J. Michael Kelly The Post-Standard
creatures that fattened the bellies of Great Lakes forage
fish for thousands of years, virtually have disappeared
from Lake Ontario during the last decade.
The quick fade-out
has ominous implications for anglers because the species
that depend on diporeia for calories are in turn eaten
by Ontario's tackle-smashing trout and salmon.
sure if other organisms can fill diporeia's niche in the
to be between 5,000 and 7,000 (diporeia) per square meter
of lake bottom," said Bob O'Gorman, a researcher with
the U.S. Geological Survey's Lake Ontario Biological Station
in Oswego. "Now we can't find any of them in most of our
sure why diporeia have vanished, but many believe the
phenomenon is related to the 1990s invasion of the Great
Lakes by two species of mollusks native to Europe, the
zebra mussel and the quagga mussel. Transported to North
America in the ballast tanks of cargo ships, mussels now
cover the bottom of Lake Ontario's shallows and mid-depths.
are suddenly gone is the $64 million question, and a lot
of people are spending a lot of money to figure it out,"
is that newly arrived mussels infected diporeia with some
as-of-yet unidentified disease. Other scientists suspect
mussels have crowded diporeia out of preferred habitats
or eaten their share of the food supply. Diporeia dine
mainly on microscopic plants called diatoms. Mussels ingest
diatoms along with a variety of plankton.
monitors Lake Ontario's aquatic community by hauling samples
aboard the trawling vessel Kaho, said the lake has become
home to "incredible numbers" of mussels.
In October 2000,
the Kaho found an average of 19,000 mussels per square
meter at a depth of 180 feet off the lake's south shore,
between Olcott and Oswego. Ninety-five percent of those
mussels were the thumbnail-size quaggas.
only about one-third of an inch long, but their loss could
have a huge impact on Lake Ontario's ecology. Historically,
the burrowing amphipods were a dietary staple for rainbow
smelt. Alewives also gorged on them at certain times of
the double bacon cheeseburgers of the fish-food world,"
O'Gorman said. "They're very high in lipids."
Lake Ontario's smelt have gone into a steep decline in recent
years. The slender, tasty bait fish used to be so abundant
that sportsmen were able to scoop buckets of them from lake
tributaries each spring. Now Ontario smelt are at their
lowest ebb in at least 25 years, according to O'Gorman's
number in the billions in the lake, but those sardine-size
fish also are showing signs of stress.
the Kaho's crew nets alewives at various points in the
lake to determine their relative abundance. The fish are
weighed and measured and their stomach contents are tallied.
surveys revealed that the Ontario alewife population is
trending downward, after a late 1990s resurgence. Bumper
crops of alewives hatched in 1998 and 1999 have been thinned
out by salmon and other aquatic predators, and the 2000
spawning run "was a total bust," O'Gorman said.
2001 hatch appears to have been a strong one.
better about that next year, when those fish reach adulthood,"
said O'Gorman. "The survival of alewives from age 1 to
age 2 is quite variable, depending on the number of larger
adults competing for the food supply, the overall productivity
of the lake and the impact of predation."
At this point, O'Gorman is less concerned
about the total number of alewives in the lake than he is
about the slender shape of individual specimens.
of adult alewives this fall was the second worst we've
ever seen, and we have records going back to 1976," he
said. "You would think, with the number of alewives being
low, that individual fish would be fat, but instead they're
likely because of a diminished food supply, he said.
that the loss of diporeia will put intolerable pressure
on other components of Lake Ontario's food chain. He's
especially worried about the mysis shrimp - sometimes
called possum shrimp - that are relished by young lake
trout, as well as smelt and alewives.
recently began a new study of the lake's mysis population.
Relatively little is known about mysis because they spend
daylight hours in deep water and migrate toward the surface
"I don't know
what we'd do if the mysis disappeared, too," O'Gorman
said. "God help us if that happens."
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