Pollock, Pollachius virens,
occur on both sides of the North Atlantic; in the Northwest Atlantic,
the species is most abundant on the western Scotian Shelf and
in the Gulf of Maine. One major spawning area exists in the western
Gulf of Maine and on Georges Bank, and several areas have been
identified on the Scotian Shelf (Mayo et al. 1989, Cargnelli et
al. 1999). Tagging studies suggest considerable movement of pollock
between the Scotian Shelf and Georges Bank and, to a lesser extent,
between the Scotian Shelf and the Gulf of Maine (Neilson et al.
2006). Electrophoretic analyses of pollock tissue samples from
the Scotian Shelf and western Gulf of Maine showed no significant
differences between areas, although differences in some morphometric
and meristic characteristics (McGlade et al. 1986) were significant
(Mayo et al. 1989). Unlike earlier assessments conducted by USA
scientists (Mayo and Figuerido 1993), the most recent assessment
of this stock (Mayo et al. 2005) was restricted to the area primarily
under USA management authority (NAFO Subareas 5 and 6, (Figure
from November through February with a peak in December (Collette
and Klein Mac-Phee 2002). Sexual maturation is essentially complete
by age 6 (Mayo et al. 1989, although more than 50% of fish are mature
before age 3 (O’Brien et al. 1993). Juvenile pollock are common
in inshore areas, but move offshore as they grow older. Pollock
attain lengths up to 110 cm (43 in.) and weights of 16 kg (35 lb).
The U.S. portion of the fishery is
managed under the New England Fishery Management Council’s
Northeast Multispecies Fishery Management Plan (FMP). Under this
FMP pollock are included in a complex of 15 groundfish species managed
by time/area closures, gear restrictions, minimum size limits, and,
since 1994, by direct effort controls including a moratorium on
permits and days-at-sea restrictions under Amendments 5, 7 and 13
to the FMP. Amendment 9 established initial biomass rebuilding targets
(NEFMC 1998) and defined control rules which specify target fishing
mortality rates and corresponding rebuilding time horizons. Amendment
13 implemented formal rebuilding plans within specified time frames
based on revised biomass and fishing mortality targets derived by
the Working Group on Re-evaluation of Biological Reference Points
for New England Groundfish (NEFSC 2002a). The goal of the management
program is to reduce fishing mortality to allow stocks to rebuild
above minimum biomass thresholds and then to remain at or near target
biomass levels. The Canadian fishery is managed under fleet-specific
quotas. The information provided herein reflects the results of
the most recent peer-reviewed assessments for the Gulf of Maine/Georges
Bank pollock stock (Mayo et al. 2005, NEFSC 2005).
Divisions 4VWX and Subareas
5 & 6
Traditionally, pollock were
taken as bycatch in various demersal otter trawl fisheries, but
directed otter trawl effort increased steadily during the 1980s,
peaking in 1986 and 1987. Directed effort by Canadian and U.S.
trawlers has since declined substantially. Similar trends have
also occurred in the U.S. winter gillnet fishery.
The total commercial catch from
the Scotian Shelf, Gulf of Maine, and Georges Bank region increased
from an annual average of 38,200 mt during 1972-76 to 68,800 mt
in 1986 (Figure
6.2 Data]). Canadian landings increased steadily from 24,700
mt in 1977 to an annual average of 43,900 mt during 1985-87 (Neilson
et al. 2004), while U.S. landings increased from an average of
9,700 mt during 1973-77 to more than 19,000 mt annually from 1985-1987,
peaking at 24,500 mt in 1986 (Mayo et al. 2005). Landings by distant-water
fleets declined from an annual average of 9,800 mt during 1970-73
to less than 1,100 mt per year during 1981-88. Distant-water fleet
landings increased to 3,300 mt in 1991, but have since declined
to negligible levels. By 1996, USA and Canadian landings had declined
to 2,963 mt and 9,145 mt, respectively, the lowest landings by
either country in over three decades. Landings by distant water
fleets fishing on the Scotian Shelf remained almost negligible.
Since 1996, USA and Canadian landings have increased slightly
but remain low relative to past levels. From 1999 to 2005, USA
commercial landings fluctuated between 4,000 and 6,500 mt and
Canadian landings ranged from 5,700 to 8,400 mt.
