Trend in Pacific walrus ( Odobenus rosmarus divergens)tusk asymmetry, 1990–2014

• Published in: Marine Mammal Science
• Main Authors: MacCracken, James G., Benter, R. Brad
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2015
• Subjects: Pacific; Odobenus rosmarus; Sea ice; walrus*
• Online Access: http://dx.doi.org/10.1111/mms.12286; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fmms.12286; https://onlinelibrary.wiley.com/doi/pdf/10.1111/mms.12286

Abstract We used the basal circumference of Pacific walrus ( Odobenus rosmarus divergens ) tusks (upper canine teeth, n = 21,068 pairs) to estimate fluctuating asymmetry ( FA 1 index) from 1990 to 2014. The mean difference in circumference between paired tusks was −0.006 ( SEM = 0.002) cm and approximately normally distributed. Measurement error was 0.6 (0.02)%, similar between biologists and lay persons ( P = 0.83), and ≤15% of FA 1. Tusk FA 1 was greatest in 1990 then declined by 56% ( P = 0.0001) through 2014. Male and female trends differed ( P = 0.0001) and male FA 1 was 40% greater ( P = 0.0001) and the rate of decline 28% steeper ( P = 0.3) than females. A quartic polynomial model ( r 2 = 0.66, w i = 0.685) fit the trend for female data better than simpler forms, whereas a linear model ( r 2 = 0.55, w i = 0.693) was a better fit for male data. Walrus tusk FA 1 reflected periods when the population was stressed due to food limitations and then recovered, and perhaps when females began to experience the loss of preferred sea ice habitat in summer and FA 1 is an easily monitored indicator. More work is needed to confirm the link between FA 1, individual fitness, and adaptive potential.