Active research on activity

Posted on May 26, 2009

In principle, bioenergetic models can give good estimates of food consumption and growth rates of predators, but they rely heavily on assumptions about the levels of activity of the animals concerned.  Activity can be measured from video records of animals held in enclosures, but to follow activity patterns over a full growing season, a very intensive sampling program is required.  A potentially much more cost-effective approach is to measure the mean concentration of a chemical tracer (such as stable caesium, 133Cs) in the bodies of sampled predators at two points in time and calculate the amount of tracer that has accumulated as a result of feeding on prey during the intervening period.  However, the tracer approach assumes a direct relationship between tracer accumulation and activity, and also assumes that the concentration of tracer in the food, and its assimilation in predator bodies, remain constant, which is unlikely.  Comparisons of the two approaches using Arctic char, a salmonid fish, suggest that video records are more trustworthy than tracer data when in situations where animal behaviour can be well described (e.g., as in enclosures or on coral reefs).  When behaviour patterns are unknown (e.g., during migrations) the tracer approach is preferable, but its reliable application will require more accurate information on tracer concentrations and assimilation.

Reference: Guenard, G., Boisclair, D., Ugedal, O., Forseth, T. & Jonsson, B.  2008.  Comparison between activity estimates obtained using bioenergetic and behavioural analyses.  Canadian Journal of Fisheries & Aquatic Sciences 65, 1705-1720.