Alaska Bathymetry, Sediments, and Smooth Sheets
NOAA is mandated to identify Essential Fish Habitat (EFH) by provisions of the Magnuson-Stevens Act, but the necessary data sets are not always available. In the marine environment, depth and sediment type are often the most important determinants of EFH for fish that live on the bottom. Bathymetry data can be further analyzed into important habitat descriptors such as slope and roughness. Marine researchers are familiar with National Ocean Service (NOS) nautical charts, which are often considered the most useful source of EFH information in Alaskan waters. The small scale (often 1:100,000 or smaller) means that the nautical charts lack significant fish habitat details. However, what most marine researchers do not know is that these NOS nautical charts are derived from more detailed, larger-scale (often 1:20,000) charts called "'smooth sheets," which are the final published product from the original charting surveys.
Digital files of the soundings from these smooth sheets are available at the National Geophysical Data Center, but the files contain numerous errors and thus need to be proofed and edited prior to use. Scientists within the Groundfish Assessment Program at the Alaska Fisheries Science Center have developed the methods for proofing and editing smooth sheets, and representing the seafloor in full detail such that individual features, such as lumps and dips, are clearly depicted (Zimmermann and Benson, 2013). Producing maps that depict accurate bathymetry, bathymetric derivatives (slope, roughness, etc.), substrate information (sand, gravel), and features (rocks, islets, kelp) provide the basis to delineate EFH. While these data sets are not for navigation, they have a wide variety of research uses.