The fish, which can reach a size of four feet in diameter with piquants a hundred feet long, have been spotted from Maine to Massachusetts.
“The ones we see here are probably not much bigger than maybe dinner plates,” says Steve Spina, assistant fish curator at the New England Aquarium. “Which is big enough.”
Due to their size, Lion’s Mane jellyfish are especially dangerous for swimmers. Their long tentacles can sting a person whose protector has been knocked down because the fish looks as if they are a few meters away.
Area officials are warning residents and visitors to be vigilant and stay safe.
Beaches fly purple flags to indicate the “presence of dangerous marine animals,” the Massachusetts Department of Conservation and Recreation tweeted.
Hingham and Scituate beaches, both popular with tourists for the fourth weekend in the weekend, have both issued public health statements advising caution when swimming in areas where there are fish.
“The abundance this year is unusual. There are a lot of them,” Spina says.
Jellyfish often appear in the deep waters of the North Atlantic in late spring and early summer. But this year they are washing out on the coast later – and in greater numbers – than before.
In the “polyp” phase of a lion’s life cycle life, an animal can “strobilize” or spawn more jellyfish than is usual if temperatures are unstable, says Amy Arnold, a senior aquarist in acquisitions and quarantine at the Georgia Aquarium.
“It could then cause more iron to be seen than usual, and later in the season, that’s when we got used to it,” she says.
However, it can be difficult to point to a clear explanation for year-to-year fluctuations. Jellyfish populations, Spina says, “are very unpredictable.”
This is what beach workers should do to stay safe
Lion’s Mane jellyfish grow the largest in ice-cold water, so people are unlikely to see record-breaking fish during their holiday weekend. However, tentacles require caution because they can float in the yard away from fish, carried by electricity and still hit.
“It’s also important to remember,” says Arnold, “that if you see them washing on land and out of the water, they’ll still have the ability to sting.” It is especially important to keep in mind that dogs and children are kept.
Although serious stings have been reported this year, none have required medical attention, and Cat Lion stings are rarely fatal. Beaches are advised not to stand outside the water in which the fish were spotted and to treat the stings with stings.