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Food and feeding habits, maturity and fecundity of spring salmon (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) in southern British Columbia coastal waters Prakash, Anand

Abstract

Food study based on the stomach content analyses of spring and coho salmon collected from various localities along the southern British Columbia coast during the summer of 1957 revealed that herring followed by Crustacea formed the most important item of the diet of the two species. Coho salmon exhibited more pelagic and varied diet than spring salmon caught in the same area. Definite seasonal fluctuations in the composition of food and feeding intensity were noticed, considerable amounts of Crustacea were taken in early summer months and after that fish assumed importance. July and August mark the period when the feeding activity is intense in both the species. Qualitative and quantitative differences in the feeding conditions on the east and west coasts of Vancouver Island warrant the establishment of two food type areas. The differences in growth of fish on the two coasts as related to feeding conditions are discussed. Although, herring is the major food item of both spring and coho salmon, evidences are presented in support of the hypothesis that a reduction in herring stock abundance due to predation would not affect salmon catches. Based on ova measurements and maturity index values fish have been classified into immature and maturing. It appears that almost all coho salmon available to the commercial fishery are maturing, spring catches on the other hand include large percentage of both immature and maturing fish. Immature and maturing female springs divide at a fork length of 74 cm., cohos do so at an approximate fork length of 52 A volume method for the determination of egg numbers present in the ovary has been developed, the average percentage error between the calculated and actual counts being 5.3. it was found that the absolute fecundity is positively correlated to fish length and negatively to egg size but the magnitude of the effect of fish length on absolute fecundity is about four times greater than that of egg size.

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