Translocation of the southern rock lobster, Jasus edwardsii, to improve yield and marketability
thesisposted on 2023-05-26, 03:52 authored by Chandrapavan, A
The Tasmanian southern rock lobster (Jasus edwardsii) fishery has a single Tasmania-wide management system despite large spatial variations in the biology (growth) and market traits(shell colour, body shape and live transport condition). This has created uneven distribution of harvest rates around the State where red, fast-growing, shallow-water lobsters are heavily targeted by fishers due to their high market demand, while pale, slow-growing, deep-water rock lobsters have a much lower rate of exploitation. In an attempt to improve yield, marketability and value of deep-water southern rock lobsters, translocation of lobsters between regions was examined as a supplementary management strategy for the Tasmanian rock lobster fishery. Adult deep-water lobsters were moved inshore to shallow-water reefs where changes to growth, market traits and body condition were monitored through recapture surveys. Red pigmentation in shell colour decreased with depth across southern Australia. Most of the catch is sold into Asian live markets where there is a preference for red lobsters. This market preference has lead to the price discounting of lobsters, which was estimated at a total of AUS$6.67 million / year for the Tasmanian Rock Lobster Fishery. Morphological market traits of leg length and abdomen shape were also different between deep and shallow-water J. edwardsii populations and between the sexes in each population. Nutritional indicators of condition did not differ among adult deep-water, shallow-water and translocated male lobsters, however fatty acid profiles indicated dietary differences between deep and shallow-water lobsters. Haemolymph condition indices detected significant differences in the post-harvest condition between deep-water and shallowwater lobsters. Translocating small, pale adult lobsters into a shallow water habitat resulted in a number of changes important to the yield and value of the fishery. Growth rates of translocated adult lobsters increased at their first moult in their new habitat, exceeding that of resident deep-water lobsters from the original site. Growth of translocated females exceeded resident shallowwater females in the first year post-release. Translocation changed the pale colouration of deep-water lobsters into the bright red grade most sought after by the Asian market, however changes in morphology were only partial and may require several moults for a complete change in shape. Dietary fatty-acid profiles of translocated lobsters matched those of the resident lobsters, while significant levels of essential omega-3 fatty acids in the muscle tissue of translocated lobsters suggest enhanced nutritional condition after translocation. The post-harvest condition of resident shallow-water lobsters and translocated lobsters were similar when recaptured 12 months later. Translocation could be an effective management tool to add value to the less marketable deep-water southern rock lobsters. These results on the magnitude and timing of improvements in market traits will now contribute towards the economic and biological evaluation of the feasibility of translocation as a fisheries enhancement strategy for the Tasmanian Rock Lobster Fishery.
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