Sexing free-ranging adult Cuvier’s beaked whales (Ziphius cavirostris) using natural marking thresholds and pigmentation patterns

Abstract

Sex identification of adult cetaceans is an important ecological parameter that should be incorporated into studies such as population dynamics and animal behavior. In Cuvier’s beaked whale ( Ziphius cavirostris ), sex determination may be achieved through genetics, observation of genitals, the presence/absence of erupted teeth, and calf association. However, these features are difficult to ascertain due to the shy behavior of this species. Therefore, this study aimed to create a robust sex identification method using only external characteristics. Particularly, this work analyzed pigmentation patterns and levels of natural marks from adult individuals of known sex in order to identify gender differences, using frequency analysis and generalized linear models. Photographic captures of 73 free-ranging animals were utilized. The frequencies of the individual pigmentation patterns were found to be sex dependent. The 63% of the animals could be classified into either a “soft” or “sharp” pigmentation cluster. The “soft” cluster was only displayed by females, while the “sharp” cluster was present in both the sexes. However, the model selection process indicated that natural marking is the best determinative factor for sex classification. The density of the visible intraspecific natural marks was found to differ between the sexes ( P value < 0.001) and was incorporated as a predictor variable into several candidate models. All candidate models had a high predictive power (mean area under the curve 0.973) and correctly predicted the sex, by means of a density threshold value, in 85–90% of the analyzed animals. The density threshold ranged from 4.1% to 6.4% according to the different body area analyzed. These density threshold values represent a robust post hoc sexing method to classify individuals to sex from opportunistic photos in the absence of other sexing methods.

First assessment of POPs and cytochrome P450 expression in Cuvier’s beaked whales (Ziphius cavirostris) skin biopsies from the Mediterranean Sea

“…These represent 20–28% of the total resident population of Cuvier’s beaked whales in the study area (100 individuals with 95% CI = 79–112; 6 ). Samples were successfully collected from individuals of three different age classes 39 , 40 : four juveniles (estimated age < 5-year-old), nine subadults (estimated age 5–10-year-old) and nine adults (estimated age > 10-year-old). Since only three females, one juvenile and two adults, were sampled, it was not possible to perform any statistical analysis between sexes.…”

“…All the whales photographed were separated into three different age classes—juveniles, subadults, adults. Animals were categorized in the age classes by both the estimated size and coloration patterns 39 , 40 . All the subadult and adult whales biopsied were well-marked allowing for individual identification.…”

Every scar has a story: age and sex-specific conflict rates in wild bottlenose dolphins

“…This pattern holds true for dolphins, as cycling females have a higher incidence of new tooth rakes than noncycling females (Scott et al 2005). Sex differences in aggression and sexual competition (male-male or male-female) have been inferred by scarring in a variety of cetacean species (McCann 1974;Best 1979;Silverman and Dunbar 1980;Payne and Dorsey 1983;Heyning 1984;Gerson and Hickie 1985;Chu and Nieukirk 1988;Tolley et al 1995;Scott et al 2005;Martin and da Silva 2006;Rowe and Dawson 2009;Coomber et al 2016). In fact, tooth rake scarring can be a reliable indicator of sex in some species (e.g., Cuvier's beaked whales Ziphius cavirostris, Coomber et al 2016; Indo-Pacific humpback dolphins Sousa chinensis, Wright et al 2017).…”

Extreme diving in mammals: first estimates of behavioural aerobic dive limits in Cuvier's beaked whales

“…Photographs of all tagged individuals were taken to determine sex and age class. Individuals with erupted teeth and heavy body scarring were classed as adult males (Baird, 2016;Coomber et al, 2016;Falcone et al, 2009;McSweeney et al, 2007). All other animals were assigned as unknown.…”