Penguins & Cormorant & Fisheries Failing, Now South African Seal Dieoff Underway - Cause Unknown
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.
EDIT
https://www.washingtonpost.com/world/2022/02/10/south-africa-seals-dying/
