Lake Michigan lake trout now reproducing naturally

Green Bay, Wis. — It appears that Lake Michigan lake trout have finally figured it out – they are reproducing naturally.

The Green Bay office of the U.S. Fish and Wildlife Service (USFWS) published a scientific report in January that announces the discovery of a significant number of young and wild lake trout in several areas of Lake Michigan. Although fisheries researchers have found that the stocked lake trout have produced some young as far back as 1981, this is the first evidence of consistent recruitment, and that provides hope to researchers and biologists that a naturally sustaining population of this native fish is on the horizon.

The report was published in the North American Journal of Fisheries Management under the title “Evidence of Wild Juvenile Lake Trout Recruitment in Western Lake Michigan.” The authors were Dale Hanson, Mark Holey, Ted Treska, Charles Bronte, and Ted Eggebraaten.

The federal government, via the USFWS, has been the major player in the establishment of lake trout. Lakers disappeared in the 1950s as a result of commercial overfishing and sea lamprey predation. The selective chemical called TFM that kills young lamprey in tributaries was first used in Wisconsin in 1960. Federal fish hatcheries geared up to stock lake trout at that time and the first 205,000 fish were stocked in northern Door County in 1965. Every one of those fish and the millions stocked over the ensuing years have had a fin removed for easy identification. This has been an incredible investment of time and money, but is the only way to tell if lake trout are reproducing naturally.

Over the years, studies have shown that as many as 3 percent of the lake trout, which are stocked at fingerling size, either grow back the clipped fin or the fin is somehow missed in the clipping process. In the past, these falsely unmarked fish have confused the search for natural fingerlings. But this study, which examines trout captured in nets set off Baileys Harbor, Manitowoc and Milwaukee, found as high as 20 percent of the fish were unmarked.

The authors state, “The occurrence of these wild fish is much higher than can be attributed to marking error and provides evidence of some successful lake trout natural reproduction during 2007-10 in northwestern Lake Michigan, in addition to the 2006 and 2007 year-classes in the southern portion of the lake.”

Illinois biologists have also found unmarked trout in their sampling and off Waukegan, Ill., in 2011 they tallied 16 unmarked fish among a sample of 154, which comes to 10 percent. This corroborates the Wisconsin discoveries and shows that lake trout are finally on their way back.

No one knows why it has taken 48 years of stocking before the lake trout could spawn on their own. Theories as to why included heavy pesticide loads, improper stocking locations, and deterioration of the quality of the spawning reefs themselves. The latest cause focused on a thiamine deficiency that came to light in 1996. It seems that the exotic invader, alewife, which make up most of the diet of lake trout, cannot provide the level of thiamine which will allow the lake trout eggs and fry to hatch and develop normally. But as alewife numbers have declined, lake trout eggs have exceeded the threshold level of thiamin since 2008 and perhaps that is the reason the fish are finally hatching and growing successfully.

Though very significant and encouraging, these findings show that lake trout are still a long way from complete rehabilitation. And, of course, without a continued commitment to sea lamprey control all would be lost very quickly. Nonetheless, this is an exciting and landmark discovery – probably rivaling in importance the introduction of Pacific salmon in the 1960s. 

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