Odontocete studies on the Pacific Missile Range Facility in February 2016: satellite-tagging, photo-identification, and passive acoustic monitoring

Citation

Baird, R.W., D.L. Webster, R. Morrissey, B.K. Rone, S.D. Mahaffy, A.M. Gorgone, D.B. Anderson, E.E. Henderson, S.W. Martin, and D.J. Moretti. 2017. Odontocete studies on the Pacific Missile Range Facility in February 2016: satellite-tagging, photo-identification, and passive acoustic monitoring. Prepared for Commander, Pacific Fleet, Honolulu, HI.

Abstract

As part of a long-term U.S. Navy-funded marine mammal monitoring program, in February 2016 a combining boat-based field effort and passive acoustic monitoring was carried out on and around the Pacific Missile Range Facility (PMRF). The U.S. Navy funded five days of small-boat effort and the National Marine Fisheries Service funded an additional two days of effort. There were 859 kilometers (49 hours) of small-vessel survey effort over the course of the seven‑day project. There were 20 sightings of four species of odontocetes, six of which were directed by acoustic detections using the Marine Mammal Monitoring on Navy Ranges (M3R) system. Bottlenose dolphins (Tursiops truncatus) were encountered on five occasions, short-finned pilot whales (Globicephala macrorhynchus) on six, rough-toothed dolphins (Steno bredanensis) on eight, and pantropical spotted dolphins (Stenella attenuata) once. This was the first sighting of pantropical spotted dolphins on PMRF as part of Cascadia Research Collective (CRC) small-boat efforts, and only the 10th sighting off Kaua‘i or Ni‘ihau since effort began in 2003. During the encounters, we took 16,806 photographs for individual identification, with photographs added to long-term CRC regional photo-identification catalogs for bottlenose dolphins, short-finned pilot whales and rough-toothed dolphins. Individual identifications were used in social network analyses to help elucidate population structure of these species relative to results from satellite tagging. One biopsy sample was obtained from a pantropical spotted dolphin, with the sample contributed to the long-term tissue archive at the Southwest Fisheries Science Center as well as used for genetic analyses through Portland State University. Nine satellite tags were deployed on three species—six short-finned pilot whales (from four different social groups), two rough-toothed dolphins, and one pantropical spotted dolphin. In addition, information from tag deployments on two short-finned pilot whales, one rough-toothed dolphin, and one bottlenose dolphin, tagged in September 2015 as part of a CRC project funded through the Living Marine Resources program, were included in the analyses. The pantropical spotted dolphin was thought to be from the pelagic population, and the tagged individual ranged widely offshore to the south of Kauaʻi. All of the tagged rough-toothed dolphins and the bottlenose dolphin remained associated with the island of Kaua‘i and Ni‘ihau for the duration of the tag attachments. Based on photo-identification and social network analyses, all were part of groups known to be resident to the islands. Probability-density analyses of all tag-location data obtained for bottlenose dolphins and rough-toothed dolphins tagged off Kauaʻi since 2011 indicate that core ranges (i.e., the 50 percent kernel density polygons) are relatively small (1,173 and 1,535 square kilometers [km2]). Tag data were available from five different social groups of short-finned pilot whales, one presumed to be from the pelagic population and four from the insular population, based on re-sighting histories and social network analyses. Probability-density analyses were undertaken separately for 17 resident short-finned pilot whales tagged off Kaua‘i since 2008, and for six pilot whales tagged off Kaua‘i and O‘ahu thought to be from the pelagic population. Core range for the pelagic population was more than 10 times larger (111,135 km2) than for the resident population (9,062 km2), and the overall range (using the 99 percent kernel density isopleth) was almost an order of magnitude larger for the pelagic population (695,419 km2). This suggests that the likelihood of exposure to mid-frequency active sonar on the PMRF varies substantially between the two populations. Continued collection of photo-identification, movement and habitat-use data from all species should allow for a better understanding of the use of the range and surrounding areas, provide datasets that can be used to estimate received sound levels at animal locations and examine potential responses to exposure, as well as estimate abundance and examine trends in abundance for resident populations.

Download PDF

Associated projects