PROGRESS IN BIOLOGICAL INQUIRIES, 1935 395 



tapering off by the middle or end of August. This proved to be the 

 case, experience differing from prediction only to the extent of the 

 disappearance of these fish about 1 week later than the predicted 

 date. As for the remainder of the season, no prediction was ven- 

 tured, for tinker mackerel were likely to dominate that portion of 

 the season and there was no means of foreseeing the abundance of 

 this category. 



More important than predictions, in the long run, is the deter- 

 mination of the best stage in the Fife history for commercial exploita- 

 tion. Generally speaking it pays to let fish "grow up" before catch- 

 ing them, for the small and young grow very fast, and the gain 

 from added weight far exceeds the loss from mortality. But in the 

 case of the mackerel it is not a matter of simply balancing growth 

 increase against mortality loss. The population appears to contain 

 two types (perhaps races) of mackerel. One type, which for con- 

 venience has been designated "persistent", has an apparent mor- 

 tality (decline in catch per unit of fishing effort) in the neighbor- 

 hood of 20 percent; the other, termed "transitory", has one of 70 

 or 80 percent.^ 



Other peculiarities of the two types such as time and place of 

 occurrence, growth rates, etc., lead one to believe that the differences 

 in apparent mortality are not merely chance variations but are linked 

 with the habits of the fish. If the high apparent mortality of 

 the transitory type is the result of fishing out too large a percentage 

 per annum because they school inshore and are readily accessible to 

 the fishermen, then it would pay to lessen the fishery strain; but if, 

 on the other hand, the mortality is apparent rather than real, and 

 disappearance is due to changes in habits of the mackerel as they 

 grow older, such as a tendency to swim deeper, or a tendency to 

 scatter rather than to school, or even to migrate to distant waters, then 

 it would pay to take them while they are easy to catch even though 

 they be small. Such little evidence as is available favors the latter 

 view; but to make certain it is necessary to perform large-scale 

 tagging operations and perhaps extend other field observations into 

 waters off the coast of Canada — projects that are beyond present 

 facilities. None the less, some work on this phase was accomplished 

 during 1935 by a less expensive (and also less promising) method 

 involving studies of meristic characters to distinguish different races 

 or types within the population. Since the subdivisions of the popu- 

 lation may be expected to occur mixed at one time and separate at 

 another, and to change in locality with increase in age, the subject 

 is more complex than the usual racial study and hence less likely to 

 yield to this method of investigation. 



SHORE FISHES OF THE MIDDLE ATLANTIC STATES 



The ultimate object of these investigations, under the direction 

 of R. A. Nesbit, is to provide a rational basis for more efficient utili- 

 zation of the fishery resources of the w^aters between Cape Cod and 

 Cape Hatteras. Two requirements must be met if this objective is 

 to be attained: (1) The life histories and conservation needs of all 



* See Outlook for the Mackerel Fishery in 1933 by O. E. Sette ; Bureau of Fisheries, 

 Fishery Circular No. 14, pp. 11-12. May 1933. 



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