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The
Fisheries Research & Development Corporation of Australia is
currently funding a joint NIWA and University of Tasmania
project to explore the feasibility of reseeding juvenile
lobsters in Tasmania and New Zealand. |
A lobster re-seeding site at
Scorching Bay, Wellington |
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In Tasmania, aquaculturists have
been granted permits to remove juvenile lobster (pueruli)
for ongrowing to market size in captivity. To compensate for
this removal from the fishery they are required to reseed
25% of their stock back into the wild after one year. This
will result in a net gain to the fishery, especially in
areas of low puerulus survival, because, at 1 year old, the
30–40 mm carapace length lobsters become increasingly
gregarious and
are more likely to survive
predation by fish. Video surveillance of juveniles raised in
captivity that had never seen a predator has shown that when
they are released on to reefs they have an innate defence
response to predators, as well as appropriate emergence
times from their dens for safer nocturnal foraging.
NIWA has been conducting a
field trial in the outer Wellington Harbour which involves
tethering lobsters in suitable dens or crevices and
investigating their survival on five reefs. Although
survival rates are usually lower with tethered than with
free-roaming prey species, tethering is still a useful
method for investigating effects on mobile prey species. In
our trial we have examined many reef and den
characteristics, such as crevice size, algal cover, and
predator abundance, to try to tease out which variable has
the greatest influence on survival of the small lobsters.
At 48 hours after release,
lobster survival at our sites ranged from 50 to 65%, which
was surprisingly high. The numbers of predatory fish, mainly
blue cod and wrasse, on the reef had little influence on
lobster survival. Of all the reef and den variables that we
tested, the presence of a low algal cover had the most
influence on survival, the suggestion being that it may
provide a visual barrier between predatory fish and the
lobsters.
We feel that there are real
prospects for successfully reseeding juvenile lobsters.
Although large-scale releases are unlikely in New Zealand in
the short term, it may be possible in the future to reseed
into discrete areas such as community-managed taiapure and
mataitai zones.
Rob Stewart,
Megan Oliver, & Alison MacDiarmid, NIWA
Caleb Gardner & David Mills, University of Tasmania
[ m.oliver@niwa.co.nz ]
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