Effect of salmon-derived nutrients on growth and condition in freshwater sculpins

Background/Question/Methods

Pacific salmon (Oncorhynchus spp.) represent an important potential source of nutrients that can cross ecosystem boundaries when the fish return from the sea to spawn in freshwaters.  Nutrients can be derived from salmon eggs and from their carcasses after spawning.  We studied prickly sculpin (Cottus asper) and coastrange sculpin (C. aleuticus) as models for how such cross-boundary nutrient subsidies can affect resident stream fishes. In particular, we determined how salmon nutrients impact aging and growth in prickly and coastrange sculpins. We have conducted our fieldwork in 28 coastal streams in the Great Bear Rainforest on the central coast of BC.  

Results/Conclusions

Measurements of sculpin otoliths and body metrics showed that increased density of spawning pink and chum salmon results in faster growth in resident sculpin populations. While the size distribution of sculpins remains consistent among streams, the sculpins in high-density salmon streams reach their maximum size two to three years earlier than those in streams with fewer salmon. This relationship is stronger with chum salmon than with pink, as the former are larger-bodied and their carcasses tend to be retained in watersheds for a longer period of time.  These results are matched with lipid analyses, as well as stable isotopes, which confirm that salmon are a major source of nitrogen in sculpins.  This study enhances our understanding of links between food webs and cross-boundary nutrient subsidies and underscores the importance of salmon for the functioning of freshwater ecosystems.