Michigan DNR Releases Lake Trout Mortality Study
OutdoorHub 10.05.11
After piloting his 30-foot Grady White out to 80 feet of water out of Presque Isle Harbor, charter boat captain Ed Retherford turns the wheel over to his buddy, Jon Gunderson, then heads to the aft where he begins setting lines.
It doesn’t take long; one of the downriggers goes off, one of Retherford’s three buddies accompanying him on this busman’s holiday grabs the rod, and Retherford hollers, “Fish on.”
Gunderson punches the button on a digital timer.
One minute and 26 second later, when a 26-inch lake trout is in the net and hoisted aboard, Retherford hollers, “Fish in.”
And Gunderson punches a second button on the timer.
Retherford goes immediately to work; he places the fish in a half-pipe section of six-inch diameter PVC and takes a photograph. Then, with a tool that looks like a knitting needle with the last inch bent into an obtuse angle, Retherford punches through the lake trout, high on the back, right below the dorsal fin.
On the end of the tool – where the knob of a knitting needle ought to be – there’s a plastic tag. Once the five-inch tag is through the fish, Retherford joins the ends into a clasp to form a loop. He takes a second photograph, steps out onto the swim platform of the Trout Scout, holds the fish in the water for a few moments, and then lets it go.
“Fish out,” he says.
Gunderson stops the timer. One minute, 37 seconds.
Retherford walks to the fore of his craft, carrying a piece of paper with a tag number on it. He grabs a data sheet and records the tag number, the time it took to land the fish, the time it took to handle it before release, and some general observations (Was it bloated? Was it bleeding?) about the lake trout’s physical condition.
Retherford, like about a dozen other Lake Huron fishermen, is a volunteer participant in a Department of Natural Resources study on lake trout mortality. The study is designed to determine the percentage of sport-caught lakers that are released by anglers and are subsequently recaptured.
The study, currently in its second summer, may have implications on fishing regulations as lake trout of certain sizes must be released. Lake trout have become the most important salmonoid in the Lake Huron sport fishery following the collapse of Chinook salmon.
But Retherford said there’s more to be learned about the Lake Huron natives than just their survival rate.
“We’re finding out that lake trout are just as nomadic as other fish,” said Retherford, who guesses he’s tagged 60 to 70 fish over the last two seasons. “I caught one the other day that was tagged in Harrisville – that’s about 50 miles – two weeks earlier.
“These lake trout are not homebodies like we’ve heard.”
A second rod – this one trailing a diving planer – is bucking in the rod holder. As one of Retherford’s buddies handles the rod, the captain calls for the clock.
This is a feistier laker and it takes longer to land (two minutes, 15 seconds) and longer to process (2:03) than the first.
“It’s a lot easier just throwing them in the live well,” Retherford says as he jots down the data.
But the information Retherford reports is important, says Jim Johnson, station manager of the DNR’s Alpena Fisheries Research Station, who is heading up the study, which compares recapture rates of trap-net caught lake trout with sport-caught fish.
“We’re assuming the commercially caught trap-net fish all survive,” Johnson said. “They were healthy and in good shape when we tagged them and they all swam away well. They’re kind of our control group.
“The assumption we’ve been operating under is that 15 percent of the hook-and-line fish die after they’re released. That 15 percent figure comes from an old study, back in the ‘80s. We’re concerned that we may be under-estimating that percentage. A lot of our anglers say they see the fish floating after they release them.”
If that 15 percent figure is low, it throws a monkey wrench into the population models.
“If the mortality rates are higher, is it beneficial enough to the population to require anglers to release those fish? “ Johnson asked. “Is there another way to protect those fish without demanding catch and release?”
Another part of the study is being conducted on Lake Superior, where there are a wider variety of angling techniques than at Lake Huron, Johnson said. At Lake Huron, the lake trout fishery is almost all trolling. At Lake Superior anglers use other traditional methods – jigging and bobbing, for instance – that may be easier on the fish, Johnson said.
Johnson is actively recruiting recreational anglers from the Thunder Bay-to-Oscoda area to participate in the study.
“Without the anglers help we can’t do this,” he said. “If there are other anglers out there who are willing to help, we could sure use them. We’ll pay volunteers $5 per fish tagged by volunteers to help them defray the cost of boat fuel.”
Although the study is on-going, Johnson said he’s beginning to tease out some information from tag returns.
“What we’re seeing is that we’re getting about twice the returns of tags from trap-netted fish than hook-and-line fish,” he said. “That’s telling us there may be higher mortality among the trolling fishery here than the trap-net fishery.”
And the angler observations?
“When we look at what the anglers are reporting, a fair number of those fish are bleeding and a smaller number are bloated,” Johnsons said. “And when we look at those photographs, we see that what the anglers are reporting about those fish are about right.
“We think these two factors may cause this lower return-rate that we’re seeing on hook-and-line fish.”
That makes the time element important, too, Johnson said.
“It could be that a fish that is eased up slowly can adjust its swim bladder and won’t bloat like a fish that’s jerked right up from 100 feet of water.”
Johnson said there is enough data to see a trend, but not enough to draw firm conclusions.
“If we get enough data, maybe we can advise anglers which fish they should box and which fish they should release.”
The study is also important because of treaty agreements with the Tribes that set exploitation rates for the angling groups, Johnson said. The study will continue until the questions are answered.
To report a tagged lake trout – there’s a $10 reward for all the fish that are reported in the study — or to volunteer to participate in the study, call Johnson at (989) 356-3232, ext. 2571.
