Status of Fishery Resources off the Northeastern US
NEFSC - Resource Evaluation and Assessment Division


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Revised
December 2006

Pollock

Pollock (Pollachius virens)

by Ralph Mayo




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Figure 6.1 Statistical areas used to define the Gulf of Maine and Georges Bank Pollock stock.

Figure 6.1 Statistical Areas Used
Distribution, Biology and Management

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 6.1).

Spawning occurs 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).

The Fishery

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 [Fig 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 [Fig 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

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 [Fig 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 [Fig 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 [Fig 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.
Figure 6.2.  Total commercial landings (metric tons, live) of pollock from the Scotian Shelf (Divisions 4VWX) and the Gulf of Maine-Georges Bank region (Subareas 5&6).
Figure 6.2

Figure 6.3.  Trends in total commercial landings (metric tons, live) and NEFSC autumn survey biomass indices (kg/tow) for pollock  in the Gulf of Maine-Georges Bank region.  The dashed line represents the Bmsy proxy (3.00) based on historical survey biomass trends.
Figure 6.3

Figure 6.4.  Age structure of Gulf of Maine/Georges Bank pollock, 1970-2004
Figure 6.4

 

Figure 6.5.  Trends in total commercial landings (metric tons, live) and a 3 year average exploitation ratio (landings/survey biomass index) for pollock in the Gulf of Maine-Georges Bank region.  The dashed line represents the Fmsy proxy (5.88). Figure 6.5

Figure 6.6.  Trends in replacement ratios for pollock in the Gulf of Maine-Georges Bank region.  The dashed line represents  the ratio where the stock replaces itself on average (1.00).Figure 6.6

Figure 6.7.  Comparison of trends in the exploitation ratio and the replacement ratio for pollock in the Gulf of Maine-Georges Bank region.  The dashed lines represent the Fmsy proxy (5.88) and the ratio where the stock replaces itself on average (1.00).
Figure 6.7

Figure 6.8.  Comparison of trends in survey biomass index and the replacement ratio for pollock in the Gulf of Maine-Georges Bank region.  The dashed lines represent the Bmsy proxy (3.00) and the ratio where the stock replaces itself on average (1.00).
Figure 6.8

Assessment Results

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 [Fig 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 Ratio Analyses

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 6.6 [Fig 6.6 Data]).

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 [Fig 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 [Fig 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 6.2).

Summary

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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Table 6.1 Recreational and commercial landings of pollock from the Gulf of Maine/Georges Bank region (thousand metric tons).

Category
1986-95
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
 
Average
                       
 U.S. Recreational
0.1
0.3 0.2 0.1 <0.1 0.4 0.6 0.4 <0.1  0.2 0.4
 Commercial                      
       United States 10.7  3.0 4.3

5.6

4.6 4.0 4.1 3.6 4.8 5.1 6.5
       Canada 2.3 1.2 1.2 1.9 1.0 1.2 1.6 1.6 1.4 2.0 1.7
       Other - - - - - - - - - - -
 Total Nominal Catch 13.1  4.5 5.7 7.6 5.6 5.6 6.3 5.6 6.2 7.3 8.6
                       

 

Table 6.2 MSY Based Reference Points for Gulf of Maine/Georges Bank pollock.

 MSY Based Reference Points
 MSY = 17,640 mt
 BMSY = 3.00 kg/tow
 FMSY = 5.88 (Relative F)

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For further information

Cargnelli, L.M., S. J. Griesbach, D. B. Packer, P. L. Berrien, D. L. Johnson, and W. W. Morse. 1999. Essential Fish Habitat Source Document: Pollock, Pollachius virens, Life History and Habitat Characteristics. September 1999. v + 30 p., 15 figs., 1 table. NTIS Access. No. PB2006-101528.

Collette, B.B. and G. Klein-MacPhee, Ed. 2002. Bigelow and Schroeder’s Fishes of the Gulf of Maine. Smithsonian Institution Press, Washington, D.C.

McGlade, J.M., M.C. Annand, D. Beanlands, and A. Sinclair. 1986. Assessment of Divisions 4VWX and SA 5 pollock, Pollachius virens. CAFSAC Res. Doc., No. 118, 45 p.

Mayo, R. K., J.M. McGlade, and S. H. Clark. 1989. Patterns of exploitation and biological status of pollock, Pollachius virens L., in the Scotian Shelf, Gulf of Maine, and Georges Bank area. J. Northw. Atl. Fish. Sci. 9:13-36.

Mayo, R.K., S.H. Clark, and M.C. Annand. 1989. Stock assessment information for Pollock, Pollachius virens L., in the Scotian Shelf, Georges Bank, and Gulf of Maine regions. NOAA Tech. Mem. NMFS-F/NEC-65.

Mayo, R.K. and B.F. Figuerido. 1993. Assessment of pollock, Pollachius virens (L.), in Divisions 4VWX and Subareas 5 and 6, 1993. Woods Hole, MA: Northeast Fisheries Science Center Reference. Document 93-13, 108 p.

Mayo, R.K and L. Col. 2002. Scotoan Shelf-Georges Bank-Gulf of Maine pollock, p 249-263. In: Assessment of 20 Groundfish Stocks through 2001. A Report of the Groundfish Assessment Review Meeting (GARM), Northeast Fisheries Science Center Reference Document 02-16, 522 p.

Mayo, R.K, L. Col, and M. Traver. 2005. Gulf of Maine/Georges Bank Pollock, p. 359-371. In: Assessment of 19 Northeast groundfish stocks through 2004. 2005 Groundfish Assessment Review Meeting (2005 GARM), Northeast Fisheries Science Center, Woods Hole, Massachusetts, August 15-19, 2005. Northeast Fisheries Science Center Ref. Doc. 05-13: 508 p.

NEFMC 1998. Evaluation of Existing Overfishing Definitions And Recommendations for New Overfishing Definitions To Comply with the Sustainable Fisheries Act. Report of the Overfishing Definition Review Panel.

NEFSC 2002a. Working Group on Re-Evaluation of Biological Reference Points for New England Groundfish. Northeast Fisheries Science Center Reference Document 02-04, 254 p.

NEFSC 2002b. Assessment of 20 Northeast Groundfish Stocks Through 2001. Groundfish Assessment Review Meeting (GARM), Northeast Fisheries Science Center, Woods Hole, Massachusetts, October 8-11, 2002. NEFSC Reference Document 02-16, 522 p.

NEFSC 2005. Assessment of 19 Northeast Groundfish Stocks Through 2004. 2005 Groundfish Assessment Review Meeting (2005 GARM), Northeast Fisheries Science Center, Woods Hole, Massachusetts, 15-19 August, 2005. by RK Mayo and M Terceiro, editors. NEFSC Reference Document 05-13, 508 p.

Neilson, J.D., P. Perley, and S. Gavaris. 2004. Assessment of pollock in 4VWX5Zc using a Framework Approach. Canadian Science Advisory Secretariat Research Document 2004/99, 53 p.

Neilson, J.D., W.T. Stobo, and P. Perley. 2006. Pollock (Pollachius virens) stock structure in the Canadian Maritimes inferred from mark-recapture studies. ICES Journal of Marine Science, 63:749-765.

O’Brien, L., J. Burnett, and R.K. Mayo. 1993. Maturation of Nineteen Species of Finfish off the Northeast Coast of the United States, 1985-1990. NOAA Tech. Report. NMFS 113, 66 p.

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