Proceedings 2009/008
Proceedings of the Pacific Scientific Advice Review Committee (PSARC) Invertebrate Subcommittee Meeting: Stock Assessment Framework for the British Columbia Geoduck Fishery; November 26, 2008
Chairperson: Raymond Lauzier
Summary
The Pacific Scientific Advice Review Committee (PSARC) Invertebrate Subcommittee met November 26, 2008 at the Pacific Biological Station in Nanaimo. The Subcommittee reviewed one working paper.
Working Paper I2008-01 Stock Assessment Framework for the British Columbia Geoduck Fishery
D. Bureau, C. Hand, W. Hajas
The working paper describes the stock assessment framework for the British Columbia (BC) geoduck fishery, starting with an outline of the early history of assessment and management and bringing up to the present day. The unique biological characteristics of geoducks and their population distribution, structure and dynamics is described to give perspective and background to the stock assessment framework. The actual mechanisms, types and sources of data as well as sources of error in the stock assessment framework are described. Sea otters have a progressively larger impact on the BC geoduck fishery as their range expands. Options to allow the geoduck fishery to co-exist in sea otter areas are discussed. The Limit Reference Point (LRP) currently in use in the BC geoduck fishery is used to close a bed to harvest once the biomass is reduced to 40% of the pre-fishery biomass. An alternative to the current LRP is required and the options are outlined and discussed. An effective conservation measure for geoducks may be a system of reserves. However, estimation of geoduck biomass outside the commercially harvested areas could be undertaken to determine the proportion of the geoduck biomass in BC that already exists in nearby de-facto reserves.
There were two reviewers of the working paper, one internal and one external. Both reviewers had concerns on the determination of mean weights and the use of correction factors. Reviewers also raised concerns on show factors and the use of Limit Reference Points (LRP). Both reviewers had suggestions as alternatives to reference points.
There was Subcommittee discussion on the appropriate size of pre-recruit cutoffs and whether they should be used at all. The issue was also raised of not surveying areas < 3 m depth. Another concern expressed was the impact of post-stratification on the overall estimate of density. There was discussion on the term Limit Reference Point that was used in the paper, and it was agreed that it is not the appropriate term. There was discussion on using a minimum density rather than trying to estimate B0 at a time when there were no sea otters present, and when B0 would be at historic highs. There was also the suggestion of using simulation scenarios if there are sufficient data in order to more realistically determine the lowest allowable level, taking into consideration the impacts of sea otters as well as sporadic recruitment events. In response to Subcommittee discussion and questions, the authors believe that surveying a greater number of transects would be a better use of time, rather that the show factor plots, which can take up to 25% of the total survey time. There was considerable Subcommittee discussion on how to improve data collection on biological sampling, especially when it came to Recommendation 1 of the working paper. It was agreed by the authors that in the interim, an 11% correction factor would be applied to Queen Charlotte Islands data, and 8% to Prince Rupert data, until further work is completed.
The Subcommittee commended the authors on the high quality of the paper and accepted the paper subject to minor revisions.
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