Turmoil in Lake Ontario

Turmoil in Lake Ontario
November 21, 2003
By J. Michael Kelly
Staff writer

Although he's been studying it intensively for 32 years, Bob O'Gorman lately
feels like he knows less than ever about Lake Ontario.

"I've never seen such a period of instability in the lake," he said.

O'Gorman, a researcher with the U.S. Geological Survey's Biological Field
Station in Oswego, said the lake's food chain is in ferment from top to
bottom. Here are some examples: Near the low end of the food web, diporeia,
the shrimp-like creatures that fed Lake Ontario forage fish for eons, have
virtually disappeared from the water column in the past decade.

The decline of diporeia means that the alewives and other small fish that
subsisted on them now have to get their calories elsewhere, most likely from
another tiny critter called the mysis, or possum shrimp.

Rainbow smelt, once one of the two or three most numerous forage species in
the lake, now are so scarce that Geological Survey trawlers can barely
collect enough for study purposes. O'Gorman suspects the smelt swoon is tied
to the shortage of diporeia.

With smelt all but absent, alewives are the only significant remaining
source of food for the lake's world-famous chinook and coho salmon. Ontario
alewives also appear to be stressed. Although the sardine-size fish had
back-to-back successful hatches in 2001 and 2002, O'Gorman frets that 40
percent of all alewives in the lake are now age 5 or older.

"Those fish are going to start dropping out of the picture pretty soon," he
said.

Meanwhile, O'Gorman noted, the alewives collected by USGS trawlers last
spring "were in the poorest physical condition of any we've seen since we
began checking them in 1978." Alewives gathered in a follow-up autumn
netting were more robust. O'Gorman thinks alewife numbers dropped sharply
between the two surveys, leaving more food for the surviving fish.

With smelt rare and alewives skinnier than usual, there are early
indications that Ontario salmon may be slenderizing, themselves. At an even
33 pounds, the grand-prize chinook salmon taken in the 2003 Lake Ontario
Counties Fall Salmon and Trout Derby was the smallest winner in the
contest's eight-year history.

What's going on?

O'Gorman suspects the turmoil in the Ontario fishery eventually will be
traced to the exotic species that have invaded the entire Great Lakes
system.

Specifically, he thinks it is no coincidence that the dramatic changes he's
seeing have taken place since zebra mussels and then quagga mussels migrated
from Europe to this side of the Atlantic.

Both species hitchhiked to North American in the ballast tanks of cargo
ships in the late 1980s and early 1990s.

Zebra mussels and quaggas are filter feeders that compete with larval fish
and other small organisms for a finite food supply of plankton. While
"zeebs" are confined mainly to hard-bottomed, near-shore environs, quaggas
thrive throughout Lake Ontario.

"They're just creeping out deeper and deeper, as if a doggone carpet was
being rolled out from the shores," O'Gorman said.

Diporeia used to be thick as fleas in the areas now dominated by quaggas.
One theory holds that the mussels have simply crowded the inch-long possum
shrimp out of their old habitats.

"There are a few deep-water areas where diporeia persist," said O'Gorman.
"Why, we don't know. Frankly, we're scratching our heads."

With the future of diporeia in doubt, researchers here and in Canada have
stepped up their studies of mysis.

Several weeks ago, a Geological Survey vessel netted thousands of bait fish
in order to analyze their stomach contents. Basically, they want to know
what alewives, smelt and sculpins are eating in place of diporeia, and if
they're getting enough of it.

A similar gut-check in 2002 produced a puzzling result.

"In that study, we found that the numbers of mysis were down in alewife
stomachs, but were not significantly lower in the stomachs of smelt or
sculpin," said O'Gorman. "Once again, we were left to wonder why. Could it
be that mysis are for some reason less accessible to alewives than to smelt
and sculpins? At this point, we just don't know."

Along with such unanswered questions, researchers must deal with a new
ecological wild card.

Two years ago, the state Department of Environmental Conservation confirmed
that a small, perch-like fish called the round goby had shown up in Lake
Ontario.

The finger-length, European-native gobies are prolific breeders that thrive
just about anywhere.

"This spring we found them in the lake out to 450 feet deep," said O'Gorman.

Gobies are expected to compete with bottom-dwelling sculpins for habitat.
Along with zebra mussels, gobies eat the eggs and fry of other small species
of fish.

The goby's taste for shellfish worries health officials because mussels take
up chemical contaminants from lake sediments. If gobies ingest mussels, and
game fish eat gobies, there's just one more step to the creatures at the top
of the food chain - you and me.

Click Here to read the article in the Post Standard.


--
James Ehlers

Outdoors Magazine
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