Research Document - 2000/142

Background information on the southern Gulf of St. Lawrence cod stock for the Fisheries Oceanography Committee workshop on the cod recruitment dilemma.

By D.P. Swain and G.A. Chouinard

Abstract

Spawning stock biomass (SSB) of southern Gulf of St. Lawrence cod declined to low levels in the mid 1970s and the early 1990s. Recovery was rapid from the earlier decline but has been slow from the recent decline. Both survey data and SPA estimates indicate that the rate of recruitment (R/SSB, where R is abundance of age-3 cod) was remarkably high during the low abundance period of the mid 1970s. Recruitment rate estimates for the recent period depend on the SPA assumptions and calibration methods. However, neither the survey data nor the SPA estimates (regardless of the assumptions or calibration methods used) indicate that recruitment rate has been unusually low during the recent period of low abundance. Instead, estimates of recruitment rates in recent years range from average levels typical of the 1950s, 1960s and early 1970s to relatively high levels. Changes in SSB depend on rates of adult growth and adult mortality as well as recruitment. Adult growth rates have been unusually low since the mid 1980s and adult natural mortality appears to be currently unusually high. The rapid recovery in the mid 1970s resulted from unusually high recruitment rates combined with high adult growth rates and average (apparently) natural mortality rates of adults. Recovery has not occurred in the 1990s despite low fishing mortality and average to high recruitment rates. The lack of recovery in the 1990s appears to be the result of unusually low growth rates and unusually high adult natural mortality rates.

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