Does tagging fish make them easy prey?

Researchers routinely tag fish with acoustic pingers, which allow the tracking their movements to determine population movements and patterns. Marine mammals may be able to use those tags to locate and eat the fish.  Researchers first measured the acoustical properties of these tags in fish in Mission Bay, San Diego, CA. We then tested these frequencies with animals in the zoological collection at SeaWorld San Diego. We found that harbor seals potentially could hear the tags and use them to locate fish from 20 to 200 meters away, while dolphins could hear them even further away. California sea lions were not able to detect any of the tested tags at useful ranges. We conducted further research to recommend the pitch of the pingers so that these tags can be picked up by acoustical equipment, but be a dinner bell for marine animals.

Bowles, A.E., S.L. Denes, and M. Shane. 2010.  Acoustic characteristics of ultrasonic coded transmitters for fishery applications: could marine mammals hear them?  Journal of the Acoustical Society of America 128:3223-3231.