Super-sized livers help shark pups survive

Sharks abandon their pups as soon as they are born, but scientists from the Bangor University (UK), the KwaZulu-Natal Sharks Board, the University of KwaZulu-Natal, and the Australian Institute of Marine Science who studied shark data records over 30 years from KwaZulu-Natal in South Africa have shown that they provide their pups with huge livers to live off while they are able to hunt.

With this study published in the Journal of Ecology* and focused on dusky and spinner sharks (Carcharhinus obscurus and Carcharhinus brevipinna respectively) captured incidentally by beach protection nets around KwaZulu-Natal, researchers revealed details on how shark mothers invest in their young, an unexpected traits for sharks.

While the use of the liver as an energy store and for buoyancy is well documented in adult sharks, this study provides the first evidence of a decline in liver mass of newborn sharks, from 20% of body weight at birth to 6% when they start to feed themselves.
The study also found evidence to suggest that female sharks choose when to give birth so that conditions are best for the pups.

The results of this study raise important questions over the reproductive success of sharks and the survival of their newborn pups. "Sharks are under severe pressure by human activity, but our current understanding of their reproductive potential remains limited. We have much work to do to improve our basic understanding of shark biology if we are to implement effective management plans" said Nigel Hussey, from Bangor University.

Nigel Hussey is one of the marine biologists working on the Cousteau shark project.

* Maternal investment and size-specific reproductive output in carcharhinid sharks, Nigel E Hussey et al., Journal of Animal Ecology, 2009.

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