 155 m (Figure
Black sea bass and L. pealeii co-occurred throughout the depth
range of the study (83 m to 155 m), but a large portion (42%) of the
black sea bass catch occurred within the depth range of 129 m to 155
m, where L. pealeii catch rates were highest (Figure
comparison, co-occurrence data from NEFSC research bottom trawl surveys,
where sampling was conducted across multiple years and a broader latitudinal
range, suggest that L. pealeii co-occurs with scup and black
sea bass at deeper depths than those sampled during the study. In
NEFSC research surveys, tows with catches of both scup and L. pealeii occurred
at depths of 30 m to 340 m during February and at depths of 20 m to
320 m during March (Figure 9). Co-occurrence during both months occurred
throughout the depth range of the L. pealeii winter fishery,
but was most common at depths of 40 m to 130 m (modes at 70 m and 120
m). Most survey tows with catches of both specieswere comprised
ofa low percentage of scup (0.1- 25%) in relation to L.
pealeii (75-99.9%). The percentage of scup catch in tows with co-occurrence
differed little by depth during either month (Figure 9).
Similar to scup, the distributions of black sea bass and L. pealeii overlap
during winter and spring (Figure 10 and Figure 11), primarily in the offshore
waters between Hudson Canyon and Cape Hatteras. In NEFSC research surveys,
black sea bass and L. pealeii co-occur at depths of 30 m to 320
m during February and at depths of 10 m to 310 m during March (Figure
12). Similar to scup, co-occurrence with L. pealeii during both
months was most common at depths of 40 m to 130 m, with modes at 70 m
and 120 m. Most of the survey tows with catches ofboth species
were comprised ofa low percentage of black sea bass (0.1- 25%)
in relation to L. pealeii (75-99.9%). The percentage of black
sea bass catch in tows with co-occurrence differed little by depth during
either month (Figure 12).
Within the latitudinal range sampled, 39º 21.237' N to 38º 27.000'
N (54 nmi.), neither surface nor bottom water temperatures were correlated
with depth (p > 0.05). Surface water temperatures were fairly constant
across station depths (83 m to 155 m) and ranged from 9.5 ºC to 10.9 ºC.
Bottom water temperatures were more variable and ranged between 9.1 ºC
and 12.6 ºC. Thermal stratification was present at some of the stations
located near the shelf edge, at depths greater than 150 m, where bottom
temperatures were warmer than surface temperatures. For example, the
water column was not stratified at a station depth of 153 m (station
16, Figure 13A), but stratification was present at a station depth of
155 m (station 4, Figure 13B). At station 4, a rapid increase in water
temperature occurred at depths beyond 100 m.
As expected for species which form schools or are distributed in aggregations,
standardized catch rates (kg/m3 x 106) of scup,
black sea bass, and L. pealeii were highly variable. Scup catch
rates were the most variable of the three species, with sizeable catches
at only five stations (Table 4). For the eight stations where both nets
caught scup and where Net C caught more scup than Net E, paired t-tests
indicated significant reductions (catch rates of Net C - Net E) in catch
numbers (p < 0.05) and catch weights (p < 0.01). On average, standardized
catch rates of scup in Net E were reduced by 79% and 78% in terms of
numbers and weight, respectively. On average, standardized catch rates
of black sea bass in Net E were significantly reduced by 75% and 69%
in terms of numbers (p < 0.0001) and weight (p < 0.0001), respectively
(Table 5). Loss of the target species, L. pealeii, in Net E was
highly significant (p < 0.0001) for catch numbers and weight, and
on average, was reduced by 88% and 84%, respectively (Table
GLM results indicated that standardized catch rates of scup in Net
C decreased significantly with depth for both numbers and weight (Table
7). However, depth explained only 42% and 30% of the variance in catch
numbers and weight, respectively. The highest catch rates of scup occurred
at shallow depths (83 m to 117 m) where L. pealeii catch rates
were lowest. Depth did not have a significant effect on the catch rates
of black sea bass in Net C (p > 0.05). Standardized catch rates of L.
pealeii increased significantly with depth and decreasing bottom
7). Catch rates at depths of 129 to 155 m (1,576 kg/m3 x
106) averaged more than ten-fold the catch rates at shallower
depths of 83 to 117 m (147 kg/m3 x 106). Station
depth and bottom temperature explained 75% and 76% of the variance in L.
pealeii catch numbers and weight, respectively.
The size selectivity of scup and black sea bass catches differed by
net type. Scup caught in Net C ranged in length from 11 cm to 37 cm with
modes at 17 cm and 21 cm (Figure 14A). A large portion (44%) of the total
scup catch, by number, was of sublegal size (Figure 15A). Black sea
bass caught in Net C ranged in length from 17 cm to 58 cm with modes
at 17 cm and 21 cm (Figure 14B). More than half (55%) of the total black
sea bass catch, by number, was of sublegal size (Figure
proportions of sublegal size scup and black sea bass were taken with
Net E than Net C. The proportion of sublegal size fish retained in Net
E versus Net C was reduced by 17% for scup, primarily in the 14 to 18
cm length range (Figure 15A), and by 20% for black sea bass (Figure 15B). L.
pealeii caught in Net C ranged in mantle length from 2 cm to 27 cm
with a mode at 10 cm (Figure 14C). For L. pealeii, there was little
difference in size selectivity between the two net types (Figure 15C).
