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Northern and southern resident orcas hunt differently, which may help explain the decline of southern orcas



A southern resident orca preying on salmon in the Salish Sea near Seattle. Credit: Su Kim/NOAA Fisheries

In the Pacific Northwest and British Columbia, scientists have been sounding the alarm about the plight of southern resident orcas. Annual counts show that population numbers, already precarious, have fallen back to mid-1970s levels. Most pregnancies end in miscarriage or death of the newborn. They may not be catching enough food. And many elderly orcas—particularly post-reproductive matriarchs, who are a source of knowledge and help younger generations—have died.

With just 73 individuals left, conservationists and members of the public alike are concerned that southern resident orcas may not survive.

Yet over the same period, the region’s northern resident orcas, who have a similar diet and an overlapping territory, grew steadily in . Today, there are more than 300 northern resident orcas, leaving scientists wondering why these two similar but distinct populations have had such dissimilar fates over the past half century.

A new study led by scientists at the University of Washington and NOAA Fisheries reveals that the two populations differ in how they hunt for salmon, their primary and preferred food source. The research, done by an international team of government, academic and nonprofit researchers, was published in Behavioral Ecology.


“For northern resident orcas, females were hunting and capturing more prey than males. For southern resident orcas, we found the opposite: The males were doing more hunting and capturing than females,” said lead author Jennifer Tennessen, a senior research scientist at the University of Washington’s Center for Ecosystem Sentinels.

“We also found that if their mother was alive, northern resident adult males hunted less, which is consistent with previous work, but we were surprised to see that southern resident adult males hunted more. Adult females in both populations hunted less if they had a calf, but the effect was strongest for southern residents.”

Northern and southern resident orcas hunt differently, which may help explain the decline of southern orcas
A southern resident orca in 2010. Credit: NOAA

The study’s five years of observational data show that southern resident males catch 152% more salmon per hour than females. In other words, for every two fish a southern female caught, a southern male would catch five. For the growing northern resident population, the trend is flipped: females caught 55% more salmon per hour than males.

This is the first study to track the underwater pursuit, hunting and prey-sharing behaviors of both northern and southern resident orcas. Their findings reveal that, though the two populations overlap significantly in territory and have similar social structures and reproductive behavior, they should not be treated identically for conservation purposes.

“In the past, we’ve made assumptions about these populations and filled in the gaps when designing interventions, particularly to help the southern resident orcas,” said Tennessen, who conducted this study while she was a research scientist with NOAA’s Northwest Fisheries Science Center. “But what we found here are strikingly different patterns of behavior with something as critical to survival as foraging. And as we develop management strategies, we really need to consider these populations differently.”

NOAA scientists and an international team of collaborators temporarily tracked the movement, sounds, depth and feeding behaviors of 34 northern and 23 southern resident adult orcas non-invasively from 2009 to 2014 using “Dtags,” cellphone-sized digital devices. Dtags attach via suction to the back of an orca and, for this study, were programmed to fall off hours later and float back to the surface so the researchers could collect them and download their data.

As the name would suggest, northern resident orcas have a more northerly distribution, preferring waters around Vancouver Island and the Queen Charlotte Strait. In contrast, core areas for southern resident orcas hug the southern reaches of Vancouver Island, inland waters surrounding the San Juan Islands, Puget Sound and the Washington coast.

Both populations were devastated by the capture of orcas for theme parks, a practice that ended in the 1970s. Since then, northern resident orcas have increased steadily, seeing at least 50% growth since 2001.

Northern and southern resident orcas hunt differently, which may help explain the decline of southern orcas
A southern resident orca calf and its mother in 2004. Credit: NOAA National Ocean Service

Both populations hunt for salmon using echolocation. Adult orcas can dive at least 350 meters—or 1,150 feet—to pursue fish on their own, though they often bring kills to the surface to share with others.

Pods travel between the outflows of major rivers and streams in British Columbia and Washington, and have been heavily impacted by dams that have reduced salmon runs. Increased vessel traffic and noise in the Salish Sea—from tourism, recreation and shipping—have also negatively affected these populations, particularly the southern resident orcas, according to Tennessen.

This new study showed that southern residents had fewer successful hunts overall, indicating that they were presumably catching less food. This impact is particularly evident with young mothers.

