Western rock lobster settlement trends

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Western Rock Lobster Settlement Trends
Western Australia's Western Rock Lobster Fishery has received international acknowledgement as one of the best managed and most sustainable in the world.
The fishery involves about 300 commercial boats and 40,000 recreational fishers. Annual catches have been monitored since the late 1960s and vary between about 5,500 and 14,000 tonnes.
The fishery isone of a handful in Australia where a long-term scientific program has provided sufficient detailed information to predict catches up to four years in advance.
The scientific program also provides estimates of breeding stock levels, and a range of information on natural variations in the fishery as it responds to both fishing activity and environmental variations.
Rock lobsters spawn in spring andearly summer and their larvae spend up to 11 months drifting in the ocean, before being swept by current systems to settle on inshore reefs.
Crucial to predicting catches is an annual sampling program that looks at the abundance of late larval-stage lobsters (puerulus) settling on inshore reefs along the west coast between August and January each year.
This ‘puerulus settlement index' has beenrunning at one site since 1968 and has always shown a strong correlation with catches of lobsters three and four years later.
Environmental factors such as the strength of the Leeuwin Current, winter/spring westerly wind patterns and water temperatures play an important role in determining the survival and settlement of larval lobsters. However, other environmental variables may also beaffecting settlement.
Another important factor is the health of the rock lobster breeding stock.
The puerulus settlement during the 2008/09 West Coast Rock Lobster season was the lowest in the 40-year time series of puerulus collections at Dongara and Jurien. This poor settlement will result in very low numbers of rock lobster recruiting to the catch in the 2011/12 fishing season.
This poorsettlement was extremely unusual as it occurred when environmental conditions were very favourable (with a strong Leeuwin Current) and were expected to lead to a good puerulus settlement; although some environmental conditions observed during this period, such as westerly winds and the Indian Ocean Dipole, were not favourable.
As well as this extremely low settlement, the settlements of 2007/08 and2008/09 were also well below average and not fully explained by known environmental factors. Combined these three years will result in low numbers of lobsters recruiting to the fishery in 2010/11 – 2012/13.
It should be noted that the current overall breeding stock estimates are above the threshold levels and that the management settings implemented during the 2008/09 and 2009/10 seasons haveimproved the status of the breeding stock.
In light of continued low puerulus settlement however, the Department of Fisheries has reviewed its methodology for estimating the breeding stock. The Department of Fisheries has also reviewed research and management priorities, in consultation with the respective Chairs of the Western Rock Lobster Council and the Rock Lobster Industry Advisory Committee(RLIAC). Key outcomes identified by this process have all been instigated. These include:
1. The biological model has been further developed and now incorporates robust estimates of efficiency creep and changing size at maturity
2. Funding from the Fisheries Research and Development Corporation has been received to (i) conduct oceanographic modelling with the CSIRO aimed at evaluating the effect ofbreeding stock in different regions and environmental factors on puerulus settlement; (ii) examine relationships between environmental factors and levels of settlement; (iii) investigate the settlement of other fauna and flora on the puerulus collectors; and (iv) examine the use of novel statistical techniques to investigate exploitation rates and efficiency creep.
3. The juvenile abundance...
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