American Dippers Indicate Contaminant Biotransport by Pacific Salmon Christy A. Morrissey,* ,†,‡ Ingrid L. Pollet, § Steve J. Ormerod, ‡ and John E. Elliott ∥ † Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan, Canada, S7N 5E2 ‡ Catchment Research Group, School of Biosciences, Cardiff University, Cardiff, United Kingdom, CF10 3AX § Department of Biology, Acadia University, 33 Westwood Avenue, Wolfville, Nova Scotia, B4P 2R6 ∥ Pacific Wildlife Research Centre, Environment Canada, 5421 Robertson Road, Delta, British Columbia, Canada, V4K 3N2 ABSTRACT: Migrating salmon can increase productivity in Pacific Northwestern streams and lakes through the deposition of nutrients from their decomposing carcasses after spawning. Several studies also report simultaneous biotransport of persistent organic pollutants that have contaminated lake food webs, although no similar effect has been shown conclusively in rivers. We tested the prediction that salmon enhance contaminants in river food webs using the American dipper (Cinclus mexicanus), an aquatic songbird and a recognized indicator of stream quality. Over 3 years, we analyzed 29 dipper eggs and aquatic invertebrate samples from 14 different rivers in 10 catchments in southern British Columbia, Canada to assess whether variations in autumn spawning density of Pacific salmon were reflected in dipper egg contamination or stable carbon and nitrogen isotopes. δ 13 C isotope signatures, but not δ 15 N, in aquatic invertebrates and dipper eggs increased among catchments in proportion to the average density of spawning salmon. Concentrations of brominated flame retardants (PBDEs), dichlorodiphenyltrichloroethane metabolites (DDTs), and chlor- dane compounds were related in part to the δ 13 C measure of salmon density, but mercury, chlorobenzenes, and polychlorinated biphenyls (PCBs) were explained better by dipper trophic level. We conclude that spawning Pacific salmon result in the increased availability of salmon fry as dipper prey and salmon are a significant source of PBDEs, DDTs, and chlordanes to river ecosystems. However, contrary to lake studies, postspawn concentrations of legacy PCBs in river birds, even in salmon-rich rivers, were not significantly higher than would be expected from atmospheric deposition alone. We recommend using δ 13 C isotopes to trace salmon-derived lipids which may persist over winter particularly in rivers, and are potentially a better reflection of lipophilic contaminant transfer. ■ INTRODUCTION Annual runs of Pacific salmon provide an important source of energy and nutrients to aquatic and terrestrial organisms. 1,2 Salmon acquire up to 95% of their biomass in marine ecosystems but return to spawn and die in lakes and streams. Large amounts of marine-derived nutrients are then deposited to freshwater ecosystems via salmon roe and decaying carcasses. 3,4 A relatively large body of literature now supports the assertion that marine- derived nutrients from decaying carcasses, eggs, and ultimately emergent salmon fry affect primary, secondary, and tertiary levels in freshwater and associated terrestrial ecosystems. 5 This nutrient-rich resource provides a positive feedback to freshwater and riparian ecosystems by increasing productivity, growth, survival, and fecundity in organisms as diverse as riparian plants, 6,7 aquatic invertebrates, 8−10 and subsequent generations of juvenile salmonids. 11,12 Recent evidence suggests riparian birds are also directly and indirectly influenced by salmon spawn- ing. Increased bird density, 13,14 species diversity, 15 reproductive success, 16 and survival, 17 have all been related to the salmon subsidy. Salmon can also act as important vectors for contaminant transfer to remote lakes. 18−20 If such effects were large and widespread, they might offset some of the benefits of enhanced productivity, for example through toxicity from accumulated pollutants. To date, the majority of work quantifying transfer of contaminant loads from salmon to freshwater ecosystems is confined to lakes occupied by sockeye salmon (Onchorhynchus nerka). 18,19,21 The role of multiple salmon species in con- tributing contaminants to other freshwater ecosystems, such as rivers and streams, is poorly understood. Large differences exist between river and lake systems in physical structure, residence Received: August 11, 2011 Revised: November 10, 2011 Accepted: December 6, 2011 Published: December 6, 2011 Article pubs.acs.org/est © 2011 American Chemical Society 1153 dx.doi.org/10.1021/es2028058 | Environ. Sci. Technol. 2012, 46, 1153−1162