Development and assessment of methods to reduce predation of ‘pot caught’ southern rock lobster (Jasus edwardsii) by maori octopus (Octopus maorum)

This project quantified the level of octopus by-catch and effects of octopus predation on the mortality rates of rock lobster in the South Australian Rock Lobster Fishery
(SARLF). It showed that current octopus bycatch levels appear to be sustainable and that approximately 4% of the annual lobster catch of the SARLF is killed by octopus
in pots. Findings suggested that small reductions in lobster mortality rates may be achieved by minimising soak times, but that more significant reductions will dependon reducing the rates of octopus entry into pots. Observations of pots in aquaria indicated that octopus were attracted to the bait in traps rather than the lobsters. A two-chambered pot was developed, which consisted of an outer chamber that was accessible to octopus but not lobsters, and an inner chamber that both could access. Aquarium trials showed that most octopus entered the outer chamber containing bait rather than the inner chamber containing lobsters, which reduced lobster mortality rates by ~70% compared to a conventional pot. In field trials aboard SARLF vessels, the  two-chambered pot reduced lobster mortality rates
by 45-48% but also reduced lobster catch rates by 28%. The effectiveness of escape gaps in reducing the level of octopus predation on undersize lobsters was also
tested. The presence of escape gaps in pots significantly reduced the retention of undersize lobsters in pots which lowered undersize mortality by approx. 65% when
compared to pots without escape gaps. The mortality rate of legal sized lobsters was unaffected. The two-chambered concept is a new and innovative concept with great potential to reduce lobster mortality in pot fisheries with significant octopus bycatch. If the design can be refined to maintain lobster catch rates, the introduction of a two-chambered pot incorporating escape gaps would result in
approximately 100,000 ($>2 million) fewer lobsters being killed each year in the SARLF.