Development and assessment of methods to reduce the predation of pot-caught southern rock lobster (Jasus edwardsii) by maori octopus (Octopus maorum)
University of Adelaide
Tim M. Ward
The predation of 'pot caught' rock lobsters by octopus is the major cause of direct loss to fishermen in South Australia. In the Southern Zone Fishery it is estimated that on average 10% of all pots are predated by octopus. Octopus kill between 200-250,000 legal sized lobsters each year which represents and annual loss to the industry of between $5-10 million. In the Northern Zone Fishery (input regulated) predation results in direct financial cost to fishermen associated with the loss of saleable lobsters. In the Southern Zone Fishery (output regulated) predation results in indirect costs associated with increased time and effort expended to catch quota. Prevention of octopus predation would generate greater income to fishermen in the Northern Zone and reduce costs and number of days required to catch quota in the Southern Zone. In addition to the economic costs, a significant consequence of octopus predation is its impact on rock lobster stocks and the sustainability of the fishery. The loss of lobsters to octopus results in increased fishing pressure on stocks. Fishermen catch more lobsters than required to compensate for those killed by octopus. A reduction in the number of lobsters killed by octopus would enable fishermen to catch less lobsters without affecting existing income levels resulting in reduced pressure on an already heavily exploited resource. Elimination of predation may provide an important buffer against the threat of overfishing and significantly enhance the sustainability of the industry by reducing harvest levels by 200,000+ lobsters each year.
1. Describe the spatial and temporal changes that have occurred in octopus predation level over the last 15 years.
2. Determine how environmental factors influence octopus predation levels over a fishing season.
3. Identify pot modifications that have the potential to prevent/reduce octopus predation of pot caught Southern Rock Lobster.
4. Trial pot designs to prevent/reduce octopus predation under laboratory conditions.
5. Develop a pot that under commercial fishing conditions, prevents/reduces octopus predation, maintains lobster catch rates and is cost effective to implement.
6. Ensure industry participation and consultation at all stages of the project.
7. Ensure adoption of the modified pot(s) by industry where appropriate.
The SARLF is the State’s most valuable wild fishery with estimated export earnings of >$100 million in 2002. The fishery is a closed entry fishery with 250 licence-holders and is divided into the Northern and Southern Zones. Lobsters are caught in baited pots that are generally set for 24 hours prior to hauling.
Mortality of lobsters due to predation in pots, especially by maori octopus is a significant problem in the SARLF, but has generally been considered to be unavoidable, and minimal effort has been expended determining the scale of the problem or investigating a solution. This project was initiated in 1998 to develop methods for reducing rates of octopus predation on lobsters in pots.