The marine mammal and sea turtle layers in MarineCadastre.gov represent habitat-based density-model estimates of animal density. The marine mammal layers are a subset of a larger data set being delivered via the Cetacean and Sound Mapping website (http://cetsound.noaa.gov) of the National Oceanic and Atmospheric Administration (NOAA). The model results show estimates of the average number of animals present per square kilometer during a given season. Most of the average estimates of animals per km2 are less than 1 because marine mammals are highly mobile and often occur in large groups. For example, an average value of 0.5 bottlenose dolphins per km2 during the summer could mean that 1 animal would be present every other day, or 1 group of 5 animals would be present once in a 10 day period, or 1 group of 50 animals would be present every 100 days, etc. These data originate largely from marine mammal observations generated through shipboard and aerial surveys conducted by NOAA’s National Marine Fisheries Service. Models explicitly incorporate environmental factors whenever possible. The model outputs were generated through a collaborative effort that included NOAA, the U.S. Navy, and Duke University. User agreements, source reports, and additional resources can be found below under Additional Information.