Native fish spawning habitat: It’s more than just rocks in the river - Part 3

Assessing reef success of an adaptive management native fish spawning habitat in the Detroit River.

Laying down fish egg mats – usually modified furnace filters – to collect eggs is one way researchers confirm spawning reefs are being used. Photo: USGS

Laying down fish egg mats – usually modified furnace filters – to collect eggs is one way researchers confirm spawning reefs are being used. Photo: USGS

Part 1 of this five-part series documented the beginning of a native fish habitat restoration project in the Detroit River. Part 2 explored how a project team that included Michigan Sea Grant, Michigan State University Extension, United States Geological Survey and others developed a strategy for defining restoration goals. Now we will discuss post-construction assessments to see if native fish were in fact reproducing on the constructed reefs.

After the native fish spawning reefs were created, researchers performed post-restoration assessment. Essentially, the area was checked for evidence of fish and fish spawning. Assessment of this kind mostly consists of collecting fish in the project area, using set lines and nets to check for spawning-ready adults as well as young fish.

Laying down fish egg mats – usually modified furnace filters – to collect eggs is another tactic to confirm spawning reefs are being used. Researchers were particularly interested in whether desirable species, meaning native species especially those that are relatively rare (e.g., lake sturgeon) or commercially important (e.g., walleye), are using the new reefs. Collected eggs were then hatched in the lab to confirm which species were successful.

In some cases, underwater cameras are sent below the surface to record whatever action may be found there. Scuba divers investigate the reefs to ensure they were constructed properly or to check the condition of reefs and may also report visual confirmation of fish on or near the rocks.

The results showed increased fish presence on the new reefs. Before the Belle Isle reefs were constructed, only two species of fish were collected in the defined space. After construction, 20 species of fish were collected, including 14 native fish species. Many of the fish that were collected were ready for spawning (had eggs or sperm).

Something else also happened. People were paying attention to the project. And the project gained momentum and media picked up on the story.

“Ecologically, this kind of thing is super important because, one, it can right some of the wrongs that were done historically to the river and, two, it can help native fish species recover,” said Lynn Vaccaro, coastal ecosystem research specialist at the University of Michigan Water Center and former Michigan Sea Grant researcher. “Among those species are fish like the northern madtom, an extremely rare native catfish species, and the lake sturgeon, a fish that is incredibly charismatic, and of course walleye and other commercially important fish.”

With positive results, the project blossomed from one stand-alone reef project to an ecosystem-wide approach with more fish habitat restoration projects following behind.

The next article in this series will describe how the success of the first spawning reef experiment led to the subsequent projects throughout the St. Clair and Detroit rivers.

Michigan Sea Grant helps to foster economic growth and protect Michigan’s coastal, Great Lakes resources through education, research and outreach. A collaborative effort of the University of Michigan and Michigan State University, Michigan Sea Grant is part of the NOAA-National Sea Grant network of 33 university-based programs.

Read the full series

“Native fish spawning habitat: It’s more than just rocks in the river”

Part 1: The beginning

Part 2: Strategy

Part 3: Assessment

Part 4: New projects

Part 5: Project benefits

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