Predation of trap-caught southern rock lobsters, Jasus edwardsii (Hutton, 1875), in Tasmanian waters by the Maori octopus, Octopus maorum (Hutton, 1880): Spatial and temporal trends

Abstract

A long-term fisheries-independent data set was used to determine differences in the catch rates of the Maori octopus, Octopus maorum, and octopus-induced mortalities of southern rock lobsters, Jasus edwardsii, in lobster traps over a range of spatial and temporal (annual, seasonal and lunar cycle) scales in Tasmania, Australia. The impact of lobster catch rates on lobster mortality and octopus catch rates was also examined. Results indicated spatial variation in octopus catch rates, but no spatial variation in lobster mortality rates. No consistent annual or lunar cycle trends were evident for octopus catch rates or lobster mortality rates within the four lobster fishery assessment areas examined. An increase in octopus catch rates during summer and spring was found within all four areas, with areas 1 and 8 having a corresponding increase in lobster mortalities during these seasons. Lobster catch rates were found to have no influence on the catch rates of octopus or lobster mortalities. These results suggest that changing fishing practices over the various scales examined in this study would not be practical for minimising the impact of octopus predation on trap-caught lobsters within Tasmania. However, these results provide a fishery-independent estimate of octopus-induced within-trap mortality that will assist in future analysis of management strategies for the southern rock lobster fishery in Tasmania.