Disentangling complexity of fishing fleets: using sequence analysis to classify distinguishable groups of vessels based on commercial landings

Capturing the diversity of fishing fleets and identifying distinct subgroups is essential for effectively directing research and management efforts. In this study, the German Baltic gillnet fleet was split into distinguishable groups of vessels by applying a stepwise approach. Monthly landing profiles were classified using clustering techniques and arranged as annual landing sequences, as the basis to form groups of vessels with distinct annual landing sequences using sequence analysis. Commercial landings from 1243 vessels across 11 years (2008–2018) resulted in 8031 annual landing sequences, which were clustered into eight groups, each with a characteristic, annually recurring, seasonal landing pattern (cod group, cod-herring group, herring-flounder group, herring group, freshwater fish group, pikeperch group, eel group and port group). The results highlight the heterogeneity of the fleet and a strong adaptation to regional and seasonal resource availability. Studying sequences of landings instead of isolated events in time provides insight into the interlinkage and succession of landings and can aid at classifying fishing fleets and better targeting groups of vessels of interest.