THIRTY-FIFTPI BIENNIAL REPORT 65 



various fishing areas. The answer to this question will affect other 

 biological work, such as studies of abundance, spawning and growth 

 rate. Our tuna program therefore includes the following investi- 

 gations : 



Yellowfin tuna and skipjack 



1. Measurements, counts and other morphological work on sam- 

 ples from different areas. 



2. Tagging to determine migrations. 



3. Collection of biological data for life-history studies. 



4. Data to determine desirability of closed seasons and revision of 

 existing size limits. 



5. Complete field investigation of the effects of various factors in 

 boat refrigeration of tuna. 



Albacore, bonito and bluefin 



1. Determine distribution and migrations. 



2. Morphological studies for comparison with the species of Japan 

 and Hawaii. 



Life-history studies. 



Bottom Fish 



As yet we have very incomplete knowledge of the life-history of 

 bottom fish (soles, flounders, sand dab, rockfishes, sablefish and Pacific 

 cultus) ; yet an outstanding accomplishment in these fisheries has been 

 the checking of the destructive fishing of small meshed trawl nets. This 

 has been accomplished by demonstrations which have resulted in the 

 adoption of modified nets of large mesh to allow escapement of 

 small fish. 



Work is being continued to determine, for the population of each 

 species, the point in intensity of fishing which will give the maximum 

 sustained yield as well as the greatest economic return. The investi- 

 gations consist of: 



1. Analysis of fishing intensity to measure changes in abundance. 



2. Determination of age, growth rate and fecundities. 



3. Extent of intermingling between geographical regions. 



4. Measures of natural mortality rates and the effect of fishing 

 upon these rates. 



Salmon 



Our salmon runs have been reduced to a small fraction of their 

 former magnitude by the long continued operation of overfishing, 

 reduced spawning area resulting from power and irrigation develop- 

 ment, and destruction of seaward migrants in irrigation ditches. The 

 immediate administrative problem is to build back the runs, chiefly by 

 catch limitation, so that the breeding stock can be increased. 



Investigations of the past have provided a great deal of the life- 

 history knowledge, such as growth rate, age and the parent stream 



