Hi mate,
You only need to add corresponding damage entry in zone.cfg as an ex:
192=pescarus
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pescarus
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[Pescarus]
Multiplier=1.0
Flotability=0.0
HitPoints=10
Destructible=No
Armor Level=-1
Critic Flotation=0.99
Critical=No
FloodingTime=60
CargoType=None
Crash Depth=75
Also don't forget to add box to your object because the box is link to the damage entry and as a bonus you can change destructible to yes and do an animated model of the shark with bullet holes slowly sinking to the bottom.
Work fine here and here a thread explaining in detail damage and zone on another forum:
http://forum.kickinbak.com/viewtopic.php?f=70&t=1378
Best regards Hans