Northern or pink shrimp,
Pandalus borealis, occur in boreal waters of the North
Atlantic, North Pacific, and Arctic Oceans. In the Gulf of Maine,
northern shrimp are considered to constitute a unit stock. They
inhabit soft mud bottom at depths of approximately 10 to 300 m (2
to 165 fathoms), most commonly in the cold waters of the southwest
Gulf of Maine (Figure
33.1). The Gulf of Maine is the southern limit
of the northern shrimp distribution in the North Atlantic, and temperature
affects growth and development rates and reproductive success in
Northern shrimp are hermaphroditic,
maturing first as males at roughly 2½ years of age and then
transforming to females at about 3½ years of age. In the
Gulf of Maine, spawning begins in offshore waters in late July.
In late autumn and winter egg bearing females move inshore, where
the eggs hatch. Juveniles remain in coastal
waters for a
year or more before
migrating to deeper offshore waters, where they mature as males.
The exact extent and location of these migrations is variable. Males
undergo a series of transitional stages before maturing as females.
Some females may survive to repeat the spawning process in succeeding
years. Natural mortality seems to be most pronounced immediately
following hatching. Most shrimp do not live past age 5.
The Gulf of Maine fishery
for northern shrimp targets females and is managed through an
interstate agreement between the states of Maine, New Hampshire
and Massachusetts. The management framework evolved between 1972-1979
under the auspices of the State/Federal Fisheries Management Program.
In 1980, this program was restructured as the Interstate Fisheries
Management Program (ISFMP) of the Atlantic States Marine Fisheries
Commission (ASMFC). The Fishery Management Plan (FMP) for Northern
Shrimp was approved in October 1986 (FMR No. 9., ASMFC), and Amendment
1 to the FMP enacted May 2004 (FMR No. 42). Amendment 1 established
and expanded the tools available to manage the fishery. The goal
of Amendment 1 is “to manage the northern shrimp fishery
in a manner that is biologically, economically, and socially sound,
while protecting the resource, its users, and opportunities for
participation by all stakeholders.”
Within the ISFMP structure, the Northern Shrimp
Technical Committee (NSTC) provides annual stock assessments and
related information to the ASMFC Northern Shrimp Section. Annually,
the Section decides on management regimes after thorough consideration
of the NSTC stock assessment, input from the Northern Shrimp Advisory
Panel and comment from others knowledgeable about the shrimp fishing
Fishing seasons can occur from December
through the following May with the allowable fishing days set
by the ASMFC northern shrimp Section. Landings in 2004 (a 40-day
season) were 1,949 mt, with 2553 mt in a 70-day season in 2005.
The 2006 140 day season landings were 1877 mt. These are all well
below the 1969 – 1972 average of 11,400 mt.
At its Fall 2006 meeting, the Northern
Shrimp Section approved a 151 day 2007 fishing season, for both
mobile and trap gear, that will be open seven days a week from
December 1, 2005, through April 30, 2006.
A directed otter trawl fishery
for northern shrimp in coastal waters of the Gulf of Maine began
during the winter months in the 1930s. Landings peaked at 12,800
mt in 1969 with the expansion of an offshore, year-round fishery;
but markedly declined in the mid-1970s and a fishery closure was
enacted in 1978 Figure
33.2 Data]). Thereafter, landings increased steadily to over
5,000 mt by 1987. Landings ranged from 2,300-4,400 mt between 1988-1994,
and then rapidly increased to 9,200 mt in 1996. Landings declined
between 1996 and 2002 but increased afterwards Landings in the 2003
38-day season were 1,211 mt, 1,933 mt (preliminary data) in a 40-day
season in 2004 and 2,146 mt (preliminary data) in the 70-day season
in 2005 (Table 33.1)
Maine accounted for 84% (1,808
mt) of the 2005 season while New Hampshire and Massachusetts landed
14% (290 mt) and 2% (48 mt), respectively. This distribution of
landings among states is similar to recent years, but has shifted
since the 1980’s when Massachusetts accounted for about 30%
of the total, (Figure
33.3 Data]). Most shrimp in the Gulf of Maine are landed by
otter trawls, although traps accounted for 4 – 20% of the
annual landings during 2000 - 2005.
