Otters are playful animals and until recently it was mostly male otters getting bitten by the sharks. Probably what we have here is some kind of initiation ritual for otter gangs--the new member has to taunt a shark as part of the ritual...and sometimes they get killed doing so.
Why there are more female otters being bitten recently is harder to explain, but they should not rule out the possibility that these are lesbian otters who are imitating male behavior.
*ouch*!