How the changing Arctic is testing the limits of walrus survival
A silent crisis is unfolding in the warming Arctic. As sea ice—the essential platform that walruses depend on for rest, breeding, and access to food—retreats further from coastal feeding areas, these iconic marine mammals face an escalating energy challenge. Understanding exactly how walruses use energy, both while resting and swimming, has become critical to predicting their fate in a changing climate. Recent scientific breakthroughs studying juvenile walruses have revealed surprising metabolic secrets that illuminate the precarious balance these animals must strike to survive.
The Arctic is warming at approximately three times the global average rate, causing dramatic reductions in summer sea ice coverage 2 .
The Arctic is warming at approximately three times the global average rate, causing dramatic reductions in summer sea ice coverage. For walruses, this represents an existential threat to their feeding strategy 2 .
Walruses have evolved to use sea ice as a moving platform that transports them between shallow feeding areas rich in clams, their primary food source. Traditionally, walruses rest on ice edges positioned directly over these productive clam beds, requiring minimal swimming between resting and feeding areas 2 .
As ice retreats further from coastlines, walruses face two difficult choices:
Both scenarios dramatically increase energy expenditure at a time when food may be harder to obtain 2 .
Visualization of September Arctic sea ice extent showing dramatic decline over recent decades.
To grasp why walrus metabolism matters, we must first understand some key concepts. An animal's metabolic rate is essentially the speed at which it burns energy to power everything from basic bodily functions to intense physical activity 1 .
The energy needed for basic life functions while at complete rest, under strict conditions including being awake but calm, and within a comfortable temperature range 1 .
Similar to BMR but with less strict conditions, often measured in animals that are resting but not necessarily meeting all BMR criteria 1 .
The total energy expenditure of free-living animals, including costs for foraging, migrating, and reproducing 1 .
For walruses and other marine mammals, these measurements are crucial for calculating how much food individuals need to survive and how environmental changes might tip the balance toward starvation 1 .
Survival = Energy Intake - Energy Expenditure
When energy expenditure exceeds intake over time, animals face:
To understand the true energetic impact of these environmental changes, Dr. David Rosen from the University of British Columbia conducted pioneering research at the Vancouver Aquarium with two juvenile walruses named Balzak and Lakina 2 .
The study employed sophisticated but animal-friendly techniques to measure energy expenditure under different conditions:
The walruses were trained to rest comfortably at the water's surface with their heads inside a custom-built floating respirometry dome. This dome precisely measured their oxygen consumption, allowing scientists to calculate their resting metabolic rate 2 .
To measure energy expenditure during swimming, the walruses were trained to swim multiple laps underwater before surfacing into the respirometry dome. This allowed researchers to capture their oxygen consumption immediately after activity, indicating the metabolic cost of swimming 2 .
The research continued over a remarkable 13-month period, providing insights into how metabolism might vary across seasons and as the animals grew 2 .
| Research Tool | Function | Application in Walrus Study |
|---|---|---|
| Floating Respirometry Dome | Measures oxygen consumption to calculate metabolic rate | Used for both resting and post-swim measurements |
| Animal Training Protocols | Enables voluntary participation in studies | Allowed safe collection of metabolic data without restraint |
| Doubly-Labeled Water Method | Tracks energy expenditure in free-living animals | Gold standard for field metabolic studies 4 |
This partnership between research institutions and aquariums has proven invaluable in collecting data that would be nearly impossible to obtain from wild animals .
The findings overturned previous assumptions about walrus energetics and revealed why climate change poses such a severe threat.
The study found that walruses have relatively low resting metabolic rates compared to other young pinnipeds 2 . This metabolic thriftiness might suggest walruses are well-adapted to conserve energy. Researchers observed considerable variability in RMR for each walrus during the year that couldn't be explained by changes in body mass alone 2 .
The modest energy savings at rest were dramatically overshadowed by the high cost of swimming. Walruses expended approximately twice their resting metabolic rate while swimming 2 . Their unique body shape—less streamlined than seals and sea lions—resulted in higher locomotor costs than predicted for most marine mammals 2 .
| Animal Group | Mean BMR as Multiple of Kleiber | Species Examples |
|---|---|---|
| Walrus (Odobenid) | 2.93 | Odobenus rosmarus |
| Otariids (Eared Seals) | 3.01 ± 0.37 | California sea lion, Steller sea lion |
| Odontocetes (Toothed Whales) | 2.18 ± 0.78 | Bottlenose dolphin, Killer whale |
| Phocids (True Seals) | 1.32 ± 0.31 | Harbor seal, Harp seal, Weddell seal |
Note: Kleiber's law describes the allometric relationship between metabolic rate and body mass across species. A value of 1 would match the expected metabolic rate for an average mammal of that size. Data compiled from studies using 'gold standard' methodologies 1 .
The long-term nature of the study revealed additional complexities:
This combination of low resting metabolism but high swimming costs creates a perfect metabolic storm in a changing climate: the very adaptation that helps them survive lean periods becomes irrelevant when they're forced to swim long distances to feed.
The metabolic findings from this research have been incorporated into bioenergetic models that predict how walruses will respond to continued environmental change 2 . These models reveal that the already-high energy costs of swimming will increase substantially as walruses are forced to travel farther between resting and feeding areas.
The situation creates a dangerous energy deficit cycle: more energy expended on swimming means more clams needed to break even, but longer feeding times require even more swimming. For young, old, or nutritionally stressed animals, this cycle may become impossible to overcome.
"If we have a choice between two scenarios, we can now predict what is going to have the greatest effect on these individual animals. This helps us determine the times of the year and the areas where industrial development will have less impact." — Dr. David Rosen
The walrus metabolic study represents a growing trend in conservation physiology—using detailed physiological measurements to predict how species will respond to environmental change .
Similar approaches are being used with other vulnerable species, including Steller sea lions, whose populations have declined by up to 85% in some regions, possibly due to changes in food availability . By understanding the precise relationship between food intake, growth, and metabolism, scientists can better identify the threats facing these animals and propose targeted conservation strategies.
The story of walrus metabolism underscores the complex interplay between animal physiology and ecosystem stability. As Arctic ice continues to retreat, the extraordinary adaptations that have served walruses for millennia are being tested beyond their evolutionary limits. The scientific insights gained from studying these magnificent creatures not only illuminate their precarious present but also equip us with the knowledge to make more informed decisions about protecting their future in a rapidly changing world.