Unbiased Methods for Calculating Mortality in Mark‐Selective Fisheries Models for Ocean Salmon

Abstract

AbstractMark‐selective fisheries (MSF) are increasingly being used as a strategy for managing fisheries for Coho Salmon Oncorhynchus kisutch and Chinook Salmon O. tshawytscha on the west coast of North America. Mark‐selective fisheries allow anglers to keep legal‐size Coho Salmon or Chinook Salmon with a missing adipose fin (typically hatchery fish) and require the release of those with an adipose fin (unmarked fish, which are usually wild fish). The objective of MSF is to provide meaningful fisheries on abundant stocks of hatchery salmon while reducing the impact on wild (unmarked) salmon stocks. As has been previously shown, the model currently used in the Pacific Fishery Management Council's preseason planning process to project mortalities for proposed Coho Salmon and Chinook Salmon fisheries underestimates the number of unmarked salmon mortalities occurring in MSF and concurrent nonselective fisheries. We propose equations that provide unbiased estimates of salmon mortalities that occur in these fisheries due to the release of fish. The performance of the proposed methods is evaluated and compared to the current methods using a simulation model. The methods are shown to provide unbiased calculations of total mortalities for unmarked salmon in both mark‐selective and concurrent nonselective fisheries. The unbiased methods are able to incorporate different release‐mortality and mark‐recognition rates for the fisheries modeled.Received July 24, 2012; accepted November 26, 2012