Predator/Prey Interaction: From Observed Behavior to Direct Measure

Acoustic telemetry methods are routinely used to estimate survival, movement and relative distributions of fish.  In instances where acoustically-tagged fish are consumed by a predator, the consumed tagged fish may be incorrectly identified as live, resulting in inaccurate study conclusions.  If tags using precisely-spaced and uniform coding schemes are employed, a review of the time-series of detections can be used to determine changes in fish behavior, (e.g., those indicative of predation). 

Single receiver detection data can indicate a predation event has occurred when a tag is shed/defecated within detection range.  If multiple receivers are deployed for fine-scale 2D/3D fish tracking, then quantifiable patterns of swimming behavior can be used to infer predation events.  Metrics employed include swimming speed, movement patterns, residence times and others. 

Recently, a new type of acoustic tag was developed to directly measure/report when a tagged fish was eaten by a fish or other predator.  These tags were designed to activate a modified signal in a predator’s gut while maintaining information needed to identify the originally-tagged fish.  In 2013, tests determined the Predation Detection Tags (PDT) functioned as designed.  Additional field tests are currently underway to evaluate performance when implanted in fish released into natural environments.