Abstract
Wound healing is important for marine taxa such as elasmobranchs, which can incur a range of natural and anthropogenic wounds throughout their life history. There is evidence that this group shows a high capacity for external wound healing. However, anthropogenic wounds may become more frequent due to increasing commercial and recreational marine activities. Whale sharks are particularly at risk of attaining injuries given their use of surface waters and wildlife tourism interest. There is limited understanding as to how whale sharks recover from injuries, and often insights are confined to singular opportunistic observations. The present study makes use of a unique and valuable photographic data source from two whale shark aggregation sites in the Indian Ocean. Successional injury-healing progression cases were reviewed to investigate the characteristics of injuries and quantify a coarse healing timeframe. Wounds were measured over time using an image standardization method. This work shows that by Day 25 major injury surface area decreased by an average of 56% and the most rapid healing case showed a surface area reduction of 50% in 4 days. All wounds reached a point of 90% surface area closure by Day 35. There were differences in healing rate based on wound type, with lacerations and abrasions taking 50 and 22days to reach 90% healing, respectively. This study provides baseline information for wound healing in whale sharks and the methods proposed could act as a foundation for future research. Use of a detailed classification system, as presented here, may also assist in ocean scale injury comparisons between research groups and aid reliable descriptive data. Such findings can contribute to discussions regarding appropriate management in aggregation areas with an aim to reduce the likelihood of injuries, such as those resulting from vessel collisions, in these regions or during movements between coastal waters.
Highlights
Exogenous wound healing is an essential physiological adaptation for vertebrate species (Han et al, 2005; Belacortu and Paricio, 2011; Jazwinska and Sallin, 2016)
Dedicated yearly photoidentification surveys of varying duration have been conducted by Marine Conservation Society Seychelles (MCSS) in Djibouti and the Maldives Whale Shark Research Programme (MWSRP) in the Maldives since 2003 and 2006 respectively
By Day 25 major injury surface area had decreased by 56.45% (± 6.06 S.E., n = 12), and minor injury surface area had decreased by 79.95% (± 7.60 S.E., n = 7)
Summary
Exogenous wound healing is an essential physiological adaptation for vertebrate species (Han et al, 2005; Belacortu and Paricio, 2011; Jazwinska and Sallin, 2016). The ability to heal from external wounds is fundamental for survival and allows animals to regain motor function and minimize any prolonged impacts of injury while managing water-borne microflora (McCallum et al, 2003). Anthropogenic injuries are likely to be more complex and destructive than those obtained naturally and have the potential to induce long-term physiological adjustments, behavioural alterations and, in the worst case, death. It is important, to establish a solid baseline understanding of the characteristics and healing processes of physical wounds, from as many origins as sample size allows, so as to better identify and inform conservation opportunities where injury instance can be managed more effectively
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