The killer whales, also called orcas, stay off the coast of the Pacific Northwest, near Washington State, Oregon and British Columbia. According to the Marine Mammal Commission, the SRKW population may have historically numbered more than 200 animals prior to the 20th century. Their numbers plummeted due to loss of prey, opportunistic hunting prior to the 1960s and the live capture of nearly 70 Resident and Transient killer whales for marine parks from 1967 to 1971, the commission found. There were only 88 of the iconic whales left when they were listed as endangered in 2005, The New York Times reported, and the population has continued to dwindle since. The birth of the newest orca, called J57, brings the population to 73.

"It's a bit of a nail-biter right now," whale researcher Dr. Deborah Giles from the Center for Conservation Biology told The New York Times. "I can't help but be thrilled that she had this baby and this baby didn't die right away. Everybody is worried and on pins and needles, wondering if this calf is going to make it."

"With such a small population … every successful birth is hugely important for recovery," said a blog post from SR3, the marine conservation group that used drone footage to confirm J35's pregnancy in July and monitor her condition.

Several factors have hurt the population's chances of rebounding, including food scarcity, toxic pollutants that bioaccumulate, and noise pollution, the news report said.

The whales are "essentially starving," reported Smithsonian Magazine. Eighty percent of the SRKW's diet consists of Chinook salmon, the Center for Whale Research wrote. The salmon have declined "significantly" due to commercial fishing and widespread habitat destruction, according to the Marine Mammal Commission.

Government reports also found that agricultural pesticides jeopardize the survival of the salmon. Then, when the orcas eat polluted fish, the chemicals and pesticides eventually end up stored in the whales' fat, suppressing their immune systems, leaving them vulnerable to disease and affecting females' ability to reproduce, reported Smithsonian Magazine.

Additionally, according to the Georgia Straight Alliance, noise disrupts the whales' echolocation and prevents them from hunting, navigating and communicating.

"Both the physical presence of vessels and associated underwater noise hinders Southern Residents' ability to perform basic life activities," the Alliance reported.

To make matters worse, many of the population's pregnancies fail, and around 40% of calves die within their first year, The New York Times reported. Recent scientific findings suggest that these reproductive failures and high calf mortality rates are linked to malnutrition and lack of their preferred salmon prey, reported the Marine Mammal Commission.

With nothing to eat and nowhere to live, the Southern Resident orcas have thus become a symbol for animals on the brink of extinction. J35 became the poster child for her population during her 17-day "tour of grief," catalyzing many groups to call for new protections for the endangered whales.

According to the Center for Whale Research, J52, another two-and-a-half-year-old calf from the J-pod, died presumably from malnutrition one ear earlier.

After the 2018 loss of J35's previous calf, Ken Balcomb, founder of the Center for Whale Research, estimated that the SRKW population only had about five years to rebound or face irreversible decline.

"We've got at most five more years of reproductive life in this population to make it happen"— meaning, to have viable offspring — "but if we don't do it in those five years it isn't going to happen," he told National Geographic in 2018.

That's why, with the birth of J57, researchers are cautiously optimistic.

The encounter report from the Center for Whale Research announcing J57's birth said, "Her new calf appeared healthy and precocious, swimming vigorously alongside its mother in its second day of free-swimming life … We hope this calf is a success story."

Balcom said, "The baby looked very robust and lively, so I have good expectations for this one surviving," reported The New York Times.

He told The New York Times he hoped that recent efforts such as the removal of a dam on the Elwah River would bring back more robust runs of Chinook salmon and issue a turning point for the orcas.

"This new birth brings new hope – for Tahlequah and for all of us," wildlife photographer Alena Ebeling-Schuld told The Guardian. "I am wishing Tahlequah and her new little one the very best with all of my being."