Publication Date

6-2009

Series Number

193

Publisher

Department of Fisheries, Western Australia

City

Perth

ISBN

1 921258 58 6

ISSN

1035 - 4549

Abstract

Final FRDC Report – Project 2003/005

Objectives:

1. To investigate the implications of the setose and maximum size rules.

2. To undertake preliminary investigations into the implications of egg diameters being significantly smaller at the Abrolhos Islands than at the coast.

3. To quantify the extent of the breeding grounds, so as to weight the overall egg production index for the stock by the contribution of the management zones.

Increases in efficiency due to modern electronic equipment, improved fishing vessels and knowledge about the grounds and lobster behaviour, have all led to western rock lobster fishers becoming more efficient at catching western rock lobsters in Western Australia. One of the outcomes of these increases in efficiency has been an increase in pressure on the breeding stock. Managers have responded by introducing measures to protect the breeders. In 1993, this involved the imposition of measures to limit the exploitation of mature female lobsters by introducing a legal maximum size for females as well as the protection of setose (mature) females.

The combination of high exploitation rates and protection of large, mature females, but not males, has since resulted in very distorted sex ratios of mature animals across the fishery, particularly those over the maximum size limit. It is well known from laboratory studies on other species of lobsters, that highly distorted female-dominated sex ratios (such as has been caused in the wild by the setose rule), and large females being forced through lack of choice to mate with small males (such as has been caused in the wild by both the setose and maximum size measures) can lead to sperm limitation effects (fertilisation of eggs but reduced brood sizes). These same management measures could have more positive effects – for instance in some species, the older individuals produce larger eggs, that in turn produce larger larvae that have been shown to have better survival characteristics.

These, and other unknowns, led to the initiation of this research project aimed at investigating these biological issues. The outputs from this research, together with other data, provide an indication of the contribution to egg production of different management zones in the western rock lobster commercial fishery.

Number of Pages

120

Keywords

Department of Primary Industries and Regional Development, egg production, selective fishing, paternity assignment, behaviour, maturity, genetic

Disciplines

Aquaculture and Fisheries | Environmental Indicators and Impact Assessment | Natural Resources Management and Policy

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