Breeding and foraging ecology of Caspian terns (Sterna caspia) in the mid-Columbia River : predation on juvenile salmonids and management implications

Graduation date: 2003I investigated Caspian terns (Sterna caspia) breeding at colonies on the\ud Columbia Plateau (southeastern Washington and northeastern Oregon), with\ud emphasis on the breeding and foraging ecology of Caspian terns nesting at\ud colonies in the mid-Columbia River. I focused research at colonies where\ud Caspian terns foraged on juvenile salmonids (Oncorhynchus spp.) because of\ud potential impacts to stocks listed under the U.S. Endangered Species Act.\ud Caspian tern colony size on the Columbia Plateau ranged from tens of breeding\ud pairs to nearly 700 pairs at Crescent Island in the mid-Columbia River; total\ud population size in the study area was about 1,000 pairs and appeared to be stable.\ud The size and number of Caspian tern colonies in the Columbia Plateau region are\ud likely constrained by the availability of suitable nesting habitat near abundant\ud prey, a resource that appears limited within the study area. Productivity of\ud Caspian terns was not affected by nest density at Crescent Island, information that\ud may be helpful for resource managers deciding minimum area requirements for\ud breeding Caspian terns at managed colony sites. At colonies on the mid-\ud Columbia River, the majority of Caspian tern prey items consisted of juvenile\ud salmonids. I estimated that Caspian terns nesting at Crescent Island in the mid-\ud Columbia River consumed 382,000-547,000 and 533,000-825,000 juvenile salmonids during the breeding season in 2000 and 2001, respectively. Total\ud salmonid predation by Crescent Island Caspian terns was less than that reported\ud for some other predators in the Columbia River that have been managed to reduce\ud predation rates on juvenile salmonids. The results of this research will be used by\ud state, federal, and tribal resource managers to decide whether Caspian tern\ud management is warranted at Crescent Island