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Recognizing the mechanisms by which environmental conditions drive population dynamics can greatly benefit conservation and management. For example, reductions in densities of spawning Pacific salmon (Oncorhynchus spp.) have received considerable attention, but the role of habitat characteristics on population sizes of breeding salmon is not fully understood. We studied relationships between habitat characteristics and stream population densities of spawning chum (Oncorhynchus keta) and pink (Oncorhynchus gorbuscha) salmon in 44 streams in the Great Bear Rainforest of coastal British Columbia, Canada, with individual streams as the unit of comparison. Our results indicate that a small number of habitat characteristics are important in predicting population density of spawning chum and pink salmon in streams, namely pH for chum salmon and riparian slope and large wood volume for pink salmon. This is the largest multivariable comparison to examine habitat-population relationships in adult spawning salmon and may provide useful quantitative emphasis in guiding management. La reconnaissance des mecanismes par lesquels les conditions ambiantes influencent la dynamique des populations peut s'averer fort avantageuse pour la conservation et la gestion. Par exemple, si des reductions de la densite de saumons du Pacifique (Oncorhynchus spp.) en frai ont recu beaucoup d'attention, l'incidence des caracteristiques de l'habitat sur la taille des populations de saumons reproducteurs n'est pas entierement comprise. Nous avons etudie les liens entre les caracteristiques de l'habitat et la densite des populations de riviere de saumons keta (Oncorhynchus keta) et roses (Oncorhynchus gorbuscha) dans 44 cours d'eau de la grande foret pluviale de Great Bear, le long des cotes de la Colombie-Britannique (Canada), l'unite de comparaison etant le cours d'eau. Nos resultats indiquent qu'un petit nombre de caracteristiques de l'habitat est important pour la prediction de la densite des populations de saumons keta et roses dans les cours d'eau, a savoir le pH pour le saumon keta, et la pente des rives et le volume de debris ligneux grossiers pour le saumon rose. Cette etude, la plus importante comparaison basee sur plusieurs variables a examiner les relations habitat-population chez les saumons adultes en frai, pourrait jeter un eclairage quantitatif utile pour orienter la gestion. [Traduit par la Redaction], Introduction Understanding species-environment relationships has always been a central challenge in ecology, with major implications in conservation and management. Physiological and ecological processes govern relationships between organisms and abiotic habitat [...]

Pacific salmon (Oncorhynchus spp.) can subsidize freshwater food webs with marine-derived nutrients from their eggs, juveniles, and carcasses. However, trophic interactions between spawning salmon and freshwater fish across natural gradients in salmon subsidies remain unclear. We tested how salmon affected the diets and condition of two dominant freshwater consumers--prickly and coastrange sculpins (Cottus asper and Cottus aleuticus, respectively)--across a wide gradient of pink salmon (Oncorhynchus gorbuscha) and chum salmon (Oncorhynchus keta) biomass from 33 streams in the Great Bear Rainforest of British Columbia, Canada. Sculpin diets shifted from invertebrates and juvenile salmonids to salmon eggs when salmon arrived in autumn, with salmon-derived nutrient contributions to diets and sculpin condition increasing with increasing biomass of spawning salmon among streams. Season, habitat, and individual sculpin body size and species also mediated the effects of salmon on sculpin diet as inferred from their carbon and nitrogen stable isotope signatures. This study shows the timing and pathways by which spawning salmon influence the diets and condition of freshwater consumers, and some of the individual and environmental factors that can regulate uptake of salmon nutrients in streams, thus informing ecosystem-based management. Les saumons du Pacifique (Oncorhynchus spp.) peuvent contribuer aux reseaux trophiques d'eau douce par l'entremise de nutriments d'origine marine issus de leurs oeufs, leurs juveniles et leurs carcasses. Les interactions trophiques entre les saumons en frai et les poissons d'eau douce le long de gradients naturels d'apports trophiques des saumons demeurent toutefois mal definies. Nous avons voulu comprendre l'incidence des saumons sur le regime alimentaire et l'etat d'embonpoint de deux consommateurs d'eau douce dominants, le chabot piquant et le chabot cotier (Cottus asper et Cottus aleuticus, respectivement), le long d'un large gradient de biomasse de saumons roses (Oncorhynchus gorbuscha) et ketas (Oncorhynchus keta) de 33 cours d'eau dans la foret pluviale de Great Bear, en Colombie-Britannique (Canada). Les regimes alimentaires des chabots passaient d'invertebres et de salmonides juveniles aux ceufs de saumon apres l'arrivee des saumons en automne, les contributions de nutriments provenant des saumons au regime alimentaire et a l'etat d'embonpoint des chabots augmentant parallelement a l'augmentation de la biomasse de saumons en frai dans les cours d'eau. La saison, l'habitat, ainsi que la taille du corps et l'espece des chabots modulaient egalement les effets des saumons sur le regime alimentaire des chabots determine a la lumiere de leurs signatures d'isotopes stables de carbone et d'azote. Ces resultats font la lumiere sur les periodes ou les saumons en frai influencent le regime alimentaire et l'etat d'embonpoint de consommateurs d'eau douce et les voies par lesquelles cette influence s'exerce, ainsi que sur certains des facteurs individuels et du milieu ambiant qui peuvent reguler la consommation de nutriments derives des saumons dans les cours d'eau, ce qui peut eclairer la gestion ecosystemique. [Traduit par la Redaction], Introduction In coastal areas of the North Pacific Ocean, marine and aquatic ecosystems are linked through nutrient subsidies to fresh waters by annual spawning migrations of anadromous Pacific salmon (Oncorhynchus [...]

