Research Document - 2006/043
An assessment of the cod (Gadus morhua) stock in NAFO Divisions 2J3KL in April 2006
By G.R. Lilly, E.F. Murphy, B.P. Healey, and J. Brattey
Abstract
The directed commercial fishery for northern (2J3KL) cod was closed in 1992, reopened for small boats in the inshore alone during 1998-2002, and closed again in 2003. Landings in 2004 and 2005 were mainly from by catch during winter (blackback) flounder fisheries in summer. Because of differences in the dynamics of offshore and inshore populations of northern cod since the mid 1990s, information is provided for the offshore and inshore separately. Populations in the offshore remain broadly distributed at very low density. The indices of biomass from research bottom trawl surveys during autumn (2J3KL) and spring (3L only) remain extremely low. The index from autumn surveys is less than 2% of the average level during the 1980s. Recruitment in the offshore has been very low and total mortality has been extremely high since at least the mid 1990s. Few fish survive beyond age 5. In the inshore, catch rates in sentinel surveys (1995-2005) and commercial fisheries (1998-2002), as well as cod by catch in fisheries targeted at other species (2004-05), indicate that there have been cod aggregations at various times and places since at least the mid 1990s, particularly in southern 3K and in 3L. Catch rate indices from linetrawl and gillnet sentinel surveys increased from 1995 to a peak in 1997 and 1998 respectively, declined by the early 2000s, and then increased during recent years. Current estimates are similar to or above average. For the purpose of this assessment, the inshore is subdivided into three areas: 1) a northern area (2J and northern 3K); 2) a central area (southern 3K and northern 3L) where most of the resident inshore fish are located; and 3) a southern area (southern 3L) that is, at present, largely dependent on cod that overwinter in inshore and offshore areas of 3Ps, move into southern 3L in the spring summer and return to 3Ps in the autumn. A sequential population analysis (SPA) was conducted for the resident cod in the inshore central area. SPA estimates indicate that spawner biomass in this area increased from 10,000 t in 1995 to 22,000 t in 1998, declined during 1998-2002 (when there was a commercial fishery) to 7,000 t in 2003, and has subsequently increased to 14,000 t by the beginning of 2006. The estimate of age 4+ biomass at the beginning of 2006 is about 23,000 t. Fishing mortality increased from 1998 to a peak of about 35% in 2001 and 2002 and has subsequently declined to relatively low levels. Deterministic projections from 2006 to 2009 were conducted for the inshore central area under three annual catch options and three recruitment assumptions (low, medium, high). Assuming removals of 1,250 t or less, spawner biomass is projected to increase for each recruitment assumption. At a catch option of 2,500 t, spawner biomass is projected to decrease if recruitment is low, but to increase otherwise. The inshore northern area appeared to have very low densities of cod up until 2005, when there was a large increase in sentinel survey catch rates. Because it is not known if this increase will persist, it would be prudent to keep catches in this area low. The inshore southern area is primarily dependent on seasonal immigration of fish, the magnitude of which cannot be predicted. Therefore, the effect of removals of various levels cannot be estimated. There is a risk that fishing in the inshore will impede recovery in the offshore, but the level of risk is difficult to quantify at this time. There is no single measure of the biomass of the 2J3KL cod stock as a whole, but current biomass is a very small proportion of the approximately 3 million t (of ages 3 and older) estimated for the early 1960s.
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