Resource utilization by deep‐sea sharks at the Le Danois Bank, Cantabrian Sea, north‐east Atlantic Ocean

Abstract

The feeding habits of birdbeak dogfish Deania calcea, velvet belly lantern shark Etmopterus spinax and blackmouth catshark Galeus melastomus at Le Danois Bank, Cantabrian Sea, south Bay of Biscay were studied in relation to their bathymetric distribution. Deep-sea sharks were collected during two multidisciplinary surveys carried out in October 2003 and April 2004 at the Le Danois Bank. Two different habitats were defined: (1) the top of the bank, ranging from 454 to 642 m depth and covered by fine-sand sediments with a low percentage of organic matter, and (2) the inner basin located between the bank and the Cantabrian Sea's continental shelf, at depths of 810-1048 m, which was characterized by a high proportion of silt and organic matter. Deania calcea was not present at the top of the bank but was abundant below 642 m, while E. spinax was abundant in the shallower top of the bank but was not found in the deeper inner basin. There was almost no bathymetric overlap between these two deep-sea shark species. Galeus melastomus was found over the whole depth range. There seemed to be an ontogenetic segregation with depth for this species, however, since 80% of the specimens collected at the top of the bank were < 600 mm total length (L(T)) (mean 510 mm L(T)), whereas larger individuals (mean 620 mm L(T)) inhabited deeper zones. Galeus melastomus exhibited a significantly higher feeding intensity than both E. spinax at the top of the bank and D. calcea in the inner basin. Little dietary overlap between D. calcea and G. melastomus in the inner basin was found, with D. calcea being an ichthyophagous predator while the diet of G. melastomus at these depths was composed of a variety of meso-bathypelagic shrimps (e.g. Acantephyra pelagica, Pasiphaea spp. and Sergia robusta), cephalopods and fishes. The diets of E. spinax and G. melastomus at the top of the bank showed a high dietary overlap of euphausiids, which represented the main prey taxa for both species. Euphausiids declined in abundance with depth which was reflected in the diet of G. melastomus. The cluster analysis of prey affinities among hauls depicted two major groups, corresponding to the two different habitats (top of the bank and inner basin). Redundancy analysis also indicated top-basin segregation, with euphausiids representing the main prey taxa at the top of the bank and bathypelagic shrimps in the inner basin. Euphausiids and Micromesistius poutassou were key prey within the Le Danois Bank ecosystem since they were positively selected by the three deep-sea shark species. These results show that the feeding ecology of these predators in Le Danois Bank ecosystem is highly influenced by depth-related variables, as a result of changes in prey availability. Overall results were analysed in relation to the deep-sea Le Danois ecosystem structure and functioning.

Feeding ecology of demersal elasmobranchs from the shelf and slope off the Balearic Sea (western Mediterranean)

“…These mesopelagic preys would be caught when the BBL remains close to the bottom, indicating the high dependence of slope demersal elasmobranchs on the pelagic ecosystem (Bizzarro et al, 2007;Rinewalt et al, 2007 ). A high dietary overlap between these two species was also reported in the Cantabrian Sea (Preciado et al, 2009) but, in contrast with the preference of E. spinax for cephalopods in our samples, that population preyed mainly on euphausiids.…”

Deep sea megafaunal assemblages off the northern Iberian slope related to environmental factors

“…Blue whiting is one of the most abundant fish in midwater ecosystems in the northeastern Atlantic, living mostly at depths between 100 and 600 m, although its range may extend from surface waters to beyond 1000 m depth (Heino and Godø, 2002;Hátún et al, 2007). This eurybathic species is dominant in the habitats studied and has been described as one of the keystone species for the Cantabrian Sea food web (Libralato et al, 2005;Preciado et al, 2008Preciado et al, , 2009. Moranta et al (2007) stated that the maximum abundances of N. aequalis and T. scabrus occur below 600 m in the Mediterranean Sea.…”

“…Cartes et al (1994) reported mesopelagic crustaceans to be predominant on the slope whereas benthopelagic fishes were predominant on the shelf. Prey availability on the middle slope is probably insufficient to sustain the huge biomass of planktonfeeding fishes such as blue whiting (Preciado et al, 2008), and fish feeding mainly on benthos (Preciado et al, 2009).…”

“…The management of deep-water fisheries off the northern coast of Spain requires a fundamental knowledge of the habitats that are being exploited by Spanish fishermen. However, studies on deep-sea ecosystem functioning in the area are scarce and geographically fragmented, and mainly focus on specific zones (Cartes et al, 2007;Sánchez et al, 2008;Preciado et al, 2009).…”

Predation on Northern Krill (Meganyctiphanes norvegica Sars)

“…Middle Atlantic (1977)(1978)(1979)(1980) 26 - Pleuronectiformes Gray sole Glyptocephalus cynoglossus Whole St. Lawrence marine system (2004) 11 - (Mattson, 1981) 27 - (Chabot, 2010) American (Neiva et al, 2006) 4 - (Preciado et al, 2009) 8 -(Klimpel et al, 2003 Cephalopoda (Squids) Teuthida…”