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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

June 1996

Trout on the rocks

The Apostle Island lake trout population flounders no more, thanks to a big heap of stony rubble.

Betsy Bartelt

On the eastern edge of the Apostle Islands archipelago, in the Wisconsin waters of Lake Superior, lies Gull Island Shoal. Covering 7,700 acres, the shoal is connected to the north end of Michigan Island and Gull Island by an underwater reef, essentially an extension of the islands' red sandstone.

Underwater photography of the shoal reveals pebbles, basketball-sized rocks and large boulders several feet across tumbled together in piles, forming shelves and steps that drop in eight- to 10-foot increments down to about 40 or 50 feet. It's a desolate scene, a gray seascape unrelieved by stands of aquatic plants. Only in summer does the shoal take on color, when algae carpets the rocks. The soft green barely lasts the season; violent waves spawned by autumn gales wipe the algae away, even on the boulders 40 feet down.

The shoal may appear inhospitable to human eyes, but lake trout have been spawning on Gull Island Shoal for as long as has been recorded. This was one of only a few locations where naturally reproducing lake trout found refuge when the rest of Superior's lake trout population was devastated by the parasitic sea lamprey in the 1950s. Today the shoal is the center of activity for the restoration of the species, and biologists are optimistic about the future of Lake Superior's native predator and favored target for anglers.

Protected just in time

Back in the 1950s, when cars were sprouting fins on land, lake trout were faltering in the water. Once the dominant predator in Lake Superior, the lake trout was in serious trouble. Over-fishing and parasitism by the sea lamprey, a non-native eel-like species with a raspy sucker mouth, caused Superior's lake trout population to collapse. Although a small number of fish survived and continued to reproduce at Gull Island Shoal, annual population surveys conducted there showed a steady decline in spawning activity. In 1961, no females were sampled during spawning assessments.

State and federal agencies working on Lake Superior started combining their resources to restore lake trout. A Sea Lamprey Control Program set up electrical barriers in tributary streams to capture and destroy sea lamprey before they could spawn. Beginning in 1962, and until 1970, commercial fishing was prohibited in Wisconsin waters of Lake Superior. Conservative fishing regulations were set, and sea lamprey control and a massive lake trout stocking program were undertaken. The population of lake trout at Gull Island Shoal responded immediately. By 1974 the population increased, but both sport and commercial fishing pressure increased, too.

A year later overfishing had again weakened the lake trout population. It was clear: Without protection, lake trout would be in jeopardy again. To give the lake trout a chance to recover, the state stepped in and established the Gull Island Refuge, prohibiting sport and commercial fishing year 'round.

Though lake trout had been stocked from the '50s until recently, biologists concluded these stocked fish did little to rebuild fish populations. Stocked fish lack a natural homing instinct and do not return to the shoal to spawn. Stocked fish also don't survive as well as their wild counterparts.

The 7,770-acre rocky shoal has just the right conditions for spawning lake trout. The trout spawn where the rocks are approximately one to three feet in diameter, packed and piled, with the largest rocks on top and smaller ones underneath.

Lake trout eggs filter down in the cracks of the rock pile, where they are protected from predators and where they can safely develop from October through early June when they hatch. At that time, the tiny fingerlings have the protection of the rock pile and can swim to safety in the cracks when danger is present. Once they reach adulthood, these same trout will heed their homing instinct, and return each year to spawn in safety at Gull Island Shoal.

A haven for lake trout and fisheries researchers

"Our studies at Gull Island Shoal provide the best lake trout data in Lake Superior and probably in the Great Lakes," says Stephen Schram, Department Fisheries Biologist in Bayfield. Lakers had disappeared from lakes farther south; the other Lake Superior populations in more remote locations were not studied as intensively, Schram said. The U.S. Fish and Wildlife Service started keeping records here of lake trout reproductive success in the early 1950s; Wisconsin took over trout-tracking duties in 1969.

During the spawning season, approximately 2,500 trout are captured and tagged at the shoal each year by Department of Natural Resources staff. Gill nets are set and checked daily for two weeks. Every lake trout caught is measured and marked with a tiny plastic tag permanently attached near its dorsal fin. Each tag has a unique number that corresponds to data collected on that fish. Over 50,000 lake trout have been tagged during the past 25 years.

Netting tagged fish from previous assessments is not unusual. Recaptures and tag returns from anglers have helped biologists piece together movement patterns and determine the home range of the refuge's lake trout. "Many fish stay within the refuge or within the Apostle Islands after spawning," says Schram. "Some move eastward along the Keweenaw Peninsula and a few even migrate around the peninsula into Keweenaw Bay."

