After a 25-acre Lake Erie wetland was reconnected, sonar recorded 3.44 million fish detections during 2,022 hours of monitoring over four years, demonstrating that the restored habitat was continually used

A 25-acre restored coastal wetland on the south shore of western Lake Erie was continually used by millions of aquatic animals after it was reconnected to nearby waterways, according to a four-year acoustic monitoring study led by researchers from the United States Geological Survey (USGS). The scientific assessment, published in the journal Aquatic Ecosystem Health & Management, tracked aquatic movement over 2,022 hours of high-resolution sonar monitoring between 2011 and 2014. During the study, the imaging team recorded 3,436,118 detections of individual fish entering and leaving the recently reopened wetland pool. The data provide clear evidence of how aquatic species use restored coastal habitats in the Great Lakes region. Historically, industrial activity, agriculture, and levee construction isolated many marshes from the open lake interior.

Acoustic tracking reveals continuous use

To measure the success of reconnecting habitat without disturbing fish, scientists used advanced acoustic sonar in a passage connecting the 10-hectare (25-acre) wetland pool to Crane Creek within the Ottawa National Wildlife Refuge in Ohio. Traditional methods, including visual counts and 24-hour trapping, can miss short-term changes in fish movement, especially in murky, murky waters. High-resolution sound waves allowed researchers to record underwater activity continuously without relying on light or physical networks. The data showed that the fish used the newly reconnected habitat during the day and night. Hourly counts ranged from just 3 fish during periods of low activity to 9,353 fish in a single hour. Follow-up work included 56 separate implementation cycles over the four years of the study. Of the 3.44 million recorded detections, the movement was divided almost equally. Researchers tracked 1,696,447 fish that moved out of the wetland into Crane Creek, while 1,739,671 fish moved into the wetland pool. The greatest activity was recorded during the first year of monitoring in 2011, when researchers recorded more than 1.52 million fish detections. Although numbers decreased in subsequent years, use remained high, with 973,453 detections in 2012, 511,905 in 2013 and 429,443 in 2014.

Seasonal and daily activity shifts.

The research team, led by USGS ecologist Kurt P. Kowalski and co-authors Alexandra A. Bozimowski, McKenzie KH Smith, Michael R. Eggleston, Maxwell F. Ramsay and Holly J. Eschenburg, found clear patterns in when fish entered and exited the marsh. “Data collected over four years (2011-2014) indicated that the 10-hectare wetland was used continuously by millions of fish, with perceptible fluctuations in usage patterns observed on both daily and annual scales,” the research team explained in the USGS report. The study examined 1,002 hours of daytime data, 529 hours of nighttime data, and 491 hours recorded during dawn and dusk. Fish movements increased during certain seasons and under special light conditions. This showed that fish in lakes, rivers and wetlands regularly use restored coastal marshes for feeding, spawning and shelter. The findings help fill an important gap in Great Lakes conservation research. Millions of dollars are spent each year restoring damaged coastal areas, but it has often been difficult to determine whether aquatic species are actually using these reconnected habitats due to the limitations of traditional sampling methods.

Implications for Great Lakes management

The coastal wetlands of the Laurentian Great Lakes are important wildlife nurseries and provide refuge and feeding areas for dozens of native fish species. Reconnecting isolated pools to natural water flows is an important goal for environmental managers across the region. Information from acoustic sonar could help wildlife authorities plan future maintenance and construction work. By knowing when fish activity naturally declines, conservation agencies can schedule disruptive activities such as dredging or water level monitoring during periods when fewer fish are present, reducing ecological damage. “These insights contribute to our understanding of how fish communities respond to restored coastal wetland habitats and can inform management decisions that may affect fish access,” the authors stated in their research findings. “Further study of short-term fish movements using high-resolution sonar and other technologies will reveal patterns that can improve the effectiveness of restoration and management efforts in Great Lakes coastal wetlands.” The study is an important step in showing the ecological value of restoring Great Lakes wetlands. It demonstrates that when former barriers to fish movement are removed, native fish populations can quickly return to restored habitats and use them as part of their natural life cycles.