Sunday, November 30, 2008

The Welland Canal ... and other thoughts about lamprey

Today marks the anniversary of two events with lasting implications for the natural history of large freshwater lakes in eastern North America. On this day in 1824, ground was broken for the construction of the Welland Canal, intended to become a bypass around Niagara Falls and allow cargo ships to move freely from Lake Ontario (which has direct access to the Atlantic Ocean) into Lake Erie (which then allows access to the North American interior as far west as Duluth, Minnesota).

And on this day in 1829, the Welland Canal was completed. Although it was modified on a series of occasions over the next several years, it was on this date that free movement upstream from the St. Lawrence River into the heart of the continent became possible. And not just for ships, mind you, but for everything else that lived in Lake Ontario.

Unfortunately, this also meant Sea Lamprey (Petromyzon marinus). Sea Lamprey are one of a handful of jawless fish that feed as adults as ectoparasites, attaching to the bodies of thin-scaled bony fish (such as Lake Trout), rasping wounds with "toothed" oral muscles, and feeding on body fluids seeping out of the wounds. Sea Lamprey, native to Lake Ontario but unknown from Lake Erie westward, colonized the interior lakes through the Welland Canal. Over the course of about 100 years, their populations grew to the point where they had decimated many of the inland cold-water fisheries, causing enough damage to inspire a massive control program.

The life cycle of Sea Lamprey is complex. Adults swim up certain rivers and streams to lay their eggs. Once the eggs hatch, the larvae settle down where the sediment is sandy-to-silty, burrowing tail first with only their mouths and gill chambers exposed into the water. Here they live for several years as filter feeders before eventually metamorphosing into ectoparasitic adults and migrating downstream to a larger body of water (such as Lake Erie).

The only control method that seemed to be effective was the use of a chemical, 3-trifluoromethyl-4-nitrophenol, aka TFM. When applied into the water of the breeding rivers and streams, TFM killed the filter-feeding larvae. (While much debate swirled around the use of TFM, there is no debating its effectiveness at controling lamprey.) By the early 1960s, more than 130 years after the completion of the Welland Canal, the controlled use of TFM final brought lamprey populations under control in the Great Lakes.

The Welland Canal. Another example of unintended ... and long-term ... consequences.

Postscript: I can't help but add a coda to this story. The success of controling Sea Lamprey in the Great Lakes with TFM has been used to justify the control of Sea Lamprey in Lake Champlain, a large freshwater lake on the border of eastern New York and western Vermont whose outlet connects to the Atlantic Ocean via the St. Lawrence River. By the 1980s, lamprey attackes on freshwater fish in Lake Champlain had grown so severe that a coalition of federal, state, and special interest group advocates successfully lobbied for a TFM program in lamprey breeding rivers flowing into the lake. The primary argument was that Sea Lamprey entered Lake Champlain following the contruction of the Champlain Canal, connecting Lake Champlain southward to the Hudson River, in 1823. Thus, just as Sea Lamprey were successfully controlled with TFM in Lake Erie following their accidental establishment, so too should Sea Lamprey be controlled with TFM in Lake Champlain. What worked for controlling an exotic species in one location could and should be used to control the same exotic in another location.

There's just one problem with that concept. Sea Lamprey are not exotics in Lake Champlain.

They are irrefutably native, and the ability of agencies to shape public and court opinion to the contrary is a marvelous example of the power of words to create perception, and the risks of not knowing enough about the natural history of one's region.

Prior to the explosion of Sea Lamprey in Lake Champlain in the 1970s and 80s, they were typically described as a native species. This language began to change, however, as their effect on game fish like Lake Trout increased. Press releases and government brochures began to describe Sea Lamprey as "native, or possibly exotic," then as "exotic, but possibly native," and then as simply "exotic." When asked to justify the conclusion that they are exotic, the answer typically invoked the argument that they were not recorded in Lake Champlain until after the completion of the Champlain Canal. Interesting correlation, but hardly evidence of causation, given how little was recorded about the natural history of aquatic ecosystems in Vermont and New York prior to the 1840s.

In any event, now that the Sea Lamprey was "officially" an exotic species, it became justifiable to wage chemical warfare on them. Afterall, they were exotic, and shouldn't be there in the first place. The fact that TFM is also lethal to other forms of aquatic life, including the rare aquatic salamander called the mudpuppy (Necturus maculosus) was unfortunate, but that's just the price that needed to be paid to control this exotic pest.

Of course, if one REALLY wanted to learn whether or not Sea Lamprey were native or exotic to Lake Champlain, one could easily imagine a simply study that could answer this question. In fact, the study is so simple and so obvious that generations of my students, when posed with the question of how to determine the Sea Lamprey's status, always came up with the answer within 5-10 seconds: make a genetic comparison of Sea Lamprey from Lake Champlain with those in Lake Ontario and the Hudson River. Surprisingly, it wasn't until 2005 until someone thought to make such a comparison. And completely unsurprisingly, at least to me and many others, the results conclusively showed that the Lake Champlain populations of Sea Lamprey are too distinct from those in the Hudson River to have been recent colonists, but rather, were native.

Of course, the response of the pro-lamprey control lobby was predictable. When confronted with evidence that their straw-man argument was false, they began the rhetorical side-step shuffle. "Well," they said, "it really doesn't matter whether they are native or exotic. They still need to be controlled."

In fact, that may well be true. Blind warfare against exotics and blind acceptance of natives no matter what the circumstances are both foolish propositions.

What has my BVDs in a bunch on this issue is not that state and federal agencies would try and control a native species. Its that by ignoring the real natural history of this species ... and in fact manipulating the perception of the natural history of this species ... these agencies blinded themselves to looking at what was really going on. The search for the cause of the lamprey's increased depredation in game fish was derailed from the start: they were exotic, end of story. By not knowing the truth, simplistic solutions (dump poisons into the rivers) could be promoted and enacted without serious exploration of the real causes. Yes, the increased rate of depredation was real. I don't doubt that. But unless the true status of lamprey is recognized, then the critical question could never be asked: If Sea Lamprey are native, why is the rate of depredation increasing now?

I don't know the answer to that question, nor at this point does anyone else. Have we critically altered the biotic communities in the lake? Altered sedimentation or nutrient loading via rivers and streams? Altered influx of air-borne pollutants? All of the above? Something else entirely? Only future work will untimately answer these questions.

My point is this: We could never answer these questions until we asked them. And we could never ask them until we got the natural history right.

So perhaps the biologists who now say that it doesn't matter whether or not the Sea Lamprey are exotic are right, but only on a superficial level. It matters a great deal when it comes to asking the right questions.

Earlier in this post I mentioned that the fact that Sea Lamprey are native was unsurprising. You might well ask why. It is simply this: Geologists have known for decades that up until about 10,000 years ago, Lake Champlain was actually a salt-water arm of the Atlantic Ocean called the Champlain Sea. This sea drained and became a small freshwater lake only after two millennia had passed since the retreat of the last glacial ice sheet from this area and the Earth's crust could finally rebound in elevation. Ten thousand years ago this region not only had open access to the Atlantic Ocean, it was the Atlantic Ocean. Sea Lamprey had to have been present, and no rational argument has ever been advanced as to how they could have been wiped out only to successfully recolonize via the Champlain Canal.

Natural history is not just telling Just So Stories about nature. It's knowing the history of where one lives. That history is written in the rocks; it's written in each species' genome; it's written in the landscape carved by glaciers, cut by axes, and broken by plows. Ignore any part of that history and not only will you fail to find the correct answers, but you will fail to even ask the correct questions.

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