Bears (Ursus spp.) and other predators can capture and transport large numbers of Pacific salmon (Oncorhynchus spp.) to riparian areas beside small coastal streams, a process that may affect site productivity and local plant communities. We used a novel experimental manipulation of salmon carcasses to analyze understory plant uptake of salmon-derived N. A hierarchical before-after, control-impact design was used with the addition of chum salmon (Oncorhynchus keta (Walbaum in Artedi, 1792)) carcasses to forest sites along 11 streams on the central coast of British Columbia, Canada. Eight months after carcass placement, the foliar %N and [d.sup.15]N in three herbaceous and one moss species had increased by an average of 14%-60% (%N) and 0.5-3.3 Percent ([d.sup.15]N) at treatment carcass sites versus control sites. Treatment effects for %N were typically greater than for [d.sup.15]N. Nitrogen isotope signatures at carcass sites were highly variable ([d.sup.15]N range = 30.1 Percent) and were mediated by plant species, stream salmon density, carcass mass, and individual plant foliar %N. These results show that understory plants use N from salmon during an important period of plant growth many months after carcasses were deposited in riparian areas. However, they also indicate that habitat variation across spatial scales from individual plants to streams needs to be considered when estimating the contribution of salmon to plant nutrition. Resume: Les ours (Ursus spp.) et autres predateurs peuvent capturer et transporter un grand nombre de saumons du Pacifique (Oncorhynchus spp.) dans les zones riveraines le long de cours d'eau cotiers, un processus qui pourrait influencer la productivite du site et les communautes vegetales locales. Nous avons utilise une nouvelle manipulation experimentale des carcasses de saumon pour analyser le prelevement de N provenant du saumon par les plantes du sous-bois. Un plan experimental hierarchique avant-apres avec temoin a ete utilise avec l'ajout de carcasses de saumon keta (Oncorhynchus keta (Walbaum in Artedi, 1792)) dans des stations forestieres le long de 11 cours d'eau sur la cote centrale de la Colombie-Britannique, au Canada. Huit mois apres avoir place les carcasses, %N et [d.sup.15]N dans les feuilles de trois especes d'herbacees et une espece de mousse avaient augmente en moyenne de 14 % - 60 % (%N) et de 0,5 Percent - 3,3 Percent ([d.sup.15]N) dans les stations traitees avec des carcasses versus les stations temoins. Les effets du traitement etaient typiquement plus importants sur le %N que sur [d.sup.15]N. La signature isotopique de N dans les stations avec des carcasses etait tres variable (ecart de [d.sup.15]N = 30,1 Percent) et etait influencee par les especes vegetales, la densite de saumon dans le cours d'eau, le poids des carcasses et le %N dans le feuillage de chaque plante. Ces resultats montrent que les plantes de sous-bois utilisent le N des saumons pendant une importante periode de leur croissance plusieurs mois apres que les carcasses aient ete deposees dans les zones riveraines. Cependant, ils indiquent egalement qu'on doit tenir compte de la variation de l'habitat aux echelles spatiales allant des plantes individuelles au cours d'eau pour estimer la contribution du saumon a la nutrition des plantes. [Traduit par la Redaction], Introduction Anadromous Pacific salmon (Oncorhynchus spp.) affect biodiversity and ecosystem processes in streams throughout the Pacific Rim. Salmon are born in freshwater, with most populations migrating as juveniles to the [...]

