PROGRESS IN BIOLOGICAL INQUIRIES, 1932 91 



but if feasible, should eventually be of far greater effect in stabilizing 

 the fishery. A continuation of the present program of analyzing the 

 catch may provide part of the knowledge necessary for such control 

 but it should be accompanied by tagging experiments to discover 

 how much of the decreased availability between yearling and 2-year- 

 old mackerel of some year classes is caused by fishing strain, and how 

 much to natural morta ity and changes in habits with increasing age. 

 For instance, the 1928 class yielded 29,000,000 yearling fish, but only 

 10,000,000 fish during the following year when they were 2 years old. 

 Was this because too many yearlings were caught? If so, would pro- 

 tection to yearlings have prevented the decline in catch in the follow- 

 ing year? A properly designed marking experiment carried on reg- 

 ularly through enough seasons to estabhsh the usual course of events 

 might indicate the value of such protection. Inasmuch as such a 

 marking program would also be useful in improving predictions, it is 

 important that means be provided for this as soon as possible. 



That fluctuations might be smoothed out eventually by controlling 

 young fish production is a remote possibility, its Hkelihood of attain- 

 ment cannot be appraised until more is known about the causes of 

 failures. Current scientific opinion is that the phenomenon of poor 

 year classes among marine fishes is due to excessive mortality in the 

 larval stage, but there are no definite data on the subject. The sur- 

 veys of the Albatross II on the mackerel spawning grounds have been 

 designed to throw light on this question as well as to be of aid in 

 predictions as previously mentioned. With the tying up of this ship 

 for want of operating funds, progress has been halted. As an adjunct 

 to the work at sea, laboratory experiments were carried on during the 

 year by Leonard G. Worley to determine the percentage of mackerel 

 eggs that hatch at different temperatures, while rearing of fish larvae 

 under laboratory conditions was undertaken by Louella E. Cable to 

 learn their food requirements. 



COD 



Studies of the migratory habits of the cod were continued during 

 1932 by William C. Schroeder, but on a reduced scale owing to 

 reduction in funds available for the purpose. 



The principal item in the year's program was the release of 1,489 

 marked cod along the coast of Maine to learn whether any of the 

 abundant stock of 2- and 3-year-old cod that inhabit the inshore 

 waters of New England move offshore as they grow to larger sizes, 

 thus contributing to the commercially important stocks of large cod 

 on the offshore banks. For this purpose it is necessary that the tags 

 remain with the fish for a number of years. Since the percentage of 

 external tags lost from the fish is sometimes large, the "belly tag", 

 a celluloid strip inserted into the body cavity according to the method 

 developed by R. A. Nesbit, was used in this experiment. Fears that 

 this type of tag might not be detected as regularly as external tags 

 proved groundless, for the 10.7 percent returned during the first 6 

 months after release about equals the percentage of returns from 

 comparable experiments with external tags. 



To provide additional evidence as to the merits of various methods 

 of tagging, last year's spawning stock of cod from the hatchery at 

 Woods Hole was used to determine the comparative durability of 



