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Research & Education
Rock Lobster Stocks Rebuilding | FN0588 |
David Hobday, PIRVic, Queenscliff
June 2006
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Rock lobster stocks in Victoria continue to show signs of rebuilding. This is the consensus of the 2005 workshop assessing the status of the Victorian rock lobster fishery.
The Assessment Workshop for rock lobster was held in Queenscliff on 17-18 October 2005. The workshop was convened and organised by PIRVic’s Marine and Freshwater Systems, on behalf of Fisheries Victoria, to summarise the status of this fishery.
Interest was high and the two-day workshop was attended by over 40 people including representatives of the commercial and recreational sectors, Fisheries Victoria, PIRVic, the Fisheries Co-management Council, Seafood Industry Victoria, Scuba Divers Federation Victoria and the Victorian Recreational Fishing peak body, VRFish.
Victorian rock lobster stocks were fished to very low levels by both commercial and recreational fishers over many years. Current management, which is outlined in the Rock Lobster Fishery Management Plan, is aimed at rebuilding stocks but this will be a long process.
The 2005 Assessment evaluated the status of this fishery against both the target and limit reference points set in the Rock Lobster Fishery Management Plan.
These reference points are derived from estimates of the size of the Victorian rock lobster population in 1951, the first year for which detailed catch and effort data for the fishery is available. Limit reference points (the minimum levels for stock conservation) are set at 20% of the 1951 reference population, while target reference points (the preferred levels for fished stocks) are set at 40% of the 1951 reference population. The breaching of these reference points requires Fisheries Victoria, in consultation with the Fisheries Co-management Council, to set in place a prescribed set of management actions.
The rock lobster fishery in Victoria is divided into Eastern and Western Zones. The Western Zone extends from the South Australian border to Apollo Bay, while the Eastern Zones goes from Apollo Bay to the New South Wales border. Management targets have been set for each zone, reflecting the different challenges faced by the two fisheries.
A computer model is used to synthesise existing scientific data on the biology of rock lobsters and the known catches from the fishery to generate predictions of how the rock lobster populations in each zone would respond to different harvest strategies.
Fisheries scientists use this model to track trends in two components of the rock lobster population to make these predictions. They look at the available biomass, which is the total weight of all rock lobsters in the population that are above the legal minimum length and which can potentially be caught by fishers. The other measure is the spawning biomass, which is total weight of all mature female rock lobsters in the population and is a measure of egg production. Model projections of these measures are then compared with the target and limit reference points.
For the Western Zone, the projections indicated in the next five years that there is 95% probability of staying above the limit point for available biomass and a 12% probability of achieving the long-term target point. The model projections for the Western Zone 5 to 20 years into the future show that at the current TAC of 450 tonnes (see graph on the next page), available rock lobster stocks (the bold solid line) would continue to rebuild toward the target levels (the thin line). The current spawning biomass is above the target reference point in the Western Zone.
The Eastern Zone spawning biomass limit reference point was exceeded for the first time during 2003/04 and spawning biomass continued to increase during 2004/05. Estimates of available biomass were also above the limit reference point during 2004/05.
Projections indicated in the next five years there is a 100% probability of staying above the limit for spawning biomass and a 39% probability of achieving the target point. Again importantly, the model projections indicate that at the current TACC of 60 tonnes, spawning biomass will continue to increase toward the target level (see graph in right column).
The workshop also suggested that future research include continued monitoring of detailed biological information and estimates of population parameters within each
management zone. Gathering of these data and their inclusion in future modelling was seen as necessary to reduce the uncertainty in the assessments and provide greater resolution to the model predictions.
The outcomes of the Rock Lobster fishery stock assessment will be used by Fisheries Victoria, in consultation with the Fisheries Co-management Council, to set total allowable catches for the coming season and to fine-tune the management arrangements for this fishery.
Further Information
For more information about this project please contact David Hobday at PIRVic Marine and Freshwater Systems Queenscliff on 03 5258 0256.
Fisheries Research and Education Notes are available on the DPI website. Follow the prompts to Fishing and Aquaculture and then to Publications then to Fisheries Notes/Research and Education.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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