Spatio-temporal patterns in demersal elasmobranchs from trawl surveys in the eastern English Channel (1988–2008)

摘要

ABSTRACT: Elasmobranchs have life-history characteristics that make them more vulnerable to fishing than many teleost fish. As commercial landings data are usually not sufficient for the monitoring and assessment of elasmobranchs, fisheries-independent data, geostatistics and Geographic Information Systems were used to investigate the spatio-temporal patterns of sharks (6 species), skates (9 species) and stingray in the eastern English Channel. Temporal trends in relative abundance and distributions of total-length frequencies were investigated using data collected over 21 yr from an annual survey using a Grande Ouverture Verticale (GOV) trawl. Temporal trends in relative abundance were examined qualitatively in relation to the reported conservation status for the various species. Most individuals captured for 7 of the species were immature. The GOV trawl was more efficient at sampling demersal sharks than batoids (skates and rays), especially small-sized batoids. Geostatistics were effectively used to explore, identify and quantify the spatial structure of the distributions of 13 species. The more abundant species displayed significantly larger patch diameters. Three shark species (Scyliorhinus canicula, S. stellaris and Galeorhinus galeus) were found to be spatially segregated by sex. The shark species tended to occur in the deeper waters of the area, while skates were found to be more coastal in their distribution. Results have contributed to a greater understanding of the spatio-temporal patterns in elasmobranch species in the eastern English Channel and are of relevance to future marine spatial planning and the development of long-term management plans for elasmobranchs in the area and elsewhere.