For scup, the SELECT model results indicated that the relative fishing
intensity of Net E (p = 0.26) was 36% of that for Net C, resulting
in a L50 estimate of17.1 cm and a selection range
of 0.98 cm (Table 8). A selection factor of 2.8 was estimated. However,
the model fit for scup was poor, as evidenced by the high model deviance
value, and an unrealistically-narrow selection range was estimated (Figure
16B). A second model run with the catch-at-length matrix truncated to
26 cm, beyond which fewer fish were caught, did not remedy either problem
and resulted in similar parameter estimates. The model run for which p was
estimated resulted in a lower Akaike Information Criterion value (AIC
= 3,316) than a model run with p fixed at 0.5 (AIC = 4,599), confirming
that the two codends did not fish with equal intensity.
For black sea bass, the results of the SELECT model indicated that
the relative fishing intensity of Net E (p= 0.36) was 57% of that
for Net C, resulting in a L50 estimate of 27.7 cm and a selection
range of 7.4 cm (Table 8). A selection factor of 4.6 was estimated. A
trend in the deviance residuals was present for fish larger than 46 cm,
the length range where fewer fish were caught. The model fit was good
with the exception of fish larger than 46 cm, which showed a positive
trend in the residuals concurrent with low sample sizes (Figure
The AIC value for the model run where p was estimated (AIC = 484)was
lower than for the model run where p was fixed at 0.5 (AIC = 549)
L. pealeii catch-at-length data could not be fit to the SELECT
model (Figure 18), which suggests that selectivity is not a logistic
function of mantle length and that other factors also affect selectivity.
The study results indicate that within the depth range of the winter L.
pealeii fishery, L. pealeii co-occurs most frequently with: summer
flounder, butterfish, silver hake, spiny dogfish, black sea bass, and
scup. The co-occurrence of L. pealeii and butterfish on the
US shelf has been attributed to similar depth and water temperature
preferences and the bycatch of butterfish in the L. pealeii fishery
has previously been documented (Lange and Waring 1992). Within the
depth range sampled, the study results suggested that scup and L.
pealeii co-occur primarily at depths of 83 m to 129 m, which overlaps
with the depth range of the L. pealeii winter fishery. However,
since the study results are based on data collected within a single
year and across a limited depth range, they were compared with co-occurrence
data from the winter and spring NEFSC research surveys conducted during
1992-2003. The survey data confirm the persistence of the 2004 co-occurrence
patterns observed for both scup and black sea bass and show that both
species have been caught with L. pealeii, within the depth range
of the winter L. pealeii fishery, during years other than 2004.
However, tows with co-occurrence tended to contain a low percentage
of scup or black sea bass (0.1 to 25%) and a high percentage of L.
pealeii (75 to 99.9%).
Escapement of finfish from diamond-mesh trawls occurs primarily through
codend meshes which are open the furthest, those located immediately
in the front of the catch (Wardle 1993). Square-mesh panels installed
in the codend or extension of a net provide an additional area for escapement
by providing a larger area of open meshes. For example, small-mesh prawn
(Nephrops) trawls which have a codend mesh size less then 100
mm are required to contain a square-mesh panel on the top side of the
trawl to reduce catches of juvenile haddock and whiting (Zuur et al.
Fishing with a square-mesh escape panel installed in a L. pealeii bottom
trawl reduced the average catches of scup by 78% in weight and 79% in
numbers. Catches of black sea bass were reduced by 69% in weight and
75% in numbers. Large portions of the scup (44% in numbers) and black
sea bass (55% in numbers) catches in the control net were of sublegal
size. However, the square-mesh panel was effective in reducing catches
of sublegal-size scup and black sea bass by 17% and 20%, respectively.
Utilization of the square-mesh panel did not affect the size distribution L.
pealeii butresulted in significantly large losses of L.
pealeii catch (on average, 88% in numbers and 84% in weight). As
a result, the use of a square-mesh escape panel in the configuration
tested is not a reasonable solution to the bycatch problem in the winter L.
pealeii fishery. However, it may be possible to modify the panel
configuration to reduce squid loss. If so, then its use in L pealeii nets
would aid in increasing the spawning stock biomass of scup because
the estimated L50 of the experimental net (17.1 cm FL) is
slightly greater than 15.5 cm FL, the length at which 50% of the females
are mature (O'Brien et al. 1993). Use of the panel would also
aid in increasing the spawning stock biomass of black sea bass. For
black sea bass, the estimated L50 of Net E (27.7 cm TL)
is greater than 19.1 cm TL, the length at which 50% of the females
are mature (O'Brien et al. 1993). Black sea bass are protogynous
hermaphrodites and the majority of fish less than 19.1 cm are females
(Steimle et al. 1999). In order to determine the reasons for
squid loss and whether such losses can be substantially reduced will
require video camera monitoring of squid behavior in the vicinity of
the square-mesh panel, during towing and at haulback. If squid loss
occurs passively through the bottom of the panel during haulback, a
simple solution might be to install a small-mesh liner in the bottom
half of the panel to retain squid but allow finfish escapement through
the top half of the panel. Extension length and codend diameter have
both been shown to affect trawl selectivity (Reeves et al. 1992).
