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SUMMARYSticklebacks in Lakes Wapato and Chelan are far inland and highly isolated from other populations. They live about one year. Rainbow trout prey on sticklebacks most heavily during the winter, and this predation is random on males and females and on the three plate morphs. However, trout show strong selective predation on sticklebacks with respect to plate number. The selective advantage of seven plated sticklebacks under predation is highly significant and consistent over three years. The frequency of seven plated adults in Lake Wapato was 56 per cent, in 1968, but increased to 65 per cent, in 1969 and has since remained at about 62 per cent. This large increase coincides with the time interval when predation was heaviest and when selective predation favouring sevens was greatest. The heritabilities for number of plates and gill rakers are high, and so the values obtained for the increase in mean relative fitness show that natural selection is acting strongly on these traits. Predation acting on the variation in plate number and food specialisation acting on gill rakers are two of the major selective agents.

SUMMARYThe simplest model that accounts for segregation of the low, partial, and complete morphs in sticklebacks is one with two autosomal loci, each with two alleles, and having the relationships between genotype and phenotype as shown in fig. 2. There is no strong evidence for linkage, but this and the modification of dominance are suggested by the data. A distinct phenotype, called minute keel, is present in Lake Wapato at a low frequency. Further data are necessary, but it seems to be multifactorially inherited and under partial control by the female parent.

This paper presents preliminary results of a study to evaluate the potential utility of supplementation of natural origin coho salmon (Oncorhynchus kisutch) on the Clearwater River, a tributary of the Queets River in western Washington. The study, initiated in 1984, involves the collection of natural origin brood stock, rearing in a combination of hatchery and natural environments, and volitional releases, combined with marking and sampling of natural origin fish. Primary findings relative to five essential research questions of this study concluded that (i) smolts from supplementation returned at a lower rate than natural smolts; (ii) the reproductive efficiency (spawner to spawner) of fish taken for supplementation was higher than that for fish allowed to spawn naturally; (iii) supplemental fish successfully reproduced and the combined supplemental-natural spawning population had a high productivity; (iv) supplementation did not appear to have affected the overall reproductive performance of the population for the duration of the project; and (v) supplementation increased the overall spawner return on the Clearwater River and is required to maximize adult production, unless conditions in both freshwater and ocean environments are optimal.Résumé : Nous présentons les résultats préliminaires d'une évaluation de l'utilité potentielle des empoissonnements d'appoint de saumons coho (Oncorhynchus kisutch) d'origine naturelle dans la rivière Clearwater, un tributaire de la Queets dans l'ouest du Washington. Cette étude, initiée en 1984, implique la récolte d'un stock reproducteur d'origine naturelle, l'élevage dans une combinaison de conditions de pisciculture et de conditions naturelles et des remises à l'eau volontaires, avec en plus le marquage et l'échantillonnage des poissons d'origine naturelle. Les principaux résul-tats de l'étude concernant cinq questions fondamentales de recherche sont les suivants: (i) les saumoneaux issus des empoissonnements d'appoint ont un taux de retour inférieur à celui des saumoneaux naturels; (ii) l'efficacité reproductive (de reproducteur à reproducteur) des poissons récoltés pour l'empoissonnement est plus grande que celle des poissons qui ont pu se reproduire naturellement; (iii) les poissons ajoutés lors des empoissonnements se reproduisent avec succès et la population combinée des reproducteurs naturels et ajoutés a une forte productivité; (iv) l'empoissonnement d'appoint ne semble pas affecter la performance reproductive globale de la population dans le cadre de ce projet et (v) l'empoisonnement d'appoint accroît le retour global de reproducteurs dans la Clearwater et il est nécessaire pour maximiser la production des adultes, à moins que les conditions à la fois dans les milieux d'eau douce et de mer ne soient optimales.[Traduit par la Rédaction] Sharma et al. 437