Was It Worth It? Insights from Systematic Health Assessments of Dolphins Incidentally Caught in the Shark Nets off KwaZulu-Natal, South Africa, over the past Seven Years (2010–2017)
Shark nets have been in use off KwaZulu-Natal, South Africa, since the 1950s.1 Besides sharks, these nets are also catching ‘harmless’ bycatch, such as dolphins.2 The most common species caught are the Indian Ocean humpback dolphin (Sousa plumbea), Indo-Pacific bottlenose dolphin (Tursiops aduncus) and long-beaked common dolphin (Delphinus capensis). Since 2010, systematic health investigations of the bycaught dolphins have been conducted under the assumption that these animals present a reflection of the wild populations found off KwaZulu-Natal. Initial findings for these populations (2010–2012) included the presence of pneumonia, enteritis, and lobomycosis.3 While these investigations provided valuable baseline information and indicated that the animals generally were in ‘good health’, they also suffered from small sample sizes, particularly for Sousa plumbea (n=5 vs. Tursiops aduncus).3 However, continued collection of data now allows us to investigate in detail our initial intuition that Sousa plumbea (total n=20) generally appears to be in ‘poor health’ compared to Tursiops aduncus (total n=62). Quantification of histopathological differences between the Indo-Pacific bottlenose dolphin (Tursiops aduncus) and the Indian Ocean humpback dolphin (Sousa plumbea) were investigated and will be presented in detail. Further biological information on diet and life history will be included.4,5 Both species have overlapping inshore distribution ranges, but while the former is more abundant and has a current conservation status of ‘vulnerable’, the latter has been declared ‘endangered’ in 2015 and represents South Africa’s first endangered marine mammal.6,7 The results from our work conducted in South Africa will also be discussed within the global context with regards to developments in marine mammal health.8,9
* Presenting author
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