Octopus as predators of abalone on a sea ranch

This study examined the occurrence of octopus across an abalone, Haliotis laevigata, Donovan, sea ranch in south-western Australia, to understand how octopus may be impacting abalone production. Commercial divers removed 654 octopus and 17,666 empty abalone shells during regular, 2 to 4-weekly surveys over 27 months. A negative binomial generalised linear model estimated a 78% increase in empty shells per artificial abalone habitat per day, when octopuses were present, after adjusting for location and season. Of the 408 shells examined for evidence of predation, 19% had a small, slightly ovoid hole consistent with those made by octopus. The mean (+/- 1 SE) length of shells with boreholes (70.3 +/- 2.2 mm) was significantly longer than those without (59.8 +/- 0.5 mm), and boreholes were concentrated over the adductor, respiratory organs and heart. This study provides important insights into the adaptable feeding regimes of octopus and their potential to impose strong top-down controls on sea ranching operations.