Application of Federal Submarine Canyon Morphometrics to Environmental Management of Marine Mammals

To facilitate improved environmental management of the United States federal outer continental shelf, submarine canyons in federal waters were inventoried, delineated, described, and categorized using a methodology consistent with terrestrial watershed mapping. A criteria-based algorithm generated spatial canyon polygons from which slope, length, and depth were calculated. A total of 130 canyons were identified using this methodology; 45 canyons were identified in the Atlantic region (mean depth = 2144 ± 933 m (mean ± SD), mean length = 90 ± 73 km; 9 canyons were identified in the Gulf of Mexico region (mean depth = 1609 ± 718 m, mean length = 104 ± 30 km); 53 canyons were identified in the Pacific region (mean depth = 2150 ± 591 m, mean length = 145 ± 84 km); and 23 canyons were identified in the Alaska region (mean depth = 2194 ± 349 m, mean length = 118 ± 56 km). A subset of 70 of the 130 canyons were selected by subject matter experts as being particularly relevant to federal environmental stewardship responsibilities and are described and documented in a freely-available atlas. The mean depth for these 70 canyons was 2118 ± 714 m; mean length 118 ± 76 km; and mean width 33 ± 30 km.

As a trial of application, the inventory was used to support an analysis of cetacean population density of Atlantic deep-diving and surface-dwelling taxa to identify preferential presence within the delineated submarine canyon polygons. Deep-diving taxa (e.g., Physeter sp.) had a significantly higher density of individual animals within delineated polygons than outside of polygons; regression analysis indicates that deep-diving taxa are more abundant within the perimeter of the canyon polygon. Shallow-feeding taxa (e.g., Eubalaena sp.) did not have a significantly different density of individual animals within delineated polygons compared to outside of polygons. Additional analyses were made relative to water depth, distance to shore, distance to the shelf-break, and distance to the toe of the slope. We concluded that the canyon atlas delineation provided a useful means of stratifying sampling to help resolve cetacean utilization patterns of these seafloor features.