Detection of Passive Integrated Transponder (PIT) tags on piscivorous avian colonies in the Columbia River Basin, 2008

In 2008, the National Marine Fisheries Service, in collaboration with Oregon State University and Real Time Research, Inc., recovered passive integrated transponder (PIT) tags from piscivorous bird colonies in the Columbia River basin (CRB). The PIT tags had been implanted in juvenile Pacific salmon Oncorhynchus spp. for studies of survival and migration behavior. Over 114,000 PIT-tag codes with no previous history of detection on an avian colony were recovered during 2008. Ofthis total, over 87,000 originated from fish released for migration in 2008. Based on these detections, we estimated that avian predators consumed a minimum of 3.7% ofthe 2.5 million PIT-tagged salmonids released into the CRB for migration during 2008. Nearly 90% of fish were consumed by either Caspian terns Hydroprogne caspia or Double-crested cormorants Phalacrocorax auritas. After adjusting for detection efficiencies on the nesting colonies, we estimated that 4.9% of PIT-tagged juvenile salmonids released for migration during 2008 were consumed by these birds. Contract no. 2RL4SPTP00