Evidence of a ‘dinner bell’ effect from acoustic transmitters in adult Chinook salmon

Abstract

The ‘dinner bell’ hypothesis posits that marine mammals hear or otherwise sense soundwaves produced by acoustic transmitters and use the signal to selectively prey on fish carrying them. A dual tagging study conducted during 2010 and 2011 supports this hypothesis. Results from this study revealed a significant difference in the survival of fish marked with passive integrated transponder (PIT) tags and those marked with active acoustic transmitters. Our objective had been to use both types of tags to study behavior and survival of migrating adult spring Chinook salmon Oncorhynchus tshawytscha at 2 different spatial scales. We tagged fish as they entered the Columbia River, USA, and monitored their survival and progress over a 193 km reach to Bonneville Dam (river km 234), its lowest impoundment. In 2010, estimated survival was 0.74 (95% CI, 0.62-0.86) for PIT-tagged fish but only 0.30 (0.15-0.45) for acoustic-tagged fish. Therefore, in 2011, we included archival tags and a sham acoustic transmitter group to help identify causes of the survival discrepancy. Survival was 0.75 (0.54-0.97) for sham transmitter fish and 0.73 (0.60-0.86) for PIT fish, but only 0.10 (0.00-0.24) for active acoustic transmitter fish. Our study area was replete with harbor seals Phoca vitulina, California sea lions Zalophus californianus, and Steller sea lions Eumetopias jubatus during both years. We suspect the most likely cause of survival differences between tag treatment groups was pinniped predation. Using temperature data from archival tags, we found evidence of such predation and support for a ‘dinner bell’ effect from acoustic transmitter tags.