Publication Date

5-2004

Series Number

147

Publisher

Department of Fisheries

City

Perth, Western Australia

ISBN

1 877098 41 8

ISSN

1035 - 4549

Abstract

Information on the size of the recreational catch was required to address resource allocation issues between recreational and commercial crabbers in Cockburn Sound and Geographe Bay. Management measures designed to allocate more of the catch to the recreational sector were put in place prior to this study at both locations. Estimates of the recreational catch were required to evaluate the effectiveness of these new management measures by comparing the catch shares with a survey conducted in 1996/97.

A 12-month creel survey of recreational boat-based and shore-based crabbing in Cockburn Sound was conducted between September 2001 and August 2002 and in Geographe Bay between September 2001 and November 2002. During the surveys 1,235 interviews were conducted at boat ramps in Cockburn Sound and 929 in Geographe Bay. An additional 619 shore-based fishing parties were interviewed in Cockburn Sound and 444 in Geographe Bay.

The bus route method, where a survey interviewer visits all boat ramps in a pre-determined area on the one day, was used to estimate the total catch and fishing effort for persons crabbing from recreational trailer boats launched at boat ramps. A roving creel survey was used to estimate the catch and fishing effort from shore-based crabbers using drop nets or wire scoop nets from the shore.

Both the recreational and commercial catch of blue swimmer crab from Cockburn Sound was lower in 2001/02 than 1996/97 due to a lower level of recruitment. Recreational and commercial catch rates and effort were also lower. The increased size limit of 130mm for commercial crabbers resulted in 16.6 tonnes of crabs being returned by commercial fishers to be potentially available to the recreational sector. However, results show that only 2.2 tonnes of crabs kept by recreational boat-based fishers have a CW of 127-129mm, which is less than the commercial minimum size of 130mm. Since the recreational and commercial sectors have different spatial and temporal fishing activities it is unlikely that the recreational sector benefited substantially from the higher size limit for commercial fishers.

The recreational catch of blue swimmer crabs from Geographe Bay was larger in 2001/02 than 1996/97 primarily due to an increase in recreational fishing effort. There was a slight decrease in the commercial catch between the two years. It is difficult to determine the effect of the individual components of the new commercial management measures since these are confounded with changes in fishing effort, gear type and recruitment (and hence abundance) between the years surveyed. However, the new management measures and higher profile of crabbing in the area may have contributed to the increase in recreational crabbing effort.

For Cockburn Sound and Geographe Bay there is considerable variation in the commercial catch and catch rates from year to year due to the level of recruitment into the fishery. Furthermore, the corresponding variations in the recreational catch may be magnified by increased effort in years where catch rates are high and reduced effort in years when catch rates are low. This will exacerbate the variation in recreational catch resulting from recruitment fluctuations.

The fishing season for crabs in each location is affected by the time at which crabs reach legal size relative to the timing of fishing effort. In Cockburn Sound, the commercial and recreational effort peaks together in Summer, following the spring closed season for commercial fishers with the result that crabs are fished at about 2 years of age. The commercial fishery continues at a lower level through Autumn and Winter when recreational fishing is minimal. In contrast for Geographe Bay, both the commercial and recreational fisheries operate year round but peak in winter/spring when most crabs first reach legal size at about 18 months of age. Lower catches in summer, the main tourist season, reflects the heavy fishing pressure in spring and possibly an offshore movement at that time.

This research has provided important catch and effort information on the recreational sector by season and location. Estimates of the recreational catch, since the introduction of new management measures, were not previously available for the Cockburn Sound and Geographe Bay recreational fisheries and this study has addressed this shortfall. Catch and effort data for this survey and an earlier survey conducted in 1996/97 has now been collated and presented in a single document along with the commercial catch for the same periods. The results show that the recreational catch share in both locations has increased, which was the objective of the recently introduced management measures.

Ongoing catches by the commercial sector, coupled with high and increasing recreational pressure, indicates that stocks of blue swimmer crabs in Cockburn Sound and Geographe Bay are in need of continued monitoring for management decision purposes.

Number of Pages

54

Keywords

Department of Primary Industries and Regional Development, Portunus pelagicus, Recreational Fishing, Blue Swimmer Crabs, Cockburn Sound, Geographe Bay, Creel Survey

Disciplines

Aquaculture and Fisheries | Environmental Sciences | Marine Biology

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