But they can be distinguished - aviation ULBs aren't coded, and transmit in bursts at 1 second intervals, not continuously.
I can't find information on what 'continuous' means in terms of marine tag pinging. One site states:
Simple 'pingers' transmit regularly and continuously,
whilst transponders transmit on receipt of an external
signal.
www.asfb.org.au/pdf/1999/1999-01-05.pdf
That suggests to me that there's a pulsing behaviour involved? I don't know whether that means microseconds or something in the order of minutes or hours. Is it implausible that a marine tag could be set to pulse at 1 second intervals? Or is this disallowed, on account of confusion with aviation ULBs? The transmission frequency detected was consistent with what marine scientists use to track animals in deep ocean, because the lower frequency travels further.