A picture of health:
Studying killer whale responses to environmental change
Left: adult female with her two offspring. Right: adult male
Killer whales live in stable populations and reproduce slowly, so assessing population health through trends in abundance can take decades. Since the 1980s we have used photo-identification to monitor killer whales in the Gulf of Alaska, notably assessing long-term effects of the Exxon Valdez oil spill on both fish-eating “Residents” and mammal-eating Bigg’s (aka “Transient”) killer whales (Matkin et al. 2008). While the AT1 Transients are on a trajectory to extinction (Matkin et al. 2012, Esler et al. 2018), we have documented long-term increases in the abundance of most Resident pods (Matkin et al. 2014). However, in recent years the abundance and occurrence of certain pods of Residents has declined in our coastal study area in Prince William Sound, responding to an intense and prolonged marine heatwave (Suryan et al. 2021). This demonstrates the potential for the impact of climatic events to permeate up through the marine ecosystem to these top predators, and has emphasized the need to understand how increasing environmental variation will affect their recovery potential.
In 2021 we began to use aerial photogrammetry alongside our photo-identification studies to provide data on the body condition of killer whales as a sensitive indicator of nutritional health. Using measurements from vertical photographs taken by non-invasive drones (e.g. Durban et al. 2021) we are assessing seasonal and interannual differences in the fatness of the whales, to understand short-term responses to changes in the food web that supports them (e.g. Stewart et al. 2021). Measurements of body lengths will allow an even longer decadal perspective on individual health (e.g. Groskreutz et al. 2019) by investigating if nutritionally-driven changes in the size of whales affects their reproductive success and survival. During our first photogrammetry trip in May/June 2022, we obtained aerial images of >90 different whales in the Kenai Fjords, and we are looking forward to adding more data during an upcoming trip to Prince William Sound in July.
Funding for this research is provided by the Exxon Valdez oil spill Trustee Council and a donation from Major Marine Tours.
Left: chasing salmon. Right: newborn calf with its mother and sibling.
Durban, J.W., Fearnbach, H., Paredes, A., Hickmott, L.S. and LeRoi, D.J., 2021. Size and body condition of sympatric killer whale ecotypes around the Antarctic Peninsula. Marine Ecology Progress Series, 677, pp.209-217.
Esler, D., Ballachey, B.E., Matkin, C., Cushing, D., Kaler, R., Bodkin, J., Monson, D., Esslinger, G. and Kloecker, K., 2018. Timelines and mechanisms of wildlife population recovery following the Exxon Valdez oil spill. Deep Sea Research Part II: Topical Studies in Oceanography, 147:36-42.
Groskreutz, M.J., Durban, J.W., Fearnbach, H., Barrett-Lennard, L.G., Towers, J.R. and Ford, J.K., 2019. Decadal changes in adult size of salmon-eating killer whales in the eastern North Pacific. Endangered Species Research, 40, pp.183-188.
Matkin, C.O., Barrett-Lennard, L.G., Yurk, H., Ellifrit, D. and Trites, A.W., 2007. Ecotypic variation and predatory behavior among killer whales (Orcinus orca) off the eastern Aleutian Islands, Alaska. Fishery Bulletin, 105(1), pp.74-88.
Matkin, C.O., Saulitis, E.L., Ellis, G.M., Olesiuk, P. and Rice, S.D., 2008. Ongoing population-level impacts on killer whales Orcinus orca following the ‘Exxon Valdez’oil spill in Prince William Sound, Alaska. Marine Ecology Progress Series, 356, pp.269-281.
Matkin, C.O., Durban, J.W., Saulitis, E.L., Andrews, R.D., Straley, J.M., Matkin, D.R. and Ellis, G.M., 2012. Contrasting abundance and residency patterns of two sympatric populations of transient killer whales (Orcinus orca) in the northern Gulf of Alaska. Fishery Bulletin, 110(2).
Matkin, C.O., Ward Testa, J., Ellis, G.M. and Saulitis, E.L., 2014. Life history and population dynamics of southern Alaska resident killer whales. Marine Mammal Science, 30(2), pp.460-479.
Stewart, J.D., Durban, J.W., Fearnbach, H., Barrett‐Lennard, L.G., Casler, P.K., Ward, E.J. and Dapp, D.R., 2021. Survival of the fattest: linking body condition to prey availability and survivorship of killer whales. Ecosphere, 12(8), p.e03660.
Suryan, R.M., Arimitsu, M.L., Coletti, H.A., Hopcroft, R.R., Lindeberg, M.R., Barbeaux, S.J., Batten, S.D., Burt, W.J., Bishop, M.A., Bodkin, J.L. and Brenner, R., 2021. Ecosystem response persists after a prolonged marine heatwave. Scientific reports, 11(1), pp.1-17.
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.
Aerial image of two mothers with their young, AK16, 'Steller,' with her 2020 calf and AK17, 'Lou' with her 2021 calf. Lactation to support dependent calves is energetically expensive, so monitoring the condition of adult females and the growth of their calves can provide sensitive insight into nutritional health. Images taken from >100ft with a remotely controlled octocopter drone under NMFS research permit #20341.
Salmon are very important in the diet of resident killer whales. Here, juveniles in the AK2 pod are chasing salmon on their own. Images taken from >100ft with a remotely controlled octocopter drone under NMFS research permit #20341.
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.