I just caught a giant spider crab just now, and the only sea creature left to catch is the horseshoe crab!! Can you find it at the island? Cause if so, what shadow size is it? I realllyyy want to get the 100% badge from Phineas!
http://animalcrossing.us/animal-crossing-new-leaf-last-chance-catch-2nd-half-september/
it says here it cannot be found on the island (it's the very last creature on the list), i guess you have to wait or time travel :^(
Well, you'll have to TT to get the horseshoe crab.
Speaking of which, I also got a spider crab today, after some failed catch attempts. I just need the horseshoe crab, flatworm, and spiny lobster to complete my seafood encyclopaedia.