Spatial distribution patterns and population structure of the bluemouth Helicolenus dactylopterus (Delaroche, 1809) in the southern Bay of Biscay

Abstract

Spatial distribution patterns of the bluemouth Helicolenus dactylopterus were analysed, using a spatial and temporal approach. H. dactylopterus is a worldwide distributed demersal fish with traditionally low commercial value in the study area. However, its economic importance has increased during the last 15 years in the north of Spain. Data come from Demersales Surveys (IBTS) carried out by IEO every autumn since 1983. A stratified sampling scheme was used with 5 geographical sectors and 3 depth strata (70-120 m, 121-200 m, 201-500 m). From each haul, number of specimens and total biomass were collected. Length structure was also recorded. Center of gravity analyses (CoG) showed significant geographic and bathymetric variations. An increasing temporal trend (in number and total biomass) was detected along the historical series. In the first 15 years the highest percentage of biomass and number was found in the westernmost part of the study area. During the past decade, an increasing frequency of occurrence was found in the Cantabrian Sea suggesting an expansion of its spatial distribution towards inner Bay of Biscay. An increased number of individuals and biomass captured in the Bay of Biscay corroborated these results. Throughout the study area, the larger abundance and biomass was detected in the deepest depth strata (201-500 m). It seems therefore, that changes observed spatially in the last decade were due to both a longitudinal expansion and a bathymetric one. Population structure and spatial distribution of juveniles have also been analyzed in order to find nursery areas