Temporal Shifts in Fish Landing Composition, Stock Status, and Diversity in Lake Volvi, Greece: A Six-Decade Analysis (1961–2024)

Long-term fishery records are essential for detecting ecological change in data-limited freshwater systems. We analyzed 64 years (1961–2024) of commercial landings for ten fish categories from Lake Volvi, Greece, combining temporal, multivariate, forecasting and catch-only approaches. Total landings fell 89.8%, from 620 t in 1962 to 63.3 t in 2024. Six categories declined significantly after autocorrelation correction, whereas Gibel carp increased; excluding a documented reporting discontinuity left the decline and all diversity trends unchanged. Changepoints in landings (~1971, ~1978, ~2002) did not coincide with a compositional boundary at 1990/1991, so production decline and reorganization were not synchronous. Composition differed strongly among three a priori periods (PERMANOVA R2 = 0.656, p = 0.001), reflecting a shift from native dominants to a low-production assemblage increasingly influenced by non-native Gibel carp; diversity increased while recorded richness showed no trend. Eight series yielded viable catch-only fits. Estimated terminal biomass lay below one-fifth of BMSY for six, irrespective of terminal year, whereas exploitation ratios were strongly terminal-year dependent: five of eight changed Kobe quadrant between 2022 and 2024, owing to carried-forward values in the final two years. Severe depletion of the native taxa is therefore the robust stock-status finding; single-year exploitation classifications remain conditional on terminal year.