the western North Pacific and Bering Sea during 

 summer and fall, and then southward and east- 

 ward in the Subarctic Current in winter and spring 

 (fig. HE ) . During summer and fall they are mixed 

 with the .1-age group of the next younger genera- 

 tion, and in winter they are joined by the newest 

 generation of juveniles coming from Bristol Bay 

 as discussed earlier. Finally, at the end of their 

 third year and the beginning of their fourth sum- 

 mer, they again migrate westward in the Alaska 

 Stream, northward through the Aleutian passes 

 and northeastward to Bristol Bay. As .3-age 

 matiu'e fish they average 57 to 59 cm. in fork length 

 and are accompanied by that part of the new .2- 

 age group that is maturing in the same year. Their 

 final migration is shown diagrammatically in fig- 

 ure IIF. 



SUMMARY 



A review of the entire ocean migration of Bristol 

 Bay sockeye salmon as summarized in figure 17 

 indicates that they make two or three circuits of 

 an elongated east-west course extending from 

 about long. 165° E. to 140° W. The diagram is 

 simplified and idealized, but it takes into account 

 the major seasonal migrations and shifts in abun- 

 dance shown by available catch and tagging data. 

 The change in age is shown for convenience as 

 occurring only at the western extremity of the 

 migration, but undoubtedly each age gi-oup is dis- 

 tributed over a considerable part of the migratory 

 path at the time the \vinter annuli are formed. 



Figure 17. — Diagram of ocean migrations of Bristol Bay 

 sockeye salmon based on U.S. seine catch data, and on 

 Canadian. .Japanese, and U.S. tagging data through 

 1966. 



COMMON CHARACTERISTICS OF 

 SALMON MIGRATIONS 



We have described the principal features of the 

 migration of three of the major stocks of salmon 

 in the North Pacific. We have postulated migra- 

 tions and behavior that seem to us to be necessary 

 if the salmon are to migrate to where they have 

 been found, even though our information has some 

 significant gaps. Many of the features of the 

 migrations and behavior of these stocks are char- 

 acteristic of most salmon stocks; we will sum- 

 marize them in this section before we turn to a 

 discussion of possible direction-finding or position- 

 finding mechanisms. 



The first outstanding feature is that each indi- 

 vidual performs the migration once with no pos- 

 sibility of learning from a parent and with a poor 

 chance of spawning successfully to perpetuate the 

 race if it becomes lost or departs from the required 

 time schedule. Clearly the navigational system is 

 an entirely inherited series of responses to stimuli. 



Second, the salmon migrate near the surface of 

 the ocean, mostly in the upper 10 m. The success 

 of the Japanese high-seas fishery, which uses sur- 

 face gill nets (about 5 m. deep), and the research 

 fishing experience with gill nets and longlines 

 indicate that the salmon are typically caught near 

 the surface. A few salmon (mostly chum salmon) 

 have been taken by gill nets set at depths of 30 

 to 70 m. (International North Pacific Fisheries 

 Commission, Annual Eeport, 1960: 26), but the 

 latter depth seems to be near the depth limit. In 

 coastal waters, coho salmon are often taken by 

 trollers at a depth of 10 to 20 m. and chinook 

 salmon between 20 and 30 m. (Milne, 1955). 

 ^ The third outstanding feature is the long dis- 

 tance traveled. The pink salmon from southeastern 

 Alaska or British Columbia and from the Kara- 

 ginski district cover 3,000 miles (5,556 km.) or 

 more in 12 to 15 months. Some of the pink salmon 

 from the Karaginski district travel more than 

 4,000 miles (7,408 km.). Even greater distances 

 are traveled by chum salmon which return to Holc- 

 kaido from south of Kodiak and chinook salmon 

 which return to the Columbia River from south of 

 the central Aleutian Islands. Further, the salmon 

 that spend more than 1 year at sea, such as the 

 chum and sockeye salmon, may well undertake an 

 annual feeding migration in excess of 2,000 miles 

 (3,704 km.). Our information about such migra- 



MODELS OF OCEANIC MIGRATIONS OF PACIFIC SALMON 



455 



