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To ensure the long-term viability and function of constructed fish spawning reefs in the St. Clair-Detroit River System (SCDRS), periodic maintenance and repair of the reefs are required. To remove sediment from reefs, researchers developed a portable pressurized water jet that can be deployed by a small vessel. Reef cleaning experiments were conducted during late summer and fall of 2018, with more planned for 2019. Evaluation of fish response to cleaned reef areas is underway for fall spawning fishes and will continue for spring spawners. The USGS Great Lakes Science Center (GLSC) is working with partner agencies, private entities, and universities to develop and deploy reef cleaning and maintenance techniques in the SCDRS and other Great Lakes reef sites that can be applied to cleaning reefs (natural and created) across the Great Lakes Basin.
Large investments are made to restore spawning habitat; however, tools and methods to maintain restoration projects are limited. Developing cost-effective methods for cleaning and maintaining natural and artificial reefs in the Great Lakes Basin is essential for increasing fish spawning activities and fish production. Methods developed for removing sediment from reefs include: 1) Using analytical models to determine the force needed to initiate movement of fine sediments (either through suction or prop wash) and develop initial protocols for field tests, and 2) Field tests conducted to verify the ability of reef cleaning methods to restore the physical condition of reefs and provide functional spawning areas for Lake Sturgeon, Lake Whitefish, Walleye, Lake Trout, and other lithophilic spawning fishes. The methods developed will be applicable to other reefs across the Great Lakes and will potentially increase fish spawning activities and fish production.
Preliminary results suggest that propulsion sled treatments had higher post-cleaning hardness compared to pre-cleaning hardness in 2018 while hydro-jet sled treatments were variable in hardness from pre and post-cleaning. Cleaning had a statistically significant effect on egg deposition on Coreyon Reef (Saginaw Bay Lake Huron) in 2018 and North Island Reef in 2018 & 2019. Cleaned areas potentially provide higher quality habitat selected for by spawning fish.