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Marine Ecology Progress Series

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MEPS 620:185-200 (2019)  -  DOI:

Validation of the photogrammetric method to assess body condition of an odontocete, the shortfinned pilot whale Globicephala macrorhynchus

S. R. Noren1,*, L. Schwarz1, K. Chase2, K. Aldrich3, K. McMahon-Van Oss3, J. St. Leger2

1Intitute of Marine Science, University of California Santa Cruz, Santa Cruz, CA 95060, USA
2SeaWorld San Diego, San Diego, CA 92109, USA
3SeaWorld Orlando, Orlando, FL 32821, USA
*Corresponding author:

ABSTRACT: Validated metrics to monitor body condition of free-ranging animals are critical to track population stability. We tested repeatability and reliability of body width and body length measurements taken from overhead photographs and validated the assumptions upon which the photogrammetric method to monitor cetacean body condition are based. Short-finned pilot whales Globicephala macrorhynchus served as models. Variability was low for multiple measurements taken from 1 photograph and across photographs of the same animal; standard deviations represented 1.2 ± 1.2% and 2.5 ± 1.3% of mean estimates, respectively. To account for body length variations across whales, we calculated mass, width, and blubber indexes as the residual values of these variables regressed against length. Across the sites examined (anterior pectoral fin, anterior dorsal fin, and posterior dorsal fin), only photogrammetric body width at the posterior dorsal fin site showed consistent significant positive relationships with measured condition indexes (i.e. width and blubber index slope = 0.10, p = 0.005; width and mass index slope = 18.1, p < 0.01). Moreover, only the body width to body length ratio at this site predicted mass index (slope = 3105, p = 0.05). Thus, changes in photogrammetrically measured body width posterior of the dorsal fin at approximately 47% of total body length from the rostrum are related to changes in underlying blubber thickness and body mass. The width:length ratio at this site can be used to monitor condition. Additional studies are warranted to determine if body width at this site reliably predicts condition across odontocete species with varying body morphologies.

KEY WORDS: Photogrammetry · Body condition · Blubber · Pilot whale · Odontocete · Disturbance

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Cite this article as: Noren SR, Schwarz L, Chase K, Aldrich K, McMahon-Van Oss K, St Leger J (2019) Validation of the photogrammetric method to assess body condition of an odontocete, the shortfinned pilot whale Globicephala macrorhynchus. Mar Ecol Prog Ser 620:185-200.

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