Density and biomass of smelt (Osmerus eperlanus) in five Finnish lakes

Hydro-acoustic stock assessment and exploratory sampling with small mesh-sized trawls and seines have sometimes suggested that the importance of smelt (Osmerus eperlanus) in pelagic fish communities might be greater than sampling from commercial fishery and gillnetting indicate. We studied the proportion of smelt in the total fish density (fish ha−1) and biomass (kg ha−1) of pelagic fish with echo sounding and trawling in five southern boreal lakes. Fish density varied between 460 and 2000 fish ha−1 in the study lakes. Smelt and vendace (Coregonus albula) accounted for more than 95% of the exploratory trawl-catches. The total fish biomass in the study areas varied between 3 and 13 kg ha−1. In four lakes the proportion of smelt was more than 60%. In one lake the proportion of vendace was over 85%. These estimates indicate the importance of smelt in the study lakes. Studies of the co-occurrence of smelt with other fish species in the pelagic area of boreal lakes are needed to get a less biased picture of the fish community. This underlines the need for relevant sampling methods for the species involved.