Aggregations and associations in deep-sea chondrichthyans

Abstract

Abstract Group living has been recorded across a diverse range of chondrichthyans, but due to a variety of factors, any inferences of social associations in deep-sea cartilaginous fishes have yet to be described. Using a companion preference analysis, aggregating behaviour and associations in deep-sea chondrichthyans (four holocephalans, ten elasmobranchs) were evaluated across class and group size from long-term archived fisheries independent research trawl survey datasets. Results indicated that not all selected species engaged in aggregative behaviour, but those that did suggested patterns of sex- and size-specific associations, which varied with catch density. Adult females were caught most frequently in low densities, and were highly associated with other adult females. Adult males were consistently associated with each other. The nature of associations has important implications for selective mortality by spatial or temporally stratified, or aggregation-targeting, fisheries.