Black River Sturgeon Study Designed to Enhance Population
There are a lot of reasons why lake sturgeon have captured the public's imagination.
Sturgeon are by far the largest fish in the Great Lakes, with individuals exceeding 100 pounds. They are often thought of as living fossils, having evolved very little from a prehistoric family of fishes. They are unusual in appearance - elongated with a wedge-shaped head and four barbels in front of their rubbery under-slung lips. And they are rarely caught, except by a tiny coterie of anglers who actively pursue them.
Native to the Great Lakes, sturgeon are rarely seen in Michigan -- except in the northeastern Lower Peninsula in spring, where sturgeon enthusiasts flock to the Black River in spring to observe the leviathans during their spawning run.
Once widespread and numerous in the Great Lakes, sturgeon populations have been decimated by overfishing, poaching and dam construction that has cut them off from their upstream spawning habitat. But a small population of fish persists in the inland lakes of the Cheboygan River system, most notably, Black Lake. Here, sturgeon are the subject of intense study as fisheries managers hope to preserve and enhance the population.
Every spring, a crew of fisheries technicians, under the direction of Michigan State University professor Kim Scribner, captures sturgeon in large landing nets in the shallows of the Black River. The staff measures, weighs and tags the fish, collecting eggs and milt from the creatures to produce young in a stream-side hatchery to be released back into the system in the late summer, giving them a helping hand during those first few months of life when they are especially vulnerable.
"We have problems with natural recruitment," said Scribner, whose work is funded by grants from a variety of sources, including the Department of Natural Resources and Environment and the Great Lakes Fishery Trust. "Almost all of them are eaten on their way downstream."
The process begins with a team of fisheries technicians working on a stretch of Black River that includes seven distinct spawning areas. This year, four technicians and an MSU graduate student (studying a somewhat-related topic) worked on the project.
Greg Hill, from Oregon, Wisc., came equipped with a wet suit, mask and snorkel. Hill, carrying a large but handle-less landing net, dives into the upstream end of the deeper pools, swimming downstream looking for sturgeon. He either nets the fish or spooks them out of the holes and into the shallows, where the other technicians use landing nets to corral the fish.
When a fish is captured, it's examined for previous tags or scars that might indicate they were previously tagged. Tags are applied near the dorsal fin, (left of the fin on females, right of the fin on males). The technicians use different colored tags for the sexes and different colored tags for early in the run and late in the run. By noting the position and color of a tag, workers can immediately identify the sex and when the fish was tagged.
The technicians perform a quick physical examination - length, weight, circumference, sex - then check the females to see if they're ready to spawn. If females are ripe, technicians take eggs, collect milt from males and send the products to the hatchery where they'll be mixed for fertilization.
The fisheries workers also implant sturgeon with passive integrated transponder (PIT) tags. PIT tags give fisheries workers the opportunity to retrieve data from the fish by using a receiver that's waved over the PIT. By comparing the data from when the fish was tagged to when it was recaptured, fisheries staffers can determine growth rates and compare other biological data.
The hatchery -- which was quickly built in a partnership involving the DNRE, hydropower company Tower-Kleber Limited Partnership, and the non-profit Sturgeon for Tomorrow -- probably exceeded expectations for a brand new facility last year: It produced about 1,500 4- to 7-inch fish that were stocked into Black Lake and the Cheboygan River system in late summer.
"As far as I'm concerned, it was a success," said DNRE fisheries biologist Kyle Kruger. "Despite dealing with a new facility, the technicians and students did a great job. We had fish in the facility, and we had fish at the end to stock out to help in the rehabilitation of the Black Lake system and even allow a couple of tiny plants over at Burt and Mullet as well.
"At one point of time, we didn't even think we'd have water in the facility. Hopefully next year we'll be even more successful."
The goal is to produce 1,500 fish annually for stocking, Scribner said. But the efforts are producing other benefits as well.
"We've captured and recaptured hundreds of these individuals and we're able to genotype the adults and the offspring," Scribner explained. "We can collect larva and trace them back to individual male and female adults, trace them to specific spawning sites and dates, and correlate that data with current flow and temperature."
Because sturgeon do not reach sexual maturity until they are 15 to 25 years of age, "it'll be a long, long time before any of the larva return to spawn," Scribner said.
Sturgeon larvae hatch with no eyes and no mouth. They burrow into the substrate and spend two to three weeks absorbing their yolk sac and developing. When they emerge, they begin drifting downstream toward the lake. Very few make it.
Scribner said the hatchery-raised fish should survive at a far greater rate. He's also hopeful that by raising the fish right on the river - instead of shipping them to an off-site hatchery elsewhere - the fish will be better suited to survive in their home habitat.
Although the future of Black Lake's sturgeon population is far from secure, sturgeon enthusiasts are hopeful that the research being conducted on the Black River will give the population of mysterious leviathans an important boost going forward.