Shark populations have been declining steadily around the world for decades. It feels like every other week a shocking new report reveals the dire straits of these vulnerable creatures. This time it is the turn of the apex predators of Australia’s east coast, whose numbers have plummeted alarmingly in the last half a century.
A new study has revealed that the numbers of iconic species such as hammerheads, tiger sharks, and great whites that live in the waters off the coast of Queensland have dropped by as much as 92 percent in just 50 years.
Researchers from the University of Queensland (UQ) used data from a shark control program, which was first instigated to minimize shark-human interactions in 1962, that now stretches over 1,100 miles (1,760 kilometers) and includes the Great Barrier Reef.
Before that there are no official records, so researchers have used the shark control data to reconstruct historical records of shark numbers and shark catches over the last half a century to understand the changes that have taken place between then and now.
“Explorers in the 19th century once described Australian coastlines as being ‘chock-full of sharks,’ yet we don’t have a clear idea of how many sharks there used to be on Queensland beaches,” Dr George Roff of UQ, who led the study, explained in a statement.
“We will never know the exact numbers of sharks in our oceans more than half a century ago, but the data points to radical changes in our coastal ecosystems since the 1960s.”
The shark control program uses baited drumlines to bring down local populations, making shark encounters with humans less likely. According to the study, published in Communications Biology, nearly 50,000 sharks have been caught by this method. Though the range of species caught has been diverse, proper species identification in the recordings only began in the 1990s, so the earliest records grouped them all into five categories: hammerheads, tigers sharks, great whites, whaler sharks, and “other”.
“What we found is that large apex sharks such as hammerheads, tigers and white sharks, have declined by 74 to 92 percent along Queensland’s coast,” Dr Roff said.
“And the chance of zero catch – catching no sharks at any given beach per year – has increased by as much as seven-fold.”
That’s not all. The decades of data revealed another trend, most likely a result of fewer sharks reaching reproductive age.
“The average size of sharks has also declined – tiger sharks and hammerhead sharks are getting smaller,” Roff said.
While human-shark interactions are not desirable, it’s the shark that usually comes off worst. Around 100 million sharks are killed each year globally by humans, while sharks kill on average six humans a year.
However, the researchers concluded that while the shark control program certainly contributed to the diminishing numbers, the likely culprit is commercial fishing, both for the Asian market and as bycatch thanks to large fishing nets.