Field Samples: Studying Fish Migrations in Great Lakes Streams

Field Samples is a weekly Q&A asking researchers what they’ve been up to and what they’ve learned. Today, Lake Superior State University professor, Ashley Moerke, talks about her time on sabbatical studying Great Lakes fish migrations at the CFL. 

Longnose suckers headed upstream for spring migration.
Longnose suckers headed upstream for spring migration. Photo: Evan Childress

Who are you, where are you from and how did you get here?
Ashley Moerke. Courtesy: Lake Superior State University
Ashley Moerke. Courtesy: Lake Superior State University

My name is Ashley Moerke and I am a professor of biology at Lake Superior State University (in the UP of Michigan) where I teach in the Fisheries and Wildlife and Conservation Biology programs.  I have been spending part of my sabbatical working on research at the CFL in collaboration with Pete McIntyre, Solomon David, and Evan Childress (a former grad student of Pete’s).
Pretend we just boarded an elevator and you only have a one-minute ride to tell me about your research – can you capture it a few sentences?
I’m interested in linkages between aquatic ecosystems, primarily between the Great Lakes and the streams that flow into them.  There are 1000s of small streams that flow into the Great Lakes, yet we have very little understanding of their importance in fueling nearshore food webs and their importance as habitat for Great Lakes fishes.  My research here at the CFL, working with Dr. McIntyre, is focusing on the latter–the importance of tributary streams to Great Lakes fishes.  We are hoping to gain a better understanding of who, when, why, and for how long Great Lakes fishes migrate into these small streams.
What question did you ask and answer or do you hope to answer? What other questions might your work lead scientists to ask?
Our research provides some of the most detailed data on spawning migrations in Great Lakes tributaries, including the variation in spawning assemblages (i.e., species using these tributaries for reproduction) and timing across multiple northern Lake Michigan streams.  We found that spawning assemblages were generally consistent, with longnose suckers arriving first, followed by northern pike, and then white suckers and steelhead.  Migrations of all species peaked within approximately 10 days of each other, indicating potential for resource overlap during spawning. Our data also suggest that temperature likely plays an important role in initiating the onset of these migrations.  Migrations generally peaked [when water temperature reached] between approximately 6-8 degrees Celsius. However, water-level fluctuations due to snowmelt runoff in the spring may be a cue for the onset of migration in Great Lakes streams as well. 
We also found that male suckers tended to hold in the streams longer and outmigrate later and in lower numbers than females, which we hypothesize has led to higher in-stream mortality and a shift to a female-biased sex ration in the spawning populations.  I think this work will help scientists determine potential impacts of climate change and invasive species on spring migrations in the future.
Moerke is, among other things, studying what makes these suckers run. Courtesy: A. Moerke
Moerke is, among other things, studying what makes these suckers run. Photo: Evan Childress

Not to sound harsh, but why should someone NOT in the field of
freshwater sciences care about your work? What’s a bigger picture implication, in other words?
The Great Lakes fishery is valued at $7 billion, and many of these species that are valued for recreational use (e.g., salmon, steelhead, pike) rely on connecting streams for spawning, refuge, or foraging.  It is important for us to understand where and when these species are using tributaries so that we can ensure protection of those critical habitats.
What do you love about your work? What do you love, well, not-so-much?
Well, most of my actual “work” is working with undergraduates at LSSU.  I teach courses in aquatic sciences and advise senior thesis students on their research projects.  I absolutely love the opportunity to figure out how to engage and challenge my students–it never gets boring.  And, I cannot think of a greater reward than seeing them excel personally and professionally.  I’ve been doing this long enough that now many of my former students are my research collaborators (and the teacher becomes the student).  It is a fabulous career path (if you aren’t driven by money).
I also equally enjoy engaging in research, particularly field research that has direct implications for conservation and management of freshwater resources.  And, it is difficult to find a better office than the banks of a forested trout stream with the odor of freshly fallen leaves or a summer rainstorm!
Tell me about one funny, memorable, exciting or awesome moment from the lab or the field.
I think my most memorable moments are those that shaped my career path.  I vividly recall my time as an undergraduate doing research in northern Alaska on stream ecology.  I can remember working in the tundra where ice was on the lakes until June, the mosquitoes were five layers thick on your jeans, and you worked until 2am in the field because it was always light–yet, I loved every bit of it!
Courtesy: A. Moerke.
Measuring a longnose sucker. Photo: Evan Childress

I also can remember a time during my graduate work when we were sampling stream fishes and ended up getting so many that we had to identify them by the truck headlights.  Of course we didn’t expect to be there that long so we didn’t bring a lunch, much less headlamps!  Field work always has surprises!  Now I tell my students that they should never expect it to go as planned in the field.
Where do you hope to go from here? New research questions? Continuing with this work?
Yes, I’m continuing this research.  I have research funded to characterize fish migrations in a few Lake Superior tribs, but we will be conducting sampling from ice off to ice on.  We are working with Bay Mills Indian Tribe to determine the importance of small tributaries for recreational and forage fishes so that they can manage their landscapes and their fishing regulations to conserve tributaries that provide important habitat for Great Lakes fishes. And, I hope to continue my collaborations with the wonderful CFL researchers I have met while visiting here this past month.