A decade of data on wild steelhead trout (Salmo gairdneri) from a coastal stream in British Columbia demonstrated large fluctuations in smolt number, age structure, size, estimates of adult run sizes, smolt-to-adult survival, and adult age. Adult runs averaged 922 (range 209–2730) with approximately 10% repeat spawning incidence. Females repeat spawned more than males and were more abundant as kelts, but maiden run adults were equally male and female. The proportion of males returning after 1, 2, and 3 yr in the ocean averaged 3, 62, and 35%, respectively; 58 and 42% of females returned after 2 and 3 yr, respectively. Adult age structure, smolt number, and smolt size varied biennially. Adult size decreased with freshwater age, but increased with ocean age of returns. Males were larger at each ocean age. Mean number of smolts (50:50 sex ratio) was 5543 and varied fivefold. Mean smolt length was 173 mm and mean weight was 49 g. Smolts were 2–5 yr old, and freshwater age 3 was most prevalent (average 56%). Mean survival from smolt to adult was 16% (7% from 1978 cohorts to 26% from 1982 cohorts). Survival was positively correlated with smolt length and weight. However, 1982 cohorts had twice the survival of other cohorts, possibly related to El Niño. No clear relationship was found between return age and mean smolt size, but on average, freshwater age was inversely related to ocean age. The relationships suggest that predictive models may be developed over the longer term from this type of study.
Lengths of wild, winter-run steelhead smolts, estimated by back-calculation procedures from adults' scales, were compared with observed lengths of migrating smolts sampled near the mouth of the Keogh River, Vancouver Island. Size-biased smolt-to-adult survival rates were estimated for several length categories by utilizing length frequencies from observed smolts, smolt length frequencies which were back calculated from adults' scales, smolt yield, and adult returns. Back-calculated smolt length (BSL) of adults returning from smolts of 1977 to 1982 averaged 193 mm compared to 176 mm for observed smolt length (OSL). Mean BSL was larger than OSL in every year. Adults from odd-numbered smolt years had larger BSL than adults from even-numbered smolt years similar to the pattern in OSL. BSL increased with increased years spent in salt water, based on ageing adults' scales. Males and females had different BSL based on number of years spent in fresh water and salt water, although they exhibited the same mean BSL overall. The smolt-to-adult survival estimates were in close agreement with previous estimates derived from the mean OSL. Predictability of survival in the ocean based on the length of smolts was extended over a broad range of the length distribution of wild steelhead smolts.
1990. increased juvenile salmonid growth by wholeriver fertilization. Can. ). Fish. Aquat. Sci. 47: 862-872.Nutrient concentrations, periphyton standing crop and size of steelhead trout (8ncsrhynehus mykiss) and coho salmon (8. kisuteh) fry increased after the fertilization of a nutrient-deficient stream with inorganic phosphorus (P) and nitrogen (N). Wh~le-river fertilimation of the Keogh River, British Columbia, during 4983-86 to increase summer average nutrient csncentrations f r~r n <1 p, g POL-' and 25 pg lal-L-' to 1661 5 pg P-h-' and 30-100 pg N -L -' resulted in five-to 10-fold increases in periphyton standing crops on artificial substrata and 1.4-to 2.0fold Increases in late-September salmsnid fry weights. Diatoms and chlorsphytes dominated the algal periphyton on artificial substrata at fertilized sites. Cyanophytes were unimportant despite low N:P ratios in some cases. juvenile salmonids fed primarily on benthic insects. These results suggest that autochthonous primary production can be an important energy source in forested, middle-order streams, and indicate that the manipulation of autochthonous primary production can be a useful management tool to increase salmonid growth in nutrientpoor coastal streams.Les teneurs en 4l6ments nutritifs, la population exploitable du periphyton et la taille des truites arc-en-eiel (Owcorhywchus mykiss) et des alevins de saurnon coho (0. kisutch) ont augment6 apres fertilisation en pkosphore (P) et azote (N) inorganique d'un cours d'eau pauvre en elements nutritifs. La fertilisation de toute la riviPre Keogh en Colombie-Britannique entre 1983 et 1986, en vue d'accroitre les teneurs estivales moyennes en 6lernents nutritifs de < I pg P-L-' et 25 pg N-L-' a 10-15 p g P.L-' et 30-1 00 pg N-L-' a entraine des augmentations de 5a 10-fsis de la population exploitable du periphyton sur les substrats artificiels et de 1,4-A 2,O-fois dans les poids des aievins de salmonides a %a fin de septembre. Aux sites fertilises, Jes diatom6s et les chlorophyc4es 6taient les plus abondants du p6ripkyton d'algues sur les substrats artificiels. Les cyanophycees 6taient plus nornbreuses malgr6 les rapports N :P faibles dans certains cas. tes satrnonides juveniles se nourrissaient essentiel lernent d'insectes benthiques. Ces r6sultats semblent montrer que la production primaire akitochtogle peut constituer une source 6nergetique importante des cours d'eau moyens, en milieu boise, et indiquent que la manipulation de la production primaire autschtone peut &re un outil de gestion utile en vue d'augmenter la croissance des salmsnides dans des csurs d'eau cdtiers pauvres en Glernents nutritifs.
When rainbow trout (Salmo gairdneri) fry (underyearlings) were introduced into laboratory channels at three different prey levels and permitted to emigrate voluntarily, their density remained highest at the highest prey level. The distribution of fry was positively associated with a gradient in prey abundance. Both territory size and frequency of aggressive encounter varied inversely with prey level; the higher the prey level, the smaller the territory and the lower the frequency of aggressive encounter. Emigration from the channels was neither as rapid nor as marked when prey level was reduced, compared to when fry were initially introduced to different prey levels. However, frequency of aggressive encounter significantly increased when the prey level was decreased and significantly decreased when the prey was increased.
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