Project number: 1995-018
Budget expenditure: $178,850.00
Principal Investigator: David Hobday
Organisation: Agriculture Victoria
Project start/end date: 16 Aug 1995 - 7 Sep 2000
1. To develop catch forecasting methods based on recruitment indices of puerulus settlement and juvenile abundance.
2. To determine the movement pattern from juvenile nurseries to commercial fishing grounds.
3. To compare the number of juveniles with the number of adults and test the assumptions of stock depletion assessments.
4. To investigate the density dependent effects on mortality at different life stages.
Author: David Hobday
Final Report • 2000-05-15 • 1.21 MB
The southern rock lobster (Jasus edwardsii) is found in Australia’s southern waters from south-west Western Australia to southern New South Wales, including the waters around Tasmania. In 1996/97, 4,835 tonnes of southern rock lobster were landed in Australia with the highest catch from South Australia (52%) followed by Tasmania (37%), Victoria (10%) and Western Australia (1%) (Anon 1999). The Victorian component of this catch was 464 tonnes in 1996/97 with 403 tonnes caught in the Western and 61 tonnes in the Eastern Management Zones (Anon 1998).
The larval stages of the southern rock lobster are relatively long, ranging between 12 and 20 months from hatching of eggs to settlement of pueruli. The planktonic larvae or phyllosomas are dispersed by ocean currents; however, this process is not well understood in southern Australia. Phyllosomas metamorphose into pueruli larvae which settle on inshore reefs. The study of settlement of pueruli is being conducted in all southern Australian states.
Little is known about the relationships between larval settlement, juvenile abundance and adult abundance for Jasus edwardsii in Australia; however, such relationships have been determined for the western rock lobster (Panulirus cygnus) and used to predict catches four years in advance.
The present study aimed to establish larval and juvenile monitoring at three sites in central Victoria, Flinders, Ocean Grove and Torquay. Larval collection sites were set up and monitored monthly. Twice yearly, commercial fishers set pots (including fine-meshed research pots) in reef areas near the settlement sites to monitor juvenile and adult abundance. Extensive tagging was carried out during this fishing and movement of subsequent recaptures analysed.
Settlement of larvae was very low at all sites and showed no pattern. The study sites appear to be in a very low settlement area compared with results from other work to the southwest at Apollo Bay.
Juvenile and adult abundance was monitored at each site although some practical problems were experienced in fishing near the Flinders site. There was a lack of animals below 60 mm carapace length in the catches and further work needs to be undertaken to enable sampling of these early benthic stages.
Tagging showed that overall movement was localised with some movement occurring from inshore reefs to deeper water. A low level of movement was observed but a small proportion of immature females and one male undertook large migrations in a south-westerly direction towards King Island.
The present study has begun the process of collection of long-term data monitoring abundance of larval settlement and juvenile abundance for catch prediction. Abundance of juveniles increased during the study and based on growth data from tagging corresponded with the high larval settlement observed at Apollo Bay during 1995. It appears that catch prediction may be achievable in the study site where lobsters are recruited to the fishery at around 4-5 years. Slower growth in western Victoria with lobsters recruiting to the fishery at 5-8 years may weaken any relationships between larval settlement and recruitment. Monitoring of pre-recruits should be increased for development of indices for short-term predictions.