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The age, growth and mortality of the lemon sole (Parophrys vetulus Girard) on the British Columbia fishing grounds Ketchen, Keith Stuart

Abstract

Part of the general investigation being conducted by the Fisheries Research Board of Canada into the condition of the Pacific coast otter trawl fishery deals with the length and age analysis of the species of fish caught. The age of one of these species, the lemon sole, Parophrys vetulus GIrard has been determined through a study of the otoliths or ear-stones. In general the older fisheries and those closest to large Canadian and American markets produce the youngest and the smallest fish. Soles of four and five years of age predominate in the catches from the Strait of Georgia and from the west coast of Vancouver Island. The comparatively recent fisheries of Queen Charlotte Sound and Hecate Strait show a predominance of six and seven year old fish. The male lemon sole reaches an age of ten years and a length of 400mm., while the female reaches twelve or thirteen years of age and grows to a length of over 500mm. The female sole, between four and eight years of age grows approximately 11 mm. more per year than the male. The fish in the Strait of Georgia and in northern Hecate Strait have a slightly greater growth rate than those on the west coast of Vancouver Island and in Queen Charlotte Sound. Marked differences in total annual mortality rates have been shown. In the Strait of Georgia and on the west coast of Vancouver Island the rate is between 60% and 70%. In Queen Charlotte Sound the rate is 52%, and in northern Hecate Strait it is between 30% and 40%. The relative recency of the northern Hecate Strait fishery has raised the suggestion that the total mortality rates of 30% in female fish and 39% in male fish approach the natural mortality rate. Dominance of the 1939 year class has been observed in the s study of fish taken during 1944, 1945 and 1946 in northern Hecate Strait. In the last year another strong year class, that of 1942, made its appearance. The relative lack of success in the brood years of 1940 and 1941 was the factor responsible for the absence of small fish in the catches during the fishing seasons of 1944 and 1945.

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