“In both populations, a mother with a young calf foraged less than other females, possibly due to the risk of leaving the calf temporarily with ‘a babysitter’—another adult—while she hunts, or because of the time demands of nursing a calf,” said Tennessen. “But for southern resident females, which are more prone to disturbance and stress from vessel traffic, there was an outsized effect: Our study found no instance of a southern resident female with a young calf who successfully carried out a hunt.”

The study also has much to say about the impact of elderly female orcas on their adult sons. Both northern and southern resident orcas are grouped into matriarchal clans, often led by post-reproductive females. They also help feed their adult sons even, as a recent study led by the nonprofit Center for Whale Research showed, at the expense of their own reproductive capacity.

The new study adds complexity to the role of elderly females. Among northern resident orcas, adult males with a living mother hunted less than adult males without a living mother, perhaps because the mother still provides food. But among southern resident orcas, the opposite is true: Adult males with a living mother hunted more.

Northern and southern resident orcas hunt differently, which may help explain the decline of southern orcas
A NOAA scientist observing southern resident orcas from a research boat. Credit: Northwest Fisheries Science Center/NOAA Fisheries

“These unexpected differences left us scratching our heads. It is possible that southern resident adult males could be sharing with other members of their group, including their mothers, to help out, especially since an adult male’s survival is strongly linked to his mother’s survival,” said Tennessen.

“Relatedly, southern resident matriarchs may be leading the group to areas where their adult sons may be able to capture more prey, since healthier sons might be more successful at mating and passing along some of their mothers’ genes. We need more studies to determine what role the presence—or absence, for southern resident orcas—of matriarchs has on male foraging behavior.”

Future studies on the behaviors of northern and southern resident orcas could bring these differences to the surface, as could studies of Alaska resident orca populations, which forage for salmon farther north, where salmon stocks are generally healthier. Such comparative studies can help isolate cause and effect, said Tennessen.

“Understanding how healthy populations behave can provide direction and goals for management of unhealthy populations,” said Tennessen. “Future comparisons to healthy fish-eating populations could help us understand whether the divergent behavior we’re seeing in the southern residents is indicative of a population trying to survive.”

More information:
Jennifer B Tennessen et al, Divergent foraging strategies between populations of sympatric matrilineal killer whales, Behavioral Ecology (2023). DOI: 10.1093/beheco/arad002

Provided by
University of Washington


Northern and southern resident orcas hunt differently, which may help explain the decline of southern orcas (2023, March 10)
retrieved 10 March 2023

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High-risk places affected by respiratory outbreaks



A respiratory virus outbreak has been declared at Southbridge Lakehead long-term care home.

The outbreak is facility-wide at the Vickers Street home. Restrictions are in place on admissions, transfers, discharges, social activities and visitation until further notice.

There are now four active respiratory outbreaks in high-risk settings in the Thunder Bay district, including at Hogarth Riverview Manor on the first floor and 2 North and on Plaza 1 at Pioneer Ridge.

A facility-wide COVID-19 outbreak is also ongoing at the Manitouwadge Hospital.


There are no active influenza outbreaks in the district.

The Thunder Bay District Health Unit reports that emergency department visits because of respiratory-related complaints have decreased and are at seasonal levels in its catchment area and the influenza A surge overall has subsided with the peak in cases and hospitalizations having taken place in November of 2022.

COVID-19 does continue to circulate with 104 new lab-confirmed cases in the last seven days.

Hospitalization numbers are stable with 23 people in the hospital with COVID in the district, including three in intensive care units.

The health unit continues to stress the importance of precautions like getting the annual flu vaccine and latest COVID booster as well as wearing a face mask, particularly indoors and crowded places. Also, stay home when sick.



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WHO advisers to consider whether obesity medication should be added to Essential Medicines List



Advisers to the World Health Organization will consider next month whether to add liraglutide, the active ingredient in certain diabetes and obesity medications, to its list of essential medicines.

The list, which is updated every two years, includes medicines “that satisfy the priority health needs of the population,” WHO says. “They are intended to be available within the context of function health systems at all times, in adequate amounts in the appropriate dosage forms, of assured quality and at prices that individuals and the community can afford.”

As the market for new weight loss drugs soars, people with diabetes pay the price


The list is “a guide for the development and updating of national and institutional essential medicine lists to support the procurement and supply of medicines in the public sector, medicines reimbursement schemes, medicine donations, and local medicine production.”

