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Below The Surface

Saturday, December 8, 2012

Lake Trout Moving "Below the Surface" of Lake Champlain


We at ECHO are fortunate to have a wonderful resource in the UVM Rubenstein Ecosystem Science Laboratory housed with us at the Leahy Center for Lake Champlain.  The "Rube" as it is called, is the home of some of the most current research on the Lake and its Basin-- all done by a dedicated, interested, and sharing group of UVM faculty, students, and staff.  Among them is Dr. Ellen Marsden, who has been studying lake trout in Lake Champlain for a long time.  As you may already know from our video about Champ, Dr. Marsden has a knack for communicating scientific concepts concisely and in an accessible manner.  Sometimes a moving picture can tell us what words cannot.  For instance, she and her graduate student, Bret Ladago, built a underwater Remote Operated Vehicle (ROV) that is capturing remarkable footage of lake trout staging for spawning in shallow reef habitats in Lake Champlain (for the best viewing, maximize the view):

In this one, several lake trout are "shoaling" -- staying in one area where they may later spawn.  Several trout in this small group have adult sea lamprey attached to them; some show wounds from previous parasitism by sea lamprey.  To my eyes, the proportion of fish with either sea lamprey attached or wounds is dramatic; yet overall I only can get a really good look at perhaps a dozen individual lake trout.
In this one, a much larger number of fish are moving past the ROV while "schooling."  Again, there are signs of sea lamprey parasitism on a portion of these fish.  In this case, I can see that there are many more fish in the area and I can examine many more fish for signs of parasitism by sea lamprey than in the previous footage.

This amazing footage provides never-before-seen glimpses into the appearance and behavior of Lake Champlain's lake trout.  But yet it is important to understand that these are glimpses- just a very small snapshots of the large population of lake trout.  For example, the shoaling video alone could make us believe that despite our efforts to control the numbers of sea lamprey in the Lake, a majority of fish show signs of parasitism.  The second video may lead us to temper that view somewhat.  More footage might reveal other impressions.  How do we know what the true rate of parasitism of lake trout by sea lamprey is?  Are efforts to control sea lamprey changing this over time?

While the video footage is certainly engaging, its not the best tool for estimating rates of sea lamprey parasitism.  For example, because we cannot always see both sides of the trout, and because we do not know if individual trout may be seen multiple times.  Furthermore, there appears to be behavioral differences between the sets of footage which might indicate that the fish we see may not be average or typical members of the population.

Fisheries science provides the tools we need to answer these questions.  By actually capturing and examining hundreds of large lake trout in a standardized way, the Lake Champlain Fish and Wildlife Management Cooperative has collected data year after year to provide answers.   According to their data (presented here from Lake Champlain Basin Program's 2012 State of the Lake Report), rates of wounding on both lake trout and atlantic salmon by parasitic sea lamprey have been declining since 2007:
Taken from: http://sol.lcbp.org/biodiversity_impact-sea-lamprey-on-salmon-trout.html
For 2011 around 40% of large lake trout had scars from infestation of sea lamprey.  Ideally, this rate will continue to drop over time and achieve the 25% target rate set by fisheries managers for lake trout.

There are many reasons that we should care about the health of lake trout populations in Lake Champlain.  As large, deep water fish-eating predators, they exist with Atlantic Salmon as one of the top predators in the Lake, playing a role in maintaining the structure of the Lake's food web.  By virtue of their size and habitat, they are part of the economic draw to the Lake, supporting the business of fishing guides, equipment sales, and fishing license sales.  Some of these dollars get invested back into conservation activities of our state and federal governments.  Additional public dollars support management activities to control the numbers of immature sea lamprey growing up in local streams and rivers and to rear young lake trout for stocking.  Last but not least, as these videos attest, they are graceful, resilient, and beautiful members of our Lake community.

For more information about lake trout in Lake Champlain, check out this story from UVM's University Communications series, or visit Dr. Marsden's website.


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