FISHERY BULLETIN: VOL. 72. NO. 2 



Immatures Age .1 (January-May) 



The immatures (age .1 on 1 January), after 

 reaching the North Pacific Ocean, move south- 

 ward through the Alaskan Stream and Ridge Area 

 and by midwinter become located primarily south 

 of lat. SO'^N in Western Subarctic Instrusion or 

 Transition Area waters. There is no evidence that 

 the young fish follow major currents during the 

 southward movement; they move southward over 

 a broad east-west area. The young immatures are 

 probably in search of food sources and favorable 

 water temperatures (3.5-6.0^C) that prevail in 

 more southern waters. 



In early spring the immatures shift somewhat 

 farther south and become more sharply separated 

 from the matures (sockeye salmon from an earlier 

 brood year). By April and May the immature 

 age .1 fish have reached their so.uthern limit of 

 migration over a broad area from about long. 

 n5^E to 145''W and are found from about lat. 

 45° to 50°N in Transition and Western Sub- 

 arctic Intrusion waters — an area of favorable 

 water temperatures, 4.5-6.0°C, and food sources. 



Second Year at Sea 



Immatures Age .1 (June-September) 



In June the immatures start a return north- 

 ward movement over a broad east-west area. 

 This movement may be related to the increase in 

 surface water temperatures and subsequent 

 zooplankton blooms from south to north. 



By July, the age .1 fish have moved north 

 from areas occupied in the spring and are mainly 

 located north of lat. SO^'N in the Alaskan Stream 

 and Ridge Areas. These waters in summer have 

 more abundant food than other water areas of 

 the Subarctic Pacific Region, which probably 

 accounts for the distribution of sockeye on the 

 north-south plane. On an east-west plane, the 

 immature sockeye are distributed over a wide 

 area, from about long. 170°E to about 160^W. 

 Most of the fish are moving in a westerly direc- 

 tion during the summer, but recirculation of im- 

 matures or limited westerly movement maintains 

 the wide east-west distribution through the 

 summer. Some elements of the population move 

 north into the Bering Sea in summer and become 

 distributed in the central Bering Sea to at least 

 lat. 60°N. The majority of the population remains 

 south of the Aleutian Islands. 



612 



The continuity of the Alaskan Stream and 

 Alaskan Gyre or the eastward intrusion of the 

 Western Subarctic Gyre are oceanic features that 

 may influence the western limits of distribution 

 of Bristol Bay immature sockeye. 



Separation of Immature and Maturing Sockeye 

 (October-May) 



In January and February of this period (the 

 sockeye now become age .2 fish), they separate 

 into immature and maturing components. The 

 immature group will remain at sea a third 

 year before maturing and will follow a somewhat 

 different migration pattern (as shown in Figure 

 25 C) than the maturing group (Figure 25 E). 

 The remaining period at sea for the immature 

 group will be discussed following the description 

 of movements of the maturing fish. 



Maturing Age .1 to Age .2 (October-May) 



The age .1 sockeye which will mature the fol- 

 lowing spring remain in the more northerly 

 waters of the North Pacific Ocean (primarily north 

 of lat. 50''N in the Alaskan Stream and Ridge 

 Areas) throughout fall, winter, and spring until 

 they begin their inshore migration. The extensive 

 east-west distribution of sockeye (which was 

 noted previously) is maintained. Evidence of vary- 

 ing catch rates of Bristol Bay sockeye by the 

 Japanese mothership fishery west of long. 175''W 

 (rates have varied between years from 2.2 to 35.2% 

 of the total run) suggests that the distribution of 

 maturing sockeye shifts to the east in fall and 

 winter and that the magnitude and extent of this 

 movement governs the availability of sockeye to 

 the Japanese fishing fleet. 



During this period, the maturing sockeye 

 salmon are associated with the Alaskan Gyre — 

 primarily the Ridge Area, but they are also 

 found in the Western Subarctic Intrusion and 

 Transition Areas, depending upon the location of 

 these oceanic features. 



The areas from which the maturing Bristol 

 Bay fish initiate their inshore migration essen- 

 tially have been established by April as a result 

 of previous migrations. At that time their routes 

 of inshore migration (and the proportion of the 

 population available to the Japanese mothership 

 fishery) have been determined, and variations in 

 oceanographic features are assumed to have little 

 effect on these inshore routes of migration. 



