Alaskan Collection
Points:


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British Columbia
Collection Points


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Video clip of
scat processing.

Measuring how much
a sea lion consumes

Research Hypothesis  > Nutritional Stress > Diet Changes > Diet Determimation

Scats
For more than twelve years Consortium researchers led by Dr Andrew Trites have been collecting sea lion scats from haulouts along the coast of the British Columbia and Southeast Alaska.

These scats are scooped into plastic bags and sent to our laboratory where they are processed in a specially designed machine called an elutriator. The elutriator flushes out water soluble parts leaving only the fish bones, eye lenses, squid beaks and other hard parts behind. It is like panning for gold! Currently the use of washing machines is also being assessed. Researchers can identify which species of prey the bones came from. For a single fish, as many as 35 different bones might be identified. The next step is to try and reconstruct how many fish the recovered bones represent and the size of prey eaten.

Researcher washing bones that have been rinsed in the elutriator

Analysis of Stomach Contents

CLICK TO ENLARGE: An example of the bones found in scat samples.

Bones as well as whole fish can be recovered from the stomachs of sea lions and can also provide valuable information on diet. Often these are collected opportunistically from dead stranded animals or from subsistence harvests (e.g. Dr Alan Springer, UAF).

Fatty acid Signature Analysis
To enable scientist to quantify diet using this new technique, calibration coefficients are required. These take account of differing rates of deposition and metabolism across different fatty acids. They are presently obtained by comparing the fatty acid composition within the fat of a sea lion with the fatty acid composition within a prey species that has been consumed for many months. As many as 70 fatty acids are identified, but only the longer chain ones (C14.0-C24.0) are used. Results to date look promising, with major prey items being identified in most cases. The technique did result in some false identifications of prey, depending on modeling parameters used. Studies are now ongoing to refine the technique and to assess it’s sensitivity. For example the model presently uses calibrations based on pure herring diets. New captive studies at the Vancouver Aquarium are assessing to what extent mixed diets or high fat diets may effect these calibrations and resulting diet quantification data.

Click on the graph below to see the enlargement:

Drs Tollit, Trites and Rosen are collaborating with Dr Iverson (Dalhousie University) on controlled feeding experiments with captive Steller sea lions to determine how well the fatty acid technique works with sea lions. The aim of these validation experiments is to answer four questions:

To enable scientist to quantify diet using this new technique, calibration coefficients are required. These take account of differing rates of deposition and metabolism across different fatty acids. They are presently obtained by comparing the fatty acid composition within the fat of a sea lion with the fatty acid composition within a prey species that has been consumed for many months. As many as 70 fatty acids are identified, but only the longer chain ones (C14.0-C24.0) are used. Results to date look promising, with major prey items being identified. The technique did result in some false identifications of prey, depending on modeling parameters used. Studies are now ongoing to refine the technique and to assess it’s sensitivity.

Discriminant function analysis plot. Six selected fatty acids correctly separated harbour seal diet groupings in 85% of cases, particularly animals on 42 days of smelt or long term herring (calibration animals).

Harbor Seal Studies Two harbor seal studies have also been carried out to assess the technique, in collaboration with Chad Nordstrom and the UBC Food Science and Nutrition Department. Results indicate good agreement between the model prediction and the diet fed. Turn over of fatty acids in blubber was faster than observed in Steller sea lions and was in the order of 2 months. The best results were based on newly developed calibrations and fatty acid subsets (both available on contact with PIs – Tollit, Trites and Nordstrom)

Stable Isotopes The chemical composition of food eaten by Steller sea lions also becomes embedded in their whiskers, bones and tissues. Certain body parts, such as the vibrissae (whiskers) that grow away from the face represent a continuous time series of what the sea lion has eaten.
Stable isotopes are a type of chemical signature that can be measured to detect changes in prey consumption. Steller sea lions at the Vancouver Aquarium were used in a study to assess the temporal scale of changes observed along the length of the vibrissae and to determine how quickly diet changes were reflected in the vibrissae isotopic 'signature'. New studies plan to compare signatures across different tissues (e.g, whiskers versus blood plasma) and compare these values with long term and short term diet.

Crittercam
In recent years, scientists have begun to study marine mammal underwater behaviour (including hunting of their prey) using waterproof digital cameras (Crittercams). A pilot study at the Vancouver Aquarium used a back-mounted camera on a Steller sea lion. However, many fish captures were not recorded because of the flexibility and length of the sea lion's neck! New smaller head-mounted cameras have since been developed and underwater film from free-ranging sea lions hunting their prey will hopefully soon be available!

updated 20 Feb. 2007

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