Back to back annual lampricide treatments are knocking down populations of young lamprey/. Source: T. Lawrence, GLFC

By Howard Meyerson

Sea lamprey numbers are dropping steadily in the Great Lakes, but nowhere more so than lakes Huron and Michigan where 20-year and 30-year lows are reported respectively. The joint U.S. and Canadian Great Lakes Fishery Commission recently announced the finding.

“Amazingly, we have 20-year and 30-year lows and we’ve seen a 40 percent drop compared to last year,” said Marc Gaden, GLFC spokesman. “All the other lakes are trending downward too. We saw a 15 percent drop in Lake Superior, about a 20 percent drop in Lake Erie and a smaller drop in Lake Ontario.”

Sea lampreys are the bane of the Great Lakes fishery, a parasitic invasive species that feeds on lake trout, salmon, steelhead and whitefish, among others. They first appeared in Lake Ontario in 1835, and then spread following improvements to the Welland Canal in the early 1900s. The Canadian ship canal is part of the St. Lawrence Seaway. It bypasses Niagara Falls which had until then blocked lamprey passage. Once it opened ship passage between Lake Ontario and Lake Erie, the lamprey spread from one to the other and beyond, according to GLFC.

The decline in recent years is attributed to an increase in Congressional funding for treatment. New control strategies have also helped, according to Gaden.

More money, new strategies

“We’ve stepped up the game and done more lamprey treatments. We’ve also become smarter about how (lampricide) applications are done,” Gaden said. “We decided a while back that if we treat rivers on consecutive years, rather than every three to four years, we could knock the population down to nothing. We get a 92 to 98 percent kill rate, but that residual does contribute. We’ve employed back to back treatments in Lake Huron, Michigan and Erie.”

Survey data collected by the GLFC shows Lake Huron lamprey populations peaked in 1993. Approximately 440,000 lampreys were estimated to live there. Today the estimate is 69,000 lampreys.  Lake Michigan populations peaked in 2004 when 175,000 were estimated. Today, the GLFC estimates 27,000 live there, an 85-percent reduction. Lake Ontario lamprey numbers dropped by 70 percent – from 77,000 in 2004 to 24,000 lampreys now. Lake Superior numbers dropped by 42 percent – from 135,000 lampreys in 2004 to 80,000. That remains above “target” for Lake Superior, according to Gaden, but the numbers are “trending downward.”

Lake Erie challenge

“Lake Erie is “an interesting situation,” Gaden added. “The good news is they are about 60 percent below the 2010 peak of 30,000, down to 10,000 today. But that still is well above (100 percent) our target of 5,000.

Target levels are established at the tipping point between cost-effectiveness and damage to the fishery. Treating populations below target are not cost-effective, according to Gaden. Populations that rise above target numbers cause increasing damage to the fishery and undermine fishery objectives.  Lake Erie lamprey populations presented the GLFC with a conundrum. Stream surveys in 2009 showed almost no lamprey remained in tributary streams, but the lake population was higher than before lamprey control was started in 1980, according to Gaden.

“We wondered how that was possible and decided they are coming in from outside of Lake Erie so we moved our assessment work from Lake Erie streams to the Huron-Erie corridor which includes the Detroit River, Lake St. Clair and the St. Clair River

“They are coming from that area, but we haven’t found the smoking gun yet. We are drilling in on it and think the source maybe on First Nation lands, so we have to arrange a partnership.”

The St. Mary’s River in northern Lake Huron is also a major lamprey contributor. Big and wide with a swift current, it provides great habitat and spawning ground, but is too large to treat with liquid TFM (3-trifluoromethyl-4-nitrophenol), the lampricide of choice for most Michigan streams. Gaden said a new approach is being employed there using a granular TFM formulation. It is applied only to hotspots where lamprey mapping efforts show the greatest populations are spawning.

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 © 2015 Howard Meyerson

Appears in Michigan Outdooor News.