Conservation value of historical data: reconstructing stock dynamics of turbot during the last century in the Kattegat-Skagerrak

A quasi-complete time series of biomass, maximum body size and spatial distribution was reconstructed for turbot Psetta maxima L. in the Kattegat-Skagerrak based on standardized research surveys extending back to 1925. Here we show that biomass has declined by about 86% over the time series, maximum body size has decreased by 20 cm and the northern component of the population has virtually vanished. These trends are likely to be underestimated due to the conservative approach we used by assuming a low level of 'technological creep' during the survey period, suggesting that the actual reduction in biomass might have been between 92 and 95%. Absence of trend in former analyses of data collected in the last 2 or 3 decades is dangerously misleading. This substantial difference in stock status, based on historical data, highlights the general importance of the historical perspective for managing natural resources.