Dungeness Crab Mortality Due to Lost Traps and a Cost–Benefit Analysis of Trap Removal in Washington State Waters of the Salish Sea

Abstract

Loss of Dungeness crabs Cancer magister in derelict crab traps was estimated from catches and mortality in 24 simulated lost traps at two locations in Washington State. Equal numbers of recreational and commercial crab traps were initially baited and monitored weekly by divers until the bait was consumed and were monitored biweekly thereafter for 1 year. Dungeness crabs caught in the traps were individually tagged. Catch, escapement, retained catch, and mortality rates were estimated. The traps caught 1,077 Dungeness crabs, of which 500 (46%) died and 421 (39%) escaped. Mortality of sublegal males and females was expressed in legal male equivalents. The overall retained catch of Dungeness crabs (caught minus escaped) was 0.082 crabs·trap⁻¹·d⁻¹. After an initial lag, the cumulative daily mortality rate of Dungeness crabs rose steadily to 0.058 crabs·trap⁻¹·d⁻¹. An estimated 12,193 traps are lost annually in Washington waters of the Salish Sea, and the estimated trap fishing duration was 126 d for traps with escape cord (i.e., reflecting decomposition of the cord) and 2.2 years for traps without escape cord. Annual Dungeness crab loss was estimated at 178,874 legal male equivalents, translating to an exvessel value of US$744,296, or 4.5% of the value of recent harvests. Average annual net value to fishers from the saved Dungeness crabs (i.e., crabs available for harvest if lost traps had been removed) was estimated at $450,657–744,296 depending upon variable costs to harvest all of the saved crabs. Estimated net exvessel value of saved crabs ranged from $36.96 to $61.04 per removed trap compared with removal costs of $92.66–193.00 per trap. Removal of lost traps may be warranted in high-density fishing areas and for ecological reasons. Reducing the diameter of the escape cord and modifying the trap design could significantly reduce Dungeness crab mortality due to lost traps.

Received May 14, 2010; accepted February 10, 2011

ACKNOWLEDGMENTS

We thank Ginny Broadhurst and Joan Drinkwin (NWSI) for securing funding for the Dungeness Bay project from the National Fish and Wildlife Foundation and the National Oceanic and Atmospheric Administration Marine Debris Program. We also thank Jennifer Sevigny and the Stillaguamish Tribe for funding the Port Susan project. We are grateful to the reviewers, who provided extensive and insightful comments and suggestions for the manuscript. This project would not have been possible without the dedication of Doug Monk, Crayton Fenn, and their teams of divers. Carl Lian (National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Northwest Fisheries Science Center) graciously provided the data analysis on VCs for the Salish Sea Dungeness crab fleet. We also thank Carol Stedman, Dayv Lowry, and Mel Stanley (WDFW) for supplying data and providing advice on how to use it.