Green Sturgeon Distribution in the Pacific Ocean Estimated from Modeled Oceanographic Features and Migration Behavior

The anadromous green sturgeon (Acipenser medirostris) is found in the eastern Pacific Ocean from Baja California to the Bering Sea. Previous studies show green sturgeon to be highly migratory throughout this range, moving long distances among estuaries, spawning rivers, and distant regions of the coastal ocean. Factors determining the distribution of green sturgeon within this region are unclear, but broad-scale ocean conditions may play an important role. We report the results of an acoustic tagging study that used data-logging acoustic receivers from the Pacific Ocean Shelf Tracking program and other studies. We connected modeled bottom temperature, dissolved oxygen, geostrophic currents, and depth to acoustic tag detections using a maximum entropy species distribution model. We delineated green sturgeon ocean distribution using the seasonal distribution of modeled oceanographic features combined with covariates that describe green sturgeon migration behavior. We found that green sturgeon migrated seasonally with the prevailing currents and that migration behavior and temperature were the most important drivers for green sturgeon distribution in the Pacific Ocean. We also learned that bottom currents may be an important migration cue or may influence sturgeon distribution directly as an energetic constraint. We estimated the predominant green sturgeon distribution in the Pacific Ocean to occur from near the Queen Charlotte Islands, British Columbia, Canada to the coast of northern California, U.S.A. We delineated less continuous green sturgeon ocean habitat from south of northern California, U.S.A. to Baja California, Mexico. Our estimated green sturgeon distribution matched data from trawl records and other independent observations, except that few green sturgeon have ever been captured south of Monterey Bay, California. The absence of model covariates that constrain green sturgeon distribution in the southern portion of their known range indicate that other habitat features such as seafloor complexity, habitat discontinuity, food resources, or predation by sharks or pinnipeds may be limiting. Our study is the first to utilize output from a regional oceanographic model system to delineate sturgeon habitat and will provide insight concerning the effects of changing ocean conditions and fisheries management.