The effectiveness of a large-mesh panel is also dependent on its placement
in the net (Armstrong et al. 1997; Graham et al. 2002).
If squid loss occurs via active escapement through the panel meshes,
varying the panel placement and/or extension length might be investigated.
For example, Glass et al. (1999) studied the inshore L. pealeii fishery
and found that the capture response of L. pealeii in bottom
trawls under ambient light conditions involves herding in the net mouth,
where squid move toward the wing ends then gradually rise to the top
of the net while maintaining school structure. Squid then turn toward
the codend and cease to swim upon tiring. Bycatch separation trials
indicated that this behavior pattern allowed the separation of squid,
caught primarily in the upper portion of the codend, from scup and
other bycatch species caught in the lower portion and that legal-size
scup tended to be caught in greater proportions in the top half of
the codend (Glass et al. 1999).
Time-area closures may be feasible as a bycatch reduction measure in
the L. pealeii fishery if there is some degree of temporal-spatial
separation between the L. pealeii and the co-occurring species.
However, this may not be possible if co-occurrence persists across years.
For example, Gabriel (1992) found that species assemblages which include L.
pealeii and many of the bycatch species from the subject study persist
interannually in the Mid-Atlantic Bight. However, she also showed that
patterns of species co-occurrence are highly variable interannually and
linked to the variability in temperature-related oceanographic features.
Consequently, the spatial distributions of such species are difficult
to predict. As a result, implementation of time-area closures like the
existing small-mesh gear restriction area for scup must be species-specific
and must encompass areas large enough to encompass the temporal-spatial
variability in co-occurrence in order to be effective.
Given the difficulties associated with implementing and enforcing species-specific
time-area closures and the unknown increase in codend mesh size that
is feasible, the preferred solution to bycatch reduction in the L.
pealeii fishery is gear modification. However, until a gear modification
solution can be found, other bycatch reduction measures can be implemented.
For example, a codend mesh size increase would allow some escapement
of juvenile finfish because the size compositions of bycatch species
in the L. pealeii fishery are likely comprised of higher proportions
of sublegal-size fish than have been reported herein. The Vessel Trip
Report data indicate that a majority (44%) of the L. pealeii catch
during 1997-2003 was obtained with 48-50 mm mesh codends. The codend
mesh size used in the subject study was 60 mm, which fell within the
mesh size range (60-63 mm) used to take 26% of the L. pealeii catch
during this time. An additional 14% of the L. pealeii catch was
taken with 76 mm mesh codends in a mixed fishery for L. pealeii and
silver hake (Merluccius bilinearis). The NEFSC Observer Database
indicates that codend covers used in the directed fishery during 1996-2003
consisted primarily of double-twine, 140 to 160-mm diamond mesh. The
regulation of codend mesh size has historically been used in the squid
fisheries (Illex illecebrosus and L.pealeii), in
U.S. and Canadian (Illex only) waters, as a bycatch management
measure. In addition, small-mesh bottom trawl fisheries have historically
been limited to specific offshore areas and seasons in both the U.S.
and Canada. Since 1977, a minimum codend mesh size of 130 mm has been
required in bottom trawls that are fished on the Scotian Shelf shoreward
of the 200 m isobath (ICNAF 1978). During 1978-1982, bottom trawlers
engaged in directed fisheries for Illex and L. pealeii in
U.S. waters were required to fish with a minimum codend mesh size of
60 mm (with specific chafing gear requirements) and were restricted to
two time periods and two offshore fishing areas which straddled the 183
m isobath (ICNAF 1978). During this time, a portion of the bottom trawl
fleet also targeted Illex with 80 to 90 mm-mesh codends (Hatanaka
and Sato 1980; ICNAF 1979). However, the use of pelagic trawls was required
for squid fishing throughout most of the year and within the offshore
areas where small-mesh fishing was allowed. In order to determine the
maximum mesh size increase possible, a mesh selectivity study of the L.
pealeii fishery would need to be conducted to quantify juvenile finfish
escapement and squid loss associated with a range of codend mesh sizes
greater than the predominant mesh size currently in use and including
testing of square-mesh instead of diamond-mesh codend covers.
This research was funded primarily by the Marine Fisheries Initiative
Program (MARFIN) Program, but was supplemented with NEFSC cooperative
research funds. I thank Victor Simon for loaning us the portable FSCS
equipment and for giving us endless technical advice. I am also grateful
to Michele Thompson for her assistance with data processing and summarization
and to Chris Glass (Manomet Center for Conservation Sciences) for providing
valuable insights regarding the panel design. I also thank Fred Serchuk
and Mark Terceiro for their thorough reviews of the manuscript and helpful
suggestions. The study would not have been possible without the cooperative
efforts of the following people:
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