Looking for juvenile sturgeon on Black Lake
Sept. 19, 2013
Black Lake is unique among Michigan's inland waters in one significant way: it is the only lake that maintains a remnant population of native lake sturgeon large enough to support a recreational fishery. The February spearing season on Black Lake is one of Michigan's most unusual (and festive) fishing opportunities.
But just how large that sturgeon population is -- and how much help it needs to continue to support that recreational fishery -- was the focus of a three-week survey effort by the Department of Natural Resources Fisheries Division this August.
In short, DNR fisheries managers wanted to figure out what's going on with the sturgeon population in the 10,000-acre Lake Huron watershed lake. Fisheries biologists wanted to know how the thousands of sturgeon stocked in the lake over the course of the last dozen years had fared.
"It's mostly a stocking evaluation, looking at juveniles," explained Ed Baker, the DNR fisheries biologist who runs the Marquette Fisheries Research Station and has been working on sturgeon since 1995. "It's a basic mark-and-recapture survey."
The DNR dispatched three crews of fisheries technicians to survey the lake with gill nets. Each crew fished two 1,200-foot gill nets -- 600 feet of 6-inch mesh and 600 feet of 8-inch mesh -- for four days a week. They set nets, let them fish for an hour, and then returned to them to check and see what showed up.
"We caught 281 unique lake sturgeon," Baker said. "The majority of those were juvenile fish. The smallest fish we caught was around 22 inches; we guess that's a 3-year-old fish. The fish in that size range were stocked in 2010 or 2011. They're really growing quite rapidly."
Many of the juvenile fish had coded-wire tags in their snouts, but DNR staff cannot gather any data from those tags without removing them. Fish captured in the survey were also marked with passive integrated transponder (PIT) tags so that, in the future, any fish handled can have that information collected electronically.
The largest fish caught in the survey measured 73 inches. The largest captured with a coded-wire tag was a 52-incher, Baker said.
"That (52-inch) fish was probably stocked in 2001," he explained. "We took fin ray samples from the juvenile fish to determine their ages in the lab, but it's going to take couple of months to section those fin rays and age the fish."
Of the fish that measured 52 inches or less -- 252 total -- about half had coded-wire tags. Still, the DNR will be able to tell whether the untagged fish came from hatchery stock or were naturally produced, Baker said.
"We've stocked about 13,000 sturgeon since 2001," he said. "There were a bunch of hatchery fish released in the lake that do not have coded-wire tags. But if the fish came out of the hatchery, we know which adults we collected eggs and milt from. So we'll be able to match the fish without tags to their parents. Once we've gone through all of that data, then we should have an answer about how much natural reproduction there is in the lake. And we'll have a better idea of survival of stocked fish."
There has not been a lot of natural reproduction on Black Lake in recent years, "certainly not enough to maintain that population," Baker said.
Although it will take some time to analyze all the data, Baker said he was able to draw some conclusions based on what fisheries crews saw. For instance, over the course of the survey, only five fish were recaptured.
"That's not a lot," Baker said. "That means the abundance estimate is going to be pretty large.
"The survival of the stocked fish is obviously very high and they're growing very well," he continued. "They're not skinny and emaciated. They're very healthy fish, so they're obviously finding lots of food out there."
Fisheries managers want that to continue, so part of the assessment is designed to make sure the DNR isn't stocking too many for the lake to support.
Overall, Baker said he was pleased with the survey. Two sturgeon died during the survey -- there is almost always some mortality associated with gill nets -- but the large mesh used allowed the lake's smaller fish to escape unharmed.
"We didn't want to fish any mesh smaller than 6 inches because we didn't want to catch a bunch of suckers or perch or any of the other fish that are swimming around in Black Lake," Baker said. "We did catch a few smallmouth bass, but they were all released alive. We really did a good job of minimizing the catch of non-target species and minimizing the mortality of that by-catch. Everything that we caught that was not a sturgeon was released alive."
Black Lake is part of the Cheboygan River Watershed (which includes Burt Lake and Mullet Lake) but is isolated from the rest of the watershed by the dam on the lower Black River. The dam, built around the turn of the 20th century, trapped the sturgeon that were upstream of Lake Huron in the lakes when it was closed. Now, more than a century later, that remnant fish population -- with a helping hand from the DNR -- continues to provide a unique recreational fishing opportunity to Michigan anglers.
For more information on Michigan's lake sturgeon, visit www.michigan.gov/sturgeon.