BEACHAM: VARIABILITY IN SIZE AND AGE OF ATLANTIC COD 



(Fig. 2). Females generally matured at greater me- 

 dian lengths than did males, and with the difference 

 between the sexes greater in the 1960's than in the 

 1970's. 



The A 50 values indicate trends similar to those of 

 length, being about 5.7 yr for males and 6.7 yr for 

 females in 1960, reaching a minimum in 1978 of 2.6 yr 

 for both males and females, and increasing in 1979 

 (Fig. 3). During 1959-63, males tended to mature at 

 younger ages than did females, but since 1969, me- 

 dian age at maturity between sexes has been similar. 

 No values were calculated for 1975 and 1976 because 

 of small sample sizes. 



Maturity ogives based on length and age were 

 calculated for four periods in this study, each corre- 

 sponding to a 5-yr interval. L 50 values during 1959-64 

 were 52 cm for males and 55 cm for females, but 

 declined significantly (P<0.01) to 36 and 34 cm, re- 

 spectively, during 1975-79. The trend towards the 

 removal of larger, immature fish with time was ap- 

 parent (Fig. 4). The transition from the all immature 

 to 100% mature condition occurred over pro- 

 gressively shorter length ranges. 



Changes in percent mature by age indicate an in- 

 crease in percent mature at age through time (Table 

 1). There was a particularly striking increase in rates 

 of maturity for males and females ages 3 and 4. About 

 90% of age-4 females were mature during 1975-79, 



Table 1. — Percentage of sexually mature Atlantic cod by age and 

 sex caught during Canadian groundfish surveys in Subdivision 4Vn, 

 1959-79. Sample sizes are in parentheses for individual ages and 

 95% confidence limits for A, (years). 



whereas only 4% were classified as mature during 

 1959-64. During 1959-64, A 50 for males was 5.4 yr 

 and that of females 6.3 yr, whereas during 1975-79, 

 these values were 2.8 yr for both males and females, 

 the decline being significant (P<0.01). A 50 declined 

 faster in males than in females. These data also indi- 

 cate that older, immature Atlantic cod disappeared 

 from the area through time, probably through com- 

 mercial exploitation. 



Subdivision 4Vs 



L 50 for Atlantic cod in Subdivision 4 Vs had the same 

 general decreasing trend with time as in other areas, 

 declining from 5 1 cm for males and 54 cm for females 

 in 1959 to about 35 cm for males and 33 cm for 

 females in 1 97 7 (Fig. 5) . There appeared to be a rapid 

 drop in the median length at maturity in the early 

 1970's, and an increase since 1977. However, given 

 the variability in the measurements, it is uncertain if 

 these were actual trends or due to sampling 

 variability. 



A 50 displayed trends similar to those of length, be- 

 ing about 5.6 yr for males and 5.7 yr for females in 

 1959, and declining to about 2.4 yr for males and 2.3 

 yr for females in 1977 (Fig. 6). Atlantic cod matured, 

 on average, at older ages in the early 1960's than did 

 those in the 1970's. Males again tended to mature at 

 smaller sizes and younger ages than did the 

 females. 



The maturity ogives for length indicate trends 

 similar to Atlantic cod in Subdivision 4Vn for the 

 periods under consideration. Larger, immature fish 

 have been eliminated from the stock over time, and 

 the transition from the immature to the mature state 

 occurred over a smaller length interval with time (Fig. 

 7). During 1959-64, the transition from 0% mature to 

 100% mature occurred over a 40 cm interval of length 

 for both males and females, but from 1975 to 1979, 

 this transition occurred over a 20 cm length interval. 

 L J0 values in 1959-64 were 47 cm for males and 44 cm 

 for females, but these values declined to 38 cm for 

 both males and females in 1975-79 (P<0.01). 



Changes in percent mature by age indicate marked 

 increases over time for age-3 and -4 Atlantic cod (Ta- 

 ble 2). However, the data for the 1965-69 interval 

 were sparse and may not be indicative of the stock in 

 this period. These data also indicate that between 10 

 and 15% of age-2 Atlantic cod became mature in 

 1975-79, whereas virtually no age-2 Atlantic cod 

 were mature in the 1960's. This trend was also ap- 

 parent in Atlantic cod caught in Subdivision 4Vn. 

 During 1959-64, median age at maturity for males 

 was 5.4 yr and that of females 5.2 yr, whereas in 1975- 



305 



