With floating ice sparse in the Chukchi Sea, an estimated 35,000 walruses were found crowded onto a beach near the Northwest Alaska village of Point Lay, according to federal biologists.

The congregation of walruses, photographed Saturday by biologists flying over the area in a plane contracted by the National Oceanic and Atmospheric Administration, is one of the biggest onshore gatherings of the animals documented in Northwest Alaska, said one walrus expert.

"It's a good-sized aggregation, definitely," said Chadwick Jay, a research ecologist and leader of the U.S. Geological Survey's Pacific walrus research program.

It's comparable to a gathering in the same area in 2011 and a few others in recent years, he said.

Walruses face perils when large crowds gather onshore, according to biologists. The animals in the Chukchi this time of year are generally females and juveniles, and the smaller walruses are in danger of being trampled to death in stampedes. The beaches are also distant from the best spots for feeding, normally at the edge of the continental shelf farther offshore.

Walruses tend to use floating ice as platforms for resting and caring for their young in between swims to find clams, worms and other food sources on the sea floor.

But -- as has been the case in most recent years -- all remnants of floating summer sea ice in the region melted away by mid-September, forcing the walruses to head to shore to rest in between dives for food, Jay said.

"Even that last little bit of ice disappeared and they came to shore," he said.

In only two of the last eight years has the Chukchi had enough floating ice to provide resting spots that allowed walruses to avoid having to swim to shore, he said.

So far, there have been no signs of major problems at the Point Lay haulout site, though some dead animals were found, said Andrea Medeiros, a spokeswoman for the U.S. Fish and Wildlife Service. The service is planning to send a team to the area to perform necropsies on the dead animals to try to determine cause of death, she said.

At least 36 dead walruses were spotted, according to the NOAA report. That group had both adult and juvenile animals, Jay said.

To environmentalists, the large walrus gathering was a warning sign.

"The massive concentration of walruses onshore -- when they should be scattered broadly in ice-covered waters -- is just one example of the impacts of climate change on the distribution of marine species in the Arctic," Margaret Williams, managing director of the World Wildlife Fund's Arctic program, said in a statement.

Because of reductions in summer and fall sea ice, the U.S. Fish and Wildlife Service is considering granting Endangered Species Act protections to the Pacific walrus. Under a 2011 legal settlement with environmentalists who petitioned for the listing, the service must make a decision by 2017.

Sea ice is near its annual low in the Arctic. After six months of melt, ice cover fell to 5.016 million square kilometers (1.94 million square miles) on Sept. 17, the low point of the year, according to the National Snow and Ice Data Center. That was well below the average recorded in the past three decades, and the sixth lowest extent since satellite recording started in 1979, but well above the record low of 3.41 million square kilometers (1.32 million square miles) reached in the big-melt year of 2012.

Ice has been particularly sparse this summer and fall off Alaska and eastern Siberia, according to the National Snow and Ice Data Center.

Jay said the tally of 35,000 walruses is a rough and preliminary estimate.

"Basically, they're just kind of looking out the window as the plane goes by. It's basically just a guesstimate," he said. And the gathering onshore represents only some of the walruses in the area, he said.

"There's at any given time some number of animals that are off the haulout in the water, feeding," he said.

Walruses usually spend about 80 percent of their time in the water, he said.

Biologists are planning to do more careful studies of the photographs to come up with a more precise estimate of the numbers, said Jay and Medeiros.

Jay was not among the biologists onboard the NOAA-sponsored flyover in the region -- a multiagency effort using a single plane to monitor marine mammals -- but he was at the site for four days earlier in the month attaching radio-tracking devices to 37 animals, part of an annual tracking program to gather information about walrus behavior in the changing Arctic environment.

Far fewer walruses were at the site when he was there in the middle of September, he said, but there were unusual signs.

"We did see a lot of signs of bear tracks in there," he said. Local hunters reported seeing brown bears, and Jay said he and his colleagues spotted a polar bear. Some walruses had moved to a grassy area, he said. The walruses were moving "in a way that made us speculate that they may have been bothered by bears," he said.

By now, the Point Lay walruses may have moved off the beach, Jay said. Some of the radio-tagged animals have already been tracked heading to the Hanna Shoal, a shallow area in the middle of the Chukchi, and to the Russian side, he said.

The thousands of walruses gathered at Point Lay may be ready to go elsewhere to find food, Jay said.

"It's not beyond reason to think that they may have wiped out the food resource, at least in that local area," he said.