OCEANOGRAPHY 197 



did not take Dr. Schaefer and his staff very long in ttiis research to find out 

 that the yellowfin and skipjack stocks were reacting in quite different ways to 

 our fishery. 



Tlie yellowfin tended, in the size classes we caught, to school at the surface 

 in some loose relationship with land masses either around islands, near sea 

 mounts, or adjacent to the continent where upwelled water occurred. They 

 tended to migrate north and south along the continents seasonally in a fairly 

 regular manner. When they had been in our fishery for 2 or 3 years they settle 

 down out of the upper layers of the ocean to just above the thermocline where 

 they spent the rest of their years and were available for catch no longer by 

 the bait boats that we used but by long lines like the Japanese used. Most 

 importantly he had a long enough historical record of total catches and fishing 

 effort to be able to plot with some assurance the affect of the fishery upon the 

 abundance of the yellowfin stocks. He was able to demonstrate with some 

 confidence that we were not overfishing yellowfin, had not been overfishing them, 

 and even more important he was able to hazard a shrewd guess at the level of 

 fishing intensity we could reach in the future without overfishing these stocks. 



With skipjack he found each of these factors, as well as others, to be different 

 from yellowfin. Skipjack tended to be the more open ocean fish with less ten- 

 dency to congregate in relationship to land masses. They appeared to migrate 

 to the fishery along the coast from the open Pacific to the west. They stayed in 

 the area of our fishery for about 2 years also, mostly as juveniles, but moved in 

 and oft" shore rather than up and down the coast. When as adults they disap- 

 peared from our fishery they did not settle down in the ocean to the thenuocliue 

 where they could be caught by long lines. They just disappeared to the west- 

 ward out into the open Pacific and were traced from this time on mostly by their 

 numerous eggs and larvae that are to be found widely in the surface waters of 

 the tropics at most seasons. Schaefer had as long a .series of historical data 

 for skipjack as for yellowfin catches emanating from the catch records of the 

 same identical vessels. The catch per unit of effort for skipjack, hov.ever, did 

 not change in any determinable way over this period of years although the catch 

 had increoserl as it had for yellowfin. From this it could be said only that the 

 stock of skipjack was so large in relation to the catch that the factor of natural 

 variability was so much larger than the effect of the fishery on the abundance of 

 the fish stock that it quite masked it. 



Thus Schaefer with a two-species fishery had one species that would require 

 regulation if the fishing intensity increased by about 50 percent and the other 

 species was so abundant in relation to the amount being caught thnt he had not 

 even any tentative guidelines as to how big catches it would stand. While it 

 caused the financial ruin of many fishermen, the economic recession we had was a 

 godsend to Schaefer and his staff. It gave them 10 years time to determine 

 these factors before our fishery again began to expand. 



There are other fisheries that are much more comi)lic.ited than this, such as the 

 trawl fisheries of the Pacific Xorthwest. of the New England area, and of the 

 North Sea, which may have one or more principal species in them and several to 

 a dozen or more quite important species, each of which react as differently to the 

 fishery and the ocean climate as our yellowfin and skipiack do in our fishery. Tlie 

 scientific and conseiwation problems in such mixed fisheries become incredibly 

 complpx. 



There are other important fisheries to which these rules and theories simply 

 do not ouite apply. An example is the shrimp fisheries of the South Atlantic 

 States and the Oulf of ^Mexico. The principal species only live for about Li 

 months and can he considered annuals like a field of wheat. Also like a field of 

 wheat what is left over and above that needed for seed at the end of the year 

 simply dies and goes to waste. Here the problem of the ocean scientist and the 

 conservntionist is to determine the rate of growth and rate of mortality over the 

 shrvrt life span to see at what point in the rapid growth curve the maximum 

 weisrht of shrimp is available for the harvest. 



Another class of fish problcTn is illustrate'^ bv the enormous fisheries for the 

 herring, auf^how. sardine. Dilchnrd. and similnr fishf's where long range cycMc 

 chances in the climate of the ocean appear to have such enormous effects on the 

 survival of sucr-essive year classes s^s to quite mask the effect of even nriite 

 huge fisheries upon the abundance of the stocks. Where the fish stock is so larsre 

 as to not be affected bv the fisherv for a decade or two or three, subtle changes 

 in the ocean climate which are nnf yet well understood althouerh they have been 

 studied elaborately for a long while, may so reduce the abundance of the stock 

 of fish that after a few years it will hardly support a commercial fishery of 