There has been no northern shrimp
fishery in the Canadian portion of the Gulf of Maine since the early
Biomass of the northern shrimp
stock is monitored in the NEFSC autumn bottom trawlsurvey and the
ASMFC summer shrimp survey. The NEFSC autumn survey biomass index
declined in the early and mid-1970s, remained relatively stable
from 1980 to 2001 and has since slightly increased (Figure
33.4 Data]). A joint State-Federal shrimp survey has been conducted
from the summer of 1984 to present. Biomass and abundance indices
from this series are the major source of information used in an
annual assessment by the ASMFC northern shrimp Technical Committee.
These indices are similar in trend to those from the NEFSC autumn
bottom trawl series. They are relatively stable from 1984 –
1990 then decline throughout the 1990s. Until 2003 the summer indices
remained low and have increased in the last 3 years. (Figure 33.4)
. Exploitation rates, calculated during fishing seasons, increased
from 20 to 38% between 1985 and 1995, peaked at 60% in 1997 before
declining to 6% during 2002 (Figure
33.5 Data]). The drop in exploitation rate is consistent with
the decline in nominal effort during the same period. Since that
time, exploitation has increased to 15%. Exploitation rates at or
near the 1997 level occurred at the time of the stock collapse in
Estimates of abundance, biomass, recruitment and fishing mortality
are available from the most recent (2006) analytical stock assessment
33.6 Data]). The assessment focuses on estimates from a Collie-Sissenwine
Analysis (CSA) (Collie and Sissenwine 1983; Collie and Kruse 1998).
This relies on the joint State-Federal shrimp survey, limiting
the period of analysis to 1985 to present . During this period,
abundance and biomass were high during the late 1980s, declined
in the 1990s but have since increased to the highest levels of
this period. When compared to the surplus production model (ASPIC)
used to corroborate results from CSA, the current estimates are
at the level of the late 1960s (Figure
Annual estimates of fishing mortality (F) (expressed as “harvest
rate” derived F’s) were relatively stable between
1985 and 1994 at about F = 0.22 (17% exploitation rate), peaked
at 1.12 (61% exploitation) in the 1997 season, and then decreased
to 0.07 (6% exploitation), due in part to a short fishing season
and poor stock conditions (Figure
33.8 Data]). Fishing mortality from 2003 –
2005 has been about 0.20, the same level as in the late 1980s.
Because of a lack of detailed information about discards, no
analyses of discarding were conducted in the recent assessment.
Fishing mortality and biomass
reference points (Table 33.2) for northern
shrimp were developed in 2004 (NSTC 2004) and adopted by AMFC (ASMFC
2004). FTarget was estimated to be 0.22 based on the
average estimates from 1985 through 1994, which represents a relatively
stable period covered by the assessment series. FLimit
= 0.6 represents the level of fishing mortality that would reduce
egg production below 20% of maximum (NSTC 2006). This level of fishing
is comparable to that preceeding the stock collapse in the late
1970s. The stock biomass threshold of BThreshold = 9,000
metric ton and limit of BLimit = 6,000 metric ton are
based on historical abundance estimates and response to fishing
pressure. Biomass dynamics during 1985 through 2006 are shown in
Landings in the Gulf of Maine northern shrimp fishery declined
from a high of 9,200 mt in 1996 to a low of 424 mt in 2002, the
result of reduced fishing. Since then, landings have increased
to 2,146 mt in the 2005 season. The number of fishing vessels
and trawl trips declined from about 310 and 10,734 respectively
in 1997 to 153 and 2,590 in 2005 (although vessel reporting, particularly
from the Maine small boat fleet, has probably improved). Fishing
mortality rates declined from 0.87 in 1997 to 0.19 in 2005, and
is currently below the 1985-1994 average (the target F in the
Exploitable biomass declined from 15,800 mt in 1996 to a time
series low of 5,800 in 2000. Since then the biomass estimate has
increased to 28,000 mt in 2006, the highest value in the assessment,
and above the biomass reference point. The estimated biomass to
the fishing year 2007 is 71,500 mt.
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Jr. 1986. Effects of temperature on the biology of the northern
shrimp, Pandalus borealis, in the Gulf of Maine. NOAA Tech.
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D.McCarron, and B. Smith. 1999. Application of catch-survey models
to the northern shrimp fishery in the Gulf of Maine. N. Am. J. Fish.
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Shrimp (Pandalus borealis) Fishery: For the Record. J.
Northw. Atl. Fish. Sci., Vol. 27: 193–226.
Collie, J.S. and G.H. Kruse. 1998. Estimating king
crab (Paralithodes camtschaticus) abundance from commercial
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McInnes, D. 1986. Interstate fishery management
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fishery in the western Gulf of Maine. Atlantic States Marine Fisheries
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