Rock Lobster Post Harvest Subprogram: development of a method for alleviating leg loss during post-harvest handling of rock lobsters
University of Western Australia (UWA)
Glen A. Davidson
At the 1998 FRDC Rock Lobster Post-Harvest Sub-program annual workshop (Hillary's Boat Harbour, Perth, W.A.), fishers, processors and scientists identified post-harvest leg loss as a major problem. Industry incurs losses due to post-harvest leg loss in several ways: 1) Loss of weight. 2) Loss of value/restricted marketing opportunity. 3) Increased mortality of returned undersized animals and reproductive females. 4) Reduced growth of damaged undersized animals. 5) Reduced reproductive success of returned, damaged, breeding females. NEED FOR REQUESTED EARLY START DATE (MAY 1, 2000) Experiments addressing Objectives 2 & 4 are contingent upon the outcome of the experiments for Objective 1 (see B11 Methods). Therefore work on Objectives 2 & 4 cannot begin until Objective 1 is met. If the project were to start on 1 May 2000, there would be sufficient time left in 1999/2000 fishing season to identify preferred cold-stunning treatments for at least 2 of the 3 proposed acclimation temperatures (see B11 Methods). The preferred cold-stunnning treatment at the third acclimation temperature could then be tested early in the 2000/2001 season and work on Objectives 2 & 4 could be completed by the end of this season, in preparation for discussion at the 2001 annual subprogram workshop. Based on the outcomes of Objectives 2 & 4, the sub-program management will decide whether to continue the research and address Objectives 5 & 6. Should the research begin after May 1, 2000, experimenatal work could not begin until November, when the season starts. The desired acclimation temperatures to be used in Objective 1 occur in the wild over the course of an entire season, therefore work on Objectives 2 & 4 could not start until the following season (2001/2002) and work on Objectives 5 & 6 could not start until after discussion of results at the 2002 Sub-Program workshop in September. Thus by starting 2 months early, approximately 12 months advantage will be gained.
1. 1a) To identify a cold water immersion treatment that rapidly immobilises western rock lobsters, while allowing swift recovery from immobilisation upon return to ambient temperature sea water.1b) To investigate the effect of season/acclimation temperature on effectiveness of cold-stunning in western rock lobsters.1c) To investigate the use of sea water sprays vs immersion for inducing cold-stunning in western rock lobsters.
2. To investigate, in captivity, the effectiveness of the preferred treatment (identified in Objective 1) for reducing leg loss in western rock lobsters during handling.
3. To test the accuracy of factory grading of cold-stunned western rock lobsters versus untreated controls.
4. To describe the occurrence of leg loss, morbidity and mortality of western rock lobsters subjected to cold-stunning prior to episodes of handling during the post-harvest process (i.e. at the time of pot-pulling and sorting, prior to factory grading) and to compare these to the performance of animals handled using current methods.
5. To investigate, in captivity, the effects of multiple simulated pot capture and release events, either with or without cold-stunning, on growth, leg loss and survival of undersized western rock lobsters. (This objective is contingent upon outcomes of Objectives 1-4, see B10 Risk Analysis)
6. 6a) To compare, in captivity, the effects of handling, with and without cold-stunning, on the reproductive success of setose, tar spot and ovigerous female western rock lobsters.6b) To investigate the effects of limb loss on the reproductive success of female western rock lobsters. (This objective is contingent upon outcomes of Objectives 1-4, see B10 Risk Analysis)
7. To conduct a survey to determine the extent and nature of leg loss in the southen rock lobster fisheries of Tasmania and South Australia.
8. To determine, under a range of unique local conditions, the effectiveness of cold water stunning for preventing post harvest leg loss in western rock lobsters.
9. To facilitate widespread acceptance of cold-stunning by demonstrating and promoting, through field trials, its use for preventing post harvest leg loss in western rock lobster.
A novel brief application of cold-stunning was identified as a practical method for preventing post-harvest leg loss at several points in the post-harvest handling chain. Using this method, there is potential for the western rock lobster industry to save in excess of $2 million per season in lost catch weight attributable to leg loss. In addition, considerable value could be added to the catch through increases in the numbers of lobsters fit for exporting as premium product forms, such as live or whole frozen boiled. Rates of leg loss occurring in different zones of the fishery have been quantified, providing an objective basis for conducting cost-benefit analysis of any preventative measures under consideration.
During the course of this study hypersaline-induced leg loss was identified as a significant cause of post-harvest leg autotomy. This finding led to a second study (FRDC Project 2001/255) which in turn identified potential six figure savings using simple, cost-effective methods.
Rates of post-harvest appendage loss in the southern rock lobster fisheries of South Australia and Tasmania have been documented as being very low. The small amount of antennal damage occurring on board commercial boats appeared to be largely preventable by making simple changes to handling practices. Further investigation of this issue does not appear warranted.