False Bay Great White Sharks May Not Have Left Because of Killer Whale Attacks

The great white sharks in South Africa's False Bay may have deserted the area because of fishing practices in the area—not because killer whales had started hunting them, as was previously thought, scientists have said.

False Bay, on the country's southwest coast, was once a prominent great white feeding ground where sharks would regularly breach the surface to catch prey. However, great white sharks have been noticeably absent from the area for over two years. Scientists are concerned that their continued absence may lead to ecological upheaval in the region. Great whites are important predators that impact the structure and function of the ecosystem, one expert previously told Newsweek.

Before their disappearance, killer whales had turned up in the area and their arrival coincided with a number of sharks—including great whites—being killed. Analysis of their bodies showed their pectoral fins had been torn off and their livers eaten, with bite marks indicating killer whales were behind the attacks.

Research from other parts of the world has found that when killer whales enter their territory, great white sharks will vacate and not return for a whole season. This led to the suggestion the False Bay great whites had left the area because of the threat posed by the killer whales.

However, Chris Fallows, a wildlife photographer and great white shark expert, says he and many scientists, naturalists and marine experts believe a shortage of food is behind the disappearance. He says smaller shark species around False Bay—a source of food for great whites—are being overfished to meet demands from Australia. According to the campaign website Shark Free Chips, Australia has limits on fishing, while South Africa does not. The species targeted are smoothhound and soupfin sharks, which are caught by Demersal Shark Longlines (DSL)—baited hoots spread across the seafloor.

Fallows says evidence suggests smaller shark species are the primary food source for great whites for 75 percent of their lives.

"Historically in False Bay, for eight months of the year, we found the bulk of the great whites exactly where the highest numbers of smoothhound and soupfin sharks were," he told Newsweek. "Nowadays, sadly, False Bay has hardly any of these sharks left when compared to historical numbers just 20 years ago." Fallows says the arrival of the killer whales has simply made False Bay even less of a desirable hunting ground for the great whites.

Mary Rowlinson, marine biologist and manager at the Shark and Marine Research Institute, says the disappearance of great whites from False Bay is likely down to a combination of factors, including fishing practices, overfishing and pollution.

"For the past few years a popular 'cause' for the fall in numbers has been the presence of orca whales, but sadly blaming the orca whales is really shadowing what the true issues are," she told Newsweek. "It is easier for people and the government to blame the orca whales as it is just nature, but in reality it is human practices that are causing the decline." She said two orca whales could not be accountable for the decimation of an entire population of great whites. The decline in great white numbers also started in 2012, long before the killer whales arrived. "I would say [the killer whales] definitely have an impact on the presence of great white sharks at the various congregation sites, but they cannot be held accountable for the fall in numbers."

In South Africa, there are no catch restrictions on DSL fishing. Critics say that as well as decimating populations of smaller species, great whites also get caught in the nets. Rowlinson said with less food, there is more competition between individual white sharks, and that juveniles are particularly at risk. Great whites are long-lived and have few offspring, so hazards for younger individuals can impact a population.

"General overfishing also has an impact on white sharks as they feed on many of the big game fish," Rowlinson said. "So declines in yellowtail, snoek, geelbek etc. can also have an impact on white sharks, through depletion of their food resources again. It is all connected so over-fishing in general has an impact as white sharks as they are the top predator."

great white shark
A great white shark emerging from the water in False Bay, South Africa. Great whites have been largely absent from the once-popular area for the last two years. iStock

Declines in great whites, she said, have also been observed in the areas of Gansbaai and Mossel Bay: "This is because our white sharks are one population around South Africa. You do not have a separate population at each site. So it is very important that whilst the most notable declines have been observed in False Bay, our whole white shark population around our entire coastline is declining in numbers and is threatened with extinction."

South Africa's Department of Environment, Forestry and Fisheries has now announced an expert panel to review the conservation and management of shark species following public concern about the fall in great white shark numbers along the coast. Nine members will look at the current plan over a three-month period to see whether it is effective and if it can be improved, as well as recommending actions to better conserve the country's shark species.

The panel will look at whether shark catches from fishing practices, both direct and indirect, are sustainable, and that the monitoring of shark catches are improved. It will also assess direct threats to shark populations in order to find ways to protect habitats, with "particular attention" being given to threatened and vulnerable species. The final report is expected by the start of October.

Alison Kock, a marine biologist at South African National Parks, who serves on the executive committee of Shark Spotters, is one of the members of the panel. She told Newsweek: "It's a fact that the white sharks have disappeared from some areas in South Africa, and it's a fact that the populations of smoothhound and soupfin sharks have declined significantly—and that many of these sharks are exported to Australia. However, the reported causal link between the white sharks disappearing and the overfishing of the demersal sharks is a theory not backed up by scientific evidence at this stage. It remains a possibility which needs to be researched, but has no evidence base at this stage."

False Bay Great White Sharks May Not Have Left Because of Killer Whale Attacks | Tech & Science