March 10, 2011
Department of Natural Resources and Environment fisheries biologists are excited about what appears to be increasing numbers of a subspecies of cisco (aka lake herring) that was thought to have disappeared from Lake Michigan.
The fish, referred to by early taxonomists and old commercial fishermen as "reef herring," is a subspecies of cisco that can grow as large as whitefish, a larger member of the same family of fishes and a popular commercial and recreational fish.
At one time, ciscoes made up the base of the food chain in Lake Michigan and were the primary prey of Lake Michigan's alpha predator, the lake trout. As other prey species, notably smelt and alewives, both exotic species became more abundant in Lake Michigan, the population of cisco dropped. Alewives and smelt apparently fed on larval lake herring, out-competing the natives.
But this subspecies of cisco has a unique life history that gave it a leg up on other cisco.
For the most part, cisco are indiscriminate spawners that produce free floating larvae, explained Randy Claramunt, a fisheries research biologist with the DNRE. This subspecies, however, selects more precise spawning sites.
"This fish selects reefs with large piles of cobble, rocks anywhere from the size of a baseball to a softball," Claramunt said. "They lay their eggs in the reef and the eggs hatch in the cobble, the larvae drift into near-shore bays and grow to a couple inches before heading to deep water.
"That's a completely different life strategy."
Although cisco continue to thrive in northern Lake Huron and Lake Superior, they are still spawning "the old fashioned way," Claramunt said.
"This is a natural selection process," Claramunt said. "I truly believe that all the other forms that did not adapt have been filtered out. This fish has chosen a life strategy that is very successful."
Female reef herring produce more eggs than other cisco species in the Great Lakes and the young are faster growing.
"Prior to the discovery of these cisco in Grand Traverse Bay, it was thought there were no reproducing cisco anywhere in Lake Michigan," Claramunt said.
DNRE creel clerks first began seeing the larger cisco being caught by recreational anglers who were trolling for trout and salmon, and thought they were catching whitefish, in the mid 1990s. Meanwhile, the fish began showing up in commercial whitefish nets and in DNRE survey nets, as well.
"Over time it appeared their numbers were increasing," Claramunt said.
Although some reef herring have been found in other parts of Lake Michigan, about 80 percent of Lake Michigan specimens that biologists see are coming from Grand Traverse Bay.
"We didn't know why they were showing up in Grand Traverse Bay," Claramunt said. "We had no idea if they were spawning in Lake Michigan, moving from other Great Lakes, or moving in from connected inland lakes. We didn't know."
As it turned out, the DNRE Fisheries Division was part of a multi-agency study investigating whitefish spawning. In 2004, fisheries researchers found spawning cisco on the same reef as lake whitefish, but separated by about a 10-day to two-week time period from the whitefish.
Since 2007, the DNRE has been setting nets in the fall to look at spawning aggregations, monitoring eggs, larvae and juvenile reef herring.
"It seems as though they've been pulling off more and more recruitment every year and are increasing in abundance," Claramunt said.
"I think it's very exciting, because we haven't found them anywhere else and they're only spawning on one reef complex," Claramunt said. "But if something were to happen to that reef, it could be the end of them."
Claramunt said that potential threats to the reef complex, such as dredging and the deposition of spoils, are real.
Under many circumstances, the immediate reaction to such a discovery would be to collect specimens and spawn them in hatcheries, to increase their numbers. Claramunt says he thinks a better strategy would be to provide more spawning habitat for them so they can continue to expand on their own. But so far, he's been unable to find a source of funding to build additional reefs, he said.
The reef cisco are utilizing a reef complex in the Elk Rapids area, Claramunt said.
"They come in, go to their prime habitat, and spawn, all within a matter of a few days," he said.
"They look like they are recovering on their own and are living in a Lake Michigan that is the Lake Michigan of today. It's such a new and unique animal to Lake Michigan, it's hard to figure out how this fits into our overall management of the lake."
Preliminary genetic testing has shown that these fish have more in common with Lake Superior cisco than northern Lake Huron fish, indicating that it is not a simple case of migration.
"Could they have hybridized with inland lake whitefish or other Great Lakes strains?" Claramunt asked. "It is a possibility, until we do more substantial genetic work, we won't know. And if it's not a pure native fish, what do we do with it?"
Even if it is a hybrid, it is the result of natural reproduction, not hatchery breeding.
It shows, as is commonly said, that nature abhors a vacuum. As Lake Michigan's ecosystem changes, reef herring have begun to find a niche in the lake.