The endangered southern resident killer whales which are normally spotted in the Salish Sea near Vancouver throughout June, haven't been seen by researchers or whale watchers in the area and the absence is considered highly unusual for this time of year.

"We believe that is because there currently aren't enough chinook salmon returning to the river area. So they have to be somewhere else to get food," said Joan Lopez, a marine naturalist with Vancouver Whale Watch, a tourism outfit.

On one of the final days in June, tourists with binoculars and cameras watched as a group of 14 transient killer whales swam off the coast of Vancouver. These orcas are a different type of killer whale and eat seals — unlike the southern residents, whose diet only consists of fish.

Joan Lopez, a marine naturalist with the guiding company Vancouver Whale Watch photographs transient killer whales and explains to tourists why the southern resident whales likely aren't around. (Chris Corday/CBC)

The southern residents' range extends from southeast Alaska to central California, but during the summer months they feed and live in the Salish Sea.

While seals are plentiful in the coastal waters of B.C. and Washington, chinook salmon — the southern residents' main prey during the months of May to August — are not.

"These whales are not getting enough to eat at any time in the year," said Deborah Giles, the director of science and research at Wild Orca, a U.S. based non-profit.

Giles, who is also a lecturer at the University of Washington, is part of a team that uses dogs to sniff out whale scat in the water, but she had to delay the start of her studies this year because the southern residents haven't been around.

In previous years, the fecal samples were analyzed in a lab for a range of substances including stress and pregnancy hormones, as well as toxins. Giles is a local coordinator for the project, which is run by the University of Washington's Center for Conservation Biology.

A dog with the group, Conservation Canines, sniffs the water to try detect whale scat. (Submitted by Maria Nangle and Alexandra Johnson)

Malnourished whales

Giles said compared to the mammal eating transient whales, the southern residents look like "minnows."

"You never should see whale bones on a living whale and we can sometimes see the outline of a rib cage or the head on these whales."

It's believed there are currently 76 southern residents as one of the last times the orcas were spotted back in May, a new calf was seen swimming alongside the rest of J-pod, one of the three groups that make up the population.

It was in that same pod last year that an orca carried her dead calf for 17 days in an apparent act of grief.

David Huff with the U.S. National Oceanic and Atmospheric Administration watches a fish in the recovery tank, after it had a tracking tag surgically inserted into its stomach. (Briar Stewart/CBC)

Giles said the whales are social animals and exhibit cultural behaviour.

She said back in the 1990s, one of the southern residents started catching fish and draping them across its head. By the end of the season, they were all doing it.

Her hope is that one day, one of the orcas decides to expand their diet and nibble on something else.

"If we can get that sort of individual that just takes a bite out of a seal or porpoise and then have that behaviour transmit culturally through the population, that would be amazing."

But for now the southern residents' diet still consists of salmon. With certain fish populations dwindling, scientists are trying to get a better idea of what fish populations are the most important for the killer whales.

Salmon surgery

Off the coast of Washington State, a team with the U.S. National Oceanic and Atmospheric Administration have been using a 24-metre long vessel as a salmon surgical ward, as part of a research project to tag and track 300 juvenile chinook.

A CBC crew accompanied them on a trip at the end of May when the boat was off the coast of Washington's Olympic Peninsula.

A researcher with the U.S. National Oceanic and Atmospheric Administration stitches up a chinook salmon after inserting a tracking tag. (Chris Corday/CBC)

As each fish was caught, they were placed in a cooler filled with clove oil and water for four minutes. The mixture acts as an anesthetic and once the fish were asleep, scientists took samples of their scales and made a small incision in the abdomen.

An acoustic tag was then inserted, and the fish were stitched back up and put into "recovery" — a cooler filled with ocean water.

Once the salmon began to swim around, they were released back into the Pacific Ocean.

Deborah Giles and a crew on board the research vessel have been studying the southern resident killer whales off Washington State's San Juan Islands. (Submitted by Northwest Fisheries Science Center)

Tracking orca food

The acoustic tags communicate with receivers that have been placed underwater, affixed at different depths to biodegradable sandbags. Once data is downloaded, the scientists will have a better sense of the chinooks' movements.

"If we understand the movement of the prey ... we can understand more about what the killer whales have to do in order to find those prey," said David Huff, a manager for NOAA's Fisheries Estuary and Ocean Ecology Program.

Similar research is ongoing in Canada, as researchers at the University of British Columbia are aiming to tag 100 adult chinook.

Huff believes the data they are collecting can help shape future government policy on how to protect the salmon and in turn the southern residents whose survival depends on them.

"There's been a tremendous interest in the United States, and in Canada as well, into the plight of the southern resident killer whales," he said.

"I think it really has raised awareness of what might be happening out in the ocean."

For more on the future of the southern resident killer whales check out a new CBC British Columbia podcast beginning July 18. Killers: J pod on the brink is hosted by Gloria Macarenko.