in all populations of sea otters, soft-bodied organisms such as worms and sea stars are the least likely to be consumed with the aid of tools. on the other hand, shelled bivalves and snails with shells are the most likely to be cracked open with tools. otters of the northern pacific consume mostly sea urchins and fish, thereby exhibiting less tool use behavior. otters of the southern pacific ocean feed on tougher macro invertebrates such as bivalves.