Tracking the Population of White Sharks, Carcharodon carcharias, in South African Waters
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Description
Many studies have shown dramatic declines in marine apex predator populations, including the white shark, Carcharodon carcharias, in South Africa which is currently listed as vulnerable on the IUCN red list. Understanding biological and ecological roles of C. carcharias is crucial for understanding the function of other apex predators in marine food webs. The objective of this study was to attain an accurate population count of C. carcharias off South Africa. Our hypothesis was that shark populations in the region are declining due to human activities. In this study, I compare multiple approaches for white shark population assessments, including my experience using distinct notches on the trailing edge of the dorsal fins to distinguish (and count) individuals, as well as genetic analysis from published literature. To identify individuals, sharks were baited to the boat and led to swim parallel so that their dorsal fin was presented from the side, and dorsal fin photos were taken. Fin ID photos were analyzed through software from Stellenbosch University, alongside fishery bycatch data. In 2014, the population was estimated to be 426 sharks. Two years later, genetic analyses produced an estimate of 333 sharks. In our study, the current population was estimated to be between 250 and 300 sharks. Additionally, we identified approximately 30 new individuals. Although this seems hopeful for the white shark population, that same number of sharks are killed annually by long lines and drum lines. Understanding and protecting C. carcharias is essential for future health of marine ecosystems and resources.
Tracking the Population of White Sharks, Carcharodon carcharias, in South African Waters
Many studies have shown dramatic declines in marine apex predator populations, including the white shark, Carcharodon carcharias, in South Africa which is currently listed as vulnerable on the IUCN red list. Understanding biological and ecological roles of C. carcharias is crucial for understanding the function of other apex predators in marine food webs. The objective of this study was to attain an accurate population count of C. carcharias off South Africa. Our hypothesis was that shark populations in the region are declining due to human activities. In this study, I compare multiple approaches for white shark population assessments, including my experience using distinct notches on the trailing edge of the dorsal fins to distinguish (and count) individuals, as well as genetic analysis from published literature. To identify individuals, sharks were baited to the boat and led to swim parallel so that their dorsal fin was presented from the side, and dorsal fin photos were taken. Fin ID photos were analyzed through software from Stellenbosch University, alongside fishery bycatch data. In 2014, the population was estimated to be 426 sharks. Two years later, genetic analyses produced an estimate of 333 sharks. In our study, the current population was estimated to be between 250 and 300 sharks. Additionally, we identified approximately 30 new individuals. Although this seems hopeful for the white shark population, that same number of sharks are killed annually by long lines and drum lines. Understanding and protecting C. carcharias is essential for future health of marine ecosystems and resources.