Fish decomposition in boreal lakes and biogeochemical implications

Abstract

A field study in a boreal lake using a remotely operated vehicle equipped with a camera established that falling fish carcasses did not tend to be buried in sediments after deposition. Decomposition rates of fish carcasses in three boreal lakes were experimentally assessed at different depths. In shallow waters (between 0 and 4 m), decomposition was fast (half lives, τ, ranging from 40 to 230 h) and controlled by vertebrates. In deep waters (below the thermocline), decomposition was slow (τ between 770 and 1,733 h) and was controlled by bacterial processes. Water temperature was a promising predictor of decomposition half‐lives in freshwater. Using a novel underwater infrared camera system, we identified the daily and seasonal patterns of scavenging activity by littoral fish. Only three species displayed scavenging behavior, with creek chubs being the most active. Fast fish‐mediated littoral recycling of fish carcass may explain the lack of direct observations of carcasses in lakes. Estimates of phosphorus fluxes in one of the studied lakes indicate that falling carcasses can represent a significant water‐to‐sediment flux of nutrient.