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ESR 40:183-188 (2019)  -  DOI:

Decadal changes in adult size of salmon-eating killer whales in the eastern North Pacific

Molly J. Groskreutz1,2, John W. Durban1,*, Holly Fearnbach2, Lance G. Barrett-Lennard3, Jared R. Towers4, John K. B. Ford4

1Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, 8901 La Jolla Shores Drive, La Jolla, CA 92037, USA
2SR3, SeaLife Response, Rehabilitation and Research, 2255 Harbor Avenue SW, Suite 101, Seattle, WA 98126, USA
3Coastal Ocean Research Institute, PO Box 3232, Vancouver, BC V6B 3X8, Canada
4Fisheries and Oceans Canada, Pacific Biological Station, Cetacean Research Program, 3190 Hammond Bay Road, Nanaimo, BC V9T 6N7, Canada
*Corresponding author:

ABSTRACT: Two populations of killer whales aggregate around Vancouver Island to feed primarily on Chinook salmon. Aerial photogrammetry of endangered southern residents has documented some adults growing to smaller lengths in recent decades, suggesting that early growth may have been constrained by low Chinook availability in the 1990s. We investigated whether growth and adult length were also constrained in the more abundant northern residents. Photographs were collected from an unmanned hexacopter at altitudes of 30 to 37 m over 4 yr, 2014 to 2017. Images were linked to 78 individuals of known age and sex based on distinctive saddle patch pigmentation. The length of each whale was estimated by measuring pixel dimensions between both the snout and dorsal fin and the dorsal fin and fluke; these were scaled to real size using camera lens focal length and altitude, determined by a laser or pressure altimeter. Total length, derived by summing the longest (flattest) of each measure, ranged from 2.42 m for a first-year calf to 7.45 m for the largest adult male. A Bayesian change point analysis revealed that adult whales <40 yr old were on average shorter by 0.44 m than older adults, which grew to typical lengths of 6.28 and 7.14 m for females and males, respectively. This mirrors the growth trends reported for southern residents, supporting demographic evidence of correlated prey limitation in both populations. The growth data suggest that the effects of nutritional stress are not only acutely lethal but also have long-term consequences for the condition of whales in both populations.

KEY WORDS: Photogrammetry · Drone · UAS · UAV · Growth · Nutrition · Orca

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Cite this article as: Groskreutz MJ, Durban JW, Fearnbach H, Barrett-Lennard LG, Towers JR, Ford JKB (2019) Decadal changes in adult size of salmon-eating killer whales in the eastern North Pacific. Endang Species Res 40:183-188.

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