Fluctuations in the cod stocks of the Gulf of St Lawrence

<p dir="ltr">Article from Marine Science Symposia Vol. 198 - "Cod and climate change". Symposium held in Reykjavik, 23-27 August 1993. To access the remaining articles please click on the keyword "MSS Vol. 198".</p><p dir="ltr">The Gulf of St. Lawrence is a semi-enclosed sea connected to the Northwest Atlantic Ocean by the Strait of Belle Isle and Cabot Strait. Two Atlantic cod stocks (Gadus morhua) inhabit the area: the southern (NAFO 4T-Vn (Jan.–Apr.)) and northern (NAFO 3Pn, 4RS) Gulf of St. Lawrence stocks. Catches since 1960 have averaged 54,000 t and 76,000 t, respectively. In recent years, about 80% of the landings were made by otter trawls and seines.</p><p dir="ltr">For both stocks, abundance was low in the mid-1970s and in recent years, and was highest in the early 1980s. Landings, abundance, and recruitment trends between the two stocks are relatively similar. Production for both stocks has been low in recent years. Although fishing mortality has fluctuated over the time periods examined, abundance changes appear to be related more to recruitment fluctuations.</p><p dir="ltr">An index of survival calculated as the ratio of recruitment numbers to parental biomass indicates that, for both stocks, lower levels of spawning biomass in the 1970s produced good recruitment, while the number of recruits produced from the large spawning biomass of the early 1980s was low. Although the lower index of survival in the 1980s corresponds with a period of colder conditions (greater ice extent, lower water temperatures), there is little correlation when the entire time period is examined. The index of survival was weakly correlated with freshwater discharge in the southern Gulf.</p><p dir="ltr">Until factors influencing survival are more clearly understood, direct estimates of pre-recruit abundance are likely to be more helpful in predicting short-term stock trends.</p>