Project number: 2007-051
Project Status:
Completed
Budget expenditure: $845,578.00
Principal Investigator: Mervi Kangas
Organisation: Department of Primary Industries and Regional Development (DPIRD) WA
Project start/end date: 8 May 2008 - 30 Jun 2010
Contact:
FRDC

Need

There is an urgent need to develop an understanding of the level of gear interaction between the prawn and scallop sectors and whether this may be a cause for the recent low scallop recruitment (and subsequent catches) in the fishery and if scallop fishing negatively impacts on prawns. This urgency was noted at a recent workshop reviewing the research and management needs in the Shark Bay trawl fisheries. Both sectors (prawn and scallop) support the need to fully and rigorously address the issue of gear interactions in those areas of the fishery where the distribution of the target species overlap. Scallop fishers are concerned that repeated trawling by the prawn fleet on scallop grounds may be affecting scallop recruitment. The use of adaptive management techniques such as trialling spatial closures within specific areas of the scallop fishery will provide key information about the usefulness of this management approach for the short-lived and sedentary scallop species Amusium balloti and to assess the impact of the closures on the capture of migrating prawns. This project will be used as a pilot study to assess whether closures can assist increase scallop recruitment and if area closures could be used as a possible management strategy in the future. Completion of this project should therefore result in information required to help optimise the use of these resources and assist in resolving the resource sharing conflicts between sectors within the region.

Developing specific models of water and scallop larval movements within Shark Bay along with an assessment of the relevant environmental variables (eg. SST) would also provide insights into the potential causes of the relatively low level of scallop recruitment in areas that were traditionally reliable scallop grounds.

Objectives

1. To determine size specific recapture mortality rates of Amusium balloti as a result of repeated capture and release experiments and gear impacts on newly recruited (juvenile) scallops.
2. To examine the impacts of various scallop mesh sizes for the capture of the target size of Amusium balloti and its impact on damage to and retention of prawns.
3. To investigate if small-scale spatial closures assist recruitment of Amusium balloti by reducing gear impacts and capture mortality but without affecting overall prawn catches.
4. To examine whether existing hydrodynamic models can guide the selection of spatial closures and to investigate the larval transport mechanisms of both prawn and scallop larvae in Shark Bay.

Final report

ISBN: 978-1-921845-39-0
Author: Mervi Kangas

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