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Research Document - 2015/080

Assessment of the southern Gulf of St. Lawrence Atlantic cod (Gadus morhua) stock of NAFO Div. 4T and 4Vn (November to April), March 2015

By Douglas P. Swain, Luc Savoie, Sean P. Cox, and Éliane Aubry

Abstract

The stock of Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence (NAFO 4T and 4Vn (November to April)) supported landings averaging 30,000 t annually between 1917 and 1940 and 56,000 t annually between 1941 and 1992. The stock collapsed in the early 1990s due to high mortality. Moratoria on directed fishing for southern Gulf cod were put in place in 1994-1997, 2003 and since 2009. Reported by-catch in fisheries for other groundfish have averaged 127 t annually since 2009. During this period,  estimated fishing mortality averaged 0.2% annually for cod aged 5-8 years and 0.7% for cod 9 years and older. Spawning stock biomass and abundance are at the lowest levels observed in the 65-year record and are declining. Estimated SSB has declined by about 70% from the already low level in 2000 and over 90% from the level in 1985. SSB is estimated to be about 40% of the limit reference point (LRP = 80,000 t) with essentially no chance of recovering to the LRP over the next five years, even with no fishing mortality. Although the 2011 year-class is estimated to be strong compared to other recent year-classes, it remains weak compared to those produced in the 1980s. SSB is projected to increase slightly in 2016 as the 2011 year-class continues to recruit to the mature stock. However, it is expected to decline from 2016 to 2019 as these fish suffer high natural mortality. With no fishing mortality, the probability that SSB in 2019 will be below the 2015 level is estimated to be 79%. The ongoing decline of this population is due to the high natural mortality of adult cod (i.e., ages 5 years and older). Natural mortality of about 18% annually is considered normal for adult cod. In this population, natural mortality of adults has increased over the past 35 years and is now estimated to be 50-60% annually. At this level of natural mortality the population is expected to continue to decline even with no fishing mortality. Predation by grey seals is considered to be a major cause of this mortality. Consequently, no recovery of this population is expected at the current high level of grey seal abundance in this ecosystem.

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