Reproductive biology and recruitment of the deep-sea fish community from the NW Mediterranean continental margin

•Fish community of the Catalan margin was sampled seasonally along a bathymetric gradient.•Reproductive cycle and population distribution of the most abundant species was analyzed.•Different reproductive patterns were observed along the continental margin.•A link between seasonality of the organic fluxes and timing of reproduction was observed.•Spatial distribution of recruitment were related to the presence of intermediate nepheloid layers.

Temporal patterns in deep-sea fish reproduction are presently unknown for the majority of deep continental margins. A series of seasonal trawling surveys between depths of 300 to 1750 m in the Blanes submarine canyon and its adjacent open slope (NW Mediterranean) were conducted. The bathymetric size distributions and reproductive cycles of the most abundant species along the NW Mediterranean margin were analyzed to assess the occurrence of (i) temporal patterns in reproduction (i.e., spawning season) along a bathymetric gradient and (ii) preferential depth strata for recruitment. The fish assemblages were grouped in relation to their bathymetric distribution: upper slope, middle slope and lower slope species. Middle-slope species (i.e., 800–1350 m) showed short (i.e., highly seasonal) reproductive activity compared to the upper (300–800 m) and lower (1350–1750 m) ones. Our results, together with those previously published for megabenthic crustacean decapods in the area, suggest a cross-phyla depth-related trend of seasonality in reproduction. In the middle and lower slope species, the reproductive activity reached a maximum in the autumn–winter months and decreased in the spring. The observed seasonal spawning patterns appear to be ultimately correlated with changes in the downward transport of organic particles and with seasonal changes in the physicochemical characteristics of the surrounding water masses. The distribution of juveniles was associated with the bathymetric stratum where intermediate nepheloid layers interact with the continental margins, indicating that this stratum acts as a deep-sea fish nursery area.