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Research Hypothesis > Nutritional
Stress > Diet Changes
| Why has
Diet Changed? |
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Scientists suspect that
the decline of Steller sea lions might be related to changes in their
diet. This is based on the observation that the abundance of different
species of fish in the North Pacific has changed in the last 30 years
- although scientists still do not know why. Some suspect it might
be due to overfishing, while others suspect
it is related to ecosystem change. |
| Diet
Determination |
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Determining what
a sea lion is eating is not easy, but scientists have developed a
number of techniques to study sea lion prey. These range from surveying
the type of fish available, to analyzing the chemical makeup of sea
lions to examining what sea lions leave behind after a meal! |
Scat Biases |
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Determining how
much of each prey type is eaten is even harder and is a major
topic of research for Consortium scientists. (see bioenergetic
models) |
| Prey DNA in scat |
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In recent years, diets of Steller sea lions have
been primarily determined by identifying undigested hard parts of
prey recovered from scats. However, this method is subject to a number
of limitations. |
| How has Diet Changed? |
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In general, the diet of sea lions differs between
areas and has changed over time. |
| QUICK LINKS: |
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Scats | Analysis
of Stomach Contents | Fatty
acid Signature Analysis | Stable
isotopes | Prey
DNA in Scat | Scat Biases |
The differences between Western and Eastern stocks.
Data from Merrick et al and Trites et al.
The scat samples we have collected to date show that the growing Steller
sea lion population in southeast Alaska eats many different types of fish.
Its diet is the most diverse of all areas that have been studied.
The least diverse diet occurs in the Aleutian Islands where the sharpest
population declines have occurred. This suggests that the key to understanding
why Steller sea lions have declined may be in the number of different
types of fish they eat, and overall energy content (calories) of their
diet (see Winship and Trites,
2003). There may well be something in the
old adage that you have to eat from all the different food groups to stay
healthy.
Updated 19 Feb. 2007
NEXT:
Steller sea lion scat studies>>>
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