A two-chambered trap reduces within-trap predation by octopus on rock lobsters in aquarium trials

Abstract

A two-chambered lobster trap was developed that in aquarium trials significantly ( p < 0.01) reduced octopus predation on trap-caught spiny lobster. The trap was designed using information gained from an investigation of the behavioural interactions of the maori octopus ( Octopus maorum) with traps used in the South Australian commercial lobster ( Jasus edwardsii) fishery. This study showed that octopuses were primarily attracted to traps by the presence of bait as opposed to lobsters and that octopus entry into traps was ‘fortuitous’ and mediated by speculative exploration. The outer chamber of the modified trap contained bait and allowed entry by octopuses but not lobster and the inner chamber allowed access to both animals. The trap worked on the principle that octopuses would enter the outer chamber containing bait via a side entrance in preference to entry to the inner chamber containing lobsters via the neck. This was found to be the case and lobster mortality was 70% lower in the two-chambered trap than a standard trap. Successful adaptation of this trap design to commercial fishing conditions could significantly reduce rates of octopus predation on rock lobsters in several important southern hemisphere fisheries for spiny lobsters.