Bottom trawling activity, main fishery resources and associated benthic and demersal fauna in a mud volcano field of the Gulf of Cádiz (southwestern Iberian Peninsula)

Bottom trawling activity, commercial species and benthic and demersal assemblages were studied integrating Vessel Monitoring System data (VMS), fishing logbook data and otter trawl samples in a mud volcano (MV) field of the Spanish margin of the Gulf of Cádiz (GoC) in 2011. High trawling activity was detected around Anastasya MV and between the Cádiz and Guadalquivir diapiric ridges, and low trawling activity around Gazul MV and in the deepest areas (Huelva Channel and southwards). A total of 11 938 individuals from 126 benthic and demersal species were collected in the samples. Multivariate analyses mainly grouped samples according to depth and sediment type and 3 different assemblages were detected. The Stratum 1 assemblage (Gazul MV, 441–470 m depth, muddy sand, low trawling activity and high near-bottom current speed) was dominated by Parapenaeus longirostris, Leptometra phalangium and Plesionika antigai, among others, and displayed high species richness and abundance. The Stratum 2 assemblage (Anastasya and Tarsis MVs, Triangle, and the External zone, 528–622 m, mud/sandy mud, medium to high trawling activity and low near-bottom current speed) was dominated by P. longirostris, Plesionika martia, Nezumia aequalis and small chondrichthyans (mainly sharks), among others, and displayed low species richness, abundance and biomass. The Stratum 3 assemblage (Huelva Channel > 700 m, sand, low trawling activity and high near-bottom current speed) was dominated by similar species to Stratum 2, but also included large demersal sharks (Centrophorus granulosus, Galeorhinus galeus, Dalatias licha) that resulted in a high biomass. Depth and near-bottom current speed showed strong relationships with the benthic and demersal assemblages in Principal Component Analyses. The occurrence of medium to intense trawling activity in and around some MVs (Habitat 1180, Council Directive 92/43/ECC-Habitats Directive) should imply an effective regulation that allows a balance between sustainable fisheries and habitat conservation.

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