Data spanning nearly half a century shows that endangered southern resident killer whales are spending less time in inland waters, whereas their larger cousins, Bigg’s killer whales, are increasingly present in Puget Sound.

The National Oceanic and Atmospheric Administration southern resident killer whales as endangered in 2005 after rapid population decline in the late 1990s. Now, , split into three pods: J, K and L. Bigg’s — sometimes referred to as transients — are more common, but difficult to count because they travel in smaller groups over wider ranges.

Looking at data from ’s Sightings Archive between 1978 and 2022, ����Ӱ�Ӵ�ý researchers modeled migratory trends based on observations from researchers, recreational boaters and whale watchers. They found that K and L pods are visiting Puget Sound less often, but the J pod remains well represented. The data on Bigg’s corroborates recent results showing a steady increase in inland waters.

The results in PLOS One.

“We do see increasing transient presence over time, but we don’t see a definitive decline or overall increase for the southern residents. Their presence here is much more variable,” said lead author , a UW postdoctoral researcher of marine and environmental affairs.

Key behavioral and subtle physical differences . The southern residents eat salmon, while Bigg’s prey on seals, porpoises and other marine mammals. Seals and sea lions rebounded in Washington after the Mammal Protection Act, which may have drawn Bigg’s killer whales to inland waters, but that doesn’t explain the changing distribution of southern residents.

Because southern residents are organized into tight matriarchal societies led by female elders, researchers believe that social cues may play an important role.

“Does J pod know something that K and L don’t? Or vice versa? We like to think about which pods have really old grandmas left and who’s teaching them where to go,” said co-author , a marine mammal specialist at the National Oceanic and Atmospheric Administration (NOAA), West Coast Regional office.

Policies to protect southern residents typically apply to all pods. With K and L spending more time in coastal waters, NOAA for southern residents in 2021 to include 16,000 square miles of marine waters between the U.S. and Canada border and Point Sur, California.

Measures like the , which encourages commercial ships to slow down where whales are present, aim to mitigate the impact of noise. Boats are also of the southern residents.

Indications of changing habitat have prompted some to question the need for such regulations in Puget Sound, but these results underscore their continued importance.

“Even though we’re seeing less of K and L pods, we still have to think about how our actions impact J pod. They’re still hanging around,” Koehn said.

The study also notes that southern residents and Bigg’s are sharing habitat more often, though it isn’t clear whether they mingle or avoid each other. This raises questions about their relationship and underscores the importance of accounting for both in management decisions.

“Having more transients around could be good for the southern residents, because they eat marine mammals that also eat salmon,” Rand said.

But if the southern residents avoid the transients, their increased presence could be disruptive. Researchers are actively studying threats to the southern residents — including prey availability — to support the imperiled population.

This analysis wouldn’t have been possible without consistent contributions from citizen scientists. People who report whale sightings using apps like Whale Alert help researchers provide data to policymakers, which can be consequential for the whales.

“This study quantitatively shows things that people have been suspecting,” Rand said. “There are more transients here in Washington, but the southern resident’s story is a bit more complicated.”

Additional co-authors include of the Whale Museum and of NOAA Fisheries Northwest Fisheries Science Center.

This study was funded by Washington Sea Grant, NOAA Fisheries West Coast and the Puget Sound Partnership. 

For more information, contact Rand at zrand@uw.edu.

Long baleen whale mothers are more likely to have female calves than males, according to a new study led by the ����Ӱ�Ӵ�ý. The findings contradict a popular evolutionary theory postulating that strong mammals benefit more from birthing males.

In 1973, that fit female mammals can improve their odds for grandchildren by having males. Large strong mothers will raise large strong offspring that, if male, can outcompete other males for mates. But, according to the theory, female fitness is less consequential. The studies backing this argument focused on land mammals, such as deer and elk, and often included just tens or hundreds of animals.

UW researchers tested the theory in marine mammals by comparing maternal length and fetal sex in more than 100,000 baleen whales. They found that the fetal sex ratio skews female for longer — and thus more fit — rorqual whales, the predominant baleen whale family that includes humpbacks and blue whales. The findings, on Sept. 24, suggest that female calves benefit more from heritable fitness than males do.

Carrying and caring for young is exhausting, and whales often breed far from food sources. They must rely on stored fat to sustain themselves and their young during and after pregnancy.

“The question we wanted to answer was: if you are in good condition, if you’re big and fat and you’re going to have a big fat calf that will survive and reproduce — do you want that calf to be a male or a female?” said , a UW doctoral student of quantitative ecology and resource management.

To answer this question, the researchers turned to historical whaling data.

Back in the early 1900s, when people hunted whales, a group from Norway began collecting data on their catch. The practice was codified into a law that required all Norwegian hunters to record the whale’s length, sex and pregnancy status, as well as the sex and size of a fetus. In the 1930s, the Norwegian regulation became international law.

“When they hunted whales, there were often biologists around who were knee-deep in the carcasses, measuring and collecting samples,” Rand said. in 1986 to protect dwindling populations from further decimation. The IWC data, however, is a treasure trove for researchers.

“We have this enormous data set with hundreds of thousands of data points that doesn’t exist for almost any other wild population,” said , a UW professor in the School of Aquatic and Fishery Sciences. In 2023, Branch and Rand helped create an interactive map depicting whale distribution from the data.

The data also gave Rand an opportunity to investigate fetal sex ratios in marine mammals. Experts argue that some animals just after conception. No one knows exactly how this works for mammals, but adapting sex ratios based on physical or environmental conditions is considered advantageous.

“I think for our mammal brains, it is a little bit confusing,” Rand said, “But insects, and ants, have a lot of control over the sex of their offspring, so it’s not entirely surprising that mammals might have a little bit of control.”

In this study, the researchers modeled maternal length against sex for fetuses measuring three feet and longer — the size at which sex becomes evident. They included seven whale species in the rorqual family, totalling more than 100,000 whales.

If the Trivers-Willard hypothesis were correct, researchers would have seen a slight increase in the number of male fetuses as maternal length increased. Instead, they observed a downward trend, indicating that fewer males were born to larger mothers. The results varied some by species: There was a 77% chance that longer female humpbacks have more female calves, and that probability increased to 99% for sei whales.

There are several possible explanations for why these findings flip the Trivers-Willard hypothesis, and the trends observed in land mammals. Some male whales compete for mates, but competition might not be as significant a pressure as female size because small female whales will likely struggle to reproduce and raise healthy young. Big whales, on the other hand, will have big female calves that will grow into long mothers with strong reproductive potential.

For baleen whale mothers, investing energy in female calves is the best way to ensure generations of grandchildren.

Research also suggests that some whale species are , which could spell trouble for future generations if females are unable to support offspring. The findings could have implications for conservation, but Rand said that this will require further research to confirm.

“Previously it was assumed that if you have male-male competition for mates, bigger mothers will have males,” Rand said. “Our paper shows that you can’t make that assumption because there’s also an advantage to being big as a female.”

Other authors include , the Leader of the USGS Washington Cooperative Fish and Wildlife Research Unit and a Professor in the UW School of Aquatic and Fishery Sciences.

This research was funded by the National Oceanic and Atmospheric Administration.

Contact Rand at zrand@uw.edu for more information.