[imagesource: Barry Christianson / China Dialogue Ocean]

Walking along the Sea Point promenade in November last year, I noticed a devastating amount of beached baby seals, one flailing on a rock as its life was slowly being sapped out.

You might have noticed a carcass or two yourself somewhere along the Western Cape’s coastline, as early as September mind you, which is precisely when researchers identified the mysterious wave of Cape fur seals’ deaths.

Tess Gridley, a behavioural biologist and director of the research organisation SeaSearch, took it upon herself to investigate this mass die-off plaguing our shores.

She and her team walked along miles of coastline, picking through seal bodies, lining them up in a funereal procession, and searching for clues to the cause of the crisis.

Image: Barry Christianson / China Dialogue Ocean

Almost half a year and several thousand corpses later, the question still remains over the deaths of one of South Africa’s most charming marine animals, reported Emma Bryce in The Maritime Executive.

The researchers have been looking at every possible angle to figure out a more precise cause, ploughing through stench and heat, and hacking through seal organs to take samples, do lab tests, and make the much-needed discovery to sound the alarm and save the species.

Sure the two-million-strong Cape fur seal population experiences “natural cycles of boom and bust”, with pregnant females occasionally aborting foetuses as they see fit.

But the sheer proportion of foetuses, juveniles, and adults washing up this time seemed completely strange:

“While it’s normal for a portion of the population to die during the breeding period, this was affecting other age groups that aren’t usually affected. I think that’s what sounded the alarm bells,” says Mduduzi Seakamela, a marine scientist at the South African Department of Forestry, Fisheries and Environment (DFFE) who monitors populations of sea animals including seals.

Researchers are aware that this die-off points to a marine ecosystem under complete stress:

“I can honestly say last year was the worst thing I have ever seen,” says Kim Krynauw, operational director of the Hout Bay Seal Rescue Centre. Based 20km from Cape Town, the center has for months been rehabilitating beached animals, nursing hungry seals back from the brink with a formula rich in electrolytes. Many rescued animals haven’t been so lucky. “What came back in our necropsies was low body fat, no food at all in their bodies – starvation,” Krynauw says.

The competition for food has become rife out at sea thanks to declining and unpredictable fish stocks caused by overfishing, pollution, as well as climate change, which combined have been interfering with where and when fish become available.

To make it worse, the seals are showing signs of having died from seizures, which paints an even more alarming picture of the state of our seas:

One theory is uppermost in researchers’ minds. Preliminary analysis shows many animals have oedema on the lungs, a type of swelling suggesting they drowned. This hints at seizures, says Luca Mendes, a veterinarian from the Two Oceans Aquarium in Cape Town who has been assisting Gridley, which may indicate poisoning by a neurotoxin called domoic acid, a by-product of algal blooms.

Algae bloom agitated domoic acid poisoning in California in 1998, where thousands of sea lions died over the course of just a few weeks – something our researchers are looking into as they uncover the local causes of the current seal die-off.

Image: Barry Christianson / China Dialogue Ocean

It could be the domoic acid or other food-related explanations, but as Mendes says, there is hardly ever just one answer.

Rather, as he believes, finding the causes behind the seal die-offs will require a multidisciplinary, ecosystem-level approach.

In that sense, researchers will have to do the hard yards to understand not only toxins and pollution but also climate change and fishing as they impact the seas altogether and cause mass species to decline.

“If anything, this whole [die-off] highlights just how little we truly understand about the ocean or the dynamics under the water,” says Mandes.

Consider donating to SeaSearch and help them fund the terribly expensive lab testing and data collating that needs to take place to figure this dire situation out.

[source:maritimeexecutive]