Research Document - 2007/033
Assessment of the southern Gulf of St. Lawrence cod stock, March 2007
By Swain, D.P., L.G. Currie, G.A. Chouinard, G.A. Poirier, L. Savoie, 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 2006, the TAC for the stock was set at 4,000 t. The 2006 fishery took place primarily between July and December. Estimated landings from all sources amounted to 2,750 t up to December 31, 2006, with an additional 140 t landed from 4Vn in January 2007. Over 60% of the landings were of fish 5 to 7 years old. In a telephone survey, fishermen indicated that the abundance of the stock was lower than in 2005. All the abundance indices for this stock indicate that it is at a record low level and is declining. The indices of abundance and biomass from the September bottom-trawl survey of the southern Gulf remained near the record-low 2005 values. Sentinel trawl surveys have been conducted since 2003 and the abundance of cod was the lowest in the survey conducted in 2006. Similarly, the catch rates in the sentinel longline survey declined in 2006 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 since then. While relative fishing mortality remains low compared to the period prior to 1993, natural mortality (M) appears to remain high and may be increasing. Two population models were used for this assessment. Model 1 assumed that M was 0.2 up to 1985 and 0.4 since 1986. Model 2 assumed that M was 0.2 in 1971-1979 and 0.4 in 1994-1997, and estimated M in other periods. The estimates for M (±SE) were 0.33±0.03 in 1980-1986, 0.50±0.03 in 1987-1993, 0.41±0.02 in 1998-2001, and 0.53±0.03 in 2002-2006. Trends in abundance and biomass were similar for the two models. Abundance and biomass have been gradually declining for several years. Spawning stock biomass is estimated to be 48,000-50,000 t at the beginning of 2007, the lowest level observed in the 58-year record, and well below the estimated conservation 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 year-class is estimated to be very weak, less than half the strength of any recent year-class. The first 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 in 2007, even with no fishery. With no catch in 2007, there is a 63% probability of a decline of 5% or more based on Model 1, and a 78% probability of a decline of 10% or more based on Model 2. Given the status of the stock relative to the limit reference point, the application of the precautionary approach would require catches in 2007 to be limited to the lowest level possible.
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