Odontocete studies on the Pacific Missile Range Facility in August 2017: satellite-tagging, photo-identification, and passive acoustic monitoring.

As part of a long-term U.S. Navy-funded marine mammal monitoring program, in August 2017 a combination of boat-based field effort and passive acoustic monitoring was carried out on and around the Pacific Missile Range Facility (PMRF) off Kaua‘i prior to a Submarine Command Course scheduled for mid-August 2017. The U.S. Navy funded five days of small-boat effort and the National Marine Fisheries Service funded an additional six days of effort. There were 1,113 kilometers (77.4 hours) of small-vessel survey effort over the course of the 11‑day project. There were 34 sightings of five species of odontocetes, with four of the five species being documented on PMRF. Of the 34 sightings, 24 were on PMRF, and of those, 15 were directed by acoustic detections using the Marine Mammal Monitoring on Navy Ranges (M3R) system. During the encounters, we took 37,727 photographs for individual identification, with photographs being added to long-term Cascadia Research Collective (CRC) regional photo-identification catalogs for bottlenose dolphins (Tursiops truncatus) and rough-toothed dolphins (Steno bredanensis). Spinner dolphins (Stenella longirostris) were seen on two occasions, both times in areas outside of PMRF. As expected based on previous CRC efforts off Kaua‘i and Ni‘ihau, rough-toothed dolphins were the most frequently encountered species, with 22 of 34 encounters (64.7 percent) being of this species. Nineteen of the 22 encounters were on PMRF, and 10 of those groups were found in response to acoustic detections from M3R (66.7 percent of all responses to acoustic detections). One sighting was of a mixed group of rough-toothed and bottlenose dolphins, only the second sighting of a mixed-species group involving those two species in a combined 722 sightings of the two species in CRC’s Hawai‘i dataset. Two tags were deployed on rough-toothed dolphins, a depth-transmitting tag and a location-only tag, although locations were only received from the location-only tag. During the seven days of location data from the functioning tag, the tagged individual remained off the west and northwest coasts of Kaua‘i, moving off and on PMRF on 10 occasions. A social network analysis of photo-identification data of rough-toothed dolphins indicated that the tagged individuals were part of the resident, island-associated population. There were four encounters with melon-headed whales (Peponocephala electra) representing two groups that were each seen on two occasions, one a large group (estimated at 300 and 200 individuals on the two different days), and one a pair of individuals found associating with rough-toothed dolphins. The large group sightings were the first time that melon-headed whales have been visually confirmed on PMRF and matched to acoustic signals recorded through the M3R system. Two satellite tags were deployed on individuals in the large group of melon-headed whales when they were first encountered on PMRF. This is only the second time that melon-headed whales have been satellite-tagged off Kaua‘i or Ni‘ihau, and the first time during coordinated small-boat and acoustic monitoring efforts. The two individuals remained together during most of the period of tag overlap. They left and returned to PMRF in the first day after tagging, then moved to the south of the range and remained off the range for the rest of the period, eventually moving east of Kaua‘i. Over the eight days of tag data, the individuals moved 786 kilometers, with a median depth and distance from shore of 3,053 meters and 44.3 kilometers, respectively. One of the pair of melon-headed whales seen on two occasions had pigmentation and morphological characteristics suggesting it may be a hybrid between a melon-headed whale and a rough-toothed dolphin. Genetic analyses of a biopsy sample obtained from the putative hybrid in comparison to a melon-headed whale and a rough-toothed dolphin indicated that the individual has the genotype expected for an F1 hybrid at 11 of 14 nucleotide positions. This is the first-known hybrid between these two species. There was one sighting of pantropical spotted dolphins (Stenella attenuata), only the second sighting of this species on PMRF as part of CRC small-boat efforts since 2003, and the first time that acoustic recordings were made on M3R of a visually confirmed sighting of this species. Two individuals were satellite-tagged, and the two individuals remained associated over the period of tag overlap. In the first two days after tag deployment the tagged individuals moved off and on PMRF three times, before moving south of Kaua‘i, eventually meandering far to the north of O‘ahu. Over the 14 days of tag data the individuals moved 1,307 kilometers, with a median depth and distance from shore of 3,603 meters and 49.5 kilometers, respectively. Movements and habitat use information suggests this group was from the pelagic stock of pantropical spotted dolphins. This sighting provides further support for the suggestion that there is no island-associated population of pantropical spotted dolphins off Kaua‘i or Ni‘ihau, as there are off the other main Hawaiian Islands. Probability-density analyses were undertaken of all tag-location data obtained for the three species tagged during this effort and two species tagged in previous Navy-funded efforts off Kauaʻi. Small core areas (50 percent kernel densities) were identified for resident populations of bottlenose dolphins (1,173 square kilometers) and rough-toothed dolphins (1,450 square kilometers). In comparison, large core areas were identified for individuals from pelagic or Hawaiian-island wide populations (7,675; 40,744; and 111,135 square kilometers for pantropical spotted dolphins, melon-headed whales and the pelagic population of short-finned pilot whales, respectively). This suggests that the likelihood of exposure to mid-frequency active sonar on PMRF varies substantially between insular and pelagic populations. Although all tagged individuals left the area around PMRF prior to the start of the surface component of the Submarine Command Course, continued collection of photo-identification, movement and habitat-use data from these species allows for a better understanding of the use of the range and surrounding areas, as well as estimation of abundance and examination of trends in abundance for resident populations. Future efforts may provide datasets that can be used to estimate received sound levels at animal locations and examine potential responses to exposure to mid-frequency active sonar.


Baird, R.W., D.L. Webster, S.M. Jarvis, K.A. Wood, C.J. Cornforth, S.D. Mahaffy, K.K. Martien, K.M. Robertson, D.B. Anderson, and D.J. Moretti. 2018. Odontocete studies on the Pacific Missile Range Facility in August 2017: satellite-tagging, photo-identification, and passive acoustic monitoring. Prepared for Commander, Pacific Fleet, Pearl Harbor, HI. 

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