Monday, November 15, 2010

Biodiversity trade-offs

(A large Chinook salmon found dead after spawning in a stream in California.)

Sometimes the decisions we have to make to conserve biodiversity are not pleasant.  I remember a news article that came to my attention last year titled “Appeals court stays execution of sea lions: Killing was set to start Thursday to save salmon in Columbia River”.  The title pretty much sums up the dilemma.  Salmon in the Pacific Northwest have been in trouble for years, due primarily to overharvesting by humans and the dams on rivers that “frustrate” their upstream migration to spawn.  In the case at hand, it is the spring run of the Chinook salmon that is imperiled, which is made worse by hungry sea lions that are camped out at the base of the Bonneville Dam.

The necessity to control one species of native plant or animal to help out another is much less common than controlling a non-native species to benefit one that is indigenous.  But there are many examples of this unpleasant trade-off when attempting to conserve native biodiversity.  Predators are sometimes controlled in an area where biologists are attempting to reestablish a species that could be taken as prey by the predators.  Snow geese are having a decimating effect through their grazing on areas of the Arctic tundra ecosystem and white-tailed deer suppress many species of woody and herbaceous plants in the eastern U.S.  Although there are not control programs for these two species as far as I know, agencies rely on the public hunting season to reduce populations of these popular game species in the hopes that the legal “take” will alleviate the problem.  Those harvests barely make a dent in the problem, however.  So the damage continues, while the public is clueless and the ecologists lament.

Good people are usually trying to do the right thing, but it is often a lose-lose situation in the eyes of the public.  “Don’t let the salmon run be extirpated, but don’t harm the sea lions.”  The public often replies that wildlife managers should just move the offending or overabundant animals.  Trapping and moving the sea lions, or any large mammal, is time-consuming, dangerous to the animal being trapped, and sometimes dangerous for the trapper.  It is expensive and it seldom seems cost-effective to me, given that conservation dollars are always scarce.  Money spent trapping and transferring animals that are neither rare nor threatened is money that could be spent to buy habitat or protection for a suite of species that is in greater need. 

As I see it, the problem is really a paradox.  Biologists are willing to sacrifice some, even many, individuals of abundant species A to help out endangered species B.  Most biologists care about individual animals just as much as animal lovers do.  But biologists are even more concerned about the genetic and demographic viability of the populations of which those individuals are a part.  Without that viability, the population goes extinct and there are no individuals to worry about.  So sacrificing individuals in a common species is a relative no-brainer if that sacrifice helps ensure the survival of another population or species that is in real trouble.  As I see it, biologists and the public are usually talking past one another on this issue.  Perhaps the public understands the trade-off perfectly, but their emotions demand that we not harm some individuals in one species now in the hope of saving all the individuals of another species later.

In the seal-salmon example at hand, the Humane Society brought the case to court, which ruled that no sea lions can be killed now, but a few can be trapped and removed.  Once again, the concern for some “individuals” by the Humane Society puts an entire “population” of another species at risk.  Any real solution will have to wait until next year’s run, so Nero continues to fiddle.

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