Estimation of roach (Rutilus rutilus (L.)) and smelt (Osmerus eperlanus (L.)) stocks with virtual population analysis, hydroacoustics and gillnet CPUE

Dynamics of roach (Rutilus rutilus (L.)) and smelt (Osmerus eperlanus (L.)) stocks were analysed with virtual population analysis (VPA), hydroacoustic s and by analysing gillnet catches per unit effort (CPUE). The research are a was the Enonselka: basin of Lake Vesijarvi in southern Finland. In 1989 i ntensive trawl fishing on previously unexploited roach and smelt stocks was started. Heavy exploitation continued until 1993. Drastic reductions in fi sh stock densities were observed. The VPA indicated a decline in the roach stock from c. 3900 ind. ha(-1) in 1989 to c. 520 ind. ha(-1) in 1993. In th e smelt stock the VPA indicated a respective decline from c. 18000 to c. 19 00 ind. ha(-1). In 1994-1996 fishing was sustained on a lower level. Anyhow , hardly any increase in stock density of roach and smelt was observed in 1 994-1996, The estimates with hydroacoustics were in concordance with the VP A estimates in both the roach and the smelt stock. The gillnet CPUE-estimat es were in agreement with hydroacoustics in roach stock assessment. However , gillnet CPUE was not suitable for analysing the dynamics of the smelt sto ck. (C) 1999 Elsevier Science B.V. All rights reserved.