The predictable annual spawning of anadromous salmon (genus Oncorhynchus Suckley, 1861) provides an important marine resource subsidy to terrestrial species throughout the North Pacific. Using isotopic ratios of nitrogen ([δ.sup.15]N) and carbon ([δ.sup.13]C), we examine pathways of salmon nutrient uptake by a ground-foraging passerine, the winter wren (Troglodytes troglodytes (L., 1758)), captured above and below waterfall barriers to salmon migration from two rivers on the central coast of British Columbia. Wren feathers exhibited substantial variation in [δ.sup.15]N (range = 18.6%o) and [δ.sup.13]C (range = 7.9%o), approximating the isotopic range of invertebrates sampled at our study sites. Mean [δ.sup.15]N values of feathers and feces representing the fall diet of winter wrens were enriched by 4.8%o and 8.0%o, respectively, below versus above the waterfall barriers. We observed positive relationships between [δ.sup.15]N and [δ.sup.13]C in fall-grown feathers and fecal samples below the falls but not above the falls, and large positive shifts (as high as 14.3%o) in [sup.15]N from summer to fall within individual birds. The large isotopic variation observed in this system likely can be explained by the mobility of wrens, isotopic variation in their prey, and individual variation in the consumption of fly larvae from salmon carcasses. Our results identify both direct and indirect pathways by which salmon-derived nutrients are cycled into top-level consumers. La fraie annuelle previsible des saumons anadromes (le genre Oncorhynchus Suckley, 1861) represente un apport marin important de ressources aux especes terrestres dans toute la region du Pacifique Nord. Les rapports isotopiques d'azote ([δ.sup.15]) et de carbone ([δ.sup.13]C) nous ont servi a examiner les voies d'introduction des nutriments provenant des saumons chez des passereaux qui se nourrissent au sol, des troglodytes mignons (Troglodytes troglodytes (L., 1758)), captures en amont et en aval de chutes formant des barrieres a la migration des saumons dans deux rivieres de la cete centrale de la Colombie-Britannique. Les plumes des troglodytes affichent des variations importantes de [δ.sup.15]N (etendue = 18,6 %o) et de [δ.sup.13]C (etendue = 7,9 %o) qui s'approchent de l'etendue des variations isotopiques des invertebres echantillonnes sur nos sites d'etude. Les valeurs moyennes de [δ.sup.15]N des plumes et des feces representant le regime alimentaire des troglodytes mignons en automne en aval des chutes se sont enrichies respectivement de 4,8 %o et de 8,0 %o par comparaison aux valeurs en amont des barrieres formees par les chutes. Il existe des relations positives entre [δ.sup.15]N et [δ.sup.13]C dans les plumes elaborees a l'automne et dans les feces en aval, mais non en amont des chutes; il se produit aussi de forts accroissements des valeurs de 15N (pouvant atteindre 14,3 %o) de l'ete a l'automne chez un meme oiseau. L'importante variation isotopique observee dans ce systeme peut vraisemblablement s'expliquer par la mobilite des troglodytes, par la variation isotopique de leurs proies et la variation individuelle de consommation de larves de mouches provenant de carcasses de saumons. Nos resultats identifient a la fois des voies directes et indirectes par lesquelles les nutriments derives des saumons sont recycles vers les consommateurs de niveau superieur. [Traduit par la Redaction], Introduction In the Pacific Northwest where streams and forest soils are nutrient-limited, the flow of marine nutrients via spawning salmon (genus Oncorhynchus Suckley, 1861) to terrestrial and aquatic systems may [...]

