Assessment of Resident Killer Whale Body Condition Using Aerial Photogrammetry and Possible Implications for Salmon Management

The southern resident killer whale population is listed as endangered in both the US and Canada and its critical habitat in the trans-border area of the Salish Sea is legally recognized by both countries. Resident killer whales feed on fish, principally salmon, and a multi-year period of low Chinook salmon abundance coastwise was associated with a spike the mortality rates of both populations (Ford et al. 2010 Biol. Lett. 6:139). Attempts to determine the impact of salmon fisheries on southern residents based on fluctuations in their mortality rate in relation to salmon abundance have had limited success (Report of the Independent Science Panel on the Effects of Salmon Fisheries on Southern Resident Killer Whales 2012). Here, we use a novel approach to address this question based on assessments of killer whale body condition from aerial photogrammetry. High quality aerial images of photo-identified members of the population are obtained at regular intervals using a small unmanned hexacopter. Measurements of length, width and shape from the photos are used to estimate growth rates and detect subtle changes in body condition. An index of body condition will be developed based on these photogrammetric measurements; changes in this index in individuals, matrilineal groups and populations will be assessed relative to changes in the abundance, distribution and timing of salmon runs. Here we describe two seasons of photogrammetric field work on northern residents (\u3e80 individuals assessed each year) and one on southern residents (all 82 population members), photogrammetric analysis methods, and plans for at least two more seasons of field work on both populations. We also describe implications of this project--and of a continuing monitoring program that may evolve from it-- for salmon fisheries management approaches that explicitly incorporate the food requirements of the two at-risk killer whales populations