Cetacean Research
Photo credit: Ed Lyman, HIHWNMS
PIFSC cetacean research is concerned with populations of whales and dolphins in the central and western Pacific Ocean.
Effective conservation of cetacean populations requires an understanding of stock structure, abundance, habitat use, natural and anthropogenic threats, and estimates of reproduction and mortality rates. Research methods currently used to collect these data include:
- Visual and acoustic line transect surveys
- Photo-Identification studies
- Passive acoustic monitoring
- Habitat modeling and ecosystem observations
Visual and acoustic line transect surveys
Visual surveys to assess cetacean abundance and distribution are conducted from the flying bridge of a large (> 200 ft.) research vessel using 25 × 150 "big eye" binoculars or from a small (<30 ft.) boat using handheld binoculars and the naked eye. Observers scan the water for cetaceans while the vessel steams along predetermined transect lines. Often cetaceans are encountered in groups. When cetaceans are seen, the observers record data such as the species, location (latitude and longitude) of the encounter, general behavior of the animals, and estimates of the number of cetaceans in the group. The sighting data are later analyzed using distance sampling statistical models and imported into a Geographical Information System (GIS) for further spatial analysis. Whenever possible, digital photographs of encountered cetaceans are obtained to help confirm the species identification and document unique characteristics that enable identification of individual cetaceans.
Photo credit: Danielle Waples, DUML
Simultaneously, observations of the underwater sound field along the survey track are made using a towed hydrophone array. A typical towed array consists of 4 hydrophone elements with linear sensitivity to frequencies between 1 kHz and 100 kHz. As the array is towed on a cable behind the ship, acoustic signals are transmitted up the cable to on-deck computers outfitted with software that allows real-time visualization, recording, and spatial localization of cetacean sounds. Acoustic detections of cetaceans are noted. Data on the location of detections can be used in line transect models and incorporated into GIS databases for comparison with corresponding visual detections and habitat data.
Photo-identification studies
Photo by Jason Baker, PIFSC
Long-term photo-identification studies provide insight into habitat use, movements, and life history characteristics of individual cetaceans. Some species of cetaceans have naturally occurring markings on their bodies, flukes, or dorsal fins. Photographic records of these scars, nicks, notches, or color patterns can be used to uniquely identify individuals. Photographs of cetaceans encountered during sighting surveys are archived and associated with other sighting data, e.g., sighting location, group size and structure, and behavior. Individual cetaceans can be tracked over time and between locations on the basis of their unique photo-IDs.
PIFSC cetacean scientists are active participants in the Pacific Islands Photo-Identification Network (PIPIN), a group of researchers from the Hawaiian Islands who are studying spinner dolphins and using photo-ID as a primary research tool. PIPIN is creating a collaborative photo-identification database of spinner dolphin populations within the Hawaiian Islands to study movements of dolphins between islands (if they occur), and to determine if dolphin populations differ from one island to the next. Results of the cooperative studies will help managers assess and resolve issues with human-dolphin interactions, e.g., impacts on spinner dolphins arising from "swim-with-the-dolphins" tourism operations.
Passive acoustic monitoring
Passive acoustics are useful for augmenting visual surveys and assessing temporal and spatial changes in the density and behavior of some marine animals. They can also provide important details about the acoustic environments of cetaceans. In collaboration with researchers at the Scripps Institution of Oceanography and Dr. Jeffery Polovina at PIFSC. we are using bottom-mounted passive acoustic data recorders called High-frequency Acoustic Recording Packages, or HARPs, to monitor cetaceans. The HARP data loggers are moored to the sea bottom and remain there for several months. When the HARP is later retrieved from its mooring, the acoustics data are downloaded. Currently three HARPs are deployed around the PIR - one at Palmyra Atoll, one at Cross Seamount, and one at Ladd Seamount in the Northwestern Hawaiian Islands.
We are also collaborating with researchers at the University of Hawai'i to study whale vocalizations detected by the newly deployed hydrophone on the Station Aloha Cabled Observatory System. This hydrophone is located on the sea floor about 100 km north of Oahu. In a joint study with scientists at Duke University, we are using T-POD acoustic data loggers to study the occurrence of echolocating cetaceans near longline gear deployed by Hawai'i commercial fishing vessels.
Habitat modeling and ecosystem observations
Understanding more about the biogeochemical characteristics of cetacean habitat may be crucial for future cetacean conservation decisions. Habitat models based on various in situ and satellite-derived observations of the sea floor, water temperature, nutrients and other ocean properties can be a used to locate essential habitat for particular species and populations of cetaceans and to provide predictions to help guide further research.
we are using habitat models for three different species: spinner dolphins, humpback whales, and right whales. One project aims to quantify physical characteristics of observed spinner dolphin resting habitats in the Main Hawaiian Islands, by conducting fine-scale physical habitat mapping, and to compare these habitats to regions not used by resting dolphins. If there are common, fine-scale features (e.g., percent cover of various bottom types) among resting habitats that can be detected by physical habitat mapping, these features could be incorporated into a quantitative habitat model and used to identify potential additional resting habitats in unobserved areas.
Some of the known resting habitats used by spinner dolphins during daylight hours are also heavily used by ecotourism operations that feature diving and snorkeling but also involve activities such as kayaking, dolphin-watching and in some cases swim-with-dolphin tours. Some of these activities have the potential for adverse impacts on the dolphins. Potential effects on spinner dolphins include habitat displacement, where spinners may simply avoid sheltered bays frequently used for ecotourism, or more subtle effects such as alteration of normal resting behaviors important to population well being. Predictions from habitat models may be used to identify important resting habitat where disturbance of dolphins should be minimized or avoided and help managers devise effective protection strategies.
We are also using simple habitat models to identify humpback whale breeding habitat in Hawai'i. Humpback whales winter and breed in the Main Hawaiian Islands (MHI) and have been well-studied there. However, almost no data have been collected on humpback whale usage of potential breeding habitat in the Northwestern Hawaiian Islands (NWHI), extending 1800 km northwest of the MHI. We have predicted the extent and spatial location of wintering habitat across the entire Hawaiian Archipelago, using bathymetry and sea surface temperature data to identify areas shallower than 200m and warmer than 21°C considered potential wintering habitat. We will compare these habitat predictions with the locations of visual and acoustic detections of humpbacks during upcoming cetacean surveys in the NWHI.
We are using similar techniques to predict potential breeding habitat for North Pacific right whales. These rare whales are currently listed as endangered under the ESA and as depleted under the MMPA. Very little is known about their long-term movements and habitats. Right whales in other oceans are known to migrate seasonally to warmer waters in lower latitudes to calve and mate. No studies have been made to assess the migratory paths and locate breeding habitats of North Pacific right whales. Locating breeding habitat of these whales and assessing threats to recovery within breeding areas is critical for effective conservation of the population. Given physical characteristics of known right whale breeding habitat in other oceans and oceanographic data for the Pacific Islands Region, we are using models to predict breeding habitat for North Pacific right whales.