Field Samples: How Fish Find Their Niche

Field Samples is a Q&A with aquatic researchers. Today the incomparable John Magnuson talks about research on how fish find their niche. John will give a public lecture today at noon in the Water Science & Engineering Lab as part of the Center for Limnology’s weekly Wednesday seminar

Who are you, where are you from, and how did you get here?    
John Magnuson. Photo courtesy: Clean Lakes Alliance
John Magnuson. Photo courtesy: Clean Lakes Alliance

I am John J. Magnuson, born in Illinois, schooled in Illinois, Minnesota, and the University of British Columbia, Canada. I came to UW-Madison as a faculty member in Zoology with an office in the Limnology Laboratory. My position before coming to Wisconsin was as a blue water fishery oceanographer in the Central Pacific stationed on Oahu.

Pretend we just boarded an elevator and you only have one-minute to tell us about what it is you’re presenting on at seminar.  

What determines where fishes are distributed? Their physiology and behavior allows them to choose places to be in a lake or stream based on water temperature, dissolved oxygen, food abundance, and other features. I will focus on what we call their “niche” in a complex of environmental features. Across Wisconsin and the world fishes move through a systems of lakes and streams that resembles what we can think of as islands isolated or somewhat isolated from other waters. Invasions and local extinctions occur in these islands that determine which fishes form the community of waters across the landscape.

Why should someone not in the field of freshwater sciences care about your work?

I was drawn to these question by curiosity and my life experiences. Being a sea-going ocean scientist in the Pacific conditioned me to later look at lakes as “islands” here in Wisconsin. The information is useful to fishery scientists, conservation biologists and agencies making decisions about fishes and conservation.

What question did you answer or do you hope to answer? What other questions might your work lead scientists to ask?  

How do fish locate a place to live in a complex environment? This includes human modifications to that environment, such as a heated effluent from a power generation facility or dams along a once connected river. Second, in what ways are fish communities in lakes and streams determined by the same process that determine the land dwelling species that live on oceanic islands? As our world climate warms and changes, how will the new environmental features of lakes and drainage systems influence fishes?

What do you love about your work? What do you love not-so-much?      

I am an emeritus professor and have the chance to do science for the same reasons I entered the field of fish and fisheries ecology. I enjoy learning,  discovery, problem solving, being out in nature, working with students and helping students and the public learn about the world around them.  

Tell me about one funny, memorable, exciting or awesome moment from your work either in the field or in the lab.

For me this is a challenge because I have been doing science for some 60 years. Picking one memorable moment is practically not possible! But to comply here is a short story:

After studying the thermal niche of fishes in the laboratory (in other words, what temperatures they preferred to hang out in), we began to ask whether the laboratory results [were reflected in] their distributions in the field. We started locally with Lake Monona and the thermal outfall from MG&E (the warm water returned to the lake via a power plant in downtown Madison). We then looked a Lake Michigan and how fishes were distributed on the bottom as the thermocline’s boundary swept back and forth at mid-depths. We then were attracted to the north wall of the Gulf Stream on the continental shelf off of Cape Hatteras in the Atlantic. The meanders of the stream, like a flag in the wind, swept north and south along the shelf [changing the water temperature wherever it meandered]. At each step to larger more complex and open waters, I was excited that we could predict the thermal niche of fishes based on what we’d learned from lab experiments. Fishes in the thermal plume in Lake Monona, the dynamic thermocline in Lake Michigan and, finally, the meanders of the north wall of the Gulf Stream in the Atlantic were all trying to stay in their ideal thermal niches.

Where do you hope to go from here either with this work, or, literally, after your time at Hasler Lab?

I hope to stay active at the Center as long as I can make contributions and not become a burden!