Seafood CRC: dynamics of growth in translocated lobsters
University of Tasmania (UTAS)
Principle Investigator: Caleb Gardner
Key words: Southern rock lobster, experimental density manipulation, stock enhancement, growth compensation, density dependence, fine spatial scale
Summary: This research is an extension of two previous projects on SRL translocation (CRC2006/220 and CRC 2011/744), which showed that translocation of slow growing lobsters to better habitat can be used as a management tool to increase production in the fishery. It’s currently being used on a small scale to increase production in the Tasmanian fishery by 50 tonnes per annum though a fully-industry funded program.
The growth rate of Southern Rock Lobsters varies spatially with a general trend of growth slowing along a gradient from western Victoria to southern Tasmania. Previous research for defining locations of capture and release of rock lobster translocation relied on general models of this spatial trend in growth. The research reported here involved more detailed spatial analyses of growth to try to refine those operations. In particular, the aim was to find locations that would provide for high growth of translocated lobsters with less travel distance (cost) than the sites currently being used.
The two components of this project dealt with changes in growth associated with changes in food availability and density, which was investigated by measuring growth of lobsters in translocation sites with a Before-After-Control-Impact (BACI) design. This involved examining growth under different conditions of prey availability and density. The third component identified fine scale spatial locations where lobsters had unusually high growth, based on a historical dataset of tag returns from non-translocated lobsters. That is, we identified the premium paddocks for release of translocated lobsters.
These analyses were data intensive and in some cases there were insufficient tag-recapture records so growth was not assessed for all release sites. Nonetheless, in TAS sufficient data was available to update and improve quantification of the scale of growth increases when lobsters from deep water were translocated to shallow sites. There was also some evidence of the scale of growth reduction that can occur at high density of SRL. Growth of lobsters at the source site increased after translocation, presumably due to lower density.
This research will enable refinement of translocation operations to lower costs and improve productivity gains. The beneficiaries will primarily be owners of quota.
1. Complete three papers dealing with growth of rock lobsters to enable improved outcomes from translocation.