As part of a long-term U.S. Navy-funded marine mammal monitoring program, in August 2018 a combination of vessel-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 2018. The purpose of the monitoring effort was to assess the spatial movement patterns and habitat use of cetaceans that are exposed to mid-frequency active sonar and how those patterns influence exposure and potentially responses. The U.S. Navy funded 13 days of small-vessel effort and the National Marine Fisheries Service funded an additional 2 days of effort. Results from this effort were compared with previous Cascadia Research Collective (CRC) survey effort and photo-identification and tag data from Kaua‘i and Ni‘ihau, based on surveys in 10 different years since 2003. During the survey, the Marine Mammal Monitoring on Navy Ranges (M3R) system was used both to direct the research vessel to potential high-priority species, and to inform the research vessel when only low-priority species were detected on the range, allowing it to survey off the range and thus increasing overall encounter rates with high-priority species.
Over the course of the 15-day project, there were 1,597 kilometers (100.0 hours) of small-vessel survey effort, resulting in 57 sightings of seven species of odontocetes. Of the 57 sightings, 24 were on PMRF representing five of the seven species, and of those, five were directed by M3R acoustic detections. During the encounters, we took 33,452 photographs for individual identification, with photographs added to long-term CRC regional photo-identification catalogs for short-finned pilot whales (Globicephala macrorhyncus), bottlenose dolphins (Tursiops truncatus), and rough-toothed dolphins (Steno bredanensis).
As expected based on previous CRC efforts off Kaua‘i and Ni‘ihau, rough-toothed dolphins were the most frequently encountered species, with 34 of 57 encounters (59.6 percent) being of this species. Nineteen of the 34 encounters were on PMRF, and three of those groups were found in response to acoustic detections from M3R (60 percent of all responses to acoustic detections). One sighting was of a mixed group of rough-toothed and bottlenose dolphins, only the third sighting of a mixed-species group involving those two species in a combined 780 sightings of the two species in CRC’s Hawai‘i dataset. One location-only tag was deployed on a rough-toothed dolphin. During the five days of location data from the functioning tag, the tagged individual remained off the west coast of Kaua‘i, moving off and on PMRF on four occasions. A social network analysis of photo-identification data of rough-toothed dolphins indicated that the tagged individual was part of the resident, island-associated population.
Short-finned pilot whales were encountered on five occasions over a three-day period, and represented three different social groups. Depth-transmitting satellite tags that included Fastloc-GPS capability were deployed on individuals in two of the three groups, with tag deployments on 17 and 19 August 2018 (the latter group cued by an acoustic detection from M3R). The group tagged on 17 August was linked by association with the main cluster of short-finned pilot whales known to be resident off the island of Hawai‘i, but re-sighted individuals have only been seen on one occasion off that island, so the group does not appear to exhibit strong fidelity to that area. The group tagged 19 August was linked by association with the western community of short-finned pilot whales known to be resident to Kaua‘i, Ni‘ihau, and O‘ahu. The third, untagged group (seen both on 17 and 18 August) had been previously tagged off Ni‘ihau in September 2015 and was thought to be from the resident western community, based on movements from tag data. The Fastloc-GPS tags were programmed to maximize obtaining Fastloc-GPS locations and dive data for a 10-day window spanning the Submarine Command Course scheduled to start on 21 August 2018. These tags produced more than twice as many Fastloc-GPS locations than Argos locations during the 10-day window, and behavior (i.e., dive and surfacing) data coverage during that period ranged from 77.4 to 99.3 percent. This programming regime was successful at producing high resolution information over a shorter-period of time in order to allow a detailed assessment of exposure and response to mid-frequency active sonar. Over a 37-day period the group associated with the eastern community (tagged 17 August) spent most of its time in deep water far offshore (median depth=4,215 meters [m], median distance from shore=73.3 kilometers [km]), with the track ending in slope waters off Hawai‘i Island. By contrast, the group associated with the western community (tagged 19 August) remained in slope waters (median depth=906 m; median distance from shore=6.9 km) around Kaua‘i over the 23 days the tag transmitted. This group remained in the area during the surface component of the Submarine Command Course, and location and behavior data will be used to assess exposure and response of the tagged individual to mid-frequency active sonar.
There were two encounters with melon-headed whales (Peponocephala electra) 10 days apart. Based on a photo-identification match between the two encounters, they appeared to be the same group seen on two different occasions. Two Fastloc-GPS dive satellite tags were deployed during the first encounter, although location data were only obtained from one individual for just over nine days. This is only the third time that melon-headed whales have been satellite-tagged off Kaua‘i or Ni‘ihau. Over the 9 days of tag data, the individual moved 830 km, with a median depth and distance from shore of 2,220 m and 14.8 km, respectively.
Sperm whales (Physeter macrocephalus) were encountered on one occasion, with the vessel directed to the group based on acoustic detections from M3R, as the sperm whale group approached the range from the south. This was only Cascadia’s fourth encounter with sperm whales off Kaua‘i or Ni‘ihau. This group was widely dispersed (>4 km) and included at least one adult male, with long dives of approximately 1 hour in duration. Individuals were not approachable for tagging.
There was one sighting of pantropical spotted dolphins (Stenella attenuata), south of PMRF. One individual was satellite-tagged, although only a single location was received from the tag. Four biopsy samples were obtained, and will be analyzed for genetics to further understand population structure of this species in the islands. Bottlenose dolphins were encountered on six occasions, and good quality identifications of 36 distinctive individuals were obtained. Of those, 32 had been previously documented, and all were linked by association with the resident community of bottlenose dolphins from Kauaʻi and Niʻihau. Spinner dolphins (Stenella longirostris) were seen on eight occasions but this was a low-priority species so limited efforts were expended to work with them.
Probability-density analyses were undertaken using 12-hour locations from switching state-space models of tag-location data obtained for the three species for which tag data were available from this effort. Core areas (50 percent kernel densities) were identified for the resident populations of rough-toothed dolphins (1,642 square kilometers [km2]), the Hawaiian Islands stock of melon-headed whales (82,431 km2), and the western community of short-finned pilot whales (7,517 km2). While the core areas for all three populations overlap with at least part of PMRF, the differences in the proportion of the core area that overlaps with PMRF suggests that the likelihood of exposure to mid-frequency active sonar on PMRF varies substantially between populations. 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.
Citation:
Baird, R.W., D.L. Webster, S.M. Jarvis, E.E. Henderson, S.L. Watwood, S.D. Mahaffy, B.D. Guenther, J.K. Lerma, C.J. Cornforth, A.W. Vanderzee, and D.B. Anderson. 2019. Odontocete studies on the Pacific Missile Range Facility in August 2018: satellite-tagging, photo-identification, and passive acoustic monitoring. Prepared for Commander, Pacific Fleet, under Contract No. N62470-15-D-8006 Task Order 6274218F0107 issued to HDR Inc., Honolulu, HI.
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