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What Our Research
Has Uncovered

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Analysis Of Our
Steller Sea Lions

The Steller sea lions at the Aquarium have helped us make a number of important scientific advances, improving our understanding of:

  • The energy requirements of Steller sea lions
  • The relationship of diet to sea lion health
  • The nutritional requirements and the value of different diets (such as pollock and herring)
  • Validating methods of studying sea lions in the wild

All of these components are key to testing the nutritional stress hypothesis and enabling us to apply the results to wild populations.

Steller Sea Lions
Steller Sea Lions Credit: Andrew Trites

Effects Of Diet

The nutritional stress hypothesis considers what happens when sea lions are forced to change diets from fatty, high-energy prey, such as herring, to leaner, lower-energy fish, such as pollock. Such a shift appears to be occurring in parts of the North Pacific and lies at the heart of the nutrition stress hypothesis. Consortium researchers recorded the effects of switching the diets of sea lions on their metabolic and growth rate. Research concluded that sea lions use more energy to digest pollock over herring and squid due to the high proportion of bony material in pollock.

Energetic Models

Traditionally, researchers rely on stomach content analysis from wild sea lions, but this is difficult to obtain. It’s also difficult to approximate conditions in the wild when researching small captive populations. A third option, the development of a bioenergetics model, was conducted by UBC’s Arliss Winship in Alaska. This estimated the amount and type of fish necessary to support each population (in effect, evaluating the nutritional stress hypothesis). A change in the energy density of a sea lion’s diet led to significant changes in the amount of fish the animal needed to eat.

Steller Sea Lions Credit: Andrew Trites
Steller Sea Lions Credit: Andrew Trites

Fasting Mechanisms

It is important to understand the physiological mechanisms Steller sea lions use to cope with poor nutrition and to develop methods of detecting this condition in the wild. The Consortium undertook a joint research project with the University of Central Florida to examine the effects of undernutrition on blood chemistry. Data from previous fasting trials suggested that sea lions experience faster rates of mass loss during the non-breeding seasons. Differences in blood chemistry suggested that sea lions, which voluntarily fast during the breeding season, do not readily enter a fasting-adapted metabolic state when forced to fast outside of the breeding season.

Growth

One of the most visible potential effects of undernutrition is size. The Steller sea lions at the Vancouver Aquarium are constantly measured for weight and whether they are getting longer or stouter, leaner or fatter. Information on growth rates, obtained from twice-weekly measurements of body length and girth—including estimates of blubber depth—give an indication of changes in growth, both during the year and with age. The sea lions are providing new insights and allowing researchers to develop measurements of sea lion health that can be applied to animals in the wild.

Steller Sea Lions Credit: Andrew Trites
Sea Lion Research Credit: Margaret Butschler

Heart Rate

Until now, energy expended by Steller sea lions in the wild could only be calculated as a gross average over an extended time period. A project led by UBC researcher Jan McPhee has established a linear relationship between oxygen consumption and heart rate, by collecting data while an animal was at rest in the metabolic chamber or swimming against different water current speeds. From this relationship, recorded heart rate may be used to estimate metabolism and energy expenditure in the wild. However, further research is needed in a more natural environment before this monitoring method is used in the field.

Hydrodynamic Forces

A team of researchers have been studying the hydrodynamic forces encountered by Steller sea lions to better estimate their energy requirements. Such information is vital for understanding their dietary choices and the possible effects of changes in diet associated with changing habitats and climate. The results of the experiments showed that Steller sea lions experience relatively low levels of drag, resulting in a swimming performance similar to that of other eared seals, including the California sea lion. They also appear to swim at close to an optimum speed, based on calculations for a minimum cost of transport.

Steller Sea Lions Credit: Andrew Trites
Steller Sea Lions Credit: Andrew Trites

Keeping Warm

Previous studies with the Steller sea lions have measured the additional energy expended to keep warm at different temperatures (thermoregulation). Using a "swim flume" (the marine counterpart of a treadmill), Dr. David Rosen of the University of British Columbia and a team of Consortium scientists have been measuring the heat generated from digesting a meal, known as the heat increment of feeding (HIF), and the cost of thermoregulation. The results from these tests suggest that, contrary to predictions, juvenile Steller sea lions do not use heat generated through digestion to offset the increased thermoregulatory costs of decreasing water temperature.

Metabolism

To determine whether Steller sea lions in the wild are obtaining sufficient energy from their food, researchers need to quantify the energy required for different activities. While a sea lion rests quietly inside a "metabolic chamber," scientists measure the amount of oxygen consumed and carbon dioxide produced. This data is converted into estimates of energy use. Results so far indicate that sea lions undergo developmental and seasonal changes in metabolism, exhibiting a fast initial decrease in metabolism within the first 18 months of life. Metabolism then decreases at a much lower rate over the next several years.

Metabolic Chamber
Jellyfish

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