230 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Such changes in the habitat of a few species of 

 fish must be evidence of fundamental environ- 

 mental changes. In seeking an explanation for 

 the change in habitat, we note that the known 

 geographical range of both the haddock and the 

 yellowtail extends only a little south of the south- 

 em New England grounds, but much farther 

 north. Bigelow and Schroeder (1953) report that 

 haddock have been found from the deep water off 

 Cape Hatteras north to the west coast of Green- 

 land and the yellowtail from Chesapeake Bay to 

 the Labrador side of the Straits of Belle Isle. We 

 note, too, a retreat of the haddock from the 

 grounds west of Nantucket Shoals northeasterly to 

 Georges Bank in the early thirties, and a subse- 

 quent retreat of the yellowtail from off the New 

 Jersey coast in the twenties to off southern New 

 England in the early forties, and then to Georges 

 Bank about 1949 (table 6). Perhaps these re- 

 treats have occurred because of the warming of 

 the area (Conover 1951). 



Some additional evidence from our study of the 

 yellowtail flounder populations supports the con- 

 cept of a retreat toward the northeast. We have 

 already noted that the summer fishery weakened 

 after 1944 and by 1949 was the smallest of all the 

 fisheries, whereas it had been the largest in 1942 

 and 1943 (p. 172) . Our tagging operations in 1942 

 and 1943 off Long Island showed that the sum- 

 mer fishery off No Mans Land included fish that 

 moved west in winter and east in summer (p. 180) . 

 Perhaps it is significant that the fishery on this 

 population was the first to fail. Perhaps, too, it 

 is significant that old fish (5 years and older) 

 were a smaller fraction of the landings (table 29) 

 during the third quarter than during most other 

 quarters even just after the peak years. Were 

 these fish migrating from the west subject to 

 greater environmental pressure than other 

 groups ? 



We also ask why the southern New England yel- 

 lowtail grew so much more slowly than Nova 

 Scotian yellowtail (Scott 1954) except during 

 their second and third years of life. Is this evi- 

 dence of greater environmental pressure on the 

 very young fish and those 4 years and older? 

 Why was the life span of the southern New Eng- 

 land yellowtail so much shorter than that of Nova 

 Scotian fish, and why did they attain a smaller 

 maximum size? Obviously, living conditions for 



the older fish from the southern New England 

 stock must have been less favorable, but why? 

 Perhaps the answers to these questions may be 

 learned from a study of changing climatic condi- 

 tions. Certainly here are problems deserving of 

 more study. 



EFFECTS OF THE FISHERY ON 

 YELLOWTAIL STOCKS, 1942-49 



How has the fishery affected the yellowtail 

 flounder stocks? Although the exact effect is not 

 known, as a result of our studies from 1942 to 1949 

 we can provide a working hypothesis. 



Unquestionably, the fishery on the southern 

 New England stock suffered a disastrous decline 

 in landings and catch per unit of effort from 1942 

 to 1949. This decline was accompanied by the 

 near disappearance of fishable schools of yellow- 

 tail from the usual fishing grounds on the Conti- 

 nental Shelf between New Jersey and Nantucket 

 Shoals. Furthermore, extensive trawling to a 

 depth of 200 fathoms by the Albatross III in 1949 

 revealed no concentrations of yellowtail outside 

 the regular fishing grounds. These declining 

 landings were accompanied by a high total mortal- 

 ity rate. On the other hand, there were none of 

 the symptoms of heavy fishing, such as a declining 

 average size, an increasing proportion of young 

 fish in the catch, or an increasing growth rate due 

 to the thinning of the stock. 



This contradictory evidence cannot be fully ex- 

 plained with the limited data from so short a 

 period of study. To it may be added the evidence 

 of a heterogeneous stock composed of an unknown 

 number of semi-independent populations; a mys- 

 terious absence of fish less than a year old and of 

 yearlings from the fishing grounds; and an ap- 

 parent northeasterly shift of the principal yellow- 

 tail population from off the New Jersey coast to 

 off southern New England, where the big fishery 

 occurred from 1941 to 1948, and then to Georges 

 Bank. 



The most striking finding from our study of the 

 yellowtail fishery has been the changing availa- 

 bility, which appears, directly, in fluctuations in 

 abundance of the fish during the year and in the 

 abundance of year classes at different ages, and, 

 indirectly, in the minus value of the average ap- 

 parent natural mortality. It is evidence either 

 that fishing pressure was not uniform on the south- 