The WHO Expert Committee on the Selection and Use of Essential Medicines is scheduled to meet April 24-28 to discuss revisions and updates involving dozens of medications. The request to add GLP-1 receptor agonists such as liraglutide came from four researchers at US institutions including Yale University and Brigham and Women’s Hospital.

These drugs mimic the effects of an appetite-regulating hormone, GLP-1, and stimulate the release of insulin. This helps lower blood sugar and slows the passage of food through the gut. Liraglutide was developed to treat diabetes but approved in the US as a weight-loss treatment in 2014; its more potent cousin, semaglutide, has been approved for diabetes since 2017 and as an obesity treatment in 2021.

Ozempic prescriptions can be easy to get online. Its popularity for weight loss is hurting those who need it most


The latter use has become well-known thanks to promotions from celebrities and on social media. It’s sold under the name Ozempic for diabetes and Wegovy for weight loss. Studies suggest that semaglutide may help people lose an average of 10% to 15% of their starting weight – significantly more than with other medications. But because of this high demand, some versions of the medication have been in shortage in the US since the middle of last year.

The US patent on liraglutide is set to expire this year, and drugmaker Novo Nordisk says generic versions could be available in June 2024.

The company has not been involved in the application to WHO, it said in a statement, but “we welcome the WHO review and look forward to the readout and decision.”

“At present, there are no medications included in the [Essential Medicines List] that specifically target weight loss for the global burden of obesity,” the researchers wrote in their request to WHO. “At this time, the EML includes mineral supplements for nutritional deficiencies yet it is also described that most of the population live in ‘countries where overweight and obesity kills more people than underweight.’ “

WHO’s advisers will make recommendations on which drugs should be included in this year’s list, expected to come in September.

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“This particular drug has a certain history, but the use of it probably has not been long enough to be able to see it on the Essential Medicines List,” Dr. Francesco Blanca, WHO director for nutrition and food safety, said at a briefing Wednesday. “There’s also issues related to the cost of the treatment. At the same time, WHO is looking at the use of drugs to reduce weight excess in the context of a systematic review for guidelines for children and adolescents. So we believe that it is a work in progress, but we’ll see what the Essential Medicines List committee is going to conclude.”


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Some pediatric surgeries may be postponed as pediatric ICU faces strain: Shared Health



Re-emerging levels of respiratory illness have caused increased patient numbers at the HSC Children’s pediatric intensive care unit over the last week, and some non-urgent procedures may be postponed, Shared Health says.

On Thursday morning, there were 17 pediatric patients in the intensive care unit, and a considerable number of which were already experiencing health issues that were aggravated by respiratory illness. The unit’s normal baseline is nine, Shared Health said in a Thursday media release.

The release said patient volumes at the children’s emergency department are stable but more children with flu-like symptoms have been recorded coming in over the last two weeks, going from a low of 22 in mid-March to 47 on Wednesday.

A variety of respiratory illnesses are spreading through the community and have contributed to the increased level of patients in the pediatric intensive care unit, according to Shared Health.


Meanwhile, the number of patients in the neonatal intensive care unit was at 51 on Thursday morning, which is slightly above the unit’s normal baseline capacity of 50.

Ten staff are being temporarily reassigned to the pediatric intensive care unit to deal with the increased level of patients, the release said.

Some staff are being pulled from the pediatric surgical and recovery units, which means non-urgent procedures may be postponed due to the reassignments, Shared Health said.

Families of patients impacted by the postponements will be contacted, they said, and all urgent and life-threatening surgeries will go unhindered.

Families can protect their children from respiratory illnesses by limiting their contact with people exhibiting cold-like symptoms, washing their hands frequently and staying up to date on vaccinations, Shared Health said.

Patient volumes increased last month

While overall wait times at emergency and urgent care centres were stable in February, Shared Health said daily patient volumes in the province went up.

The daily average of patients seeking care was 750 last month, which is an increase from 730.4 in January, according to a separate Thursday news release.

The average length of stay for patients in emergency or urgent care units to be transferred to an inpatient unit went down to 21.77 hours last month, which is an improvement from 22.5 hours in January, the release said.

The overall number of people who left without being seen went down last month, from 13 per cent in January to 12.1 per cent in February, according to Shared Health. It also decreased at the HSC emergency department, from 25 per cent in January to 23.4 per cent last month.

Shared Health is reminding Manitobans to continue to call 911 in case of an emergency, and said the sickest and most injured patients will remain their priority.



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