Tagging also helped solve a mystery concerning the age of some lake trout. Biologists had a clue that some recaptured fish were older than they appeared. The span of years the fish had actually been "at liberty" did not jibe with the age indicated by the traditional method of aging – counting rows of annual growth on fish scales.

Biologists began using a different procedure for aging in the mid 1980s using cross-sections of ear bones, called otoliths. The otolith is a calcified structure located in a fish's inner ear which shows annual growth zones much like tree-rings. Otoliths are removed from dead fish and examined under a microscope. Age data gathered with this new method did jibe with recapture dates of lake trout. The tags on the fish had helped validate this more accurate method of aging.

Several years ago, two lake trout provided researchers with an example of just how old some of the Gull Island Shoal population can grow. The fish were first captured and tagged in the early 1970s. From the tag information and otolith examination, researchers determined that both fish were about 26 years old. The oldest Gull Island Shoal lake trout ever aged was 32 years old. The fish was tagged in 1974 while spawning at the shoal and recaptured in 1995.

Sport anglers have helped researchers learn more about the lake trout population by relaying tag information when they catch a lake trout. Location of catch, date, length of fish, tag number and color are sent to the DNR office in Bayfield, providing additional data to supplement what's collected during annual assessments. In return, the angler receives a letter from the biologists with the information gathered on the fish to date.

Anglers can help by releasing large lake trout, says Schram. The big fish are valuable as spawners; their genes can help build a long-lived, sturdy stock. "Catch it, take a picture of it and release it," he says.

"You have to take the long view when you work to restore lake trout," Schram notes. "These fish are slow-growing, late-maturing and they may be caught once they leave the refuge." There's plenty of reason to be hopeful now: More than 450 wild, female lake trout were tagged last year. Back in 1961, no females were recorded at the shoal. "We haven't reached a maximum amount of fish this shoal can produce," says Schram, "but the lake trout population has rebounded nicely from dangerously low levels just a few decades ago."

The essential fisheries management tool

Aboard the research vessel Hack Noyes, Stephen T. Schram, DNR Lake Superior fisheries biologist, and his crew had just completed a difficult morning lifting gill nets at Gull Island Shoal. Braving rough water conditions, the Hack was chugging back to Bayfield. As some of the crew washed down the interior of the vessel, removing fish slime, scales and eggs that were splattered over every surface, Schram was busy cutting otoliths, tiny ear bones, out of fish that did not survive the netting.

Schram worked quickly and with precision, removing the gills, cracking the spine open and locating two otoliths. Carefully removing the flecks of white with his tweezers, he transferred them to another crew member who placed them into a small envelope onto which was recorded corresponding fish data. The otoliths would be used later to determine the age of the fish.

"The Hack Noyes is the backbone of our whole program," said Schram of the good old boat. Once a commercial fishing tug on Lake Michigan, the Hack will be fifty years old in 1996. During that time, the vessel has seen a variety of duties, including ice breaking and rescue operations.

The 55-footer was built in 1946 by Burger Boat of Manitowoc, Wis. The state bought the boat in 1951 from a commercial fisherman for $17,000. It was moved to Bayfield in the mid 1950s, and went to work enforcing commercial fishing regulations, mainly assisting in locating illegal nets. There were many to be found, with one bust of 25,000 feet of net worth $2,000.

The Hack Noyes became part of the Lake Superior fisheries program in 1970. New equipment was added and today the boat contains a bow thruster for fine maneuvering, a spacious working area, fish tanks, a desk for data recording and specialized navigation equipment.

Renowned for being highly seaworthy, the Hack is also known for "rocking and rolling" in rough water. The crew has plenty of stories about days when the Hack handled ten-foot waves or better. "Trying to work under these conditions takes some getting used to," said Schram, who has been on board when 18-footers crashed across the bow. Regardless of the weather, the crew must work every day during the assessment period, because leaving gill nets unattended means dead fish.

Named for the former head of the Wisconsin Conservation Commission, Haskell P. Noyes, the Hack Noyes will continue its service to the department. Biologists collecting Lake Superior's fish population statistics will continue to depend on this reliable vessel, maybe for another 50 years.

Betsy Bartelt writes about fisheries issues from the DNR office in Bayfield, Wis. She also works as a park ranger and is president of a local Audubon chapter.