Photogrammetry: A non-invasive health check for the whales
Research on endangered Southern Resident killer whales off Washington State has demonstrated the utility of aerial images taken from drones for assessing whale health. Vertical images taken under research permit from high (>100ft) above the whales can be used to generate photogrammetry measurements to assess the growth, body condition and pregnancy status of the whales without disturbance. Unfortunately, these data have revealed signs of nutritional stress in the Southern Residents, with periods of constrained growth, poor body condition and low reproductive success that are correlate with declines in the availability of their primary prey, Chinook salmon. However, there is a clear link between poor body condition and subsequent mortality of these vulnerable whales, enabling photogrammetry to provide an early-warning system to guide management actions before whales die.
Aerial image of part of the AD8 pod off Kenai Fjords, Alaska, in late May 2021. Annotations show photogrammetry measurements of total length (TL), breadth (B) used to infer pregnancy of females and the eye patch ratio (EPR) indicating body condition by measuring divergence of the eye patches with increased fat deposits behind the head. Image taken from >100ft with a remotely controlled octocopter drone under NMFS research permit #20341.
In contrast to the declining abundance of Southern Residents, the Alaska Resident killer whales frequenting the coastal waters around the Kenai Peninsula and Prince William Sound have been increasing in abundance in recent decades and offer the opportunity to study the health of a robust population. In May 2021, NGOS initiated a photogrammetry study of our whales here in Alaska, in collaboration with SR3, to initially provide a comparative assessment of the two populations to help establish healthy benchmarks to guide conservation measures for Southern Residents. In the longer term, photogrammetry will be routinely used to monitor changes in the body condition of Alaska Resident killer whales to understand and monitor the link between ecosystem changes that affect their prey base and the population status of the whales.
Durban, Fearnbach, Barrett-Lennard, Perryman, Leroi. 2015. Photogrammetry of killer whales using a small hexacopter launched at sea. Journal of Unmanned Vehicle Systems 3: 131-135.
Fearnbach, Durban, Ellifrit, Balcomb. 2011. Size and long-term growth trends of endangered fish-eating killer whales. Endangered Species Research 13: 173-180.
Fearnbach, Durban, Barrett‐Lennard, Ellifrit, Balcomb. 2020. Evaluating the power of photogrammetry for monitoring killer whale body condition. Marine Mammal Science 36: 359-364.
Stewart, Durban, Fearnbach, Barrett-Lennard, Casler, Ward, Dapp. 2021. Survival of the Fattest: Linking body condition to prey availability and survivorship of killer whales. Ecosphere, in press.