According to George Bernard Shaw: “We don’t stop playing because we grow old; we grow old because we stop playing,” but how fast does that aging occur once started" In the case of populations of salmon in Alaska studied by Stephanie Carlson and colleagues at the University of Washington and McGill University and reported on in this week’s PLoS ONE, it all depends on how choosy are the bears which feed on them.
Pacific salmon are noted for not feeding during their breeding period, relying instead on stored energy reserves and for their rapid senescence – the physiological deterioration associated with aging – once breeding is over. It is, thus, more beneficial for bears to consume fish with fewer signs of senescence because these fish have more energy reserves. However, these “fresh” fish are also more vigorous and harder to catch and so are more effectively caught in smaller, shallower streams.
Carlson and colleagues studied populations of salmon and brown bears in six creeks in southwest Alaska to determine whether the rate of senescence in salmon was driven primarily by the rate of predation by bears or by the tendency of the bears to prey on salmon with less evidence of senescence. They measured the reproductive lifespan of each fish as the number of days between stream entry and death and recorded the mode of death for each fish. They found that the selectivity of the bears for salmon of various senescent conditions was the prime factor determining the rate of senescence in the salmon.
In populations where bears killed old, decrepit salmon, the salmon senesced more slowly relative to populations where bears killed young, “fresh” salmon. This result contrasts with the established expectation that senescence evolves because of the number of individuals killed by predators, rather than their physical characteristics.
“The work offers new insight into the relationship between an individual’s senescent condition and it’s susceptibility to predation and the long-term consequences of this relationship” says Carlson, corresponding author on the publication.
Source: Public Library of Science
Related stories:
Loss of Wolves Causes Major Ecosystem Disruption at Olympic National Park
(PhysOrg.com) -- Olympic National Park was created in 1938, in part “to preserve the finest sample of primeval forests in the entire United States” – but a new study at Oregon State University suggests that this preservation goal has failed, as a result of the elimination of wolves and subsequent domination of the temperate rainforests by herds of browsing elk.
Fish farms drive wild salmon populations toward extinction
A study appearing in the December 14 issue of the journal
Science shows, for the first time, that parasitic sea lice infestations caused by salmon farms are driving nearby populations of wild salmon toward extinction. The results show that the affected pink salmon populations have been rapidly declining for four years. The scientists expect a 99% collapse in another four years, or two salmon generations, if the infestations continue.
Hitchin' a ride: Stray penguins probably reached northern waters by fishing boat
Guy Demmert got quite a surprise when he hauled a fishing net into his boat off the coast of southeast Alaska in July 2002. There among the salmon, in living black and white, was a Humboldt penguin, thousands of miles from where any of its kind should have been.
Save the whales? Sure, but how many?
How many wildebeest should live in the Serengeti? How many grizzly bears should call Yellowstone home? Are there too few tigers in the world? Conservationist biologists grapple with the task of setting population targets for the species they are trying to protect – a decision steeped in politics, emotion, and sometimes, science.
Is a Russian peninsula really part of North America?
For many years geologists have harbored a belief that the Kamchatka Peninsula, shrouded in mystery and secrecy on Russia's east coast, actually sits on the same tectonic plate as the mainland United States, Canada and Mexico.
Volcanic overflow ruins Alaska salmon run
Salmon fishing along the King Salmon River on the Alaska Peninsula has been canceled -- primarily because no salmon showed up this year.
Dog helps track mystery of orcas' decline
Researchers trying to learn whether orcas are starving have turned - with the help of a dog - to a new source of information: orca scat.
US biologists: 3 common pesticides harm salmon
(AP) -- Farms and orchards that continue to use three pesticides that harm salmon will have to greatly expand buffer zones around their fields so the chemicals don't reach streams, federal biologists ruled Tuesday.