Where do they live? What do they eat? What can we do to help them? Seattle Times environment reporter Lynda Mapes answers common questions about the region's orcas.

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The Seattle Times has been covering the plight of the southern resident killer whales, which have lost three members this summer. Another orca, K25, is ailing — while at least three females are pregnant.

The Pacific Northwest’s orcas are at grave risk of extinction.

Here’s a primer on why:

Who are they?

The southern resident orcas are a unique population of killer whales. They are critically endangered, with an extended family of only 74 members in three pods, named J, K and L.

What is an orca?

An orca, or killer whale, is actually not a whale at all, but the largest member of the dolphin family. Orcas live in every ocean of the world. Part of the suborder of mammals called toothed whales, they have 10 to 13 conical teeth in each jaw that interlock to crush and shred their prey. Apex predators with almost no enemies, only large sharks can challenge them.

The pods have intensely strong family bonds, staying together through the generations for life. They share food, sleep together, play, hunt, explore and travel as a group.

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Orcas swim about 75 miles per day traveling 8 mph on average, however they can burst through the water at 30 mph when they choose. Each black and white orca has a unique grey saddle patch on its back, enabling researchers to identify them individually.

Their dorsal fins also often are distinguishing, with unique scarring and shape. Playful and athletic, orcas can leap from the water in a spectacular behavior called breaching. They spy hop to take a look around, belly flop, roll and slap their dorsal and pectoral fins. Yet they are big animals, typically up to 26-feet long and weigh as much as 12,000 pounds for males, and 23-feet long and 6,000 pounds for females. Males can sprout a dorsal fin as tall as 6 feet at sexual maturity.

With brains larger than a human’s, orcas use language to communicate. Each pod has calls unique to them and their calls can travel as far as 10 miles underwater. Above the water, orcas have excellent vision, good as our own. Underwater even in the dark they are just as acute, using echolocation to “see” their prey, even to the size and the species of fish.

What do orcas eat?

Orcas have the most varied diet of any whale, dolphin or porpoise, and can take on prey of all types, from stingrays to salmon, depending on the type of orca. They often hunt as a pack, like wolves. The southern residents are strictly fish eaters, consuming as much as 386 pounds of fish a day, and pregnant females need even more. They have a distinct culture, including their own language. Theirs is a matriarchal culture, with the oldest female leading each pod.

There are three types of killer whales in the northeastern Pacific:

  • northern residents and southern residents, both of which primarily eat chinook
  • transients, also called Bigg’s killer whales, which eat marine mammals, including seals, sea lions, dolphins and even minke whales
  • offshore killer whales, which eat fish and squid, and even sharks

Where do the southern residents live?

The southern residents’ primary habitat is wide-ranging, from the inner waters of Puget Sound, to the U.S. and Canadian waters of the Salish Sea, and along the west coast of Washington, Oregon and California.

When are they most often seen?

Southern resident killer whales typically are seen in the the Salish Sea from spring through summer, especially around southern Vancouver Island, the Strait of Juan de Fuca, and south and west of San Juan Island, as they follow Fraser River chinook runs. In fall, they will follow chum runs all the way into central Puget Sound. In winter they expand their range, following food along the outer coast, from as far north as Haida Gwaii in B.C. to as far south as California’s Monterrey Bay.

Why are the southern residents in trouble?

There are at least three primary threats to the survival of the southern residents.

Their main food, chinook, is in decline in the southern residents’ home waters, denying them a consistent, adequate food supply.

Vessel noise underwater also disrupts their ability to hunt.

And when they can’t get enough to eat, orcas burn their fat to survive, releasing toxins stored in their blubber, compromising their immune system.

These three threats — most especially being food-limited — also have hurt the orcas’ ability to reproduce. The southern residents have not had a successful pregnancy in three years.

Do you have a question about the orcas? Ask it here.