Sequestered Paralytic Shellfish Poisoning Toxins Mediate Glaucous-Winged Gull Predation on Bivalve Prey

Kvitek, R

Glaucous-winged Gulls (Larus glaucescens) avoid paralytic shellfish poisoning by conditioned aversions developed after the regurgitation of contaminated bivalve prey. In feeding experiments with free-ranging Glaucous-winged Gull chicks, toxic (445 ,ug saxitoxin equivalents per 100 g) butter clams (Saxidomus giganteus) were regurgitated in less than 5 min (n = 58), and nontoxic butter clams were never regurgitated (n = 30). Chicks that had ingested toxic S. giganteus then refused to eat either toxic or nontoxic butter clams offered later, but they accepted other bivalve prey. In feeding experiments with wild adult and juvenile L. glaucescens, gulls took significantly fewer butter clams at a site where S. giganteus has been chronically toxic for greater than 14 yr than they took at a nontoxic but otherwise comparable site. These preferences were species-specific and independent of prey toxicity or whether the live clams were intact or removed from their shells. The gulls showed no difference between sites in their preferences for three other bivalve species (Clinocardium nuttalli, Protothaca staminea, Tresus capax), all of which contained either no or very low levels of toxins at both sites. The aversion to intact but not to shucked butter clams was more strongly developed in adults than in juveniles. Most of the gulls that ate butter clams at the toxic site discarded the siphons (which account for the majority of the toxicity in contaminated butter clams) of both toxic and nontoxic butter clams, but they never discarded siphons of other bivalves. Gulls at the nontoxic site never discarded the siphons of bivalve prey. I suggest that avian predators generally are not at risk from paralytic shellfish poisoning toxin via bivalve vectors because they can detect and avoid toxic prey. Because of the apparent inability of gulls to discriminate between toxic and nontoxic individuals of the same prey species, avian predation pressure on some bivalve populations may be greatly reduced. Received 16 July 1990, accepted 8 November 1990.

Sequestered Paralytic Shellfish Poisoning Toxins Mediate Glaucous-Winged Gull Predation on Bivalve Prey

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