A baby orca found dead near Tofino, B.C., is a member of a transient pod, not of the population that frequents Puget Sound waters.

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A baby orca was found dead Tuesday afternoon on the beach near Tofino, B.C.

The whale was a female transient whale, not a member of the southern resident population of orcas that frequents Puget Sound waters.

The eight babies born in 2015 to the southern residents are alive and well, good news for the endangered orcas with only 84 members in three pods, J, K and L.

Only once before, in 1977, were more babies born to the southern residents, with nine calves in all. While the baby boomlet is good news, orcas are still challenged for survival in Puget Sound.

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By contrast, the West Coast transient population of orcas has been growing steadily since the 1970s and is estimated at more than 500 whales, perhaps their carrying capacity, according to the Washington Department of Fish and Wildlife. Offshore killer whales also are estimated at a stable population of about 300 animals.

Southern residents are found coastally from central Southeast Alaska to central California. West Coast transients occur from Southeast Alaska to Southern California. Offshore whales range from the eastern Aleutian Islands to Southern California and probably Mexico. Both the southern residents and transients regularly use the inner marine waters of Washington and British Columbia, but offshores rarely do.

The difference between the struggling southern resident orcas and their thriving neighbors appears to be food.

Transients and offshore killer whales eat marine mammals, including seals. But southern residents primarily eat Puget Sound chinook salmon, a threatened species. Not only are the numbers of wild chinook far lower today than historically, individual fish are smaller. Chinook are hurt, as orcas are, by development, pollution and loss of habitat. Whales are also bothered by vessel noise.

The southern resident orcas that conceived all the babies born this year probably did so while outside of their home waters — perhaps because they were in search of food, said Deborah Giles, research director for the Center for Whale Research in Friday Harbor. The summer 2013-14 that the babies were conceived coincided with the lowest number of southern resident sightings in local waters since 1976, Giles said.

Scientists at the Center for Whale Research are investigating whether social dynamics amid the southern residents are changing because of their constant search for food. They may no longer be living in the same tightly organized pods that researchers have documented in the past. Researchers from Canada’s Department of Fisheries and Oceans are also observing similar fragmentation of the familiar pod structure in the northern resident community, which primarily uses the waters in Johnstone Strait and northern Vancouver Island.

The cause of death of the young whale found this week has not been determined. A necropsy is being done by the Department of Fisheries and Oceans.

Killer whales have been listed as a state endangered species in Washington since 2004 and as a federally endangered species since November 2005.

The southern residents’ numbers have been relatively stable since 2001, but remain 17 percent below their recent peak population of 98 whales recorded in 1995. Their population growth also remains below the goals set by the federal government in its 2008 recovery plan.

In a draft state periodic status review for killer whales released this month, the state Department of Fish and Wildlife recommended orcas continue to be listed as a state endangered species.

Killer whales, actually the world’s largest dolphins, live in all the oceans.

Survival rates are lowest amid the small calves and oldest orcas, with about 43 percent of small calves dying. For calves that survive their first six months, life span can be as long as 100 years in females and 70 years in males.

On average, it takes a female 14 years to reach maturity to produce her first calf, and a female will give birth about five times.

Southern residents are spectacular swimmers, diving as deep as 866 feet. They also travel widely for food.

Brad Hanson, a wildlife biologist at the Northwest Fisheries Science Center in Seattle tracks the orcas’ diet and travels. His research has documented the pathos of one listed species depending on another for survival.

One orca male Hanson tagged and tracked in winter 2012-13 ranged up and down the coast as far as California at least three times, and hung around the mouth of the Columbia River just in time for the spring run of threatened chinook — the biggest and fattiest salmon of them all.