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Field & Street



How would you react to a suggestion that we grow alewives in hatcheries and release them into Lake Michigan? Doubtless you know about alewives, the silvery little fish from the Atlantic Ocean that invaded our lake a few decades back. In the late 60s, it seemed like alewives were put on earth to die and wash ashore in great stinking heaps. This spring they worked a variation on that morbid task by dying and floating into the quiet corners of our harbors.

The rotting mounds of alewives achieving their destiny on Chicago's beaches 25 years ago helped stimulate the introduction of coho and chinook salmon to our lake. These alien salmon--along with hatchery-raised specimens of the native lake trout--were supposed to eat enough alewives to keep the population at a level low enough to prevent the mass die-offs that buried our beaches.

They accomplished that task so well that by the early 70s ichthyologists were predicting the salmon and trout would soon be in danger of having nothing to eat. This became more likely as the states around Lake Michigan reacted to the boom in sport fishing by growing and releasing huge numbers of trout and salmon. "Depleting the forage base" became the apt descriptive phrase as alewife populations continued to decline and the average size of the salmon anglers caught went down.

Of course there are other small fish in the lake, and as alewife numbers were reduced, native fish like bloaters and yellow perch showed good population growth. Some fisheries biologists began predicting that the salmonids--salmonids, or salmonines, is a general term that describes both salmon and the closely related lake trout--would change their eating habits and go after the more abundant species. Theory says that predators act like people playing the stock market. They look for a maximum return in calories for the time and energy they invest. Rather than spend all day searching for scarce alewives, the salmonids would conserve their energy by eating bloaters or smelt.

But so far all indications are that the salmonids have not made the switch. Alewife numbers continue to decline, and perch and bloater populations to burgeon.

Do fish think? asks the philosopher. Yes, but not fast enough. Maybe the salmonids have just not caught on to the fact that meat is swimming all around them, that life could be an endless feast if they could give up their fixation on alewives. Or maybe some other factors are involved.

When I have fish questions, I go to my old friend Allen Feldman. Allen used to be an aquarist at Shedd Aquarium, where he was in charge of the displays of Great Lakes fish. He left the Shedd to become assistant curator of fish at a new aquarium in New Jersey.

He agreed that stupidity on the part of the salmonids could play a role in this failure to act according to theory. "These are hatchery fish," he told me, "Frankenstein fish. Idiots.

"Go to a hatchery. Stick your finger in the water in a tankful of young trout, and they'll try to bite your finger. They think you are something to eat."

So you take millions of hatchery fish--fish that grew up in a situation where they were never hungry, never faced danger, never had to worry about competition, never had to work for a living. Dan Quayle fish. And you let them loose in the wild. It should not surprise you that they are not as flexible or adaptable as fish that came up the hard way.

There could be other explanations, and Allen examined one of them in his master's thesis. "Most research was looking at things from the predators' point of view," he said. "I looked at it from the opposite side. Maybe prey behavior is limiting their ability to switch."

Two years ago Allen set up a 5,500-gallon concrete aquarium in one of the back rooms at the Shedd. He put in cooling coils to keep the temperature constant at nine degrees Celsius, the midpoint in the preferred temperature regime of the lake trout. He got some lake trout from the Illinois Department of Conservation's Jake Wolf Memorial Fish Hatchery in Pekin, spent two weeks teaching them to eat live fish instead of the pelleted food they got at the hatchery, and released them in the tank. Then he began to release prey fish in the aquarium and recorded what happened with a video camera mounted above the water.

He first discovered that the lake trout would happily eat alewives, yellow perch, bloaters, or rainbow smelt when these species were released--one species at a time --into the aquarium. But in multispecies trials, in which two or three species were released at a time, the trout consistently ate more alewives than anything else. And the major reason for this preference seemed to be the behavior of the prey fish.

Consider, for example, the yellow perch, the fish that was most successful in avoiding capture. The perch has a weapon going for it besides behavior. Its dorsal, ventral, and anal fins are all equipped with sharp, erectile spines that make it difficult and uncomfortable to swallow. As the trials went on, the lake trout became less and less interested in trying to eat a perch.

But the perch also protected themselves by hiding. According to Allen's thesis, they would "take up positions along walls, in the corners, behind the cooling coil, or near the surface and remain absolutely motionless for hours. Sometimes for days."

Bloaters and smelt tended to form schools when they were released, but once they realized there was something dangerous in the tank, they too hid, remaining motionless along the walls, on the bottom, or at the surface. Fish holding still at the surface were well camouflaged, and tricks of light apparently made the trout go after reflections rather than the fish themselves.

Alewives had only one protective response: they schooled. This was effective up to a point. Trout attacking a school were often so confused by all the moving bodies that they missed what they were aiming for. But by staying in constant motion in the open water, the alewives invited repeated attacks, and eventually some fish would be separated from the school and eaten.

So we can reasonably conclude that salmonids in Lake Michigan prefer to prey on alewives because they are much easier to catch than other potential prey fish. So much easier that even their scarcity doesn't prevent them from being the preferred prey. Which brings us back to the question that opened this column: should we grow alewives in hatcheries to provide food for the huge salmonid populations we need to sustain our multibillion-dollar sport fishery? The idea has been discussed by the Great Lake Fisheries Commission, a body that includes representatives of all the state fisheries agencies. It would be difficult and expensive to do because alewives are very delicate fish. The techniques for large-scale production that work for salmonids would kill alewives.

My own reaction to such an idea is abhorrence. It seems to me an insult to the dignity of the lake to turn it into a sort of roadside trout ranch where, for a fee, you can have the thrill of hooking a hatchery fish that is about as wary as a barnyard chicken. Stocking alewives is also a good example of the sort of blinkered straight-ahead thinking that has helped us get in so much ecological trouble.

Allen Feldman is a lake trout supporter. "We have to manage everything," he told me. "Nothing is pristine anymore. But we should try to manage toward more natural balance. Managing for salmon is labor intensive and not good for the ecological community. We should be managing in the long term--over the next century--for a self-sustaining lake trout population."

That is what used to be here. Before the alien coho and chinook were introduced, before the lamprey and overfishing combined to drastically reduce the number of native trout, the lake trout was the top predator in the Lake Michigan ecosystem. But could it be that again? The hatchery lake trout that have been released in the past 25 years have not been able to establish themselves as a breeding population.

"It may be that they cannot," Feldman says. "But we shouldn't be too impatient. These are all hatchery fish--idiots. It takes four to five years for them to mature, and with heavy fishing pressure how many are left to reproduce by that age?

"We have only been trying to reintroduce them for 25 years, and maybe you can't retrain hatchery fish that fast."

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