The death of a single wild animal is not usually scientifically significant, but for an endangered species of killer whales, the loss of a young female has some experts worried about the future growth of the population.

There are only 80 whales among the southern residents — a clan of orcas that live in the waters off southern British Columbia and Washington State — and the death of each female is a lost opportunity to increase the pod.

J28 southern resident orca dorsal nick

J28, born in 1992 or 1993, was recognizable by a nick on her dorsal fin, which she sustained in 2002. (Dave Ellifrit/Center for Whale Research)

Ken Balcomb, senior scientist for the Center for Whale Research, said the recently deceased orca called J28 follows a trend of females dying either late in pregnancy or not long after giving birth.

"This has got to stop," he said. "The population is not going to recover if we don't have reproductive females." 

J28 gave birth to a male calf in October last year. Researchers noticed something was wrong last January, Balcomb said, when she began losing weight.

J50 female baby orca

J50 and her brother J26 off San Juan Island, Wash. J50 is known for her 'rambunctious behaviour and seeming joie de vivre,' according to Michael Harris of the Pacific Whale Watch Association. (Janine Harles/Puget Sound Express Whale Watching)

The 23-year-old orca died in October near the Juan de Fuca Strait that separates Vancouver Island from Washington state.

Her new-born calf also looked thin, and Balcomb said his survival without a mother was unlikely.

Low food supply, toxins suspected

J28's body was not recovered, so the cause of death remains uncertain, but Balcomb said he suspects an inadequate food supply and toxins are to blame.

Killer whales have been found to carry high levels of toxins in their blubber, the result of pollutants in the water and in their food.

Orca J54 and J28

Newborn orca J54 swims alongside its mother J28 after being born in Haro Strait. (Dave Ellifrit/Center for Whale Research)

The whales — and the neighbouring northern residents, which ply the waters off B.C. and Alaska — rely predominantly on chinook salmon, but also eat chum and coho.

Balcomb said in years in which chinook and other fish stocks are poor, the orcas are forced to metabolize their blubber, subsequently releasing toxins into their blood and organs.

Hunger is particularly problematic for pregnant orcas that need extra food to carry their babies to term, he said.

Another female orca died over the summer, and more than 50 per cent of pregnancies end in miscarriage.

Aerial photos show good condition

But Lance Barrett-Lennard, director of cetacean research at the Vancouver Aquarium, said aerial photos he has been collecting on southern residents don't show the appearance of starving whales, despite a poor chinook run this year.

Barrett-Lennard said the photos, collected in partnership with the U.S. National Oceanic and Atmospheric Administration, provide accurate information on the orcas' body composition.

Images captured in September found that although the orcas were thinner compared with images captured in Sept. 2015, they appeared to be in generally good condition.

New orca calf

New orca calf J55 swims in Puget Sound (NOAA Fisheries)

"Most of them are not emaciated by any means," he said. "[J28] was the outlier, she was the unusual one."

That doesn't rule out the possibility that J28 died as a result of an illness triggered by toxins.

John Ford, a research scientist for Canada's Fisheries Department, said there are a lot of uncertainties about how toxins affect orcas, but most researchers believe they suppress their immune systems, making them more susceptible to diseases.

'Make their habitat better'

The effects of toxins also appear to vary between pods, which leaves researchers with even more questions about how to protect the orcas, Ford said.

Efforts to increase salmon stocks and other environmental protections that include monitoring and restricting shipping traffic and industrialization of the coast are in place to give the orcas a better chance at survival, Ford said. 

Orca J53

J53, a female calf born as part of the 2015 southern resident killer whale 'baby boom.' (Jill Hein and Sara Hysong-Shimazu/Center for Whale Research)

"All you can do is make their habitat better for them," Ford said.

While the population of the southern residents is down, Ford said the whales aren't in crisis yet. Their numbers are stronger than they were in the 1970s, when they dwindled to only 71 orcas.

Northern residents are faring even better, with a population of about 300. 

Orphan Orca 20130708

Springer the killer whale swims with her calf near Bella Bella, B.C., in this undated handout photo. (The Canadian Press/Cetacean Research Program)

But Balcomb said the death of J28 should sound an alarm that stricter measures are needed to limit fishing and environmental degradation of rivers and waterways, including the installation of dams, to protect the orcas' food supply and prevent more deaths.

"It is a human problem, but the whales are suffering from the effects of these problems," he said.