Evacuation of passive integrated transponder (PIT) tags from northern pikeminnow consuming tagged juvenile Chinook salmon

Prey fish implanted with passive integrated transponder (PIT) tags can be used in predation studies if the timing of tag evacuation from the predators is understood. Laboratory experiments were conducted to determine how PIT tags in juvenile Chinook salmon Oncorhynchus tshawytscha that were consumed by northern pikeminnow Ptychocheilus oregonensis were evacuated in relation to various parameters. The rate of evacuation was directly related to temperature, while predator size and the number of prey consumed had less effect on the timing of tag evacuation. A power model was fitted to predict the proportion of tags expected to be evacuated at different intervals after ingestion. These results could be used in planning field or laboratory predation experiments with PIT-tagged prey fish.