Skin Deep: An Assessment of New Zealand Blue Whale Skin Condition

Dawn R Barlow,Acacia L Pepper,Leigh G Torres

doi:10.3389/fmars.2019.00757

Dawn R Barlow, Acacia L Pepper + Show 1 more

Open Access

https://doi.org/10.3389/fmars.2019.00757

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Abstract

Skin condition assessment of wildlife can provide insight into individual and population health. Yet, logistics can limit skin condition assessment of large whales. We developed a standardized, quantitative protocol using photographs to assess skin condition of blue whales in New Zealand, and demonstrate the value gained by testing hypotheses, documenting new morphologies, and establishing baselines that can be monitored for change. We reviewed a photo-identification catalog to compile common markings, categorized markings according to existing definitions, and described markings not previously documented. Photographs of blue whale skin (n=1,466) were assessed to quantify marking prevalence, severity, and co-occurrence patterns. Of the whales assessed (n=148), 96.6% had cookie cutter shark bites, 80.4% had blister lesions, 56.0% had pigmentation blazes on the dorsal fin, and 33.7% had holes in the dorsal fin. Additionally, 35.8% had “starburst” lesions, a previously undocumented marking. Blister and cookie cutter shark bite severity did not accumulate linearly, indicating that the two marking types are unrelated. There was a positive relationship between blister severity and number of starbursts, indicating that the two could be related; based on morphological similarities, starburst lesions may derive from ruptured blisters. Whales with holes in their dorsal fin had significantly higher blister severity than those without, indicating that these markings could be related; this is supported by observed blisters on dorsal fins of blue whales. There was a significantly higher probability of fresher cookie cutter shark bites on whales observed at more northerly latitudes, but no relationship between blister severity or number of starbursts and latitude. These latitudinal patterns indicate that blue whales in New Zealand accumulate cookie cutter shark bites at more northerly latitudes; this finding is supported by the known range of cookie cutter sharks in New Zealand waters. Of the eight individual whales re-sighted across multiple years, there was no uniform pattern in lesion change over time, however individual cases revealed lesion healing over a multi-year timeframe. Our protocol for quantifying skin condition can be applied to any cetacean photo-identification catalog, and can be used to compare across individuals and populations, and explore causal links between skin condition and cetacean health.

Highlights

Wildlife population health can be difficult to quantify noninvasively
Our final dataset contained 138 unique individual blue whales photographed around New Zealand
Using individuals with fair or better quality photographs for both sides (n = 23), we determined no significant difference in cookie cutter shark bite severity score, blister severity score, presence or absence of blazes, or the number of starbursts between the left- and right-hand sides

Summary

Introduction

Wildlife population health can be difficult to quantify noninvasively. Yet, visual assessment of external morphology including skin condition has been used as an indicator of underlying individual and population health in several species including wolves (Oleaga et al, 2011), lemurs (Berg et al, 2009), and elephants (Wemmer et al, 2006). Markings on cetacean skin have long been used to identify individuals, and more recently studies have used photographs to assess and monitor cetacean health (Thompson and Hammond, 1992; Wilson et al, 2000; Van Bressem et al, 2003; Hamilton and Marx, 2005). While skin condition of wild cetaceans is difficult to study due to the logistical constraints of data collection, it can be done non-invasively via photographs and used to monitor health, as well as impacts of environmental changes and anthropogenic pressures. Population-level assessments of baleen whale skin lesion prevalence have proven useful to understand changes over time and infer population health (Hamilton and Marx, 2005)

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