Lake Michigan chinook may be finding balance

Chicago – For Lake Mich-igan chinook, there is good news to be
found in numbers big and small.

Although the 2009 annual lake survey showed the alewife
population – those are popular forage fish for all kinds of salmon
– doubled over the previous year, that news was tempered by the
fact that the 2008 population was the lowest on record.

However, biologists believe reduced chinook stocking numbers in
the lake has restored some balance in the predator-prey
relationship. This means that survival of chinook smolts should be
improved, and there will be continued improvement in anglers’ catch
rates.

But the on-going shortage of nutritionally beneficial alewives
will probably keep the average size of the fish lower than the
long-term average.

In any case, there can be no doubt that Lake Michigan’s chinook
wild salmon are here to stay, even if all stocking of
hatchery-raised fish are likely to be discontinued.

The real key to more and larger chinook is the ability of the
forage base to support them. Along these lines, the lake may be in
for a recovery of quality chinook fishing, since the 2009 alewife
hatch was a good one, as indicated by unusually large cohos, which
thrive on young bait fish.

Initially stocked in Lake Michigan in 1967, the chinook reached
its highest peak of abundance during the late 1980s, but then the
population went into a serious decline beginning in 1989 and
continuing through 1994.

Up until that time, it was assumed the chinook population in
Lake Michigan consisted entirely of hatchery-raised fish, and that
pressure on the forage base of alewives could be regulated by
simply cutting back on their stocking numbers.

When thousands of dead chinook were discovered littering the
lake bottom in the ’80s, red flags went off within the Great Lakes
fishery management agencies.

When necropsies revealed the chinook had died of bacterial
kidney disease, it became apparent something was amiss that the
biologists had not anticipated. BKD is a disease in fish brought on
by stress, and in the chinook’s world this stress was wrought by a
decrease in the alewife population which forced the salmon to
expend excess energy earning their daily bread.

In short, the chinook were using more energy than they were
taking in chasing hard-to- find bait fish. To make matters worse,
due to the explosion of exotic critters, such as zebra mussels,
which competed with the alewives for food, the alewives were
becoming smaller and less nutritious for the salmon.

As the fishery managers studied the dead chinook, they began to
realize a number of them did not bear the distinctive identifying
fin clips of hatchery- raised fish. It became apparent they were
dealing with an unappreciated population of truly wild chinook. And
wild or hatchery raised, all these chinook spend a lot of time
gobbling down alewives, which contributed further to the stress-
inducing conditions that brought on the BKD epidemic.

Investigations revealed that in 2006, 54 percent of Lake
Michigan chinook were wild, naturally produced fish.

In 2007 that estimate dropped slightly to 52.8 percent, before
sinking to 42.7 percent in 2008. This decline is thought to be
related to smaller-sized female chinook as a result of reduced prey
abundance.

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