YELLOWTAIL FLOUNDER OFF NEW ENGLAND 



191 



quarter of the year is almost exactly the same as 

 the average for the year. Therefore, if 1942 were 

 an average year, insofar as the size of the yellow- 

 tail is concerned, we would expect our average 

 (mostly during the fourth quarter) to be fairly 

 representative of the entire year. 



This lack of a decrease in the average size during 

 a period of heavy fishing is particularly signifi- 

 cant because it is not in agreement with theory 

 or with actual events in closely comparable fish- 

 eries. The theory of the effect of fishing devel- 

 oped by Baranoff (1918) and expounded by 

 Thompson (1937) indicates that a marked de- 

 crease in the proportion of older and larger fish is 

 to be expected when fishing mortality increases. 

 The development of Baranoff's theory was stimu- 

 lated by observations on the plaice, which was be- 

 ing heavily fished in the North Sea. Russell 

 (1942, p. 77) reported that in 1907 the relatively 

 unfished plaice population in the Barents Sea was 

 almost entirely mature and averaged about 48 

 cm. in length. At the same time in the North Sea 

 the marketable plaice population was more than 

 one-half immature and averaged less than 40 cm. 

 in length even though their size at maturity was 

 about the same as that of the Barents Sea plaice 

 (39^0 cm.). 



The European plaice and the yellowtail which 

 it closely resembles belong to the same family, 

 the Pleuronectidae, The plaice attains almost the 

 same maximum size as the yellowtail, although 

 it grows a little more slowly. The plaice appears 

 in maximum numbers in the catch at age 4 and 

 individuals as old as ages 10 and 11 are fairly 

 common, whereas the yellow T tail is taken in maxi- 

 mum numbers at ape 3 (p. 209), and few individ- 

 uals older than age 7 are found. Both species are 

 subject to otter-trawl fisheries, though the North 

 Sea plaice has been subject to a heavy fishery for 

 70 years or more, whereas the American yellowtail 

 has been especially sought only since about 1938. 



Despite the difference in the length of time 

 the plaice and the yellowtail fisheries have been 

 in operation, a nearly parallel situation is to be 

 found in a comparison of the peak and decline of 

 the yellowtail fishery with the peak and decline 

 of the plaice fishery immediately after World 

 War I. That war caused almost a complete cessa- 

 tion of fishing in the North Sea for about 4 years 

 and permitted the stocks of fish to accumulate far 



above their prewar levels. Thursby-Pelham 

 (1939, p. 53) has shown that the proportion of 

 large plaice in the landings began to decline about 

 2 years after fishing was resumed, and reached a 

 minimum in about 7 years. 



That reduction in size of the fish did not occur 

 in the yellowtail fishery as a result of fishing is 

 shown in figure 11, where part of Thursby- 

 Pelham's figure 6 has been reproduced for com- 

 parison of plaice length data with similar data 

 from the yellow T tail. We have arbitrarily estab- 

 lished a large yellowtail category as including 

 fish of more than 40 cm. total length and a small, 

 as including fish of less than 30 cm. These cate- 

 gories differ somewhat from the large and small 

 market categories of Thursby-Pelham, but each 

 category forms a significant fraction of the land- 

 ings. There obviously was no trend toward a de- 

 creasing proportion of large fish in the yellowtail 

 fishery during the period of observation, 1941^9. 



~ 



-r- 



YELLOWTAIL 



-• LARGE - OVER 40 CM 



-o SMALL -JJNDER 30 CV 



1941 1942 1943 1944 1945 1946 1947 



PLAICE 



™??f V BRITISH MARKET 

 SMALL' CATEGORIES 



1919 1920 1921 1922 1923 1924 1925 



YEAR 



Figure 11. — Comparison of the trends in proportions of 

 large and small yellowtail from the southern New 

 England stock and of European plaice of the North Sea 

 stock. The medium-size category has been omitted 

 from both graphs. 



