38 U. S, BUKEAU OF FISHERIES 



covered in a single report. This new plan has been followed in the 

 present document, which covers investigational work in progress 

 from July 1 to Dec: mber 31, 1924. 



Organization of the division's Avork along the lines suggested in 

 the report for the fiscal year 1924 has been continued and may 

 now be considered as fairly complete. Emphasis has been placed 

 upon the development of a system of what may be termed major 

 researches, with a thoroughly competent investigator in direct 

 charge of each investigation and assisted by on? or more of the 

 younger and less experienced men on the staff. The men in charge 

 of these units are practicalW independent of any immediate direc- 

 tion by the administrative head of the division and are held directly/- 

 responsible for the success of the work with which they are con- 

 cerned. The results obtained since the establishment of this system 

 have been most encouraging. 



In the following report the predominating part taken by studies 

 of the life histories of our important food fishes is apparent. These 

 life-histor}^ studies provide such fundamental data as the rate of 

 growth, age at maturity, time and manner of spawning, habits of 

 the young, feeding habits of both young and old, extent and direc- 

 tion of migrations, extent to which various groups of fish mingle 

 particularly with respect to their interbreeding, and the enemies 

 or other elements in their environm nt which tend to reduce the 

 abundance of those fish and other forms from which we obtain our 

 fishery products. 



One of the most important aims of the student of life histories is 

 to determine the relative success of each breeding season and the 

 factors that determine success or failure. In order to achieve this 

 it is important to mak' age determinations for a sufficient number 

 of individuals each j^ear so that reliable figures may be obtained. 

 In forms for which age determinations can not be made the methods 

 used to determine the degree of success in breeding in different 

 years are more difficult and frequently involve extremely compli- 

 cated procedures. Such researches as these must be conducted over 

 a long series of yi ars if reliable results are to be obtained. In fact, 

 in many cases it may be necessary to continue indefinitely such a 

 yearly census of the age groups represented in a given population. 



These life-history studies are not only of prime importance in the 

 conservation of biological resources but also have a real though 

 perhaps not generally recognized place in the biological sciences. 

 We are studying species as a unit, with the idea always in mind of 

 determining the factors that adapt the species to its environment 

 and which make for its continued existence. None of the other 

 biological sciences is primarily concerned Avith this particular prob- 

 lem. Most of them consider the individual as the unit and discuss 

 its structure, physiology, development, classification, etc. The 

 geneticist is concerned in part with a consideration of species as a 

 unit, but from the standpoint of its origin rather than of its mainte- 

 nance. The very broad science of ecology may possibly be con- 

 sidered to treat of species as units, but as at present developed 

 ecology is so loosely organized and so broadly inchisive a branch of 

 biology that it is difficult to set its boundaries. Perhaps these life- 

 historv studies may properly be considered as a specialized and 



