FORAGING BY MARINE SCAVENGERS - EFFECTS OF RELATEDNESS, BAIT DAMAGE AND HUNGER

Field studies using fish-baited creels have confirmed that Carcinus ma enas, Necora puber and Pagurus bernhardus (Crustacea: Decapoda), Bucci num undatum (Gastropoda) and Asterias rubens (Echinodermata) are promi nent scavenging species in shallow waters in the Clyde Sea area. Captu re rates of these species by creels baited with dead fish plus various ly damaged C. maenas were examined in the field. The addition of subst antially fractured C. maenas significantly reduced the capture of cons pecifics, but significantly enhanced the capture of the taxonomically unrelated species A. rubens. The remaining crustacean taxa (of the abo ve) were unaffected by this treatment. The magnitude of the response w as related strongly to the extent to which C. maenas were damaged. The effects of hunger on these responses were tested in a laboratory expe riment in which the responses of starved and fed batches of C. maenas were investigated. Starved crabs remained attracted to fish bait, desp ite the proximity of dead conspecifics. Conversely, crabs of the fed b atch were significantly more reluctant to enter creels containing dama ged conspecifics. The localized presence of odours emanating from dead conspecifics did not cause crabs to remain inactive in shelter. We co nclude that taxonomic relatedness to bait, degree of carcass damage an d hunger of the scavenger all interact in determining foraging decisio n-making even by so-called generalist scavengers.