FISHERY BULLETIN: VOL. 81, NO. 2 



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Figure 1.— Northwest Atlantic Fisheries Organization areas on the Scotian Shelf (Divisions 4VWX). 



of Atlantic cod were recorded at sea, and otoliths 

 were saved for later age determination according to 

 the method of Kohler (1964). The validity of using 

 otoliths in determining age of Atlantic cod was 

 demonstrated by Kohler (1964) and May (1967). 

 Powles (1958) outlined the classification of the 

 gonads used in assessing maturity stage for this 

 study. 



The transition from immature to the mature condi- 

 tion in fish usually occurs over a range of length and 

 age in the form of a sigmoid curve. From the percent- 

 ages of mature Atlantic cod (gonads in ripening, ripe, 

 spawning, spent, or recovering condition) in 2 cm 

 length intervals in the survey or period under con- 

 sideration, the median length at sexual maturity (L 50 ) 

 was calculated by probit analysis following the 

 technique of Leslie etal. (1945). Median age at sexual 

 maturity (A 50 ) was calculated in a similar way by 

 grouping the data in 1-yr intervals. Maturity ogives 

 were plotted by eye. In some cases on the Scotian 

 Shelf, annual values for median size and age at sexual 

 maturity could not be calculated because Atlantic 

 cod were not sampled in that year or because so few 

 Atlantic cod were sampled that insufficient data were 

 available for probit analysis. 



RESULTS 



Subdivision 4Vn 



Atlantic cod caught in Subdivision 4Vn may be 

 derived from three stocks. Atlantic cod from Division 

 4T overwinter in Subdivision 4 Vn (McCracken 1959; 

 Martin and Jean 1964), so that Atlantic cod caught 

 between January and April may be from the Division 

 4T stock. Atlantic cod from Subdivision 4Vs migrate 

 into Subdivision 4Vn during the summer, and 

 Halliday(1974) assumed that Atlantic cod caught by 

 commercial otter trawlers in Subdivision 4Vn during 

 May-December were migratory cod from Subdivi- 

 sion 4 Vs or Division 4 W. There is also a local stock in 

 Subdivision 4Vn that is exploited by the inshore 

 fishery. Research vessel trawl surveys have been 

 used previously to assess stock status of the inshore 

 cod stock (Beacham et al. 1 980) , so it was assumed in 

 the present analysis that the inshore stock was sam- 

 pled by the surveys. 



The L 50 values of Atlantic cod sampled in Subdivi- 

 sion 4 Vn declined from a high of 6 1 cm for males and 

 65 cm for females in 1959 to a low of 34 cm for males 

 and 32 cm for females in 1978, but increased in 1979 



304 



