FISHERY BULLETIN: VOL. 81, NO. 2 



55 t -r 



a Female 



o Male 



No Data Available 



50 



~ i5 



O 



E 



E 

 u 



CTl 



c 

 a> 



_J 



c 

 a 



■D 



a> 



40 



35 



30 



i i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 r 



1953 1965 1967 1969 1971 1973 1975 1977 1979 



FIGURE 11. — Median length at sexual maturity for Atlantic cod caught during summer Cana- 

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

 limits. 



males and about 2.9 yr for females on the Scotian 

 Shelf. Bottom water temperatures derived from the 

 groundfish surveys indicated that Subdivision 4Vn 

 had the coldest water temperatures during 1970-74 

 (3.6°C) and Division 4X the warmest (6.9°C), with 

 the rest of Scotian Shelf temperatures between these 

 extremes. There was a general trend for greater A J0 

 values to be found in stocks in colder waters, and 

 Atlantic cod growth rates on the Scotian Shelf were 

 correlated with water temperature (Beacham 1982), 

 so there was a trend for stocks that have a lower 

 growth rate to have a higher median age at sexual 

 maturity. 



DISCUSSION 



The Atlantic cod stocks on the Scotian Shelf were 

 subject to high rates of exploitation in the 1960's and 

 early 1970's and consequently declined in biomass 

 (Gray 1979). The declines in median size and age at 

 sexual maturity were thus concurrent with declines in 

 stock biomass. However, with the introduction of 

 quota management and improved recruitment, stock 

 biomasses have generally increased since 1975. 



The mean size and age of Atlantic cod in the land- 

 ings of the commercial fishery in Subarea 4 have 

 declined with time (Beacham 1982), but this cannot 



316 



