Voracious predators at the top of Great Lakes food chains, lake trout (Salvelinus namaycush) in Lake Superior sustained a tribal and commercial fishery for centuries. Even after other fish populations crashed under commercial fishing pressure, pollution, and habitat loss, lake trout appeared to be surprisingly resilient. But in the mid 20th century, their populations fell off the edge of a cliff . In 1944, the commercial catch of lake trout in Wisconsin alone totaled more than 6 million pounds; a decade later, only a few fish were caught, and by 1956, lake trout had vanished from most of the Great Lakes. As top predators, the loss of lake trout had rippling effects. Populations of rough fish such as alewives and smelt exploded when their predators vanished, and zooplankton populations dropped sharply.[ii] When commercial and tribal fisheries shut down, leaving local economies with little to support them, the social effects were devastating.
Why did lake trout crash so suddenly? Fisheries biologists usually blame the sea lamprey (Petromyzon marinus), which the United States Geological Survey calls "a marine invader from the Atlantic Ocean" that "quickly devastated the fish communities of the Great Lakes."[iii] The historical narrative offered by fisheries biologists is that sea lamprey invaded the upper Great Lakes after modifications to the Welland Canal around Niagara Falls in the 19th century. Sea lamprey sucked the fluids from lake trout, devastating their populations. Eventually, chemists and fisheries biologists managed to restore lake trout with the help of TFM, a synthetic chemical that kills developing lampreys without hurting too many young lake trout.[iv]
This is a satisfying story for many folks, perhaps because it essentially takes the blame off people. Yes, people did modify the Welland Canal in this story and open the Pandora's box of invasive species. But they didn't intend to do this, and anyway, scientists saved the day.
The problem is that the evidence supporting this story is equivocal at best. Sea lamprey did indeed parasitize a lot of lake trout, but it's not clear that the sea lamprey really were non-native invaders who snuck into the upper Great Lakes and then wiped out their hosts. Nor is it clear that lake trout would have been fine if only the sea lamprey hadn't shown up. While sea lamprey were an important factor in the collapse of lake trout populations, focusing on them alone ignores the larger context of ecological change in the Great Lakes....
The best historical analysis of Great Lakes fisheries is Margaret Beattie Bogue's Fishing the Great Lakes, and I won't repeat her detailed arguments here about commercial fishing and regulatory paralysis. Anyone interested in Great Lakes fish should start with her book, which reveals how rapid was the growth of commercial fishing, and how useless were Canadian and US attempts to control the harvests. Bogue shows how wholesale fish dealers such as A. Booth and Company quickly monopolized the industry. Fishers squeezed by declining harvests and predatory pricing used ever more intense technologies to catch ever declining fish. Governments tended to blame the fishers for dwindling fish populations, while fishers tended to blame habitat destruction, and everybody blamed the tribes. When governments did try to respond to clear signs that fish populations were collapsing, their measures were ineffective because jurisdictions were fragmented across two nations, several tribes, three states, and one province.[v]
I am currently revising an essay for Border Flows, a volume edited by Dan Macfarlane and Lynne Heasley, that will build upon Bogue's analysis by focusing on a single fish--lake trout-- in Lake Superior, asking how multiple stressors interacted in changing social and ecological landscapes.
NOTES [i] Quoted in M B Bogue, Fishing the Great Lakes: An Environmental History, 1783-1933 (Univ of Wisconsin Pr, 2000). 128.
[ii] H M Tyus, Ecology and Conservation of Fishes (CRC Press, 2011). 130-131.
[iii] "Sea Lamprey Fact Sheet," USGS Great Lakes Science Center, http://www.glsc.usgs.gov/main.php?content=research_lamprey&title=..nu=research_invasive_fish (accessed July 12, 2012).
[iv] B R Smith and J J Tibbles, "Sea Lamprey (Petromyzon Marinus) in Lakes Huron, Michigan, and Superior: History of Invasion and Control, 1936-78," Canadian Journal of Fisheries and Aquatic Sciences 37, no. 11 (1980): 1780-1801, Daniel W Coble and others, "Lake Trout, Sea Lampreys, and Overfishing in the Upper Great Lakes: A Review and Reanalysis," Transactions of the American Fisheries Society 119, no. 6 (2011): doi:10.1577/1548-8659(1990)119<0985:LTSLAO>2.3.CO;2, John W Heinrich and others, "Sea Lamprey Abundance and Management in Lake Superior, 1957 to 1999," Journal of Great Lakes Research 29, Supplement 1, no. 0 (2003): doi:10.1016/S0380-1330(03)70517-6. http://www.sciencedirect.com/science/article/pii/S0380133003705176, Michael J. Hansen, "Lake Trout in the Great Lakes," in Our Living Resources: A Report to the Nation on the Distribution, Abundance, and Health of US Plants, Animals, and Ecosystems (US Dept. of the Interior, National Biological Service, 1995).
[v] Bogue, Fishing the Great Lakes: An Environmental History, 1783-1933.