Assessing the Relative Importance of Estuarine Nursery Habitats - a Dungeness Crab (Cancer magister) Case Study.

Abstract

Estuaries serve as important nurseries for many recreationally and commercially harvested fisheries species. Recent conceptual approaches (i.e., seascape) for assessing the value of estuaries to fisheries have advocated for complex habitat-scale assessments that integrate multiple life-history responses (e.g., abundance, growth, reproduction) and ecological processes across heterogeneous landscapes. Although ecologically compelling, implementing seascape approaches may not be feasible for resource-limited management agencies. In such cases, we propose that resource managers can enhance the identification of fishery-important estuarine habitats by integrating attainable aspects of the seascape approach into a more traditional single response (e.g., abundance) model. Using Dungeness crab (Cancer magister) as a case study, we applied a spatially-explicit hybrid approach to assess the relative contribution of different estuarine habitats to that important fishery species within three Oregon estuaries (Tillamook, Yaquina, and Alsea bays). We measured the abundance of juvenile C. magister from low-tide trawls in estuarine channels and the mosaic of habitat characteristics within defined home-range distances for the crabs. After identifying and reducing strong intercorrelations among habitat variable data, we developed a best-fit model that associated crab abundance with the most influential habitat variables. We found that lower-estuary side channels supported the highest abundance of juvenile crabs; furthermore, crab abundance was positively associated with high salinity and burrowing shrimp (Upogebia pugettensis) density on adjacent unvegetated tidal flats. This hybrid method produced a habitat-specific model that better predicted juvenile C. magister abundance than did a model based on generalized habitat categories.