Norfolk/VA Beach Inshore Vessel Surveys

Original provider:
HDR Environmental, Operations and Construction, Inc.

Dataset credits:
The U.S. Navy Marine Species Monitoring Program

Abstract:
A combination of visual line-transect survey, photo-identification (photo-ID), and automated acoustic monitoring methods was used to gather important baseline information on the occurrence, distribution, and density of marine mammals near Naval Station Norfolk (NSN) and adjacent areas. The study area was designed to cover areas where United States Navy activity is substantial, including Chesapeake Bay waters near NSN and Joint Expeditionary Base Little Creek-Fort Story, as well as a Mine Exercise (MINEX) Area (W-50) in the Atlantic Ocean off the coast of Virginia Beach, Virginia. Sixty-one line-transect surveys were completed in two zones (INSHORE and MINEX) between August 2012 and August 2015, with 6,550 kilometers (km) and 349.6 hours completed on-effort. The majority of sightings were of bottlenose dolphins (Tursiops truncatus), although humpback whales (Megaptera novaeangliae), harbor porpoises (Phocoena phocoena), and short-beaked common dolphins (Delphinus delphis) were also sighted in the study area on occasion. In addition, loggerhead sea turtles (Caretta caretta), leatherback sea turtles (Dermochelys coriacea), and a Kemp’s ridley sea turtle (Lepidochelys kempii) were sighted during surveys. Conventional line-transect analysis of bottlenose dolphin sightings showed both spatial and seasonal variation in density and abundance, with greatest density in the INSHORE zone during fall months. Densities in the INSHORE zone were calculated as 3.88 individuals per square kilometer (km2) (abundance[N]=1,203) in fall, 0.63 individuals per km2 (N=195) in winter, 1.00 individuals per km2 (N=311) in spring, and 3.55 individuals per km2 (N=1,101) in summer. Densities in the MINEX zone were calculated as 2.14 individuals per km2 (N=1,277) in fall, 0.06 individuals per km2 (N=37) in winter, 1.53 individuals per km2 (N=913) in spring, and 1.39 individuals per km2 (N=829) in summer. Twenty-seven photo-ID surveys were completed, and a photo-ID catalog was created using photos taken during both dedicated photo-ID and line-transect surveys through May 2014; it contains 878 identified individuals to date. Subsequent photos will continue to be added and analyzed. One hundred ten individuals were re-sighted; however, most re-sightings were less than 4 months and 30 km apart. Additional survey effort and further analysis will be required before any clear movement patterns can be determined. C-POD acoustic data-loggers were initially deployed at four sites throughout the study area to cover areas of high United States Navy activity. Bottlenose dolphins were detected in each deployment location during all deployments from August 2012 to December 2015. Though deployments did not provide consistent coverage in all seasons for all sites due to loss of gear, results from two deployment sites nearest to NSN showed a greater level of occurrence during fall months, and a diel pattern of occurrence with increased detections during nighttime hours for three deployment sites.