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Kootenay Lake is a large, oligotrophic waterbody in southern British Columbia renowned for recreational fisheries for piscivorous rainbow trout (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus). Long-term datasets showed an increase in large-bodied (>2 kg) piscivore abundance followed by a collapse of the kokanee (Oncorhynchus nerka) prey population in 2013 and subsequent decline of large-bodied piscivores. An unprecedented post-collapse state formed in 2015-2018, characterized by low kokanee spawner abundance and biomass and high catch rates for small-bodied ( Le lac Kootenay est un grand plan d'eau oligotrophe du sud de la Colombie-Britannique, reconnu pour ses peches sportives a la truite arc-en-ciel (Oncorhynchus mykiss) et a l'omble a tete plate (Salvelinus confluentus), deux especes piscivores. Des ensembles de donnees sur de longues periodes montrent une augmentation de l'abondance de grands (>2 kg) piscivores suivie de l'effondrement de la population de kokanis (Oncorhynchus nerka), des proies, en 2013 et le declin subsequent des grands piscivores. Une situation sans precedent est apparue dans la foulee de l'effondrement, en 2015-2018, caracterisee par une faible abondance et une faible biomasse de kokanis geniteurs et des taux de prises eleves de petits piscivores (, Introduction Large lake and reservoir ecosystems in northwestern North America often contain populations of large-bodied piscivorous salmonids. These fish are commonly supported by a relatively simple foodweb in the pelagic [...]

In this experiment, competition was observed among native bull trout (Salvelinus confluentus (Suckley, 1859)) and non-native brook trout (Salvelinus fontinalis (Mitchill, 1814)) in artificial streams. In intraspecific competitions, brook trout engaged in territorial interference foraging strategies, and their foraging success was correlated with occupancy of the lead position in the stream. No correlation was apparent for bull trout, most of which engaged in nonterritorial scramble foraging tactics. In interspecific competitions, four stream environments were constructed in which fish density, habitat complexity, and current velocity were altered. Bull trout outcompeted brook trout for food in simple pool habitat devoid of cover when competition was head-to-head (density = 3 fish x [m.sup.-2]) between the species. When competitor number was doubled in this habitat, the two became equal competitors. At this higher density, bull trout again outcompeted brook trout for food when the habitat was changed to a complex riffle with substrate cover. Brook trout were more aggressive towards bull trout than vice versa, and interspecific aggression was decreased by low density, cover, and high stream velocity. Territorial brook trout aggressively interfere with their competitor for access to resources, but the success and intensity of this tactic against bull trout may be mitigated by environmental factors. Key words: invasive species, laboratory stream, behaviour, Oncorhynchus, Salmo, interference competition, exploitative competition. Dans cette experience, la concurrence entre l'omble a tete plate (Salvelinus confluentus (Suckley, 1859)), une espece indigene, et l'omble de fontaine (Salvelinus fontinalis (Mitchill, 1814)), une espece introduite, a ete observee dans des cours d'eau artificiels. La concurrence intraspecifique chez l'omble de fontaine comprenait des strategies territoriales d'interference dans l'approvisionnement, et le succes de l'approvisionnement etait correle a l'occupation de la position de tete dans le cours d'eau. Aucune correlation apparente n'a ete decelee pour l'omble a tete plate, dont la plupart des individus empruntait des strategies d'approvisionnement non territoriales en melee. En ce qui concerne la concurrence entre especes, quatre milieux de cours d'eau ont ete reconstitues dans lesquels la densite de poissons, la complexite de l'habitat et la vitesse du courant variaient. Les ombles a tete plate avaient le dessus sur les ombles de fontaine pour ce qui est de s'approvisionner dans un habitat de mouille simple denue de couverture, dans les cas de confrontation directe (densite = 3 poissons x [m.sup.-2]) d'individus des deux especes. Pour un nombre de poissons deux fois plus grand dans ce meme habitat, les deux especes devenaient des concurrents egaux. A cette plus grande densite, les ombles a tete plate avaient encore le dessus sur les ombles de fontaine en matiere d'alimentation pour un habitat consistant en un banc complexe avec couverture du substrat. Les ombles de fontaine etaient plus agressifs envers les ombles a tete plate que l'inverse, et une faible densite, la presence d'une couverture et une vitesse du courant elevee entramaient une reduction des agressions entre especes. Les ombles de fontaine territoriaux font preuve d'interference agressive envers leurs concurrents pour l'acces aux ressources, mais le succes et l'intensite de cette tactique contre les ombles a tete plate peuvent etre modules par des facteurs du milieu. [Traduit par la Redaction] Mots-cles: espece envahissante, cours d'eau laboratoire, comportement, Oncorhynchus, Salmo, concurrence par interference, concurrence par exploitation., Introduction Competitive interactions between non-native and native fishes can be an important determinant of invasion success, and if non-native species are to propagate and spread, it is often at the [...]

An information-theoretic approach was used to determine the association between brook trout (Salvelinus fontinalis) invasiveness and a suite of abiotic and biotic factors, measured at 80 sites from 51 streams in the Canadian Rockies. The streams selected had confirmed brook trout invasions and were identified as current or historical nursery habitat for native bull trout (Salvelinus confluentus). The biomass at most sites was strongly or completely dominated (95%- 100%) by one species or the other, and sites were classified as having high brook trout invasiveness (>60% of the biomass of the community relative to remnant bull trout) or low invasiveness ( Une approche basee sur la theorie de l'information a ete utilisee pour determiner l'association entre l'intensite de l'invasion par l'omble de fontaine (Salvelinus fontinalis) et un ensemble de facteurs abiotiques et biotiques mesures dans 80 sites en 51 cours d'eau des Rocheuses canadiennes. Les cours d'eau selectionnes etaient caracterises par des invasions confirmees d'ombles de fontaine et reconnus comme etant des habitats d'elevage actuels ou passes de l'omble a tete plate (Salvelinus confluentus). La biomasse dans la plupart des sites etait fortement ou entierement dominee (95 %-100 %) par une espece ou l'autre, et les sites etaient classes selon la forte (>60 % de la biomasse de la communaute par rapport aux ombles a tete plate restants) ou faible (, Introduction Invasion success for many species is spatially variable, ranging from unsuccessful to complete dominance of the invasive species over ecologically similar natives, and underlying reasons for this variation are [...]

Genetic assignment methods were used to assign 104 adult migrant bull trout Salvelinus confluentus from five recreational fisheries in the Oldman River drainage (Alberta, Canada) to a baseline of three coarse-scale genetic stocks that had been previously identified with a model-based Bayesian clustering method. Based on individual assignment and genetic stock identification, most fisheries were largely dominated by the stock with the most proximate spawning tributaries; however, assignment tests suggested variation among source stocks in the proportions of long-range (>90 river kilometers) migrants relative to short-range migrants (i.e., that used nearby river systems draining spawning streams). Migrants originating from a subset of the drainage were then subjected to a finer-scale mixed-stock analysis in which populations at near-tributary scales were used as the baseline. These stock proportions were compared with estimates from direct observations and were found to yield similar values to stock proportions derived from 2 years of trapping in several spawning streams. These genetic assignment methods may be used to infer contributions of large and fine-scale hierarchical populations to mixed-stock recreational fisheries and are especially applicable for use by inland recreational fisheries managers, which have traditionally not taken advantage of spatial genetic analysis tools to the extent used by coastal commercial fisheries managers. [ABSTRACT FROM AUTHOR]