Infected salmon might be an obstacle to a planned grizzly bear recovery in the US northwest.

Charles Robbins.
Charles Robbins

Salmon poisoning disease (SPD), caused by a bacterium, is most commonly associated with dogs that have eaten raw salmon. Now, a newly arrived species of bacterium could have the same effect on grizzly bears once they’re moved to the North Cascades region in Washington. The threat was identified by Charles Robbins, a wildlife ecologist at Washington State University, and his colleagues who in recent experiments showed that any bears brought west to start a new population will be susceptible to a new form of SPD that’s taken hold in the region.

The bacterium that causes SPD infects grizzly bears in a devious way—by hitching a ride in a parasitic worm. The worm infests and destroys the gonads of stream snails. Unsatisfied with simply destroying the family-making dreams of the snails, the worm leaves this host and enters salmon or other fish. It finishes its life cycle in the guts of wolves, dogs, skunks, raccoons, or bears that have fed on the infected fish. When these predators defecate, they spread worm eggs to nearby streams, giving rise to a new generation of parasites to infest other snails.

Knowing this new bacterium was lurking in the environment, the researches wanted to see what effect it might have on planned grizzly recovery efforts. To do so, Robbins and his colleagues conducted an experiment over two consecutive years in which they fed salmon to captive bears and monitored them for signs of SPD, such as diarrhea, lethargy, or anorexia.

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