JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 128.235.251.160 on Sun, Abstract. The goal of this study is to identify the mechanisms and measure the strengths of interactions within and among size classes in experimental populations of rainbow trout, Onchoranchus mivkiss. The metric that we used to assess the density-dependent effects was based on consumptive allometry and predator-prey theory. We demonstrate that the interactions among size classes were asymmetrical, favoring larger-bodied individuals. Descriptions of diet and spatial resource use, measures of prey availability, and risk to intra-specific interactions allowed assessment of the relative contributions of exploitative and interference competitive interactions among size classes.Growth of the larger classes was strongly density-dependent and driven primarily by exploitative competition. Growth of the smallest size class was controlled by a combination of exploitative competition within and among size classes and interference competition with larger-bodied conspecifics. This combination of interactions among size classes within populations resulted in a body-size-based asymmetry favoring the larger size classes. Survival of all size classes was positively related to both body size and growth rate. We speculate that the net result of these processes within size-structured populations is compensatory, leading to stable population dynamics. Key w'ordcls: (ci/aiibalisni,; completitive initercictions; Lon1sumllptive alloinetrv; (lenisitV-(lepenld(lence; lCdilsit'-(le/peliClenlt groYwthl (i/1C! sulirvivil; exploitaltive co)p/)etitiOll, relative co0/1tribiitioi Of io'-iteractioni streiigtlhs; iiiterfe'eice CoI1letitiOll, relative contribiitiOii Of; OncorhynchuLs mykiss, rainbowl trout; whlole-lalke experiments.

The goal of this study is to identify the mechanisms and measure the strengths of interactions within and among size classes in experimental populations of rainbow trout, Onchorynchus mykiss. The metric that we used to assess the density‐dependent effects was based on consumptive allometry and predator–prey theory. We demonstrate that the interactions among size classes were asymmetrical, favoring larger‐bodied individuals. Descriptions of diet and spatial resource use, measures of prey availability, and risk to intra‐specific interactions allowed assessment of the relative contributions of exploitative and interference competitive interactions among size classes. Growth of the larger classes was strongly density‐dependent and driven primarily by exploitative competition. Growth of the smallest size class was controlled by a combination of exploitative competition within and among size classes and interference competition with larger‐bodied conspecifics. This combination of interactions among size classes within populations resulted in a body‐size‐based asymmetry favoring the larger size classes. Survival of all size classes was positively related to both body size and growth rate. We speculate that the net result of these processes within size‐structured populations is compensatory, leading to stable population dynamics.

We used natural variation in sockeye salmon (Oncorhynchus nerka) spawner biomass among sites and years in three undisturbed, forested watersheds in interior British Columbia to test the hypotheses that salmon were a major source of particulate organic matter inputs to the streams and that carcass biomass determined stream-water nutrient concentrations and epilithic algal production. Sockeye carcasses were retained at the spawning sites, primarily (75–80%) by large woody debris (LWD) or pools formed by LWD. The abundance and distribution of sockeye salmon determined stream-water nutrient concentrations and epilithic chlorophyll a concentrations during late summer and early fall when most primary production occurred in the oligotrophic streams. Periphyton accrual rates were elevated at sites with high salmon biomass. Peak chlorophyll a concentration increased with increasing carcass biomass per unit discharge above a threshold value to reach maxima 10-fold greater than ambient levels. Epilithic algae were dominated by a few common, large diatom taxa. Salmon carcasses were the dominant source of particulate organic carbon in low gradient stream reaches. Nutrient budget modeling indicated that most of the salmon-origin nutrients were exported from the spawning streams or removed to the terrestrial ecosystem; diffuse impacts may extend over a much larger area than simply the sites used for spawning.

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.

Mandatory catch and release of wild fish and supplementation with hatchery-reared fish are commonly used to sustain sport fisheries on low-abundance populations of wild steelhead. However, their effectiveness in limiting angling mortality on wild fish is uncertain. We radiotagged 226 (125 wild, 101 hatchery) angled adult steelhead Oncorhynchus mykiss near the mouth of the VedderϪChilliwack River, British Columbia, in 1999 and 2000 and monitored their subsequent movements to determine survival to spawning and overlap in the distributions of inferred holding sites, spawning sites, and spawning times. The distributions of prespawning holding sites did not differ between wild and hatchery fish in either year, but spawning locations differed. Holding and spawning sites used by hatchery fish were restricted to the lower two-thirds of the river, downstream of the hatchery where they were reared but well upstream of their smolt release site. Wild fish spawned throughout the watershed. Spawning times did not differ between wild and hatchery fish, but varied with run timing. The maximum mortality from the initial catch and release and radio-tagging was 1.4% in 1999 and 5.8% in 2000; true mortality rates were lower because tag regurgitation was indistinguishable from death. The fishery subsequently killed 2.5% of tagged wild fish and harvested 20% (1999) and 43% (2000) of the hatchery fish. Seventy-two tagged fish were recaptured and released in the sport fishery up to three times without any mortality before spawning. Hatchery fish were recaptured at twice the rate of wild fish. At least 92% of unharvested fish spawned, and 75% of successful spawners survived to emigrate from the watershed. The incidence of postspawning death did not vary with the frequency of capture and release. Catch-and-release angling imposed small costs in terms of survival; however, behavioral differences existed between adult wild fish and the adult F 1 progeny of wild fish reared to smolt stage in a hatchery.