Experimental evaluation of
the use of hatchery-reared juveniles to enhance stocks of the topshell Trochus
niloticus in Australia, Indonesia and Vanuatu
T.P. Crowe, C.L. Lee, K.A. McGuinness, M.J. Amos, J.
Dangeubun, S.A.P. Dwiono, P.C. Makatipu, J. Manuputty, F. N'guyen, K. Pakoa,
J. Tetelepta-2002
Aquaculture, 206(3-4): 175-197
Abstract:
Stock enhancement is an attractive option for the
management of fisheries but needs to be carefully evaluated before
large-scale implementation. We advocate an experimental approach to test the
hypothesis that reseeded stocks will yield greater harvests than unseeded
controls. We tested the effectiveness of releasing hatchery-reared juveniles
to enhance stocks of the topshell Trochus niloticus in Australia,
Indonesia and Vanuatu using a rigorous design enabling direct comparisons
among countries. Trochus were released at different sizes (6-12, 16-27 mm)
and densities (2-8 m2) at replicated sites in each region.
Populations at those sites were subsequently compared with those at unseeded
controls. Temporal variation in success was also assessed by repeating the
experiment in Indonesia. Initial survival was monitored by tagging the
juveniles with aluminium foil and recapturing them using underwater metal
detectors. The majority of juveniles released in Australia and Indonesia
died or disappeared within a month of release and stocks were not enhanced
relative to controls. Predation, especially by fish, was considered likely
to be the most important cause of loss, but further investigation is
required. Losses in Vanuatu were also substantial, but up to 4.4% of 10-27
mm juveniles were recaptured alive after 12 months. Results from Australia
and Vanuatu suggested that survival may be improved by releasing juveniles
in greater densities and at greater sizes. We discuss additional strategies
for improving survival of free-released juveniles in Vanuatu and suggest
alternative approaches for Australia and Indonesia.