YELLOWTAIL FLOUNDER OFF NEW ENGLAND 



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FEMALES 

 MALES 



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AGE - YEARS AND QUARTERS 



Figure 17. — Mean lengths of yellowtail, by ages and quar- 

 ters, in the landings from the southern New England 

 stock, fourth quarter 1942 through 1947. 



grow faster than the males, as was to be expected 

 from the observation that females attain a greater 

 size. They were 4.5 percent longer than the males 

 at age 2 and up to 9.1 percent longer at age 5. 

 The lack of males prevents such comparison in the 

 older age groups. 



On the other hand, figure 17 indicates an unex- 

 pected constant seasonal cycle in the growth 

 curve. The mean length during the fourth quar- 

 ter of the fish's year of life (first calendar quar- 

 ter) is usually slightly greater than during the 

 succeeding first and second quarters, in both of 

 which the fish are of about the same average size. 

 One would expect slow growth in winter and 

 rapid growth in summer, except perhaps during 

 the spawning period from April through June. 

 Although reduction of the mean length of an age 

 group might occur among the younger groups be- 

 cause of seasonal changes in gear selectivity, it 

 would not be expected consistently in all age 

 groups. 



The possibility of this seasonal change in aver- 

 age length being due to errors in reading the 

 scales was not overlooked. If too few rings were 



counted in the fourth quarter of the fish's year of 

 life and/or too many rings were counted in the 

 succeeding first quarter, such a cycle might result. 

 Error in reading the scales seems improbable, 

 however, because any evidence of a new annulus 

 forming at the edge of a scale during the fourth 

 quarter was disregarded, and too few rings could 

 have been read only by disregarding annuli which 

 were counted in similar scales from second and 

 third quarters. Most important is the similarity 

 of the cycle in all age groups after the yearling. 

 Since scales from the 2- and 3-year-old groups are 

 so much easier to read than from the older age 

 groups, we feel certain that any reading errors 

 would have been much more common among the 

 older fish; consequently, a change in the cycle 

 would have occurred between the young and old 

 groups. We, therefore, believe that reading 

 errors are not responsible for the seasonal change 

 in average length. Bather, the most probable ex- 

 planation of this seasonal growth pattern is that 

 different populations of flounders occurred in the 

 landings in different quarters of the year and that 

 these populations were growing at slightly differ- 

 ent rates. 



The differences in rate of growth of yellowtail 

 among quarters are accentuated when the lengths 

 are converted to weights (using the formulas 

 from table 16), because when the fish were longer 

 they were also correspondingly heavier. The 

 weights (table 27) when plotted (fig. 18) show a 

 markedly faster growth in the first quarter of the 

 fish's year of life, intermediate and about equal 

 growth during the second and fourth quarters, 

 and slow growth during the third quarter. The 

 differences, especially among females, are so great 

 that they indicate population differences rather 

 than seasonal differences. For example, females 

 with three annuli were heavier in the first quarter 

 than in the following second and third quarters, 

 and in their next year of life were heavier in the 

 first quarter than during the subsequent second, 

 third, and fourth quarters. In addition, the 

 heaviest fish were found during the coldest season 

 when we would expect the rate of growth to be 

 minimal. 



These curves (fig. 18) , which are nearly straight 

 lines passing through the point of origin, indi- 

 cate nearly equal weight increments during each 

 year of life in the fishery. This results, in part, 



