Diet and feeding behaviour of longnosed skate Dipturus oxyrinchus

A total of 255 longnosed skate Dipturus oxyrinchus caught in Sardinian waters (central-western
Mediterranean Sea), was analysed with respect to fish total length (LT), season and depth, in order to
provide information on diet and feeding behaviour. Specimens ranging from 93 to 1153mm LT, were
collected at depths between 121 and 671 m, during experimental trawl surveys carried out from 2005
to 2010. The diet comprised crustaceans [prey specific index of relative importance (%IPSRI)=72⋅69],
teleosts (%IPSRI =10⋅28) and molluscs (%IPSRI =10⋅94). Levins’ index (Bi) showed a narrow niche
breadth (Bi =0⋅35). The mean±s.e. trophic level (TL) was 3⋅63±0⋅50. The analysis showed major
ontogenetic changes in the feeding behaviour. Early life stages were characterized by a benthic
diet, which changed to benthopelagic during growth. Mysids, particularly Lophogaster typicus
(%IPSRI =34⋅51), were the main prey items of immature individuals, replaced by euphausiids, mainly
Meganyctiphanes norvegica (%IPSRI =13⋅19), in maturing fish. Crustaceans became less important
in mature specimens, being replaced by molluscs (%IPSRI =28⋅99) and teleosts (%IPSRI =24⋅56). A
concomitant increase of the TL was recorded (mean±s.e.=3⋅41±0⋅44, 3⋅75±0⋅54 and 4⋅28±0⋅61
for immature, maturing and mature individuals). These feeding patterns ensured low levels of
intraspecific competition. This study provides new information about the role that the D. oxyrinchus
plays in the marine food chain and data now essential to formulate new and effective management
plans for this species.