PROGRESS IN BIOLOGICAL, INQUIRIES, 1930 



563 



From analysis of these data we shall have successive pictures of 

 hydrographic conditions and of the horizontal distribution of plank- 

 ton during the months of February, April, May, June, and July, 

 the months that probably are most significant in the life history of 

 the principal food fishes of that region. 



In addition to the regular j)hinkton collections, which are intended 

 to show only the horizontal distribution, series of hauls have been 

 taken at different levels at 11 stations to determine vertical dis- 

 tribution. The data from these series are expected to facilitate the 

 interpretation of j:)eculiai-ities in the horizontal distribution and to 

 throw light on the ecology of the plankton community. 



Surface drift bottles were released in eight series, a total of 953 

 bottles. Returns have been so few and their paths so divergent that 

 interpretation of drifts is difficult. It is possible that further light 

 may be cast on the question by additional returns during the coming 

 year. 



Table 2. — Rernrd of releases and returns of drift bottles in 1930 



COD 



The initial step in the study of the codfishery has been the deter- 

 mination of the natural divisions of the cod population. An under- 

 standing of a fishery obviously requires knowledge as to whether 

 each locality supports a distinct stock or whether the fish of various 

 localities mix freely. The changes in abundance and the effects of 

 fishing must be interpreted differently depending on which of the 

 two conditions exists. The method of wholesale tagging of adult cod 

 has been efficacious not only in determining the movements of the 

 .fish but also has provided a wealth of material on life history and 

 kindred subjects. 



During 1930 the cod investigations were continued by William C. 

 Schroeder. Marking experiments, which included the tagging of 

 such haddock and pollock as were caught along with the cod. were 

 made in the following localities : 



