Visual Observation updates from the PIFSC Blog
Cetacean observations are collected following line-transect protocols. Observers continuously search for animals using 25x150 "big-eye" binoculars, scanning 180° forward of the ship. When whales or dolphins are spotted, the visual team identifies the species and each observer 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 some 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. This detectability, along with other key data such as the average group size of the species and the length of tracklines surveyed, allow us 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, such as by using passive acoustics.
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" or not like water and whitecaps. Sometimes, the observer will first see the animals, 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 additional data 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. Tissue samples are used for genetic analysis to determine the sex of an animal and the population to which it belongs. Tissues are also used to understand disease, identify contaminants that accumulate in the animal's blubber, and determine pregnancy. We occasionally deploy satellite tags on a handful of animals that allow us 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.