“What a shame,” she said. “Pardon me for being nosy, but do you know what’s killing them?”
Tess Gridley, a scientist who doesn’t study seals normally but has taken it upon herself to find out what’s been killing thousands of the animals along southern Africa’s Atlantic coast over the past six months, looked between the tourist and dead seals in front of her.
“That’s what we’re trying to figure out,” Gridley said. The seals were some of more than 50 she has necropsied on the region’s beaches.
Marine species on the coasts around Cape Town are facing multiple crises. A bird flu outbreak last year took out nearly a fifth of an endangered cormorant population in South Africa. Local penguin numbers are declining precipitously, in part because overfishing is depleting their sources of food. Further north, in Angola, fish stocks are plummeting as climate change rapidly warms the ocean.
But seals? Who cares about seals? Most fishermen certainly don’t — the mischievous creatures snack on their catch. And while they may be cute, they aren’t endangered, not even close. Furthermore, seal mortality is famously high — as much as 40 percent of pups don’t survive. So who’s to say that the current die-off is even abnormal?
Gridley, 40, is convinced this is abnormal, and a mystery worth solving that has potential implications reaching far beyond seals.
“Seals are just gone from whole areas of coast, and no one has batted an eye,” she said. “I’m filling a gap because it seems nobody else will.”
It is understandable why endangered bird populations get attention. Bird flu can jump to mammal populations and, at worst, turn into a pandemic. More commonly, it can infect poultry and ostriches, both of which factor heavily into the South African diet and economy.
But Gridley’s leading theory for what’s killing the seals is also a toxin that in high concentrations can pose a threat to humans and their food.
Domoic acid, released in some algae blooms, is ingested by plankton and then moves up the food chain through shellfish and anchovies and so on. In humans, it can cause what is called amnesic shellfish poisoning, which, as the name suggests, primarily affects memory, but also balance, and can be fatal.
Domoic acid poisoning has been linked in peer-reviewed studies to sea lion die-offs in California. In some instances, the animals were seen stumbling, bewildered, along coastal roads, their memory and balance seemingly gone.
“There are huge parallels” between California and South Africa, said Frances Gulland, commissioner of the U.S. Marine Mammal Commission. “And that’s concerning in part because the economic impacts were massive in California. When domoic acid spiked in samples, the whole shellfish industry shut down for months.”
In the late 1990s, Gulland and other researchers faced a similar mystery to Gridley’s, but publicity
