now there are available reasonably complete data 

 on the abundance and distribution of the salmon 

 and on their Nortli Pacific environment (Hartt, 

 1962; Ridgway, Klontz, and Matsumoto, 1962; 

 Fukuhara, Murai, LaLanne, and Sribhibhadh, 

 1962; Callaway, 1963; Dodimead, Favorite, and 

 Hirano, 196.3; Mosher, 1963; Favorite and Hana- 

 van, 1963; Amos, Anas, and Pearson, 1963; 

 Margolis, 1963; Kasahara, 1963; Manzer, Ishida, 

 Peterson, and Hanavan, 1965; Godfrey, 1965; 

 Mason, 1965; Tanaka, 1965; Kondo, Hirano, 

 Nakayama, and Miyake, 1965; Hartt, 1966). 



The abundance and distribution of salmon at 

 sea are dynamic and variable. Tlie salmon occupy 

 almost all of the Nortli Pacific Ocean north of 

 about lat. 41° N. in the winter or lat. 48° N. in 

 the summer and all of the Bering Sea south of the 

 ice pack. They are found mostly in the upper 

 10 m. — far from any contact with the bottom. The 

 maturing individuals, which are due in their 

 spawning streams sometime between June and De- 

 cember, begin to move rapidly 1 to 2 months before 

 their arrival dates and commonly maintain aver- 

 age speeds of 30 miles (55 km.) per day = for many 

 hundreds of miles. Major numbers of several 

 groups of salmon may, thus, pass through a par- 

 ticular ocean area within 3 weeks. The immature 

 salmon, which remain in the ocean at least another 

 year, commonly undertake extensive feeding 

 migrations generally in a counterclockwise cir- 

 cular pattern that is repeated annually. Tlie salm- 

 on of the different species are usually mixed. 

 The mature and immature sabnon of one species 

 are sometimes mi.xcd and sometimes segregated. 

 The different stocks of a single species commonly 

 vary as much in their distribution as do the dif- 

 ferent species, altliough in tiie early spring sock- 

 eye salmon {Oncorhynchus nerka) tend to pre- 

 dominate at the northern boundary of salmon 

 waters and pink salmon {O. gorlntscha) at the 

 southern. 



The information on ocean migrations is as yet 

 only fragmentary, partly because of the difficulties 

 and expense of working in the autumn and winter 

 and partly because of the lack of suitable gear and 

 techniques for the study of the distribution and 

 migrations of the young salmon after they have 

 left the estuary. We do have enough information, 

 however, on .some important stocks to describe their 



^The mlleR used throuRhout this paper nre nautlonl miles. 



migrations in considerable detail and to make some 

 inferences to fill the gaps in our information. We 

 shall undertake, therefore, to construct models of 

 the ocean migrations of three typical stocks orig- 

 inating in diverse geographical areas : southeastern 

 Alaska and central British Columbia pink salmon ; 

 East Kamchatka pink salmon; and Bristol Bay 

 sockeye salmon. Suljstantial information is avail- 

 able on these stocks, and all three arc large enough 

 to have been identifiable in the ocean with reason- 

 able certainty. Fragmentary data on other stocks 

 and species agree with tliese in principle. The 

 models will illustrate the features of tlie migration, 

 the navigational problems of which we are now 

 aware, and the kinds of position- and direction- 

 finding information that we presume are available 

 to the salmon. 



Our discussion rejects or extends and comple- 

 ments the sunnnaries and hypotheses about high- 

 seas migrations that some authors have set forth 

 recently. We reject tlie general apjilicability of the 

 hyiiothesis about random movement of salmon sug- 

 gested by Saila and Shappy ( 1963) . We extend the 

 hyjiotheses about electric navigation presented by 

 Waterman (1959). We extend witli new informa- 

 tion the thorough review of the oceanic migrations 

 of Pacific salmon by Xeave (1964). We question 

 and limit the applicability of .sun-compass and 

 odor-perception mechanisms hypothesized by 

 Hasler (1966) ; Hasler. Horrall, Wisby, and Brae- 

 mer ( 1958) ; and Hasler and Schwassmann ( 1960) . 



Perhaps our information concerning salmon mi- 

 gration will Jielp to explain the mechanisms used 

 by other aquatic species that undertake long-range 

 oceanic migrations and about which much less is 

 known. In the Pacific these fishes now include the 

 albacore {Thunnui^ alalunga), skipjack tuna 

 (KatswiDoniuH pelamis), bhiefin tuna (Thunmu^ sa- 

 liens), black cod (AnopJopama fmbria), and dog- 

 fish {Squalus a-canthias) ; numerous species of ma- 

 rine mammals and turtles also are known to mi- 

 grate extensively at sea. 



The migrations of the salmon begin when the 

 fry emerges from the gravel. These first few iiiclies 

 of migration through the gravel may well be the 

 most hazardous of its entire life. It then moves 

 downstream (or occasionally upstream) to shel- 

 tered waters. Coho salmon {O. kiautch) and chi- 

 nook salmon ( (). fshnwytscha) usually find shelter 

 and food in rivers iuid streams; sockeye salmon in 



442 



U.S. PISH AND WILDLIFE SERVICE 



