Biodiversity Assessment and Geographical Affinities of Discards in Clam Fisheries in the Atlantic-Mediterranean Transition (Northern Alboran Sea)

This study focused on the assessment and quantification of discards generated by clam fisheries along the northern Alboran Sea (western Mediterranean). Discard samples (n = 278) were collected throughout one year on board nine commercial vessels. A total of 129 species were identified, mostly represented by molluscs (72 spp.), arthropods (20 spp.) and echinoderms (12 spp.). Molluscs dominated in terms of abundance (67.5%) and biomass (94.2%). The superfamily Paguroidea (i.e. hermit crabs), together with undersized target individuals, were the most abundant taxa. The abundance and biomass of discards displayed significant maximum values in winter, which could be partly related to biotic factors including population dynamics of some dominant species. Multivariate analyses indicated the presence of different assemblages related to the targeted bivalve species, reflecting the transition between a fine surface-sands biocoenosis exposed to wave action and a well-sorted fine sands biocoenosis below 5 m depth. Analysis of biogeographical affinities showed that most discarded species (73.2%) have an extensive Atlantic range, whereas 7.1% have a restricted distribution within the Mediterranean. The presence of subtropical species highlights the uniqueness of this area (the Atlantic-Mediterranean transition) in European seas. The usefulness of discard analysis for biodiversity assessment is discussed.

Automated summary

This study focused on assessing and quantifying discards generated by clam fisheries in the northern Alboran Sea. Molluscs dominated in terms of abundance and biomass, with discard levels peaking in winter. Multivariate analyses revealed different assemblages related to targeted bivalve species, indicating transitions between surface sands and deeper biocoenosis.