That's where it gets sticky. And depends on the state and possibly the area, as in you cannot collect on public lands/parks. If private, you'd better check with the owner. Federal regulations allow collecting the remains of dead Sea Otter, Walrus, and Polar Bear, but you have to register them and cannot sell, trade, or give them away without the express permission of the USF&WS. You can collect on the beach or within 1/4 mile of the ocean (i.e., shores of backwaters), but cannot collect in the ocean itself. Now whales, seals, sea lions, dolphins (not the fish mahi-mahi), and porpoises are regulated by the National Marine Fisheries Service and cannot be collected. There may be some type of registration/license you may be able to get for scientific purposes, but otherwise, no.