206 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



l — r-ji — I — I — I — I — i — i — i — i — i — i — i — i — r 



1942 



N =703 



1944 



N-2508 



\ 1946 



\ N = 5963 



20 22 24 26 26 30 32 34 36 38 40 42 44 46 48 50 52 

 LENGTH - CENTIMETERS 



Figure 19. — Deviations from the mean percentage length 

 distribution of female yellowtail from the southern New 

 England stock, 1942-47. (N=numlier of fish.) 



year class which were 31.5 and 34.9 cm. during the 

 third quarters of 1946 and 1947. 



It is highly significant that there was no trend 

 in the mean length (and consequently in the 

 growth rate) of each age group during the period 

 of our study. The mean lengths of both males 

 and females (table 26) for comparable quarters 

 from 1942 to 1947 reveal no tendency toward an 



increasing or a decreasing growth rate among 

 either older or younger fish. It is surprising that 

 an increased growth rate has not occurred during 

 this period of intense fishing in view of the both 

 theoretical and empirical determination for many 

 species that the growth rate increases as the stock 

 decreases. Since we found no change in rate of 

 growth, we conclude that the total environmental 

 pressure remained essentially constant during the 

 period of this study. 



The rate of growth in the young yellowtail ap- 

 pears to be rather unusual. The proportions of 

 the scale suggest that growth to the first annulus 

 is only from 3 to 5 cm., whereas during the second 

 year the fish attains a length of nearly 30 cm. 

 Such a method of estimation is not precise, how- 

 ever, because some measurements of the scales 

 from fish in the commercial catch showed that in- 

 crease in size of the scales is not proportional to 

 increase in size of the fish: the scale growth is 

 heterogonic. For this reason and because we 

 could not obtain appreciable numbers of juvenile 

 yellowtail to determine the relation between scale 

 size and fish size, we have not attempted to cal- 

 culate fish lengths at early ages from scales. 



Age Composition of the Landings 



The proportion of each age in the landings is 

 readily determined from the samples (appendix 

 D, p. 246) because all of the yellowtail used in 

 making the age determinations except those taken 

 during the first three quarters of 1942 were taken 

 at random from the landings (table 25). The 

 samples not taken at random during the early 

 part of the investigation may not be representa- 

 tive and must be considered with caution. These 

 proportions, when plotted by quarters (fig. 20) 

 offer rather striking evidence of an alternation of 

 the populations between winter and summer from 

 the winter of 1942-43 to the winter of 1944-45. 

 The distribution of age groups was similar in the 

 fourth quarter of 1942 and the first quarter of 

 1943. Then a marked change to a summer pat- 

 tern existed in the second and third quarters of 

 1943. This pattern was followed by a winter pat- 

 tern in the fourth quarter of 1943 and the first 

 quarter of 1944, a summer pattern in the second 

 and third quarters of 1944, and another winter 

 pattern in the fourth quarter of 1944 and the first 

 quarter of 1945. 



