Whale and Dolphin Surveys in the Pacific Islands
Surveys for cetaceans to assess abundance across broad areas of the Pacific.
Our program conducts visual and acoustic cetacean (pronounced "seh-tay-shen") surveys and monitoring around the main and Northwestern Hawaiian Islands, Mariana Archipelago, American Samoa, and Pacific Remote Islands. We search and listen for whales and dolphins from a NOAA ship going 10 knots along predetermined tracklines (line-transect methodology).
The visual team continuously watches for cetaceans using 25x150 "big-eye" binoculars, scanning 180° forward of the ship. When an observer spots whales or dolphins, the team identifies the species and each person independently estimates the number of animals in the group. Observers measure the distance to the group, using markings on the lenses of the big-eyes, and the angle of the group from the ship's heading. The combination of distance and angle, together with geometric calculations, provide the perpendicular distance from the group to the trackline. At the end of the survey, it is the collection of these trackline distances that allow us to estimate the detectability of cetacean groups. The length of the survey tracklines, as well as species detectability and average group size, are some of the data we use to estimate abundance.
Why use visual observations?
Cetaceans are mammals and therefore must breathe air to survive. Although they spend most of their lives underwater, they must come to the surface to breathe. It is this obligation to the surface that makes visual observation the primary mode for cetacean surveys. Visual observers can estimate the number of animals in a group, identify the presence of young animals, and describe the behavior of the group--characteristics of the sighting that are difficult to measure or observe in other ways.
How do we find cetaceans and what do we collect?
Observers find cetaceans by scanning through the big-eyes, looking for anything that looks different from water and whitecaps. Sometimes, the observer will see the animals right away, especially if they are in large groups or very active at the surface. Other times, the observers see a splash or a group of birds or fish that alerts them to the presence of cetaceans. Whatever the "cue," once the group is spotted, we collect the data necessary to make abundance estimates. We often take the opportunity to collect photographs and tissue samples from some groups, either from the ship itself or from a small boat launched from the ship. Photographs of the animals allow us to track individuals using identifying marks on the dorsal fin, tail flukes, or body. We use tissue samples for genetic analysis to determine the sex of an animal and the population to which it belongs. We also use them to understand disease, identify contaminants that accumulate in the animal's blubber, and determine pregnancy. Occasionally, we deploy satellite tags on a handful of animals to track how the species move over a longer period than we can observe from the ship. The satellite tags last for many months and help us to understand population range and migration.
Towed Passive Acoustic Surveys
Although we most commonly study cetaceans through visual surveys, we are only able to count them when they surface to breathe. To improve our abundance estimates and provide additional information, we eavesdrop on the sounds cetaceans produce below the surface.
Why use towed passive acoustic monitoring?
Sound travels much farther in water than light, and cetaceans commonly use sound rather than vision to communicate with each other and to find food. Just as cetaceans listen for each other and for their prey, we can listen for their sounds to locate groups of whales and dolphins. Some cetaceans exhibit cryptic behavior and can be very sneaky, avoiding the boats and ships that we use to study them. Poor weather and rough seas can also make it difficult for the visual team to observe animals from the ship, but the acoustics team can still detect animal sounds in rough conditions. The act of quietly listening for marine mammal sounds is known as passive acoustic monitoring. By monitoring the ocean for cetacean sounds, the acoustics team can locate and track animals, including some that might otherwise go unseen by the visual team.
How does towed array acoustic monitoring work?
We use an acoustic array to eavesdrop on vocalizing marine mammals. The acoustic array consists of a series of hydrophones (underwater microphones) that are towed behind the ship (a "towed array") while it is moving along the trackline. The hydrophones immediately transmit sounds back to the ship. Scientists monitor the sounds by listening with headphones and watching a visual representation known as a spectrogram to see what cannot be heard by the human ear. Using these two techniques, the acoustics team can determine when a whale or dolphin is present and what species it is based on various characteristics of its vocalizations. Once animals are detected, the time difference between the arrivals of their sounds to the hydrophones is used to locate and track them as they move. Depending on the species and its location, the acoustics team may alert the visual team to the presence of animals in the area and help guide the ship to them.