[Image: Wikimedia Commons]
The great white sharks of False Bay have pulled a vanishing act, and it’s throwing the entire marine ecosystem into chaos, according to a new study.
Once the stars of dramatic, seal-snatching breaches, great white sharks used to rule the waters off South Africa’s False Bay. Now, it’s practically a blue-hued ghost town. And scientists are sounding the alarm because, naturally, the sharks’ mysterious disappearance has triggered a cascade of knock-on effects through the food web.
The research, published in Frontiers in Marine Science, is led by Neil Hammerschlag of the University of Miami Rosenstiel School, and it leans on over 20 years of meticulous data, per Discover Wildlife. Yeah, they’ve been watching this unfold for decades.
So, what’s going down in False Bay?
Back in the day, great whites were permanent residents, cruising the coastline in summer and haunting the eerie waters around Seal Island in winter. You’d see them year-round, apex predators in their prime.
But now, the sharks are gone. Researchers spent twenty years monitoring them with boat-based surveys, only to witness their numbers crash like a rogue wave.
“The overall trend in the relative abundance of white sharks was relatively stable in the first fifteen years of monitoring; however, their relative abundance began to precipitously decline after 2015, leading to a complete disappearance of white sharks from the standardised surveys since mid-2018.”
That’s not a dip – it’s a wipeout. And what’s to blame? Scientists suspect a grim combo of human interference – like shark nets- and nature’s own apex disruptors: orcas. Yes, orcas have been seen several times hunting our great whites. It’s top predator vs. top predator, and the sharks are losing.
Sadly, the ripple effect is no joke. Call it a full-blown ecological domino effect. The study didn’t stop at boat surveys; researchers also used underwater video footage taken over a decade apart to paint a before-and-after picture of False Bay’s food chain.
“The number of individuals of a given species recorded on the videos not only informs us about their numerical abundance, but also their behaviour, as species under increased predation risk often become more elusive and are thus less likely to be detected on our cameras,” explains Yakira Herskowitz, a co-author of the study.
That means when big sharks disappear, the smaller players change their game.
Since the white sharks vanished, cape fur seals have been throwing a party, their numbers surging. Sevengill sharks are also booming. But it’s not a win for everyone, as the fish that seals prey on are getting hammered, and smaller sharks that sevengills feast on are in decline.
“These changes align with long established ecological theories that predict the removal of a top predator leads to cascading effects on the marine food web,” says Hammerschlag.
Why should we care?
Because this isn’t just about sharks. It’s about the balance of power in the ocean. Apex predators like great whites are like ecosystem architects – without them, we lose a lot!
“Without these apex predators to regulate populations, we are seeing measurable changes that could have long-term effects on ocean health,” says Hammerschlag
So yeah, it matters. A lot. The study isn’t just a eulogy for False Bay’s sharks, it’s a red flag for the rest of the planet. If apex predators vanish, the oceans unravel. And when the oceans unravel, we all feel it.
Shark conservation is thus incredibly noble and increasingly necessary.
[Source: Discover Wildlife]
