Biology of the deep-sea octopus Bathypolypus sponsalis (Cephalopoda : Octopodidae) from the western Mediterranean Sea

Several aspects of the biology of Bathypolypus sponsalis were studied from 297 individuals (115 males, 180 females and 2 indeterminates) caught in a d epth range of 200-800 m depth in the western Mediterranean Sea. The paper p resents data on sizes (length-weight relationships, size-frequency distribu tions) and reproduction (sex ratio, maturation, condition), and also analys es of the diet of B, sponsalis from samples taken throughout the year. Leng th-weight relationships showed that females are heavier than males at the s ame mantle length. Although mature individuals were found all year round, t he maximum number occurred in spring and summer. Sexual maturation data rev ealed that males mature at smaller sizes than females. The gonadosomatic in dex increased with maturity in both sexes; the increase was gradual in male s, but abrupt in females. The digestive gland index was used as a condition index and showed a differential behaviour with maturity: it increased grad ually in females, but decreased in males. Like other octopus species, B. sp onsalis appears to be an opportunistic predator, feeding on a great variety of preys. Stomach content analysis yielded a total of 19 different prey it ems belonging to four major groups (Crustacea, Mollusca, Ophiuroidea and Os teichthya). The first three groups were the more frequent preys, since crus taceans, molluscs and ophiuroids appeared in 76%, 49% and 30% of the stomac hs, respectively. Decapoda Reptantia (among crustaceans) and cephalopods an d bivalves (among molluscs) constituted the more abundant prey items. While the Decapoda Reptantia group was significantly more abundant in stomach co ntents of females, gastropods were taken more frequently by males. These di fferences in diet could reveal females as a more active predators than male s.