New Zealand Journal of Marine and Freshwater Research abstracts
Depletion-based population estimates for western rock lobster (Panulirus cygnus)
fishery in Western Australia
Ian Wright
Nick Caputi
James Penn
Western Australian Marine Research Laboratories
Department of Fisheries
P.O. Box 20, North Beach
WA 6920, Australia
Abstract A depletion technique was applied to the western rock lobster
fishery in Western Australia for the non-migrating part of the season, March
to June. The catch for the migrating part of the fishery was used to estimate
the annual exploitation for the whole season. To take into account environmental
effects (water temperature and swell) on catchability that affect the assumptions
of the depletion technique, estimates of the changes in catchability between
March and June of each year were obtained. The trends in catchability, residual
biomass and exploitation for three zones of the fishery since the 1983/84 season
were examined. These show that the exploitation in the north coastal zone decreased
from c. 75% in the early 1990s to c. 60% in the mid 1990s as a result of a major
change in management in 1993/94 (including 18% nominal effort reduction and increased
protection of mature females). However, in the last 10 years exploitation has
increased again to c. 75%, mainly owing to increases in catchability (e.g., efficiency
increases) as there has been little change in the nominal effort. The results
from this study provide some insight into changes in catchability that can be
used in other stock assessment techniques such as length-based assessments.
Keywords rock lobster; DeLury; fishing efficiency; corrected catchability;
exploitation; depletion estimate; residual biomass; Bayesian estimate
New Zealand Journal of Marine and Freshwater Research, 2006, Vol. 40:
107–122
0028–8330/06/4001–0107 © The Royal Society
of New Zealand 2006
M04085; Online publication date 9 February 2006 Received 31 March 2004;
accepted 17 May 2005
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