MOMBETSU, Japan. — The sea ice that normally cloaks Japan’s northern coastline in the winter is receding as the oceans around here warm dramatically. For the seals that make these seas their home, that is proving to be a mixed blessing.
The La Pérouse (or Soya) Strait, a 26-mile wide body of water dividing Japan’s northern island of Hokkaido and Russia’s Sakhalin peninsula, is no longer icebound throughout the winter, and spotted seals are pouring through the strait from their traditional habitats in the Sea of Okhotsk to access the rich fishing grounds of the Sea of Japan along Hokkaido’s western coast.
There, they feast on salmon and octopus in the nets placed along the coast by Japanese fishermen before returning north to the Sea of Okhotsk to give birth on the sea ice in March.
“Fishermen use fixed nets, and that means the area has become a convenient, perfect feeding place for seals,” said Mari Kobayashi, a professor at Tokyo University of Agriculture. “Once some find out about it, others follow. Today, seals can be seen in droves in a region that they weren’t found before, arriving early and staying late.”
That’s already bringing them into conflict with humans, causing millions of dollars a year in losses to fishermen through lower catches, and prompted the Hokkaido government to step up seal culling to reduce numbers.
The population of spotted seals in the Sea of Okhotsk began to recover with the decline in seal hunting from the 1970s, with Russia’s commercial hunting operation finally collapsing in 1994 after the fall of the Soviet Union and the withdrawal of subsidies.
But the receding sea ice could reverse that process, experts warn.
Spotted seals need the ice to give birth, spending two or three weeks on it from mid-March to look after their newborn pups. Poor quality or insufficient sea ice could reduce survival rates.
But the indirect implications of the ocean’s rapid warming could be even more serious, given the crucial role sea ice plays in nourishing the rich waters of the Sea of Okhotsk, experts say.
In the spring, as the ice melts and sunlight hits the water, the sea blooms with phytoplankton, the anchor of marine life and the base of the ocean's food web. These seas nourish not only seals and sea lions but whales and dolphins, scallop and crabs, and hundreds of species of fish, while its shores are home to many migratory and sea birds.
“Less sea ice arriving means less ice algae brought with it,” Kobayashi said. “We may be in a transitional period right now, where the seal population can grow smoothly. But if global warming continues to intensify, in the long-run I think they will face something of a crisis.”
Spotted seals live on ice floes and nearby waters in the north Pacific region, from Canada and Alaska to Russia, Japan, Korea and China, with a global population in the hundreds of thousands. Shy of humans, adults are typically about 60 inches long, weigh between 180 and 240 pounds and can dive to 1,000 feet in search of food.
In the city of Mombetsu on Hokkaido’s northeastern tip, Seals Land is Japan’s only shelter for the marine mammals.
It provides a sanctuary for 22 spotted seals and four ringed seals, who were generally rescued as newborns and are mostly now between 20 and 35 years of age.
“Typically, local people come across a seal wounded on the beach on the shore of the Sea of Okhotsk, and they call us,” said Masako Okazaki who is in charge of seal welfare at the shelter and has worked there for eight years. “Most of them are newborns, who are too weak to survive on their own.”
The shelter initially opened in 1987 with a temporary pool in a private house sheltering four stranded seals, before moving to bigger premises the following year and finally to the Mombestu shoreline in 1999. Formerly known as the Okhotsk Tokkari Center after the indigenous Ainu word for seal, it charges tourists just $1.80 to enter.
But in recent years, the number of seals being rescued has fallen, Okazaki said.
“It could be that with less sea ice, fewer seals are coming here, or there may be seals who are too weak to reach the shore with the sea ice receding offshore,” she said. “I haven’t seen them, but I think there are some feeble seals who die in the water or on a fragile piece of sea ice before they reach the shore.”
In the past, the center used to release healthy seals back into the wild, Okazaki said, but grew concerned about their ability to survive there after spending most of their lives in captivity. Seals Land has also scaled back their release program out of respect to fisherman who are angry at the damage seals are causing their nets.
“Seals come to us after somebody calls for help. Once we see them, we cannot just let them go,” she said. “At the same time, it has become difficult to return them back to the sea given the situation.”