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A new scientific paper has just been published on the incidence of scarring on whale sharks in the Indian Ocean from Ningaloo, Mozambique and Seychelles. The paper published in the Journal of Fish Biology was a collaborative effort between researchers working in these three areas and is a part of the on-going sharing of data and collaboration between Indian Ocean whale shark scientists.
The article reports that scarring was most prevalent in the Seychelles aggregation (67%, 534 of 797), followed by Mozambique (37%, 67 of 180) and Ningaloo (27%, 84 of 311).
Scarring was separated into seven categories based on images present from each region: (1) abrasions, (2) lacerations, (3) nicks, (4) bites, (5) blunt trauma, (6) amputations and (7) ‘other’. Predator bites were the most frequent source of scarring (aside from minor nicks and abrasions) and 27% of individuals had scars consistent with predator attacks. A similar proportion of whale sharks had blunt trauma, laceration and amputation scars, the majority of which appeared to be caused by ship collisions.
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| Examples of major and minor scars: a) large bite & b) blunt trauma, both major injuries; d) abrasions & e) nicks from trailing edge of fin are minor injuries.
Images courtesy C. Speed et al. |
The scars were also classified into two groups with respect to severity: ‘major’ scars were potentially life-threatening and included complete or near-complete amputation of the fins, while minor scars were superficial and included abrasions, partial amputations, small bites and nicks. After the removal of minor scars (nicks and abrasions), the total percentages of scarred individuals per aggregation dropped to 45.3% (361 of 797) for Seychelles, 22.7% (41 of 180) for Mozambique, and 20% (62 of 311) for Ningaloo Reef.
The researchers used this data to see if there was any effect of scarring on the apparent survival rates of the sharks but could not detect and significant effect on survival. They did note, however, that while scarring from natural predators and smaller vessels appeared unrelated to whale shark survival, the effect of mortality related to ship strikes need to be quantified to assist in future management of this species.
The full citation for this paper is:
Speed CW, Meekan MG, Rowat D, Pierce S, Marshall AD, Bradshaw CJA (2008) Scarring patterns and relative mortality rates of Indian Ocean whale sharks. Journal of Fish Biology 72:1488-1503
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