Maybe I'm not translating correctly "sounding beacon", but I would assume that what you see was just an (I don't know the exact term) "electronic tag". This is standard procedure in ecology, veterinary and animal husbandry. We did it sometimes. Is a rice grain size object, and does not left any noticeable scar in fishes.

All good, I don’t have any issue with attaching or implanting tracking devices for research purposes in what looks like a wholly harmless way.

From what they were saying, it emitted a ping every ten minutes, wasn’t entirely clear if it was acoustic or radio. Shark didn’t seem to mind.