For the most part, seals don’t feed on jellyfish. Seals prefer ocean delicacies that are easy to nab, abundant and not filled with poison. Seals prefer fish and crustaceans, but when their normal food populations are low they’ll put their health at risk and feed on jellyfish, prompting many to wonder how they do it. Seals are sometimes able to bypass the dangers of a jellyfish’s tentacles and find nutrients in the non-poisonous parts.
Parts of a Jellyfish
Not every part of a jellyfish is filled with venom. For a seal, the head of a jellyfish makes a filling meal – if he can reach it. The very top of the jellyfish, or the exumbrella, is edible and not poisonous. Under its soft surface is the mesogloea, gastrodermis, gonads, radial canal, gastic cavity and circular canal. All of these parts, of a jellyfish’s head, are edible. Unfortunately, the head is completely surrounded by short poisonous tentacles. Many mistake a jellyfish’s oral arms for tentacles. The long arms that descend from the subumbrella are actually oral arms, while tentacles are the shorter pieces that surround the head. In almost all jellyfish species, both the tentacles and oral arms contain venom.
The Dangers of Venom
Jellyfish tentacles, and sometimes their oral arms, are lined with venom releasing nematocysts. Nematocysts look like small capsules, inside which is an abundance of poison. When a predator comes near, jellyfish will whip their tentacles. If a tentacle comes in contact with a seal, the nematocysts will activate, injecting the seal with venom. For a seal, in order to successfully feed on a jellyfish, he must bypass the tentacles and feed on the head of the jellyfish. If he’s stung, he’ll become temporarily paralyzed and lose his meal. Jellyfish stings have been known to kill small predators, so ringed seals, the smallest of all seals, are especially vulnerable to a jellyfish’s sting.
Bypassing the Venom
Seals have slick bodies, making them capable of top speeds under water. They’re able to ambush their prey, ripping into them with their sharp teeth. All seals are carnivores and although jellyfish aren’t a normal part of their diet, they will attack a jellyfish when other food sources are low. The seal will lie in wait, waiting for his prey to come near. His slick body makes it possible to quickly dive at the jellyfish’s head. If he’s lucky, he’ll bypass the tentacles and oral arms. Once he’s met with the jellyfish’s head, he tears in with his sharp teeth. Seals have incredibly strong teeth, so one bite should instantly kill the jellyfish causing it to go limp. The seal will bite off the jellyfish’s head, leaving the poisonous parts to float away. If he’s unlucky, he’ll be stung and paralyzed, or worse die from the venom injection.
It Doesn’t Happen Very Often
Jellyfish have very few predators because of their ability to sting and paralyze anything that attacks them. They travel in groups, often numbering in the hundreds in just ten square feet of ocean. Because of this, jellyfish are not a regular part of a seal’s diet. Entering this dense thicket of poisonous tentacles isn’t appealing to many of the ocean’s inhabitants. In truth, it’s rare a seal eats a jellyfish and even rarer that he’s able to do it without being stung.