YELLOWTAIL FLOUNDER OFF NEW ENGLAND 



205 



Ricker 1945). The values for each quarter were 

 then combined in a geometric mean for each age. 



The resulting growth rates commence at 0.673 

 between ages 1 and 2, drop abruptly to 0.291 the 

 next year, and then decrease to 0.173 between ages 

 6 and 7. The first of these growth rates is prob- 

 ably much too low — not only because of the gear 

 selectivity mentioned earlier, but because the year- 

 ling group was represented only during the last 

 half of its year of life (fourth and first calendar 

 quarters) when the fish had already accom- 

 plished most of their season's growth. The growth 

 rate from 2 to 3 years is probably somewhat low 

 also because of gear selectivity. 



The measurements of the fish for which we have 

 scale readings provide valuable checks on the va- 

 lidity of the readings. First, the mean lengths 

 are in close agreement, except in the older age 

 groups, with those obtained by Scott (1954), who 

 aged his fish by otoliths. In table 28 we have 

 compared Scott's readings from otoliths collected 

 during July 1946 in the New Bedford fishery with 

 our determinations from scales collected during 

 the entire third quarter of 1946. Agreement be- 

 tween scale and otolith readings is very good 

 except among age-groups 5 to 7 where the mean 

 lengths of the fish whose ages were determined 

 by otoliths are somewhat less. This lack of agree- 

 ment in the older groups might be attributed to 

 the finding of a greater number of annuli on the 

 otoliths because a slightly greater proportion of 

 older fish were found; but we also notice that no 

 fish of greater age were found in either sex by 



Table 28. — Mean lengths of yellowtail flounder, by age 

 groups and sex, as determined from otoliths and from 

 scales, third quarter 1946 



[In centimeters; number of specimens in parentheses] 



' Collected in July (Scott 1954). 



means of the otoliths. Moreover, the possibility 

 remains that the scales and otoliths were obtained 

 from somewhat different populations because of 

 an abrupt change in the principal fishing grounds 

 between July and August 1946 (table 3). There- 

 fore we do not consider that these discrepancies 

 indicate faults in the scale-reading technique. 



The differences among populations within the 

 southern New England stock, as suggested by com- 

 parison of the otolith and scale samples and by 

 the discrepancies in attained size in different 

 quarters, are much smaller than those between the 

 southern New England and Nova Scotian yellow- 

 tail. Scott (1954) found that the yellowtail on 

 Middle Ground and Western Bank areas of the 

 Nova Scotian Banks grew much more rapidly than 

 the Cape Cod yellowtail, except during the second 

 and third years of life. However, in the second 

 year the growth of the southern New England 

 yellowtail so far exceeded the growth of the Nova 

 Scotian fish that the attained length of the south- 

 ern New England fish was the greater until about 

 the seventh year. At this age, when the southern 

 New England yellowtail had nearly all died, the 

 female Nova Scotian yellowtail were just matur- 

 ing. They continued to grow until the modal ages 

 in the catch were 9 and 10 years at lengths of 44 

 to 47 cm. Contrast this with maturity and a 

 modal age of 3 years at about 34 cm. in the southern 

 New England stock. 



Additional evidence of the reliability of the scale 

 readings is available in a comparison of the at- 

 tained sizes (table 26) with modes in the length 

 frequencies of the females. We have plotted the 

 percentages at each length as deviations from the 

 grand mean for the years 1942 to 1947 (fig. 19). 

 Two modes, suggestive of dominant year classes, 

 progress from year to year. An eye-fitted line 

 faired through one series of modes commences at 

 25.5 cm. in 1942, is missing in 1943, but continues 

 to 34.5, 37.5, 41.0, and 42.5 cm. in the succeeding 

 years. This is in good agreement with the mean 

 attained lengths of the 1941 year class from scale 

 readings which averaged 33.8, 37.4, 40.1, and 42.8 

 cm. in the third quarter (the season of heaviest 

 landings) of the corresponding years. The shorter 

 series of modes commences at 28.5 cm. in 1945 and 

 continues at about 31.5 and 34 cm. in the following 

 years. This also is in good agreement with the 

 mean attained length of the females from the 1944 



