Ongoing Collapse of Coral Reef Shark Population
source : William Robbins James Cook University , Queensland, Australia
News Item entry - 10th June 2007
Article date - Dec 10 - 2006
Investigators have revealed that coral reef shark populations are in the midst of a rapid decline and that 'no-take' zones - reefs where fishing is prohibited - do protect sharks, but only when compliance with no-take regulations is high. The findings, reported by William Robbins and colleagues at James Cook University, Queensland, Australia and its ARC Centre of Excellence for Coral Reef Studies, appear in the Dec 5th issue of Current Biology.
Reef sharks are so-called 'apex predators' on tropical coral reefs and are therefore of significant potential importance to the functioning of coral reef eco-systems. The reproductive biology of reef sharks makes them particularly vulnerable to fishing, but until now, there have been no studies of the response of these sharks to fishing pressure.
The new work focussed on Australia's Great Barrier Reef, which is widely considered to be one of the world's least degraded, and best managed, reef systems. For balancing conservation with sustainable use, the Great Barrier Reef is regulated through an extensive series of management zones in which different areas are open to different levels of fishing.
In their study, the researchers determined the status of two species of reef shark - the white-tip and grey reef sharks - by employing a unique combination of fisheries-independent abundance estimates and measurements of the survival and reproduction of individual sharks. Their findings show that reef shark abundance on reefs open to fishing are ten times lower than on unfished reefs. Moreover, high reef shark abundance was only apparent on the most strictly-enforced of the 'no-take' zones, suggesting that even moderate levels of poaching can derail attempts to protect shark populations. These observations, coupled with population modelling showing ongoing .rapid declines on population size in fished areas, led the authors to conclude that reef sharks are approaching'ecological extinction' - that is becoming so rare that they can no longer perform their natural role in the functioning of coral reef eco-systems.