Study to look into sea lamprey, trout

February 24, 2010 at 03:22 PM

ASHLAND, Wis. (AP) - Despite 70 years of control efforts, a University of Wisconsin researcher said climate change and a warming Lake Superior could lead to a rise of the invasive - and destructive - sea lamprey.

Methods ranging from chemicals to barriers have been tried to control sea lampreys, which have a round mouth full of teeth and attach to fish, draining their blood until they drop dead to the bottom. Those who study sea lamprey readily admit complete eradication throughout the Great Lakes is all but impossible.

But UW-Madison zoology professor Jim Kitchell will dig into whether the impact of climate change on Lake Superior - namely, that “it is the most rapidly warming lake in the world” - and is leading to an increased population of sea lamprey.

Kitchell’s project and a number of others ranging from lake trout to wild rice genetics around Lake Superior recently received nearly $2 million in grants through the National Oceanic and A tmospheric Administration’s Wisconsin Sea Grant program.

With less ice cover over Lake Superior, the lake absorbs more heat, and has warmed 1.2 degrees Celsius per decade since 1980, Kitchell said.

“It doesn’t sound like much, but it’s about five times that of what most lakes are doing and it’s much more rapid than air temperatures are warming,” he said.

Lampreys’ favorite prey in Superior is lake trout, which have returned to historically high averages, giving fewer lamprey more fish on which to feed, Kitchell said.

“They’re going to feed until they’re satiated, drop off and find a new host, and the bigger they get, the bigger their appetites get so the more hosts get attacked,” he said.

In the fall and spring, they congregate around the warm nearshore waters, preying upon the same lean lake trout sought by commercial fishermen, tribes through treaty rights and recreational anglers, Kitchell added.

Yet by the 1990s, lake trout were alread y considered abundant and the lampreys continued to grow bigger, leading researchers to think other factors were in play.

Kitchell said lake trout typically aren’t found in water above 10 degrees Celsius, or about 50 degrees Fahrenheit. As the lake warms to that point earlier in the year, and remains warmer for longer, it gives the lamprey more time to feed and grow.

“The combination of (trout abundance and temperature) has basically caused lamprey size to increase by more than 30 percent, much the way temperature is doing,” he said.

Bigger lamprey kill more and bigger fish, and therefore “impose more mortality” down the line of the food chain. They also spawn more eggs, and Kitchell said even though control efforts from a variety of different angles have been extremely successful, there is a limit.

Say, for example, a lamprey yields 10,000 eggs, and 9,500 are wiped out through chemical application. A bigger lamprey could yield 15,000 eggs, but the er adication effort still knocks out 95 percent, more eggs survive and migrate downstream, Kitchell said.

Studying the lamprey presents its challenges, however, as Kitchell said they spend more of their time in the deep, colder water and out of sight.

The challenge is especially acute in analyzing the effect of lamprey on Siscowet Lake Trout, which roam even deeper in Lake Superior. Kitchell said what is known is lamprey that prey on Siscowet end up bigger than their brethren.

Lamprey typically spend one summer growing before returning to streams to spawn, and spawning for the species is dependent on size, not age. Siscowet-eating lamprey grow slower in the colder, less-productive water and end up spending a second growth period in the depths, Kitchell said.

They emerge to spawn at 300 grams, 50 percent larger than the average adult, and able to kill more and bigger fish, Kitchell said. Although the extent of the impact from lamprey on Siscowet is unknow n, Kitchell added the interaction could be more significant if a commercial market develops for the high quality fish oil for which Siscowet are known.

Much of what is known comes from carcass trawls in shallower areas where the bottom of the lake is around the 10 degrees Celsius that lake trout favor. Of the dead trout hauled up during one Lake Ontario trawl, 82 percent had a lamprey hole in their sides, Kitchell said.

Still, despite 70 years of research, answers about the lamprey are far from solved, he added.

“Most of what lampreys do remains a bloody mystery, largely because it’s done in dark, cold water and we just don’t see what’s going on,” he said. “The only direct evidence we have is the carcass trawls, and that dead fish sink, and a lot of the dead fish were killed by lampreys.”