Graduate Thesis Or Dissertation
 

The migratory pattern of audlt sockeye salmon (Oncorhynchus nerka) in Bristol Bay as related to the distribution of their home-river waters

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  • The individual stocks of sockeye salmon that make up the annual spawning migration to the Bristol Bay region of Western Alaska are produced in the lakes and streams of ten major river systems, which discharge into the bay over a shoreline distance of 120 miles. The hypothesis adopted in this study was that the bay distribution of the waters from these river systems and controlling factors such as tide, wind and bottom topography determine the distribution of the individual stocks of sockeye salmon in Bristol Bay. This hypothesis was based on the premise that mature sockeye salmon return to their river system of origin to spawn and in doing so utilize recognizable characteristics of their home-river waters to guide them to its source. Hydrographic studies were carried out in upper Bristol Bay to determine the seaward course and distribution of the waters of major sockeye salmon-producing river systems draining into Bristol Bay. These studies included determination of the vertical and horizontal salinity distribution in the upper bay, tracking and plotting the distribution and course of individual river waters, which had been tagged with Rhodamine B dye, during flood and ebb tide and plotting the seaward course of plastic drift cards released at various strategic locations in upper Bristol Bay. From the results of these studies the course and distribution of the waters of each major sockeye salmon-producing river system was described for upper Bristol Bay. The distribution and migration routes of the individual stocks of Bristol Bay sockeye salmon were determined from analysis of the results of exploratory fishing operations carried out by research vessels of the United States and offshore and inshore adult sockeye salmon tagging studies conducted by the United States and Japan. The results of this analysis showed that the main migration route of all stocks of Bristol Bay sockeye is in the offshore waters of the southern half of the entrance to the bay and in the bay itself. All stocks remain in the offshore waters until within 20 to 50 miles of their home-river systems. They were, however, already beginning, to segregate according to, river of origin in the offshore waters when still as much as 150 miles from the mouths of their home-river systems. From this point to the head of Bristol Bay there was a progressive segregation of sockeye salmon stocks according to their river of origin. From these studies the general distribution and migration route of all major stocks of Bristol Bay sockeye salmon was described and illustrated on a chart of the area. Comparison of the distribution of the major river-system waters with that of their respective sockeye salmon stocks showed that the distribution of river water in outer Bristol Bay did not conform to the distribution of sockeye salmon whereas in the upper bay the individual sockeye stocks assumed a distribution which was very similar to that of their river-system waters. The conclusions reached were that the migration route, distribution and initial segregation of sockeye- stocks in the clear offshore waters of Bristol Bay are not influenced by the distribution of river water, but once in the turbid upper bay these features must somehow be related to the distribution of home-river waters and the recognizable properties they contain.
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