Research Document - 2003/023
An assessment of the cod stock in NAFO Divisions 2J+3KL in February 2003
By Lilly, G.R., Shelton, P.A., Brattey, J., Cadigan, N.G., Healey, B.P., Murphy, E.F., Stansbury, D.E., Chen, N.
Abstract
The directed commercial fishery for northern (2J+3KL) cod was closed in 1992 and reopened for small boats in the inshore alone in 1998. In 2002, the total allowable catch (TAC) for commercial and recreational fisheries and sentinel surveys was 5,600 t. The reported catch was 4,200 t, of which 3,500 t were taken by the index (commercial) fishery. Because the dynamics of populations of cod in the inshore have been different from those in the offshore since about the mid-1990s, and the fishery has been conducted in the inshore alone, the status of populations in the inshore and offshore are reported separately. Populations in the offshore remain broadly spread at very low density. The indices of biomass from research bottom-trawl surveys in autumn (2J3KL) and spring (3L only) are at less than 2% of their levels during the 1980s. Mortality of fish in the offshore has been extremely high since the moratorium and few fish survive beyond age 5. Population trends of cod in the inshore have been monitored by fixed-gear sentinel surveys since 1995. Indices increased from 1995 to a peak in 1997-1998, and have since declined to levels below those in 1995. Catch rates in the index fishery declined steadily from 1998 to 2002. Catch rates in sentinel surveys and commercial fisheries have been consistently low in 2J and northern 3K. Since the fishery opened in 1998, catch rates have declined in both southern 3K and southern 3L, and have remained high only in northern 3L, most notably in southern Bonavista Bay and northern Trinity Bay. Hydroacoustic surveys in January in Smith Sound (Trinity Bay) provided average indices of biomass that increased from 1999 to a peak of 26,000 t in 2001 and then declined to 20,000 t in 2003. Results of tagging experiments indicate a harvest rate close to 20% in the inshore in 2002 and an exploitable biomass (approximately ages 4+) of 22,000 t in the inshore regions of 3KL. The tagging studies provided evidence of natural mortality of 55% in 3K and 33% in 3L. A sequential population analysis (SPA) was conducted based on those cod in the inshore since the mid-1990s. SPA estimates indicate that spawner biomass in the inshore increased from 1995 to 41,000 t in 1998, but has subsequently declined to only 14,000 t at the beginning of 2003. The estimate of 4+ biomass at the beginning of 2003 is about 30,000 t. Fishing mortality on older age classes has been increasing and is currently at approximately 35%. Both the SPA and a recruitment model indicate that the 1999 and 2000 year-classes are stronger than other year-classes since the mid-1990s, but are very weak compared to historic levels. Deterministic projections indicate that the stock will grow slightly in the short term as a consequence of the incoming recruits, but will decline thereafter if exploitation rates remain at current levels. Projections also indicate that even without fishing the spawner biomass will not grow during the next decade to the level reached in 1998. The stock as a whole is clearly far below a conservation limit reference level which, although not well-determined, is expected to be greater than 300,000 t of spawner biomass. The information on feeding by seals and trends in the harp seal population indicate that predation by seals is a factor contributing to the high total mortality of cod in the offshore and the high natural mortality of adult cod in the inshore.
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