ESTIMATING TOTAL MORTALITIES ON ENDANGERED CHINOOK
February 6, 2020
Fisheries managers, First Nations, and stakeholders are becoming more aware that Fisheries Related Incidental Mortality (FRIM) can contribute significantly to Total Mortalities (TM) in fisheries. As a case study on one fishery, we examine potential FRIM and TMs in Spring and Summer Fraser River Chinook populations designated as ‘Endangered’ by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) (Table 1).
The South Coast Juan de Fuca recreational fishery encounters Spring and Summer Fraser River (42 and 52) Chinook from Southwest Vancouver Island to the mouth of the Fraser River (DFO fishery management areas 18,19,20,29,121). As the largest and oldest Chinook that return to the Fraser River, these fish are important to endangered Southern Resident killer whales and as a source of food for interior First Nations.
We apply the guidance provided in Patterson et al. (2017b) and interviews with anglers to identify risk factor ranges for Capture, Injury, Handling, and Predation Mortality. These are combined with drop-out mortality and a Monte Carlo simulation to estimate a range of FRIM. Other factors that may affect estimates of FRIM, such as the stock composition of releases, are also investigated.
Our results suggest that current methods for estimating FRIM employed by both DFO (15% x releases) and the Pacific Salmon Commission (PSC) Chinook Technical Committee (15% drop-out mortality on catch and 10% immediate mortality on releases) likely underestimate FRIM when compared to the Patterson et al. (2017b) approach.
In conclusion, we discuss management recommendations for improved monitoring and identify information needs in both this fishery and others that effect endangered chinook.
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