J.S. Barber, T. Mitchell, J. Gibson, T. Hoyopatubbi, T. Gobert, A. Ferderer. 2012. Clam population variability within a Puget Sound bivalve management region. Swinomish Indian Tribal Community Technical Report #SWIN-TR-2012-01. 32 pp.
Puget Sound beaches support extensive recreational and commercial shellfisheries that are of significant economic, cultural, and ecological value. In order to best co-manage bivalve resources, state and tribal managers divide public tidelands into eight distinct bivalve management regions. We used data gathered during our annual bivalve surveys to examine how clam populations vary within one of these regions. Specifically, we were interested in quantifying the following: temporal change in clam biomass at a single beach, differences in weight frequency distributions of clam species among multiple beaches, and variation in clam biomass among beaches within a management region. We also collected temperature data at one of the surveyed beaches and developed length-weight models within Bivalve Management Region 4, which was one of the few management regions lacking length-weight models for hardshell clam species. The Region 4 length-weight model was sufficient at predicting weights for various clam species at all of the individual beaches except one, where the beach-specific model for Clinocardium nuttallii was significantly different from the Region 4 model. Butter clam (Saxidomus gigantea) biomass decreased significantly from 2007 to 2011 at one beach within our management region. Individual beaches within this region had significantly different weight distributions when compared to one another for all considered clam species. We also found that biomass per m2 quadrat varied significantly by species and beach within the management region. Ultimately, our goal is to combine these data with information on harvesting and environmental factors (e.g. current regime, temperature, larval supply, competition) to determine what drives clam variability within a management region.