PROGRESS IN BIOLOGICAL INQUIRIES, 1924 15 



not some time attain an efficiency far greater than that of to-day. 

 If the fisheries are to be ntihzecl to the fullest extent compatible 

 Avith their maintenance, it is especially important to understand 

 fully the biolog}^ of the fishes, since only in the light of such knowl- 

 edge can they be given scientific care. 



AVith the comparatively limited funds at its disposal, it has been 

 necessary to plan the work of the division with the greatest care. 

 An effort has been made to attack those problems most likely to 

 prove of value in the work of conservation. A general plan was 

 outlined in the report of the division for the fiscal year 19"23, and 

 this plan has been followed as nearly as practicable. A great deal 

 of effort has been devoted to the study of the life histoi'ies of the 

 important food fishes, crustaceans, and mollusks. These life-history 

 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 direction of migra- 

 tions, extent to which various groups of fish mingle, particularly 

 with respect to their interbreeding, and the enemies or other ele- 

 ments in their environment which tend to reduce the abundance of 

 those fish and other forms from which we obtain our fishery 

 products. 



In addition to these studies of the adult and young of the food 

 fishes themselves it is important to laiow the plankton, the minute 

 animals and plants found eveiywhere but in varying abundance in 

 both fresh and salt water. Very young fish of all species, and the 

 adults of many species, feed directly on the plankton, and their 

 survival in a given locality is dependent upon the presence there of 

 the proper planktonic forms. Moreover adult fish that do not feed 

 directly upon plankton are dependent indirectly upon plankton 

 for their nourishment, since the animals on which they do feed in 

 their tuin feed upon plankton. The abundance of food fishes is 

 therefore directly dependent upon the abundance of plankton, and 

 a knowledge of the plankton is as important in the husbandry of 

 fish as is a knowledge of forage plants and grasses in animal hus- 

 bandry as practiced on our farms and ranges. But even with a 

 knowledge of the plankton there is still left a gap in our informa- 

 tion on the causes affecting the abundance of food fishes. Just 

 as the abundance of fish is dependent on the abundance of plank- 

 ton so is the abundance of plankton dependent upon various 

 physical and chemical factors. Temperature, salinity, and the pres- 

 ence or absence of various substances in solution in the water all 

 affect the abundance of plankton. The oceanic currents, likewise, are 

 important factors in the distribution of both plankton and young 

 fish. These studies of the oceanic currents and of the phvsical and 

 chemical characteristics of both salt and fresh water constitute the 

 sciences of oceanogi-aphy and hydrography, and are of the greatest 

 importance if we are fully to understand the fluctuations in 

 abundance of our food fishes. Slight changes in temperature or 

 shifts in the oceanic currents may cause extensive migrations or 

 the destruction of great numbers of young and adult fish. 



A comprehensive program of fishery investigations must there- 

 fore include three fairly distinct though closely correlated lines of 

 study: First, the study of the biology of the fishes, crustaceans, and 



