Norfolk/VA Beach MINEX 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 is being 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 chosen to cover areas where United States (U.S.) Navy activity is substantial, including Chesapeake Bay waters near Naval Station Norfolk, Joint Expeditionary Base (JEB) Little Creek (LC), and JEB Fort Story, as well as a Mine Exercise (MINEX) Area (W-50) in the Atlantic off the coast of Virginia Beach, Virginia. Twenty-five line-transect surveys were completed in two zones (INSHORE and MINEX) between August 2012 and November 2013, with 2,810 kilometers (km) and 8,942 minutes completed on-effort. The majority of sightings were bottlenose dolphins (Tursiops truncatus), although humpback whales (Megaptera novaeangliae) and short-beaked common dolphins (Delphinus delphis) were also sighted in the study area on occasion. In addition, loggerhead sea turtles (Caretta caretta) and leatherback sea turtles (Dermochelys coriacea) were sighted during the study period. Conventional line-transect analysis of bottlenose dolphin sightings showed both spatial and seasonal variation in density and abundance, with greatest abundance in the INSHORE zone during summer months. INSHORE densities were calculated as 3.05 individuals per square kilometer (km2) (N=948) in fall, 0.40 individuals per km2 (N=123) in winter, 1.09 individuals per km2 (N=337) in spring, and 3.52 individuals per km2 (N=1,094) in summer. MINEX densities were calculated as 0.11 individuals per km2 (N=105) in fall, 0.00 individuals per km2 (N=0) in winter, 0.10 individuals per km2 (N=90) in spring, and 0.16 individuals per km2 (N=148) in summer. A photo-ID catalog was created using photos taken during both dedicated photo-ID and line-transect surveys through July 2013; it contains 308 identified individuals to date. Thirty-three individuals were re-sighted; however, most sightings were less than three months and 15 km apart. Additional survey effort will be required before any clear movement patterns can be determined. C-POD acoustic data loggers (www.chelonia.co.uk) were deployed at four sites throughout the study area to cover areas of high U.S. Navy activity. Harbor porpoises (Phocoena phocoena) were detected in low numbers near NSN and JEB-LC during winter and spring deployments, and bottlenose dolphins were detected in each deployment location during all deployments from August 2012 to September 2013. Deployments, however, did not provide consistent coverage due to loss of gear. Further study is required to improve accuracy in seasonal density estimates and allow further stratification of those estimates, and to better describe the movement patterns and site fidelity of the bottlenose dolphins in these waters. Visual surveys and additional C-POD deployments are currently planned through August 2014.