| Hydroelectric reservoirs are regulated systems that can sometimes experience extreme fluctuations in seasonal water level. These fluctuations can result in low biodiversity and productivity in littoral areas, which may have major impacts on reservoir ecosystem structure and functioning. Understanding reservoir ecosystem structure and function is especially relevant to the management of fish production in these systems. For instance, knowledge of fish diet is necessary in order to implement appropriate management actions to maintain or increase fish production, because if food for fish is mainly produced in the reservoir, this has quite different implications than if the main food supply is brought in from outside via streams. Using stable isotope analysis, I investigated fish food webs in Carpenter reservoir, a hydroelectric reservoir that experiences extreme seasonal fluctuation and is located on the Bridge River, British Columbia. I sampled fish tissues and macroinvertebrates from the reservoir, the mainstem river, and three major tributaries. I also sampled pelagic zooplankton and terrestrial leaf litter. I found that fish stable isotope signatures were most similar to those of macroinvertebrate drift from the mainstem river and Chironomidae from the reservoir littoral zone, while pelagic zooplankton, tributary macroinvertebrate drift and terrestrial vegetation have stable isotope signatures that are different from those of fish tissues. These findings seem to indicate that production from the mainstem river and reservoir littoral benthos is utilised more by fish than that from other sources. This is contrary to former beliefs that reservoir food webs are primarily driven by pelagic energy sources, and supports recent work describing the importance of benthic-pelagic coupling in lacustrine systems. |
