seals eating salmon - #wetrackthat HTI Acoustic Telemetry

Sea Lions & Seal

Ok, technically, we’ve not tracked individual sea lions or seal. However, it is known that both love to eat salmon, and we’ve tracked hundreds of thousands of salmon. Why do we note them? Because they are a major predator of fish that are tracked with acoustic tags for survival data. To help improve their survival and increase their populations, this is vital (pun intended).

For survival studies to be accurate, acoustically tagged fish (e.g., salmon) need to be swimming freely. A critical assumption of survival estimation for acoustically tagged migrating species is that the detected tag signals are from distinctly unconsumed and freely migrating fish. Protocols for determining predatory-like movement has been objectively defined for use in analyzing telemetry data, however, they were not definitive. These questions are what led HTI to develop a new technology that goes beyond defining predatory-like behavior and definitively answers the predation question; the Predation Detection Acoustic Tag (PDAT).

To take it a step further, recently scientists have learned (via NOAA Fisheries Northwest Fisheries Center studies) that another factor may need to be considered in the predator/prey dynamic with seals, salmon, and acoustic tags. The frequency that marine mammal predators, in particular harbor seals, can detect some acoustic tag emissions resulting in increased fish predation, referred to as the “Dinner Bell Effect“. HTI engineers and fisheries biologists took that finding into account when designing the newest marine-focused acoustic tag at 80 kHz. With that, they found the best compromise for maximizing resolution and range while still being outside of the auditory of most marine mammals.

Learn how we did it by reading “The Importance of Frequency in Acoustic Tag Selection“.


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