Table 1 Summary of classification scheme to infer fates based on predation transmitters
From: Identification of predation events in wild fish using novel acoustic transmitters
Fate | Transmitter state | Movement patterns | Notes |
|---|---|---|---|
Predated | Code switched | Distinct changes in spatial use (sometimes followed by a drop in spatial use) | Sudden changes in movement patterns during early phases of predation event and continued detections could be inferred as a resident predator that remains in the area. Sometimes followed by reduced activity where tag appears stationary, likely indicative of the tag being expelled from the predator’s digestive tract. |
Predated | Code switched | Similar spatial use throughout first three phases of predation followed by decreased activity | Despite no changes in spatial use, the occurrence of a code switch as well as eventual reduced overall activity is indicative of a tag that has passed through a predator’s digestive system and been expelled. |
Predated | Code switched | Few detections post-predation | Little movement pattern information for predators to infer fate based on behavioural changes, likely the outcome when there are migratory predators that move away from focal areas shortly after predation or in studies with fewer receivers. Unlikely to be false positive which would result in continuous detections in array unless tag completely malfunctioned |
Unclear (predated or false positive) | Code switched | Similar spatial use throughout phases of predation or few detections pre- and post-predation | Increasing possibility of a false positive as movement patterns remain consistent after a predation event was identified. If too little detection data exists overall, it is hard to draw any conclusions with certainty. Based on laboratory trials, false positives are possible, but relatively rare |
Non-predated | Non-predated code | No drastic changes | Assumes that fish are regularly detected during transmitter lifespan. Fish that exhibit a change in behaviour immediately prior to exiting the study area were likely predated but undetected due to signal lag period or immediate emigration |
False positive | Code switched | Tag appears to be stationary prior to code switch | Based on laboratory trials it is unlikely, but possible, that tags will falsely identify predation after a tagged fish dies. Tag will likely appear stationary before the code switches |
False negative | Non-predated code | Distinct changes in spatial use | Unlikely based on laboratory trials [4]. Difficult to decipher from a change in the tagged individual’s movement patterns (e.g. ontogenetic or seasonal shifts in diet and habitat use) |