As part of a long-term U.S. Navy-funded marine mammal monitoring program, in February 2020 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-February 2020. 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. Results from this effort were compared with previous Cascadia Research Collective (CRC) survey effort and photo-identification and tag data from Kaua‘i, based on surveys in 11 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 increase overall encounter rates with high-priority species.
Over the course of the 13-day project, there were 1,064 kilometers [km] (71.3 hours) of small-vessel survey effort, 47 sightings of seven species of odontocetes, 23 sightings of humpback whales (Megaptera novaeangliae), and one sighting of an unidentified odontocete. Of the 48 odontocete sightings, 20 were on PMRF representing four of seven species, and of those eight were directed by M3R acoustic detections. During the encounters, we took 26,178 photographs for species and individual identification, with photographs added to long-term CRC catalogs for short-finned pilot whales (Globicephala macrorhynchus), false killer whales (Pseudorca crassidens), pygmy killer whales (Feresa attenuata), common bottlenose dolphins (Tursiops truncatus), and rough-toothed dolphins (Steno bredanensis). Nineteen biopsy samples were taken from five species. Spinner dolphins (Stenella longirostris) were seen on 12 occasions, but this was a low-priority species so limited efforts were expended to work with them.
As expected based on previous CRC efforts off Kaua‘i and Ni‘ihau, rough-toothed dolphins were the most frequently encountered species, comprising 18 of 47 encounters with known species (38.3 percent). Ten of the 18 encounters were on PMRF. A social network analysis of photo-identification data of rough-toothed dolphins indicated that all but two of the identified individuals from this project linked to the main cluster of the resident, island-associated population. In three of the sightings a single melon-headed whale was present, as well as a melon-headed whale x rough-toothed dolphin hybrid, both of which had been previously documented off Kauaʻi during CRC’s August 2017 field effort. The melon-headed whale was not approachable for tagging. For two of the three sightings of the hybrid and melon-headed whale, the individuals were not noted at the time of the encounters but were only recognized from later analysis of photographs.
Short-finned pilot whales were encountered only once, and a single SPLASH-10F depth-transmitting satellite tag that included Fastloc®-GPS capability was deployed. The group with the tagged animal had been previously documented in five different years (all off either Kauaʻi or Oʻahu), and was considered to belong to the resident western community of short-finned pilot whales. A crawl model (continuous-time correlated random walk state-space model) of the tag data produced a total of 372 locations at 1-hour intervals compared to 314 total Argos locations, and 277 combined Argos and GPS locations. Behavior (i.e., dive depths and durations of dives and surfacing periods) data coverage during the 12 days that behavior was recorded was 86.8 percent. Over the 16-day period during which the tag transmitted, the group spent most of its time in deep water far offshore (median depth=3,504 meters, median distance from shore=28.1 km), remaining in the area where the Submarine Command Course took place.
Pygmy killer whales were sighted once. This group was not approachable for tagging, but identification photos were obtained for 15 individuals, none of which had been previously identified. This species is among the least likely to be encountered off Kauaʻi or Niʻihau; in previous CRC surveys they have only been documented on two occasions. Neither of these groups have been documented prior or subsequently, providing additional evidence that there is no resident population of this species off Kauaʻi or Niʻihau.
False killer whales were encountered on three occasions over two days (14 and 15 February 2020), with all sightings on PMRF and two in response to acoustic detections. None of the groups were approachable for tagging, but identification photos were obtained for the two encounters on 14 February 2020. Eight identifications were obtained from the first encounter on 14 February 2020, four of which had been previously documented and linked by association to the Northwestern Hawaiian Islands population of false killer whales. Only a single identification was obtained from the second encounter on 14 February 2020. While the individual had not been previously documented, it was most likely also from the Northwestern Hawaiian Islands population, given the proximity to the first encounter. Three biopsy samples were obtained, from individuals in both of the encounters on 14 February 2020. The 15 February 2020 encounter was brief (<1 minute), with a single individual lost shortly after being sighted.
Common bottlenose dolphins (hereafter bottlenose dolphins) were encountered on nine occasions, and 46 good-quality identifications of 24 distinctive individuals were obtained. Of those, 23 had been previously documented, and all were linked by association with the resident community of bottlenose dolphins from Kauaʻi and Niʻihau. Two SPLASH10 depth-transmitting satellite tags were deployed onto bottlenose dolphins during the project, on 15 and 17 February 2020. Both individuals tagged are known members of the resident Kauaʻi and Niʻihau community, and one of the two individuals had been previously tagged during a 2013 CRC field project. The tags produced 223 and 383 Argos locations over 13.9 and 20.0 days, respectively, and generally remained close to the islands (median depth=119 m and 180 m, median distance from shore=3.1 km and 3.7 km, respectively). Behavioral data (i.e., dive and surfacing) coverage during deployment was 100 percent for both tags.
Probability-density analyses were undertaken using 12-hour locations from crawl state-space models of tag-location data obtained for the two species for which tag data were available from this effort, incorporating data from all previous tag deployments on individuals from these populations. Core areas (50 percent kernel densities) were identified for the resident populations of bottlenose dolphins (1,852 square kilometers) and the western community of short-finned pilot whales (8,736 square kilometers). While the core areas for both 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., C. J. Cornforth, S. M. Jarvis, N. A. DiMarzio, K. Dolan, E. E. Henderson, S. W. Martin, S. L. Watwood, S. D. Mahaffy, B. D. Guenther, J. K. Lerma, A. E. Harnish, and M. A. Kratofil. 2021. Odontocete Studies on the Pacific Missile Range Facility in February 2020: Satellite-Tagging, Photo-Identification, and Passive Acoustic Monitoring. Prepared for Commander, Pacific Fleet, under Contract No. N62470-15-D-8006 Task Order N6274219F0101 issued to HDR Inc., Honolulu, HI.
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