Research Document - 2008/045
Assessment of the southern Gulf of St. Lawrence cod stock, February 2008
By G.A. Chouinard, L. Savoie, D.P. Swain, T. Hurlbut, and D. Daigle
Abstract
The cod stock of the southern Gulf of St. Lawrence (NAFO 4T and 4Vn (November to April)) has not recovered since it collapsed in the early 1990s. In 2007, the TAC for the stock was reduced from 4,000 t in 2006 to 2,000 t. The 2007 fishery took place primarily between July and December but there was some catch during the winter (January-February) in 4Vn. Estimated landings from all sources amounted to 1,442 t up to December 31, 2007, including about 130 t landed from 4Vn in January-February 2007. About 70% of the landings were of fish 6 to 8 years old. In a telephone survey, fishermen indicated that the abundance of the stock was about the same as in 2006. The abundance indices for this stock indicate that it is at a record low level and 2 of the 3 indices indicate that it is declining. The indices of abundance and biomass from the September bottom-trawl survey of the southern Gulf declined from the 2006 level and are about at the record-low 2005 values. Sentinel trawl surveys have been conducted since 2003 and the abundance of cod was slightly higher than the 2006 value which was the lowest in the survey series. The catch rates in the sentinel longline survey declined further in 2007 and were the lowest in the time-series starting in 1995. Estimates of total mortality (Z) from survey data were about 0.45-0.55 during the moratorium in the mid 1990s and have increased to near 1.0 since then. While relative fishing mortality remains low compared to the period prior to 1993, natural mortality (M) appears to remain high and appears to be increasing. The August trawl sentinel survey was included in the population model. Abundance and biomass have been gradually declining for several years. Spawning stock biomass is estimated to be 36,000 t at the beginning of 2008, the lowest level observed in the 59-year record, and well below the limit reference point for the stock of 80,000 t. Year-class strength has been well below the historical average since the late 1980s. The 2003 and 2005 year-classes are estimated to be extremely weak, less than half the strength of any recent year-class. The estimate of the 2004 year-class is also relatively low. Assuming continued high M and given the estimates of recruitment of recent years, spawning stock biomass is almost certain to decline by 10% in 2008, even with no fishery. With no catch in 2008 there is a 52% probability of a decline of 15%. Given the status of the stock relative to the limit reference point, the application of the precautionary approach would require catches in 2008 to be at the lowest level possible. While it is recognized that the main reason for the current decline of the stock is linked to natural mortality, it is considered important that actions to preserve the remaining spawning biomass be taken so that if the productivity improves, there is a higher chance for the stock to recover.
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