Research shows freshwater fish like complicated shoreline environments, just as saltwater species do

LAWRENCE — As an avid fly fisherman, Keith Van de Riet spends a lot of time trying to think like a fish does.

He does likewise in his day job as an associate professor at the University of Kansas School of Architecture & Design, having now conducted nearly a dozen experiments seeking to ascertain how fish react to waterfront edges using a variety of underwater seawall panels made to resemble plant roots.

Van de Riet is a co-author of a new paper titled “Multi-Species Fish Habitat Preferences for Various Modified Concrete Armouring Designs to Enhance Shoreline Biodiversity,” published in the journal Aquatic Conservation: Marine and Freshwater Ecosystems. The KU researcher’s co-authors are Steven Cooke and Acacia Frempong-Manso, both of Canada’s Carleton University.

As the study’s title indicates, the hope is that attaching these tangled faux-root structures to otherwise artificially smooth-sided waterways will attract wildlife — both plant and animal — improving species diversity and water quality and thus benefiting the humans living on shore.

All of Van de Riet’s previous “reef wall” experiments have taken place in Florida, where the Atlantic Ocean and Gulf of Mexico meet the land. He said the Canadian scientists read about that work and asked him to be involved in their related experiment using freshwater fish.

They introduced four different species of fish (bluegill, rock bass, yellow perch and banded killifish) one at a time into a test tank with four increasingly complex “treatment panels” to see how they interacted, as compared to a nearby flat wall, or “control” panel.

Van de Riet said he first got the idea for a variegated panel whose design simulates native plant roots while living along a Florida canal many years ago.

“We saw bait fish being chased by predators literally leaping up against the flat side of the seawall, trying to evade them, because they had nowhere else to go,” he said. The roots of mangrove trees that once lined almost all of Florida’s shoreline “were a logical source of inspiration” for the nooks and crannies of an artificial reef wall panel, Van de Riet said, “given what we've replaced.”

The ultimate purpose of the panel is not just to save little fishes’ lives from big predators but, by providing fish hiding places and surfaces for water-filtering bivalves to attach, to improve the surrounding water quality. He envisions the concept to primarily address waterways that have been altered beyond any recognizable semblance of natural shorelines and can no longer accommodate living shorelines due to navigational and recreational requirements.

The Canadian scientists wanted to see if the results of Van de Riet’s previous studies — showing that intertidal fish generally liked hanging around the rootlike wall panels more than straight-sided walls — could be replicated with freshwater fish in seawall-lined canals and lakes.

The study showed that all the Canadian fish liked the variegated walls more than the flat ones. But their preference for the artificial panel with the highest-relief design “turned out to be fairly species-specific,” Van de Riet said. Bluegill liked (or at least hung out near) those panels the most, followed by banded killifish.

“Rock bass and yellow perch, on the other hand, showed more versatility, preferring a range of relief depths,” the authors wrote.

Van de Riet called it “a challenging study because it's so nuanced in terms of ... each species has different behavior. And they behave differently at different ages. When they're younger, they're going to seek refuge, no matter what. As bluegill age, they prefer open spaces because they can see everything around them. So they tried to account for those things, based on what they already know about the species.”

He added that, “across those different degrees of complexity, we could actually see fish responding more positively to the wall once you hit the middle level of complexity and upwards. So that was a key finding that made the study outcomes worthwhile.”

Van de Riet continues to experiment with root-inspired panels in concrete and other materials, and in both fresh and salt water. This year, with his collaborators in Canada, he is tracking the results of an ongoing study submerging them in a lake, rather than a manmade tank, or “raceway,” as in the newly published study.

“The work includes reaching out to waterfront property owners, doing surveys and trying to figure out what's the best way to roll out ideas and concepts that would impact how they build on their shorelines,” he said.

As an architect, he’s most interested in how these ideas can be expanded upon to foster biodiversity and other sustainable goals within the broader context of constructed environments.

“Construction technologies are historically anthropocentric and need to pivot toward more holistic approaches to address the diverse needs of our planet, whether carbon neutrality or supporting biodiversity,” he said.