Large apex sharks have declined over the past half century

Shark populations off the east coast of Australia have been declining over the past 55 years and show little evidence of recovery, reports a studied published this week in Communications Biology. These findings may have implications for shark-control programs and conservation efforts.

The Queensland Shark Control Program (QSCP) was established in 1962 with the aim of minimizing dangerous shark-human interactions. It now spans 1,760 km of Australian coastline and has caught nearly 50,000 sharks to date. However, long-term effects of shark control programs on the marine ecosystem are unknown.

George Roff and colleagues analysed data for four large shark groups - hammerhead sharks, whaler sharks, tiger sharks, and white sharks - collected daily for over 55 years by the QSCP. The authors found substantial declines in the abundance of sharks, including a 92% decline for hammerhead and great white sharks. The data also showed that the sizes of adult sharks have declined, which makes the populations vulnerable. In addition, the authors found that the most likely cause of shark population declines is overfishing, rather than environmental changes.

The authors’ analysis of the QSCP data implies that, contrary to the general perception, recent increases in unprovoked shark incidents in Queensland and New South Wales are not due to recovering shark populations. The data suggests that apparent increases in human-shark interactions are occurring at a time when shark populations are severely depleted compared to historical baselines.