Improving monitoring and stock assessment for Dungeness crab by measuring recruitment of larval megalopa

With many salmon fisheries on the decline or failing and the paucity of fishery alternatives, harvest of crab has become critical in supplying a large share of the region’s fishery-related socio-economics. Larval crab are a critical food source to endangered juvenile Chinook during the early marine stage. Crab are facing increasing threats from climate change and degraded habitat including ocean acidification, increases in harmful algal and noctiluca blooms, lower growth rates, and in some areas, lack of recruitment. While bottom-up forcing may have deleterious effects to the population, top-down forcing from increased predation and fishing mortality. Although there were studies in the early 90s aimed at defining stock structure, studies 10 years ago demonstrating a method to better understand and even predict recruitment, and a recent genetic study examining larval crab sources, none of this information has been translated and incorporated into improving stock assessment and harvest management. Management methods remain largely unimproved with assessments from fishery-dependent data, the least desirable and most bias stock assessment information compared to other methods. Management is also based on a single stock population structure despite the evidence to the contrary. For this study, we review population trends and spatial patterns from mature and immature crab catches and provide a preliminary view of the ongoing larval crab monitoring program underway at Lummi Nature Resources. Using light traps, we documented waves of megalopa larval crab recruitment to the nearshore in northern Puget Sound near the Canadian border. We will report on among and within site variability and compare the results to another region in Puget Sound conducing similar monitoring. We provide some interpretation of these results in terms of monitoring in the face of climate change and recommend a direction for monitoring in the future