Research Document - 1999/169
Status of Clockwork Chum Salmon Stock and Review of the Clockwork Management Strategy.
By P. Ryall, C. Murray, V. Palermo, D. Bailey, and D. Chen
Abstract
This review examines the assessment of Inner South Coast (ISC) Clockwork chum stocks and the corresponding fishery management. The purpose of the paper is to provide: 1) an up to date stock-recruit analysis, including the large 1997 returns, for both Fraser and non-Fraser Clockwork stocks. The analysis focuses on wild stocks but an assessment of the enhanced component is also presented, 2) an updated assessment of escapement patterns, 3) an updated assessment of the Mission fry estimates and it's relationship to subsequent returns, 4) a retrospective analysis of in-season run size estimates in Johnstone Strait, and 5) a review of the fishery management (1983 through 1997) with respect to the effectiveness of the Clockwork management strategy.
Stock-recruit analysis was done on the 1959-1992 brood years for wild Fraser and non-Fraser Clockwork chum. Results show that for Fraser chum, the optimal harvest rate is approximately 45% which is almost identical to that found by Joyce and Cass (PSARC 92-02). However, unlike the earlier report, the optimal stock size was found to be 738,690 which is substantially greater than 485,320 estimated by Joyce and Cass. Further, evidence of density dependence was found for Fraser stocks that was not found in earlier work. For the aggregate wild stocks, the optimal harvest rate was 44% with optimum stock size calculated at 2.6 million and evidence for density dependence was also noted.
Chum escapement patterns and production has varied based on stock. For the overall aggregate production has increased. However, it would appear that not all areas have responded equally. Fraser River chum stocks have shown greater production and increased escapement relative to the other stocks and are driving the aggregate. Some stocks appear to be decreasing in spite of management and conservation actions. Specifically, escapement records to Upper Vancouver Island, Kingcome Inlet, Bond and Knight Inlets and Toba Inlet show declines in escapement levels. Factors such as lack of escapement enumeration effort and habitat issues may be responsible for the decline and these need to be explored in greater detail. Increased escapement levels for certain ISC chum stocks may be required to stop marked declines in escapement.
Heuristic analysis of the predictive ability of the Mission downstream fry data has shown that although the data correlates with subsequent stock size, it is still too variable to be considered a useful tool for prediction.
Six models were tested and analyzed as to their value for in-season stock size estimation. In general, no one model performed markedly better than any other model. Although run size estimates have been reasonably accurate in comparisons to the final run size, there have been a number of years when the in-season and final estimates have been significantly different. The current models are dependent upon the assumption of average migratory timing of the Clockwork chum stocks. In-season models based upon average migratory timing will under or over-forecast population abundance's because of run timing variability. Incorporating sex ratios with the best performing run model may improve forecasts over the best model without sex ratios.
The results from the review would indicate that overall the Clockwork management strategy has been successful in achieving a number of its objectives. Namely the strategy has allowed for limited commercial fishing in most years, increased wild escapement levels overall, and helped to increase our understanding of the optimal target escapement levels. When viewed from an aggregate viewpoint and taking the associated uncertainties into account, the Clockwork management strategy has worked reasonably well in meeting escapement and harvest rate targets and therefore should continue. That said, there remains significant concern over the level of escapement enumeration and accuracy of the escapement estimates upon which the Clockwork strategy and this stock status review depends. There is a need to standardize data collection methods to improve escapement estimates.
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