| Summary: | Composition and length-frequency are important attributes considered in the management of fish communities and can be affected by both exploitation and environmental forces. Vulnerability to these effects varies among species depending on environmental tolerance, ecological traits, and life-history strategies. In the present study, data from scientific bottom trawl surveys conducted between 1991 and 2018 were analysed to identify long-term changes in community structure and length-frequency of demersal fish species of the east coast of the South Island, New Zealand. Analysis of variance, hierarchical clustering analysis and multidimensional scaling relationships demonstrated that community composition has changed significantly over the last three decades, with a tendency towards greater spatial overlap among species in the most recent periods. Changes in depth distribution were identified but were mainly correlated with shifts in relative biomass. Total catch rate (kg km −2 ) of the whole community has increased significantly over time, while the average trophic level decreased, primarily explained by an increase in relative biomass of intermediate trophic level species. Fishing activity was significantly related to the variation in length-frequency of species at intermediate trophic levels, confirming that the impacts of fisheries are heterogeneous throughout the community, providing vital information to support multi-species management of fishery resources.
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