BEACHAM: VARIABILITY IN SIZE AND AGE OF ATLANTIC COD 



TABLE 5.— Median length (cm) at sexual maturity of Atlantic cod in areas 4Vn, 

 4Vs, 4W, and 4X, as calculated from Canadian groundfish surveys from 1959- 

 64, 1965-69, 1970-74, and 1975-79. 95% confidence limits are in parentheses. 

 Sample sizes are indicated in Figures 4, 7, 10, and 13. 



maturity for Division 4T Atlantic cod was inves- 

 tigated by Powles (1958), who found that during the 

 summers of 1955 and 1956, median lengths at 

 maturity for females were between 52 and 57 cm, and 

 those for males between 50 and 53 cm. Wiles and 

 May (1968) found that, by grouping data between 

 1947 and 1966, the median lengths at sexual maturi- 

 ty in the northern Gulf of St. Lawrence cod stock 

 (Divisions 3Pn-4RS) were 46 cm for males and 50 cm 

 for females, corresponding to median ages at maturi- 

 ty of 5.1 and 6.1 yr, respectively. Minet( 1978), inves- 

 tigating the same stock in 1973, found results very 

 similar to those of Wiles and May (1968). Pinhorn 

 (1969) found similar results for Atlantic cod in Sub- 

 division 3Pn in 1952, but median ages apparently in- 

 creased to 6.3 yr for males and 6.7 yr for females in 

 1957. Fleming (1960) found that Atlantic cod in the 

 same area matured between 6.6 and 6.8 yr from 1947 

 to 1950. Thus it appears for the northern Gulf of St. 

 Lawrence cod stock, there has not been a marked 

 decline in median age at sexual maturity with time. 

 Hansen (1949) reported that size and age at maturity 

 of Atlantic cod in the West Greenland stock declined 

 from 1917 to 1936, an analogous trend to that in- 

 dicated for Atlantic cod on the Scotian Shelf by the 

 present study. 



Gunter (1950) found that fish inhabiting regions of 

 higher water temperature grew faster initially, at- 

 tained sexual maturity earlier, and were of smaller 

 final size than the same species in regions of lower 

 water temperature. However, Fleming (1960) found 

 that Atlantic cod in the Labrador area of Newfound- 

 land attained sexual maturity at younger ages, but 

 grew more slowly than did Atlantic cod in stocks 

 further south. Fleming attributed this result to Atlan- 



tic cod in poorer environments maturing earlier than 

 those in more favorable environments. The present 

 study, in agreement with Gunter's (1950) con- 

 clusions, indicated that Atlantic cod stocks inhabit- 

 ing regions with warmer water temperature matured 

 earlier than did those in colder regions. 



Median size and age at maturity are heavily depen- 

 dent upon growth rate. Molander (1925) found that 

 in Baltic witch flounder, Glyptocephalus cynoglossus, 

 stocks with faster growth rates matured at younger 

 ages but at larger lengths than did fish in slower grow- 

 ing stocks. During 1975-79 in the present study, 

 Atlantic cod tended to mature at the same length (Ta- 

 ble 5), but northern stocks matured at older ages than 

 did Atlantic cod in more southerly stocks. Aim (1959) 

 noted that faster growing fish attained sexual matu- 

 rity earlier than did slower growing fish, and the 

 results of the present study support that conclu- 

 sion. 



Growth rates in Atlantic cod have been shown to be 

 inversely related with stock biomass (Lett and 

 Doubleday 1976; Beacham 1980), with growth rates 

 increasing as stock biomass declines. Templeman 

 and Bishop (1979) attributed a decline in median age 

 at maturity in haddock, Melanogrammus aeglefinus, 

 to an increase in growth rate coincident with declin- 

 ing stock density, an idea that implicitly assumes a 

 minimum threshold or minimum range for size at 

 maturity. They also suggested that a decline in me- 

 dian length at maturity occurred, owing to a decrease 

 in growth rates, implicitly assuming a minimum 

 threshold for age at maturity. If Templeman and 

 Bishop's (1979) assertions are general, then declines 

 in median length and age at maturity should not occur 

 concurrently. 



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