Since 1984, the USA fishery
has been restricted to areas of the Gulf of Maine and Georges
Bank west of the Hague line delimiting the USA and Canadian fishery
zones. The Canadian fishery occurs primarily on the Scotian Shelf
and additional landings are obtained from Georges Bank east of
the line delimiting the USA and Canadian fishery zones. The Canadian
fishery on the Scotian Shelf has shifted westward over time and
the contribution to the total catch from larger, mobile gear vessels
has steadily diminished since 1981 (Neilson et al. 2004).
Subareas 5 & 6
The commercial fishery in Subareas
5&6 is dominated by United States vessels; additional catches
are taken by Canada and, for a period primarily during the 1970s,
by some distant water fleets. Total landings increased steadily
from less than 10,000 mt during the 1960s to a maximum of over 26,000
mt in 1986 (Table 6.1,Figure
6.2 Data]). Landings declined sharply during the late 1980s
and have remained below 10,000 mt throughout most of the 1990s.
Total commercial landings since 1999 have fluctuated between 5,200
and 8,300 mt.
Research Vessel Survey
Indices of relative biomass (ln
re-transformed), derived from NEFSC autumn research vessel bottom
trawl surveys covering Georges Bank and the Gulf of Maine have varied
considerably since 1963 (Figure
6.3 Data]). Indices generally fluctuated between 2 and 5 kg
per tow throughout most of the 1960s and 1970s, peaking at over
8 kg per tow in 1976, reflecting recruitment of several moderate-to
strong year classes from the early 1970s. Strong year classes were
also produced in 1979 and 1980, after which recruitment began to
diminish during the 1980s. The survey age composition data illustrate
this pattern and reveal a persistent truncation in the population
age structure from the early 1990s onward (Figure
6.4 Data]). Although there is very little evidence of a subsequent
expansion of the age structure, some relatively large year classes
(1999 and 2001) are poised to contribute to a future expansion if
fishing mortality remains reasonably low.
Biomass indices declined rapidly
during the early 1980s, and continued to decline steadily through
the early 1990s, remaining below 1 kg per tow and reaching a minimum
during the mid-1990s (Figure
6.3 Data]). Since then, biomass indices have generally increased,
fluctuating after 2000 between 2 and 2.5 kg/tow. Current biomass
indices are higher than those obtained since the late 1970s.
NEFSC autumn biomass indices
and total landings from the Gulf of Maine and Georges Bank region
were used to compute relative exploitation ratios, defined as
the catch in the current year divided by the 3 year average survey
biomass index for the current year and the previous 2 years. These
relative exploitation ratios (or relative F values) may be considered
a proxy for F on that portion of the pollock stock under USA management
authority. Exploitation ratios peaked in the mid-to-late 1980s
after which they steadily declined (Figure
6.5 Data]). At the same time, biomass indices began to increase
and they now indicate that biomass may have returned to levels
evident during the early 1980s.
Relative Exploitation Rate and Replacement
Autumn NEFSC survey biomass indices
from 1963 through 2001 were used to calculate replacement ratios,
defined as the biomass index in the current year divided by the
average biomass indices from the previous 5 years. When the replacement
ratio falls below 1.00 the stock is not able to replace itself.
This occurred during most of the period between the early 1980s
and the mid 1990s (Figure
The relationship between replacement
ratios and relative F was used by the Working Group on Re-Evaluation
of Biological Reference Points for New England Groundfish (NEFSC
2002a) to derive an estimate of relative F corresponding to a replacement
ratio of 1.0. On average, when the relative F is greater than 5.88
the stock is not likely to replace itself in the long-term. This
value is considered to be a proxy Fmsy reference point.
The index of exploitation remained well above 5.88 from the mid-1980s
through the mid 1990s (Figure
6.7 Data]). Comparisons between trends in biomass and replacement
ratios reveal that most of the replacement ratios below 1.0 occurred
when the biomass index was less than about 3.0 kg/tow (Figure
6.8 Data]). This value is considered to be a proxy Bmsy reference
point. The Working Group also established MSY to be 17,640 mt (Table
Since the mid-1990s, the NEFSC
autumn survey biomass index has been increasing towards the 3.0
kg/tow Bmsy proxy and the replacement ratio has remained
at or above 1.0. Since 1999, relative F has been below the 5.88
Fmsy proxy. In 2004, the 3-year average biomass index
for pollock was 1.99, approximately 66% of the 3.00 Bmsy
proxy, an increase from the 2001 value of 1.601. In 2004, the 3-year
average relative F was 3.57, approximately 61% of the 5.88 Fmsy
proxy, a slight decrease from the 2001 value of 3.55. Thus, in 2004
the stock was not overfished and overfishing was not occurring.
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