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Variability in life-history characteristics of steelhead trout (Salmo gairdneri) along the Pacific coast of North America Withler, Ira Lewis


This study compares life-history characteristics of steelhead populations within a restricted area of the southwest coast of British Columbia, and within streams of the Pacific coast from central California to British Columbia. Variations observed within features of the life-histories of steelhead trout are related to physical features of stream environments and to the geographical location of study streams. Within British Columbia data relating to time of stream entry, sex ratios, repeat spawning, mean lengths and duration of fresh and salt-water residence of winter and summer steelhead have been obtained from samples voluntarily submitted by anglers. Data relating to study streams have been obtained from map study, personal observation and through the courtesy of various governmental and municipal agencies. Several published studies from the coastal United States have permitted comparison of steelhead populations over a wide geographic range. Within a limited area steelhead enter and ascend spawning streams throughout all months. Fish which enter streams between October 1 and April 30 are termed "winter steelhead*', while "summer steelhead" enter streams between May 1 and September 30. Cheakamus River is exceptional in that initial stream entry of winter steelhead is delayed until April 1, with most fish entering during April and May. Late entry is related to delayed freshet conditions within the stream. Almost twice as many female as male steelhead were angled. Comparison with trapping results suggests that sport fisheries select for females of anadramous rainbow trout populations. Repeat spawning of winter steelhead was found to range from 5.0 percent for fish from the Seymour River to 31.3 percent for Cheakamus River. Repeat spawning among summer steelhead ranged from 4.4 percent (Seymour River) to 6.3 percent (Coquihalla River). Mean fork lengths of steelhead populations of winter and summer steelhead showed little variation (range 26.3 to 31.0 inches). Winter steelhead from the Cheakamus River were larger than fish from all other populations, and summer steelhead from the Coquihalla River had the least mean length. Mean fork lengths of winter and summer steelhead were not significantly different, despite the five to eight month shorter term of salt-water residence of the latter. Variations of mean lengths of steelhead among different river systems is a result of differences in mean time of salt-water residence. Mean lengths increase with increased salt-water residence. Steelhead spent from one to four years in fresh water and from one to four years in salt water. Along the Pacific coast from Central California to southern British Columbia, timing of initial stream entry showed little variation and the sex ratio was near one male to one female. Repeat spawning decreases from south to north. Mean fork lengths of steelhead populations are greater and fish spend more years in fresh and more years in salt water in northern areas. Possible factors causing variations in life history characteristics of steelhead along the Pacific coast are discussed.

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