An assessment of the natural marking patterns used for photo-identification of common minke whales and white-beaked dolphins in Icelandic waters

Abstract

Natural marks occurring in cetaceans are used to measure population parameters, social structure and movements. However, the changeable nature of these marks can originate bias in these estimates. The aim of this work was to calculate abundance and prevalence of 28 mark types observed in common minke whales and white-beaked dolphins photographed in Icelandic waters for 11 years (2002–2013) in order to identify reliable markings which could be suitable for capture-mark-recapture studies. In the common minke whale subsample the most prevalent occurring marks were cookie-cutter shark bite, notch and lamprey bite, and herpes-like lesions and blisters were the most abundant. White-beaked dolphins had notch, fin patches and fine scrape as the most prevalent, and black mark and fine scrape were the most abundant. Loss and gain rates were also estimated resulting in eight mark types with no losses in common minke whales including fin outline and injury marks. In white-beaked dolphins there were 13 mark types with null loss rate among which there were notch, distinct notch and amputation. Our findings confirm that fin and injury marks are among the most accurate features to use for capture-mark-recapture studies as noted for other cetacean species. We also suggest including cookie-cutter shark bites for common minke whales and fin patches for white-beaked dolphins due to their low loss rate. These two mark types were amongst the most prevalent in both species, so their addition will be pivotal in increasing the power of analysis conducted using photo-identification data obtaining more accurate population estimates.

The incidence of bent dorsal fins in free‐ranging cetaceans

“…, ; Bertulli et al. ). The present review adds 12 species to the list of free‐ranging cetaceans displaying bent dorsal fins.…”

Color patterns in white‐beaked dolphins (Lagenorhynchus albirostris) from Iceland

“…A total of 26 color pattern components were observed, listed below using the seven terms previously applied to white‐beaked dolphins, and 12 terms previously defined for other dolphin species (Perrin , , ; Mitchell ; Mercer ; Webber ; Bertulli et al . ) applied here for the first time to white‐beaked dolphins: beak blaze, lip patch, flipper stripe, helmet, fin patch, spinal field, thoracic field, flank patch, throat chevron, chin blaze, midventral streak, and genital patch. In addition, we propose new terms for the following seven components: mouth band, postocular crescent, flipper patch, semicircular head blaze, peduncular ridge stripe, lateral patch and umbilical patch.…”

“…Fin patch (referred to as “fin patches” of white color in Bertulli et al . ) are reliable secondary features with a low loss rate (0.029 marks/year/individual). A total of 121 adults were resighted with intervals ranging from 1 to 1,317 d. All color components that could be assessed for these animals remained stable over this timespan.…”

“…According to a recent study (Bertulli et al . ) on the stability of natural marks in the same population of Icelandic white‐beaked dolphins, lateral patches (referred to as “hypo‐pigmentation” marks) have a loss rate of zero, although this was based on small sample sizes. Fin patch (referred to as “fin patches” of white color in Bertulli et al .…”

“…; Cipriano and Webber ; Bertulli et al . ). Here, we use an extensive sample of photographs of free‐ranging white‐beaked dolphins collected in three areas around Iceland to describe the components that make up the color patterns and, where possible, ascribe them to ontogenetic variation.…”