CONSERVATION OF THE HALIBUT — THOMPSON 367 



banks. On the Pacific coast of America there remained but the south- 

 eastern edge of Bering Sea, which vessels have already entered, to 

 find of doubtful value. 



The waters into which commercial fishing had extended and over 

 which the Commission had jurisdiction, therefore, formed a more 

 or less natural unit outside of which no great supply could be ex- 

 pected. Connecting the Pacific coast of the United States and the 

 small area of halibut banks on the Japanese coasts are two chains 

 of islands, the Aleutians and the Kuriles. Along these the banks 

 are narrow, quickly deepening, so that but few halibut can be ex- 

 pected. Connecting the Pacific coast and Bering Sea are the narrow 

 passes through the Aleutians at the end of the Alaska Peninsula. 

 Through these there cannot be expected any extensive migration 

 of halibut. The coast line from California to the Aleutians seems, 

 therefore, to comprise a natural unit of distribution. Within this 

 distribution the supply must reproduce itself. 



Yet within this the Commission found that it was not dealing 

 with one stock of fish. That much was hinted at by the fact that 

 each bank could be depleted in turn. The Commission demonstrated 

 the existence of different stocks by several different types of research. 



The first was by scientific experiments in marking. Halibut were 

 caught by research vessels, tagged with numbered metal strips on 

 the cheek bones, and liberated, and rewards were offered for their 

 return when caught by the commercial fishermen. (PI. 1, fig. 1.) 

 Nearly 13,000 of these fish were marked throughout the whole ex- 

 tent of the fishing banlis. The returns indicate that the immature 

 smaller fish, on the average under 12 years of age, migrate very 

 little. They seem to mill around inside the bounds of their native 

 banks. When maturity is attained, these fish become more migra- 

 tory, but they still remain within certain districts. Thus the mature 

 fish tagged on the eastern side of the Gulf of Alaska on the famous 

 spawning grounds called " Yakutat Spit " and " W Grounds " moved 

 freely westward as far as the entrance to Bering Sea; but rarely 

 southward. Other stocks of fish collected for spawning at various 

 points along the banks to the south and during the summer scattered 

 to adjacent feeding banks. But so intense had been the fishery on 

 these older southern banks that very few mature fish were left. 

 The great majority of fish were immature and stayed strictly at 

 home, forming as many stocks of fish as there were banks. But on 

 these southern depleted grounds conditions were so similar that the 

 various banks could be grouped as one from the viewpoint of the 

 regulation needed. 



Occasionally tagged fish travel great distances. Tags placed on 

 fish at the entrance to Bering Sea were sometimes recovered 1,500 



