Research Document 1998/94

Size-at-age and condition of cod in Subdivision 3Ps in 1972-1997

By G.R. Lilly

Abstract

The size-at-age and condition of cod in the offshore of Subdivision 3Ps were monitored by sampling catches during research bottom-trawl surveys in the winter/spring of 1972-1997. There are strong year effects in the size-at-age data that have not yet been explained. Peak length-at-age occurred in the mid-1970s for young ages and progressively later to 1980 for older ages. From the mid-1980s to the late 1990s, length-at-age and weight-at-age varied with no trend (younger ages) or declined (older ages). Condition, as measured by somatic (gutted) weight and liver weight relative to length cubed, was low in fish sampled during the 1993-1997 surveys. However, there is no evidence that these values are unusually low because sampling was conducted in April when condition is near the low point of the seasonal cycle. There are few comparable data from previous years. During previous assessments of this stock, weights-at-age on January 1 were estimated from the mean weights-at-age derived from sampling of commercial catches. A preliminary investigation of the utility of using January 1 weights-at-age derived from the research sampling found that the research data were more variable than the commercial data and that estimates from research data tended to be much higher than those from commercial data during the 1970s and early 1980s.

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