New higher resolution habitat mapping and analysis is currently underway on the lower river from Croton to Muskegon Lake. Habitat segments are being identified within each sub-vsec and unique habitats important for fish spawning, nursery and forage are being mapped. Other habitat characteristics are quantified and mapped such as substrate size and % composition, bank condition, flow hydraulics and channel geomorphology.
We divided the river VSEC units below Croton into 12 major channel subunits, 2 lake subunits, and 3 more channel subunits in each of the four major tributaries (Brooks Creek, Cedar River, Mosquito River and Bigelow Creek). The main river channel subunits included the large wetland complexes in the lower estuary. During 2003 we selected 5 main river and 8 tributary subunits for sampling and habitat mapping. The remaining subunits will be sampled and mapped in 2004.
Within each river channel unit we selected 8 randomly distributed 100 m sites (where possible) for biological sampling and detailed habitat mapping for a total of 33 sampling sites. An example of the sample sites in one channel unit is shown below. Shape file versions of the unit maps will eventually be available in the Investigator Resources page.
Within the 5 selected channel subunits we mapped macro-habitat units and collected data for all habitat elements within the units at various river stages throughout the summer and early fall. We used 3000khz Pulse Coherent acoustic doppler profiling referenced to GPS lat/long locations to collect depth and velocitydistribution data for in the main river. Using visual inspection, aerial photographs, video and underwater photography we described and quantified other physical habitat elements in the four study areas including substrate size and distribution, location and character of typical (e.g., scour pool, riffle, backwater) and unique (e.g. hydraulic jumps, extensive shallow riffles) habitat macro-units, anthropomorphic alterations of the landscape, and notable biological activity (e.g., sturgeon spawning sites). This data has been incorporated into GIS maps to provide both visual identification of key areas for fish production and quantification of macro-units and other habitat features. An example of the GIS habitat mapping and a summary data table follows.