BEACHAM: VARIABILITY IN SIZE AND AGE OF ATLANTIC COD 



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1963 



1965 1967 1969 1971 



1973 



1975 1977 1979 



FIGURE 12.— Median age at sexual maturity for Atlantic cod caught during summer Canadian 

 groundfish surveys in Division 4X, 1959-79. Vertical bars indicate 95% confidence limits. 



account for the decline in median size and age at sex- 

 ual maturity. Larger Atlantic cod are less abundant 

 than they once were, but during 1975-79, virtually all 

 Atlantic cod 60 cm long were mature in the stocks ex- 

 amined, while in the 1960's, 50% of 60 cm Atlantic 

 cod could be immature. For the decline in median 

 size and age at sexual maturity to be accounted for by 

 a decline in mean size and age of the stock, sampling 

 gears in the 1960's would have to have selected 

 larger, immature fish while avoiding smaller, mature 

 ones, an unlikely situation. 



Median length and age at maturity of the 4VsW 

 Atlantic cod stock declined rapidly between 1969 

 and 1972. Nominal catches from this stock peaked in 

 1968, with over 80,000 t reported by all countries, 



and with the Spanish catch reported at over 50,000 1 

 (Halliday 1976). Halliday noted that there were 

 sharp declines in the catch rates of Spanish pair 

 trawlers subsequent to 1968. The rapid decline in 

 median size and age at sexual maturity subsequent to 

 1968 may suggest that these parameters were re- 

 sponding rapidly to a decrease in stock biomass, 

 although this interpretation is open to question. 

 Stock biomasses have increased in the late 1970's 

 (Beacham etal. 1980; Gray 1979), but there has been 

 no corresponding increase in median size or age at 

 maturity. 



Median length and age at sexual maturity for Atlan- 

 tic cod in the northwest Atlantic have been an area of 

 some research. Variability in median length at sexual 



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