Aging in Salmon Depends on Choices of Bears
December 13th, 2007 Posted by: Dr. Cox
(Ivanhoe Newswire) â How choosy a bear is may determine how fast salmon age.
Pacific salmon do not feed during their breeding period and rely instead on stored energy reserves for their fast senescence â the physiological deterioration associated with aging â after breeding is over. So it is more beneficial for bears to eat salmon with fewer signs of senescence because these fish have more energy reserves. But these fish are also more vigorous and harder to catch so it is better to catch them in smaller, shallower streams.
A new study from the University of Washington and McGill University looked at populations of salmon and brown bears in six creeks in southwest Alaska. They wanted to determine whether the rate of senescence in salmon was driven mainly by the rate of bears eating them or by the bearsâ tendency to prey on salmon with fewer signs of senescence.
Researchers measured the reproductive lifespan of each fish as the number of days between when they entered a stream and when they died. They also recorded how each fish died. Results show the selectivity of the bears for salmon of various senescent conditions was the main factor that determined the rate of senescence in the salmon.
For example, the study found in populations where bears killed old, decrepit salmon, the fish senesced more slowly compared to populations where bears killed young, âfreshâ salmon. These findings go against the expectations that senescence evolves because of the number of individuals killed by predators rather than how they look.
âThe work offers new insight into the relationship between an individualâs senescent condition and itâs susceptibility to predation and the long-term consequences of this relationship,â study author Stephanie Carlson, University of Washington, was quoted as saying.
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SOURCE: PLoS ONE, published online Dec. 11, 2007