The Return of the Oolies! Using Spatiotemporal Species Distribution Models to Estimate Trends in Eulachon Density from Fisheries and Research Vessel Data

Identifying spatiotemporal hotspots is important for understanding ecological processes, and is particularly important for species at risk. A number of aquatic species are indirectly affected by anthropogenic impacts, simply because they tend to be associated with species that are targeted for removals. Using newly developed statistical models that allow for time-varying spatial effects, we examine how the co-occurrence of a targeted and non-targeted species can be modeled as a function of environmental covariates (temperature, depth) and interannual variability. The non-target species in our case study (eulachon) is listed under the US Endangered Species Act, and are encountered by fisheries off the US West Coast that target pink shrimp. Results from our spatiotemporal model indicate that eulachon bycatch decreases with depth and has a convex relationship with SST. Additionally, we found that over the 2007-2012 period, there is support for an increase in eulachon from both a fishery dataset (+ 40%) and a fishery independent dataset (+ 55%). Eulachon bycatch has increased in recent years, but the agreement between these two datasets implies that increases in bycatch is not due to an increase in incidental targeting of eulachon by fishing vessels, but because of an increasing population size of eulachon.