Abstract: Anadromous Pacific salmon (Oncorhynchus spp.) subsidize terrestrial food webs with their nutrients and carcasses, a process driven largely by selective foraging by bears (Ursus spp.). We quantify wildlife transfer [...]

Abstract Background Bi-directional flow of nutrients between marine and terrestrial ecosystems can provide essential resources that structure communities in transitional habitats. On the Pacific coast of North America, anadromous salmon (Oncorhynchus spp.) constitute a dominant nutrient subsidy to aquatic habitats and riparian vegetation, although the contribution to terrestrial habitats is not well established. We use a dual isotope approach of δ15N and δ13C to test for the contribution of salmon nutrients to multiple trophic levels of litter-based terrestrial invertebrates below and above waterfalls that act as a barrier to salmon migration on two watersheds in coastal British Columbia. Results Invertebrates varied predictably in δ15N with enrichment of 3–8‰ below the falls compared with above the falls in all trophic groups on both watersheds. We observed increasing δ15N levels in our invertebrate groups with increasing consumption of dietary protein. Invertebrates varied in δ13C but did not always vary predictably with trophic level or habitat. From 19.4 to 71.5% of invertebrate total nitrogen was originally derived from salmon depending on taxa, watershed, and degree of fractionation from the source. Conclusions Enrichment of δ15N in the invertebrate community below the falls in conjunction with the absence of δ13C enrichment suggests that enrichment in δ15N occurs primarily through salmon-derived nitrogen subsidies to litter, soil and vegetation N pools rather than from direct consumption of salmon tissue or salmon tissue consumers. Salmon nutrient subsidies to terrestrial habitats may result in shifts in invertebrate community structure, with subsequent implications for higher vertebrate consumers, particularly the passerines.

Noel R. Swain, Morgan D. Hocking, Jennifer N. Harding, and John D. Reynolds Ref.: Can. J. Fish. Aquat. Sci. 71(4): 521-532. In the Acknowledgments, we accidentally omitted an important thank [...]

Background: Bi-directional flow of nutrients between marine and terrestrial ecosystems can provide essential resources that structure communities in transitional habitats. On the Pacific coast of North America, anadromous salmon (Oncorhynchus spp.) constitute a dominant nutrient subsidy to aquatic habitats and riparian vegetation, although the contribution to terrestrial habitats is not well established. We use a dual isotope approach of δ15N and δ13C to test for the contribution of salmon nutrients to multiple trophic levels of litter-based terrestrial invertebrates below and above waterfalls that act as a barrier to salmon migration on two watersheds in coastal British Columbia. Results: Invertebrates varied predictably in δ15N with enrichment of 3-8 ‰ below the falls compared with above the falls in all trophic groups on both watersheds. We observed increasing δ15N levels in our invertebrate groups with increasing consumption of dietary protein. Invertebrates varied in δ13C but did not always vary predictably with trophic level or habitat. From 19.4 to 71.5% of invertebrate total nitrogen was originally derived from salmon depending on taxa, watershed, and degree of fractionation from the source. Conclusions: Enrichment of δ15N in the invertebrate community below the falls in conjunction with the absence of δ13C enrichment suggests that enrichment in δ15N occurs primarily through salmon-derived nitrogen subsidies to litter, soil and vegetation N pools rather than from direct consumption of salmon tissue or salmon tissue consumers. Salmon nutrient subsidies to terrestrial habitats may result in shifts in invertebrate community structure, with subsequent implications for higher vertebrate consumers, particularly the passerines. [ABSTRACT FROM AUTHOR]