Data teach researchers about Lake Huron fish
Written by The Alpena News   
Tuesday, 01 May 2007 04:35

We were hoping to gain information that will be of use to sportsmen,” said Roger Bergstedt, field station supervisor at the Hammond Bay Biological Station, U.S. Geological Services.

But as is the case with any good science one conducts, the solid data produced by the Lake Huron Data Storage Tag Study only induce more questions.

In the autumns of 1998 and 1999, researchers implanted data storage tags in lake trout. About the size of a disposable lighter, each tag recorded the date, time and temperature. The problem, though, says Bergstedt, is that those tags “don’t tell us where the fish were.”

Starting in 2001, researchers began using tags about 84 percent smaller than the originals but with more memory and the ability to record data more frequently. More important, they measure both temperatures and depths.

So far, researchers have recovered the data storage devices for 31 percent of the lake trout and 15 percent of the chinook (king) salmon. Bergstedt shared some of the preliminary findings.

In winter, lake trout “remain in water of the same depth as in summer, where the winter temperatures are close to freezing.”

Two strains of lake trout have been stocked in Lake Huron

“The Seneca Lake strain prefers water about five or six degrees cooler than the Great Lakes strain does. The biggest difference occurs in June. The Seneca strain seems to have fewer lamprey attacks and to survive better. What we think is that the sea lampreys’ preference matches up better with the Great Lakes strain.”

This scientific study also confirmed what human observation had noticed long ago.

“Lake trout and lake whitefish overlap most of the year,” says Bergstedt. “In late fall there’s minimum overlap. Native Americans had figured that out based on what they caught.”

For example, in Hammond Bay where tribes have a limited whitefish gill netting season during September/October, “Whitefish are at 11 degrees Celsius and a depth of 20 meters. Lake trout are at approximately 8.5 degrees and 30-40 meters. That’s the maximum separation of the two species.”

Chinook salmon were tagged from Alpena to Rogers City. Tags have been returned from places as far away as Georgian Bay, the Thumb of Michigan and Detour.

“We learn they came from all over,” Bergstedt said. “By far, the majority appears to be wild fish reproduced in Canada. The implication is that 85 to 90 percent of the chinook population consists of wild fish.”

Researchers also learned that kings distribute themselves at several depths and temperatures.

The annual average depth of the chinook is 31 meters. But they range from about 12 meters in late September to over 165 meters in late March. In the winter, “the chinook need water at 35 or 36 degrees and have to go to more than 450 feet to get those temperatures. That’s a small zone, off Alpena and south, near the maximum depths of Lake Huron. You have to go a considerable distance offshore to get that kind of depth.

“So, they have a distance to move in the spring before they are closer to shore. That’s why, we think — and this is just speculation — that you don’t have much success with chinooks until early summer,” Bergstedt said.

He’s also inclined to think there’s little sense for anglers to use temperature as the determining factor for the depths at which to target fish, saying they “will turn out to be so variable as to be of little practical value. These fish move constantly during the day and definitely don’t hunker down at specific temperatures.”

Another secret the study revealed: “Most chinook are going deeper than we ever troll.”

Bergstedt mentions that the purpose of the study was not to prove any specific theories but only to gather data.

“How could we know what to expect when we didn’t have any of this data before? The fun part is this is information we’ve never ever had. You have to have information to form a hypothesis and that’s what we’ve got here.”

For example, the data produced at least two theories about why chinook tend to collect at a fairly specific depth and temperature at night. Bergstedt’s associate, Ray Argyle, now retired, speculated that might be the depth where the fish have neutral buoyancy, where they don’t need to expend energy to maintain their positions. Another speculation is that some sort of prey collects at those depths.

“These devices don’t tell us that,” said Bergstedt.

Anglers should be on the lookout for fish with yellow or, more commonly, orange tags. The tags offer a $100 reward and give a phone number (989-734-4768; the earlier, yellow tags will give a 517 area code). Biologists will retrieve the fish or anglers may bring them either to the DNR Fishery station in Alpena or to the Hammond Bay USGS facility, 13 miles north of Rogers City.

Researchers need the entire fish and tag.

Bergstedt advised anglers to put the fish on ice, but “don’t freeze it! Freezing can damage the tag and cause us to lose the information.”
 
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