Growth pattern and age determination by scales of lacustrine sockeye salmon [Oncorhynchus nerka] in lake Toya [Japan]
1996
Sakano, H. (Hokkaido Univ., Hakodate (Japan). Faculty of Fisheries) | Kaeriyama, M. | Ueda, H. | Sakurai, Y. | Shimazaki, K.
Life history patterns of sockeye salmon (Oncorhynchus nerka) are classified into anadromous, lacustrine (lake resident), and kokanee types. Sockeye salmon inhabiting Lake Toya is considered as a lacustrine type. Although life history studies of anadromous sockeye salmon are mumerous, those of lacustrine sockeye salmon are very limited. The present study was conduced to develop the age determination method using scale analyses, and tried to determine factors responsible for growth variation of different brood stocks of lacustrine sockeye salmon in Lake Toya. Checks formed from April to June were defined as annuli. Formation of annuli on the scale was considered to be irregularly because number of circuli between two checks was significantly different among individuals. Age of fish was determined by the following method after counting the number of circuli between two checks. The fish which had a large number of circuli between two checks was added one age as lacking an annulus. When fish had a few number of circuli between two checks, their age was reduced one year as pseudoannulus. Growth patterns were different between the 1990 and the 1991 brood stocks. Growth rates of the 1990 brood stock were much higher until age 1+ and little lower after age 2+ than those of the 1991 brood stock. For lacustrine sockeye salmon in Lake Toya, their growth variation among brood stocks may be influenced by fluctuations of lacustrine environmental factors
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