evilbob
Adventurer
Of course I forgot the one best tactic, of course: bring a druid! Turn into an octopus, grab 7 seahorses each round and eat them. Done. 
(I know, I know it won't work - but it'd be funny. Honestly I am not sure how you'd complete this scenario without just using the skill checks if you didn't think any of those other ideas would work. Minor illusion is the only one I could come up with. Actually, I guess as long as you had 4 party members, you could ready an action each round to grab a seahorse when it was swallowing the egg and break its little neck. They'd still get 9 but otherwise you'd win without blood! I'm guessing that's more or less what you expected - each member ambush or otherwise attack a seahorse? Seems like the most straightforward way. Maybe try to "capture" at least 3 of them with a crab trap or something. But that will likely take too long. Oh, and I would probably rule that if you did get the statue going, the shark would leave at that point - then again, if you fixed the statue, you wouldn't care about the shark.)

(I know, I know it won't work - but it'd be funny. Honestly I am not sure how you'd complete this scenario without just using the skill checks if you didn't think any of those other ideas would work. Minor illusion is the only one I could come up with. Actually, I guess as long as you had 4 party members, you could ready an action each round to grab a seahorse when it was swallowing the egg and break its little neck. They'd still get 9 but otherwise you'd win without blood! I'm guessing that's more or less what you expected - each member ambush or otherwise attack a seahorse? Seems like the most straightforward way. Maybe try to "capture" at least 3 of them with a crab trap or something. But that will likely take too long. Oh, and I would probably rule that if you did get the statue going, the shark would leave at that point - then again, if you fixed the statue, you wouldn't care about the shark.)