As you may be aware, war is being waged in Washington and Oregon on the northern
pikeminnow (Ptychocheilus oregonensis) because it preys on the smolts of salmon
and steelhead. The pikeminnow isn't at fault. Dams are. The proliferation of
dams have all but wiped out natural salmon runs. To make up for these losses,
fish and game agencies and the power companies behind the dams have been
stocking hatchery raised salmon by the billions. But the very dams that are
fatal to flow-adapted fishes such as salmon are favorable to lake-adapted fishes
such as the northern pikeminnow. In dam-created reservoirs, juvenile salmon are
veritable sitting ducks for the predatory minnow. In just one year, pikeminnow
in the Colorado River were estimated to have eaten 16 million salmon and
steelhead smolts, or about 8% of the run.
(Compare this to the Willamette River, also in Oregon, where dams have not
disrupted the water flows that allow juvenile salmon to swim over and around the
bottom- and bank-hugging pikeminnow. Here pikeminnow and salmon coexist in the
predator-prey balance that nature intended.)
Anyhow, a similar problem was perceived to have existed below Red Bluff
Diversion Dam on the Sacramento River in California. Here the Sacramento
pikeminnow (Ptychocheilus grandis) was allegedly wiping out salmon runs.
(Actually, according to the biologist, the degree of predation was greatly
overestimated.) So dam officials came up with a brilliant idea -- electrocute
the pikeminnow as they ascended the dam's fish ladder. As migrating pikeminnow
ascended the ladder on the way to their spawning grounds, a person viewing the
site through a security camera would employ the fatal zaps.
But the geniuses behind the project obviously didn't study up on minnow biology,
for it's a well-known fact that minnows release a fear scent (called
Shreckstoff) whenever they're bitten by a predator. This sends a message to
their schoolmates which says, basically, "Let's get the hell outta here!"
The electrocution device worked for a while, but then the pikeminnow abruptly
stopped entering the ladder. Apparently, the shocked pikeminnow were releasing
their Shreckstoff, which alerted the pikeminnow below the dam that danger lurked
ahead and to stay where they were.
This only served to compound whatever predation problem may have existed,
because a huge mass of adult (and therefore large--we're talking 3-4 ft)
pikeminnow congregated below the dam, feasting on whatever salmon congregated
there as well!
The "problem" more or less took care of itself when the dam managers merely left
the gates of the dam open, allowing the passage of migrating salmon
through the dam. Which, not coincidentally, allowed pikeminnows to complete
their spawning migration as well.
Suffice it to say, the electrocution device was subsequently removed.
Christopher Scharpf
Baltimore
"The secret of life is to have a task....And the most important thing is -- it
must be something you cannot possibly do!"
Henry Moore, sculptor
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