Like an armada of small rototillers, female salmon can industriously churn up entire stream beds from end to end, sometimes more than once, using just their tails.
For decades ecologists have believed that salmon nest-digging triggered only local effects. But a University of Washington researcher writes in this month's BioScience journal that the silt, minerals and nutrients that are unleashed have ecosystemwide effects, causing changes in rivers and lakes far from the nests.
From decreasing the amount of algae there is to eat to possibly influencing when aquatic insects emerge, spawning salmon can be extraordinary "environmental engineers," says Jonathan Moore, a UW graduate student in aquatic and fishery sciences.
Ignoring this role can cause missteps in managing salmon runs or attempting to rehabilitate habitat, he says. A major loss in the number of salmon, for example, doesn't just affect future generations of that fish alone.
"In streams with high densities of salmon, the disturbance from spawning impacts virtually all aspects of stream ecology," he says.
The female salmon, of course, isn't concerned about all that. She simply wants to lay her eggs in a nice, gravel-bottom bowl that's free of fine sediments that can smother them.
But consider the efforts of the grand dames of the salmon world, the female chinook ?or king ?salmon. The largest females are more than a yard long and tip the scales at 45 pounds or more. The biggest nests are nearly a foot and a half deep and extend up to 17 square yards –about the size of two parking-lot stalls. The rims around these craters can be the bane of boaters who, even with boats meant to navigate in shallow waters, can find their vessels grounded.
Smaller species of salmon that spawn at higher densities are capable of even more widespread tilling, according to Moore, who has for six summers worked with sockeye salmon through the UW's Alaska Salmon Program. Using count
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Source:University of Washington
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