Resource subsidies from adfluvial fishes increase stream productivity

• Published in: Freshwater Biology
• Main Authors: Jones, Nicholas E., Mackereth, Robert W.
• Other Authors: Ministry of Natural Resources and Forestry
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2016
• Subjects: Catostomus catostomus; Pink salmon
• Online Access: http://dx.doi.org/10.1111/fwb.12762; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Ffwb.12762; https://onlinelibrary.wiley.com/doi/pdf/10.1111/fwb.12762

Summary Anadromous fishes are well known to shape the structure and function of recipient ecosystems by introducing nutrients and rich organic matter from the ocean. In contrast, the importance of potamodromous migrations, confined to freshwater, and the subsidies they provide to stream ecosystems has received much less attention. Our objective was to determine the importance of excretion, eggs, milt, and carcasses as nutrient and energy sources from a large population (82 449 suckers) of migrating longnose ( Catostomus catostomus ) and common white ( Catostomus commersonii ) suckers into a small (wetted width c . 10 m) oligotrophic river system. We hypothesise that the adfluvial suckers provide a large material subsidy that increased the productivity of the Cypress River and that this resource subsidy rivals or exceeds those delivered by other native and non‐native fishes (e.g. Pacific salmonids). In total there was an estimated 5635 kg of eggs, 2025 kg of milt, and 1 kg of carcasses from suckers that spawn in the Cypress River. Relative to other mainly non‐native fishes, suckers provided 92% of the annual egg biomass and 95% of the milt. Suckers, however, only provided <1% (1 kg) of the annual carcass biomass, whereas, pink salmon provided 50% (600 kg). Overall, suckers provided 84% and 78% of the annual subsidies of N and P, or 212 and 14 kg respectively. Ambient NH 4 concentrations in the river were consistently below that predicted from excretion equations suggesting that microorganisms may have rapidly taken up much of the released ammonium. Downstream of the falls, epilithon biomass was over nine times more abundant, benthic invertebrate densities were approximately two times higher, and fish biomass was eight times greater compared to upstream. There were no upstream–downstream differences in substrate organic matter biomass. Fishes downstream of the falls had higher δ 13 C and δ 15 N values than biota upstream of the falls consistent with the anticipated effect of lake derived subsidies. Using stable ...