Bottom Hardness and Surficial Substrate Composition of Fish Spawning Reefs in the St. Clair-Detroit River System from 2012 - 2018

This data set contains bottom hardness and surficial substrate compositions measured as part of a study evaluating the maturation of fish spawning reef restoration projects in the St. Clair-Detroit River System. Five spawning reef complexes (Middle Channel, Harts Light, Pointe Aux Chenes, Grassy Island, and Belle Isle) constructed with 10-20 cm broken limestone from 2012-2016 were evaluated as part of the study. Sonar surveys began in 2012, following the construction of the Middle Channel Reef complex and expanded to additional projects, as they were completed (Harts Light and Pointe Aux Chenes Reefs in 2014, Grassy Island Reef in 2015, and the Belle Isle Reef complex in 2016). Sonar surveys over the Fighting Island Reefs (constructed in 2008 and expanded in 2013) also began in 2015. Sonar surveys were conducted yearly along multiple transects oriented parallel with flow and spaced 5-10 m apart. A Humminbird 998c SI sonar unit was used during all sonar surveys. Sonar data were processed in the BT+SS edition of DrDepthPC v5.1.8 using the bottom type toolkit to calculate bottom hardness, an index of substrate type, with lower values corresponding to finer substrates. Annual underwater video surveys began in 2015, following the construction of the Harts Light and Pointe Aux Chenes Reefs and expanded to include the Middle Channel and Grassy Island Reefs in 2016 and Belle Isle Reef complex in 2017. Underwater video data also includes surveys of other reefs and sites that were not included in the reef maturation study. Video was recorded at each site along two transects to quantify surficial sediment composition at reef sites and adjacent areas. Sediment classification was based on a modified Wentworth scale, with sediments less than 2 mm classified as fines, sediments 2-100 mm classified as gravel, sediments > 100 mm classified as reef rock (reefs were constructed with 100-200 mm limestone), and dreissenid mussels and shells identified by their distinct shape and coloration. A cutoff of 100 mm was used to segregate gravel and coarse sediment to capture the proportion of reef rock (100-200 mm) present in the video frames.