BUREAU OF FISHERIES 101 



indicates a progressive decline in natural productivity, the returns 

 being below normal. 



From the marking experiments it is apparent that mortality from 

 the seaward migrant stage to adult stage is about 75 percent. Mor- 

 tality during the fresh-water period from eggs to seaward migrants 

 is calculated to be 99.5 percent, hence the determination of the factors 

 causing this extensive mortality during fresh-water existence is of 

 great importance since any material increase in survival during this 

 period would have the greatest effect in increasing the commercial 

 runs. 



Similar studies on the supply of pink salmon, the most valuable 

 species in southeastern Alaska, were continued during the year. Pink 

 salmon were also studied in cooperation with the National Canners' 

 Association from the standpoint of physical and chemical changes 

 that occurred in the body during their spawning and migration from 

 the sea. The results provide information relative to the seasonal 

 changes in the market quality that is of primary importance in the 

 canning industry. 



During the past 2 years a statistical study of the commercial salmon 

 fishery in southeastern Alaska has been under way involving the 

 collection, compilation, and biometrical analysis of the daily catch 

 records of various types of fishing gear employed in the Alaska 

 salmon fishery. These records provide the basic data for studies on 

 changes in the abundance and character of the salmon runs and com- 

 petition between the various types of fishing gear, as well as informa- 

 tion for the future delimitation of the fishing districts and the estab- 

 lishment of closed seasons for fishing in the region. 



During previous years investigations of the herring fisheries in 

 Alaska have demonstrated the existence of a considerable number of 

 distinct races of herring, each inhabiting a restricted area. In some 

 of these areas serious overfishing that has resulted in virtual destruc- 

 tion of the industry has occurred. Investigations have been con- 

 ducted during the past year to delineate more accurately the areas 

 inhabited by the separate races. Notable results include the perfec- 

 tion of a new method of tagging herring to trace their migrations 

 and to secure the return of tagged fish. 



Great Lakes -fisheries investigations. — It is generally conceded that 

 certain important fisheries in the Great Lakes have been depleted 

 or are undergoing depletion from overfishing. The virtual disap- 

 pearance of the cisco in Lake Erie since 1926 has been so dramatic 

 that the fact of depletion brooks no argument, and the decline of 

 the whitefish yield in the lake system in general and its rapid dis- 

 appearance from formerly productive grounds in more recent years 

 is well known. The valuable fisheries in the Great Lakes, however, 

 are being maintained at only moderately reduced levels, chiefly by 

 increasing dependence on other species such as the pike-perch, the 

 yellow perch, the lake trout, and the various species of herrings and 

 suckers. In order to measure the annual fluctuations in the abund- 

 ance of these species, to discover the need for protection and to 

 determine the value of fishery regulations, an analysis of the catch 

 statistics gathered by the State of Michigan in Lake Erie, Lake 

 Huron, and Lake Michigan has been undertaken as a major project. 

 The basic tabulations have now been completed for all Great Lakes 



