Project number: 1999-154
Project Status:
Completed
Budget expenditure: $216,657.93
Principal Investigator: Ian Potter
Organisation: Murdoch University
Project start/end date: 6 Sep 1999 - 29 Jun 2005
Contact:
FRDC

Need

Since the commercial catches of the champagne crab Hypothalassia armata are rising sharply, there is an urgent need to ensure that appropriate management arrangements are set in place for this fishery. The information required as the basis for this management is biological data on such features as growth, size composition, size at first maturity, fecundity and yield and egg (or mature biomass) per recruit relationships. There is thus clearly a crucial need to determine the biological characteristics listed below under Objectives (B4).

Objectives

1. The composition by sex, size (carapace length (CL), to the nearest 1mm) and weight (to the nearest 1g) of crabs in commercial crab pots from different depths in the two regions in which the champagne crab are fished, i.e. Geraldton to Fremantle and Augusta to Albany.
2. Using traps with a small mesh size, determine the full range in size (CL) and weight of crabs in different depths in the two sampling regions.
3. Preliminary estimates of growth curves of female and male crabs, based on growth increments and intermoult periods.
4. Preliminary indications of the movements of crabs and their relationships to body size and reproductive status.
5. The carapace length at which 5 and 50% of female and male crabs first reach maturity.
6. The duration and location (area and water depth) of spawning and the fecundity and its relationship to body size.
7. The diets of crabs and how they vary with body size and shell state. N.B. This study, which will also provide information on the type of habitat occupied by champagne crabs, will be carried out by a student at no cost to the project.
8. Distribution patterns, size composition and the prevalence of ovigerous females, and other biological variables, observed by fishers and recorded in log books.
9. The yield and egg (or mature biomass) per recruit relationships.
10. Assess the management implications of the biological data, and provide the results to managers in a form that can be used to help manage and conserve the fishery for the champagne crab.

Final report

ISBN: 0-86905-883-5
Author: Ian Potter
Final Report • 2005-03-10
1999-154-DLD.pdf

Summary

During recent years, commercial trap fisheries have developed for the champagne and crystal crabs in deep waters off the lower west and south coasts of Western Australia. Thus, data on crucial aspects of the biology of these species were required to enable plans to be developed for conserving their stocks. No such biological data were previously available.

Commercial catches of champagne crabs in south-western Australia rose from negligible levels in 1990 to peak at ~73 000 kg in 1998 and then declined progressively to ~17 300 kg in 2003, due mainly to fishers on the west coast shifting their effort towards crystal crabs. The catches of champagne crabs underwent a progressive seasonal change, particularly on the south coast where they reflected a decline in fishing effort during the inclement late autumn to middle spring months. Commercial catches of crystal crabs in south-western Australia, which came almost entirely from the lower coast, rose from very low levels in 1997 to reach ~222 000 kg in 2001 and then remained close to this level in 2002 and 2003. Catches and catch per unit effort of crystal crabs remained similar throughout the year. For the fisheries for both champagne and crystal crabs, the mean carapace lengths and catch rates were greater for males than females. Enclosure of traps in fine mesh did not lead to the capture of a relatively greater number of small crabs.

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