Analysis of fishery exploitation parameters of lakes and assessment of their suitability for observation of trends in fish catches

Long-term studies on catches from 757 lakes in northeastern Poland served to analyse fishery exploitation parameters available from the records in lakes books. Yield (kg.ha-1), annual frequency of exploitation and relative catch (kg.ha-1.month-1) were analysed in five size classes of lakes, together with the relations occurring between these parameters. Linear correlation was determined between yield versus the number of months of exploitation when the catches were made and relative catch. The latter parameter was characterised by a slightly smaller variability of real values and consequently by a higher concentration along the adjusted trend line compared to the catch per lake area unit.