206 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



and Hodgson (1937) reported correspondence of relative success of six herring year 

 classes and the strength of winds from certain quarters as inferred from pressure 

 gradients; and Carruthers (1938) amplified these findings, presenting the relation 

 for 11-year classes in the East Anglian herring fishery. He concluded: "It is reason- 

 able to argue along these lines: — as from year to year, increased 'from-Channel' air 

 flow means increased 'from-Channel' water flow, and this in turn means: — (1) Tbat 

 the passively drifting spawning products will be drifted farther afield — apparently 

 a good survival augury for the herring * * *." In the same paper, Carruthers 

 demonstrated the parallelism between changes in both certain pressure gradients 

 and east wind component, on the one hand, and relative strength in a series of 15 

 haddock year classes on the other hand. These illustrations support the theory that 

 local winds affect year-class survival. Though they demonstrate the importance of 

 transport, the remainder of the survival (or mortality) mechanism, particularly its 

 biological aspects, has yet to be elucidated. 



For the mackerel of the American Atlantic seaboard, however, it is possible to 

 advance a reasonable explanation for the connection between wind direction and 

 survival. The center of spawning, it will be remembered, is southwest of Fire Island. 

 The juvenile nursery grounds, judging from relative quantities of young mackerel 

 usually found along various parts of the Atlantic seaboard, is along the coast of 

 southern New England from Cape Ann to about the eastern end of Long Island. 

 Therefore the prevalent southwest winds during May of 1930, 1931, and 1933 con- 

 veyed the larvae toward the nursery grounds. Conversely, the prevalently north- 

 easterly winds of May 1932, on the average, were of hindrance rather than help to 

 the larvae in reaching their nursery ground. 



If this be true, there is the further probability that the significantly higher mor- 

 tality in 1932 at the transition phase when fins were developing was a consequence of 

 the pattern of drift in that year. The formation of fins and their subsequent use 

 undoubtedly enlarged the expenditure of energy and hence increased the food re- 

 quirement at the transition phase. At this time, on the average, the larvae were still 

 distant from their nursery ground and if feeding was poorer where they were than on 

 the nursery ground, the observed heightened mortality at this phase would thus be 

 explained. Shortly after, by directional swimming, and with some assistance from 

 favorable winds, some of the larvae did reach the presumedly more favorable location 

 and thereafter were subject to a distinctly lower mortality rate. 



Thus, there are evident two influences that contributed to the failure of the 1932 

 class. One was the general paucity of plankton, which probably increased mortality 

 throughout the entire early life history; the other was the apparently unusual direc- 

 tion of their drift, which probably heightened mortality mainly during the transition 

 from larval to post-larval stages. Though either one of these influences might con- 

 ceivably have been the sole cause of the failure of the 1932 class, the shape of the 

 survival curve suggests that both contributed substantially. Indeed, the two might 

 be related to each other as well as to the mortality of the mackerel. To be sure, these 

 are speculative conclusions. However, they furnish hypotheses that should be useful 

 in planning further observations, especially in seasons of successful survival. 



Significance of observed mortality in 1932. — Although one season's observations on 

 one species of fish form a slender basis for generalizations, the fact that it is perhaps 

 the only determination of mortality of a marine species under natural conditions 

 gives special significance to the results, for it affords opportunity, for the first time, of 

 comparing actual observations with theory. 



