64 FISH AND GAME COMMISSION 



]\Iigrations by 



Sampling bait and commercial catch in different areas 

 Fish tagging 



Spawning 



Areas 

 Intensity 

 Larval drift 



Growth 



Size of maturity 



Duration within range of commercial sizes 



Rate of decline in abundance of each age class 



The threatened collapse of this our most important fishery empha- 

 sizes the benefit of having at hand the accumulated knowledge of this 

 fishery and accentuates the need for strict regulation of future catches 

 based upon the accumulated research data. 



Mackerel 



The mackerel canning industry developed suddenly, late in 1928, 

 and in less than ten years the signs of depletion of the mackerel supply 

 had appeared. Biological studies have already yielded us much infor- 

 mation as to age and size composition of the catch, spawning season, 

 distribution, migrations and population replacements. The greatest 

 need, from an administrative standpoint, is some approximation of the 

 possible maximum sustained yield for this fishery and the present inves- 

 tigations therefore include : 



1. Analysis of boat catches to show eifect of each year's catch upon 

 the supply. 



2. Yield from each fishing area. 



3. Estimates of amount of young fish replacements contributed by 

 each area. 



4. Age composition and mortality rate of year classes in tlie pop- 

 ulation. 



5. Migrations. Tagging to show dependence of each area upon 

 migrants from other regions. 



6. Spawning. Extent and volume of eggs and larvae by areas. 



7. Determination of the most feasible and effective method of regu- 

 lating the fishery to check the present over-utilization. 



Tuna 



The tuna fishery, involving at least five species, is scattered over 

 a fishing area extending soutlnvard to the Equator in which our boats 

 make catches for delivery to California canneries. Yellowfin and skip- 

 jack account for most of the cannerj* supplj- and these two species 

 are widely distributed whereas bluefin tuna are found locally off our 

 own coast. Albacore and bonito are handled in smaller quantities. 



The key question in greatest need of solution and upon which 

 several other problems depend is whether we draw upon single migra- 

 tory populations or upon several localized and separated groups in the 



