Why Thousands of Seal Pups Died at Namibia's Pelican Point in 2020

First published October 21, 2020.

In September and October 2020, thousands of dead Cape fur seal pups, most of them born too early or aborted before birth, were found at the Pelican Point seal colony near Walvis Bay, Namibia. First estimates of more than 5,000 rose to about 7,000 within weeks. Scientists suspected that many pregnant females were starving and had lost their pups, though pollution and infection were also investigated.

Below is what was observed, why seals can lose pregnancies in large numbers, what researchers suspected, and what an event like this means for one of southern Africa's best-known marine mammals.

What was found at Pelican Point

Pelican Point is a narrow sand spit that shelters Walvis Bay on Namibia's Atlantic coast. Its seal colony is a favourite with tourists, who come on kayak and boat trips to see seals and dolphins up close.

From August 2020, local researchers began noticing more dead seals than usual. In the first half of October the numbers jumped. Marine biologist Naude Dreyer of the charity Ocean Conservation Namibia photographed the beach from above and marked each small carcass with a red circle; his rough count for that one colony was over 5,000. The post spread rapidly online, and Namibia's fisheries ministry opened an inquiry.

An unprecedented die-off of over 5,000 Cape fur #seal pups on a Namibian beach is being probed by #Namibia’s #fisheries ministry.#marineconservation #oceans https://t.co/spvRiWJupH

— African Conservation Foundation (@AfricanConserve) October 16, 2020

WATCH: An estimated 5,000 premature Cape fur seal pups have washed up dead at Pelican Point in Namibia. Seals can naturally abort their young when there is lack of food, but samples have been taken to determine the cause of this tragedy. https://t.co/dSosqiXITP pic.twitter.com/sxoLjeXENk

— Getaway Magazine (@GetawayMagazine) October 14, 2020

By late October, Tess Gridley of the Namibian Dolphin Project estimated that between 5,000 and 7,000 females had miscarried, and Al Jazeera reported a total of around 7,000 dead seals. Dreyer also began seeing a new and worrying pattern: fewer fresh pup carcasses, but more dead adult females.

This is the situation at Pelican Point. All the little red circles mark dead seal pups. A rough estimate brings the...

Posted by Ocean Conservation Namibia on Tuesday, 13 October 2020

About the Cape fur seal

The Cape fur seal, also called the brown fur seal (Arctocephalus pusillus pusillus), lives along the coasts of Namibia and South Africa, from Cape Cross in the north round the Cape of Good Hope to the Eastern Cape. It is the largest of the fur seals. Researchers quoted at the time put the total population at about 1.7 million, with roughly a million in Namibia.

Its diet is mostly fish, together with squid, crabs and other crustaceans. Mating takes place in November and December, shortly after the females give birth. Implantation of the embryo is then delayed for about four months, so the full cycle from mating to birth takes about a year, and pups are normally born between mid-November and mid-December.

That timing is what made the 2020 event so striking. Large numbers of dead foetuses and tiny premature pups were appearing in August, September and early October, weeks or months before any healthy pup should have been born.

Why a pregnant seal may lose her pup

Like many mammals, a pregnant fur seal can end a pregnancy when her own body is under severe strain. If she cannot find enough food to build her fat reserves, aborting the foetus can improve her own chance of survival. Dreyer explained that a handful of such losses each year is normal, but stressed that "thousands of premature dead pups is extremely rare."

Gridley described some of the dead females as thin and emaciated, with very little fat. That fitted the idea that food shortage was at the heart of the problem.

Suspected causes

Scientists considered three main explanations, and they are not mutually exclusive:

• Lack of food. Annely Haiphene, executive director of Namibia's Ministry of Fisheries and Marine Resources, said she suspected the seals had not had enough to eat. Fish stocks in the Benguela upwelling system off Namibia shift with ocean temperature and currents, and a poor year can hit predators hard.
• Pollutants or toxins. Harmful algal blooms and chemical pollution can both cause abortions and deaths in marine mammals. A toxin that lingers in the food chain would be the most worrying outcome for the long term.
• Disease. Bacterial infections can trigger abortions and can spread quickly through a crowded colony.

Samples were taken for testing. In the public reporting we reviewed, no single cause was confirmed, and malnutrition remained the leading suspicion. Namibia has seen a similar disaster before: in 1994 around 10,000 seals died and about 15,000 foetuses were aborted at the Cape Cross colony, an event linked to starvation, possibly from a fish shortage, along with a bacterial infection.

Does this threaten the species?

On the numbers, Cape fur seals are not endangered, and a population of more than a million can absorb a bad year. Gridley noted that the species is relatively resilient. Her concern was the knock-on effect: with thousands of females dead, there could be a dip in births in the years that follow.

The losses also come on top of other pressures. Namibia still issues permits for an annual seal harvest, killing pups for fur and adult males for their genitals, which are sold as supposed aphrodisiacs. The government justifies this by citing seals' impact on fish catches, a claim environmental groups dispute. Entanglement in fishing gear and plastic debris kills more. Dreyer has said that while South African numbers look healthy, Namibian numbers appear to be falling.

How scientists investigate a die-off

Mass deaths like this are hard to explain quickly, and early headlines can blur important details. Counting carcasses is only the first step. Researchers need to know whether they are looking at full-term pups, premature pups or aborted foetuses, because each points to a different problem at a different time.

They also record when the deaths started and peaked, the body condition of the dead animals, and whether adults are dying too. Tissue samples are tested for toxins, bacteria and viruses, and the findings are compared with data on sea temperature and fish stocks. Until those results are in, food shortage, pollution and disease should be treated as possibilities to test, not as conclusions.

For visitors to the Namibian coast, the best help is simple: keep a respectful distance from seal colonies, never handle sick or dead animals, and report unusual numbers of carcasses to local conservation groups or authorities.

Sources: Al Jazeera (AFP), 25 October 2020; IOL, October 2020; Africanews, 16 October 2020; Wikipedia: Brown fur seal; photographs and count by Ocean Conservation Namibia.