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We tested the hypotheses that marine-derived resource subsidies (salmon carcasses) increase the growth rates of stream-resident salmonids in southeastern Alaska and that more carcasses translate into more growth. Five carcass treatments of pink salmon Oncorhynchus gorbuscha (0, 1, 2, 3, and 4 carcasses/m 2 or 0, 1.9, 3.7, 5.6, and 7.4 kg wet mass/m 2 ) were replicated six times in once-through artificial channels, then each channel was stocked with three live age-0 coho salmon O. kisutch. The experiment spanned more than 9 weeks: 16 August to 24 October 1998. The body mass and fork length of the young coho salmon significantly increased from carcass additions, but the incremental increases sharply diminished at carcass-loading levels above 1 carcass/m 2 . Further, in a small stream in which we added salmon carcasses to a cumulative density of 0.54 carcasses/m 2 , both cutthroat trout O. clarki and Dolly Varden Salvelinus malma grew significantly faster during the 2 months in which carcasses were added (September-October) compared with fish in control reaches. Fish maintained their assimilated body mass through winter into the following spring. This study illustrates that marine nutrients and energy from salmon spawners increase growth rates of resident and anadromous salmonids in streams. This elevated growth should translate into increased survival and reproduction, ultimately elevating freshwater and marine salmon production. Ecological relationships between salmon runs and aquatic community nutrition and productivity may be important considerations for salmon stock protection and restoration and for freshwater and marine ecosystem management.

An experiment in >1000 river and riparian sites found spatial patterns and controls of carbon processing at the global scale.

Abstract:We conducted this study to determine the relationship between salmon spawner abundance and stream biofilm and benthic macroinvertebrate abundance in Southeast Alaska. Experiments took place in outdoor artificial and natural streams. Six pink salmon (Oncorhynchus gorbuscha) carcass treatments (0.00, 1.45, 2.90, 4.35, 5.80, and 7.25 kg wet mass) placed in artificial channels were subsampled repeatedly for biofilm ash-free dry mass (AFDM), chlorophyll a, and macroinvertebrates. In a small (nonanadromous) forest stream, we sampled benthos throughout a 66-m reach 17 days after distributing 60 carcasses along the lower half of that reach. All response variables significantly increased in response to carcass additions in both artificial and natural streams. Chlorophyll a continued to increase across all loading rates, while AFDM and total macroinvertebrate densities showed no further response to loading beyond the first treatment (1.45 kg) in artificial streams. In the natural stream, AFDM and chironomid densities continued increasing across loading levels. These results indicated that increased spawner densities increased lower trophic level abundance until a trophic capacity was reached. Salmon escapement goals should consider food web effects, especially on trophic levels that support juvenile salmonids, that ultimately affect freshwater salmon production.Résumé : Nous avons entrepris cette étude pour déterminer la relation entre, d'une part, l'abondance des saumons reproducteurs et, d'autre part, l'abondance des films biologiques fluviaux et des macroinvertébrés dans le sud-est de l'Alaska. Les expériences ont été effectuées à l'extérieur dans des canaux artificiels et un cours d'eau naturel. On a procédé à cinq traitements consistant en l'introduction de carcasses de saumon rose (Oncorhynchus gorbuscha) (1,45, 2,90, 4,35, 5,80, et 7,25 kg poids humide) avec témoin (0,00 kg) dans des canaux artificiels; on y a prélevé à plusiers reprises des sous-échantillons pour mesurer la masse à sec sans cendre des films biologiques ainsi que la chlorophylle a et les macroinvertébrés. Dans un petit cours d'eau forestier non fréquenté par des saumons anadromes, nous avons échantillonné le benthos d'un tronçon de 66 m 17 jours après avoir distribué 60 carcasses dans la moitié inférieure de ce tronçon. Toutes les variables mesurées se sont significativement accrues en réponse aux introductions de carcasses tant dans les canaux artificiels que dans le cours d'eau naturel. La quantité de chlorophylle a n'a pas cessé de s'accroître d'un traitement à l'autre, tandis que la masse à sec sans cendre des films biologiques et les densités de macroinvertébrés ont plafonné dès le premier traitement (1,45 kg) dans les canaux artificiels. Dans le cours d'eau naturel, la masse à sec sans cendre des films biologiques et les densités des chironomides n'ont cessé de s'accroître d'un traitement à l'autre. Ces résultats ont indiqué que l'accroissement des densités de reproducteurs a eu pour effet d'accroître l'abondance des organismes des ...