Should we be afraid of seals?

The science, sorrow and unsolved enigma of aggressive Cape fur seals

04 February 2024 - 00:00 By Amy Donovan
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Sea Search Research and Conservation, in an effort led by Dr. Tess Gridley are doing everything they can to figure out what is sickening Cape Fur seals. Without formal funding, the work is slow.
Sea Search Research and Conservation, in an effort led by Dr. Tess Gridley are doing everything they can to figure out what is sickening Cape Fur seals. Without formal funding, the work is slow.
Image: Steve Benjamin

In the small necropsy lab, a green tablecloth covers the steel worktable. A black plastic garbage bag covers the tablecloth. Clothes pegs fasten the bag to the table’s edges. The table’s occupant is the body of a juvenile Cape fur seal. She arrived in Cape Town after being collected the previous day at a beach just outside the city. She was transported in one of the same black bags, her weight stretching the plastic earthward when we carried her. The new bag will eventually fold over her, making a neat packet of guts.

Several weeks earlier, another Cape fur seal, seemingly out of nowhere, violently attacked two women on Fish Hoek Beach, on the eastern coast of the Cape Peninsula. A couple of weeks later, others would assail nature guides out on the water around Hout Bay, on the peninsula’s Atlantic coast.

Scientists believe these seals are not vicious, but confused; they suspect illness is to blame — possibly a toxin called domoic acid, which overstimulates some neurons, causing brain damage and erratic behaviour.

As more and more distressing human-seal encounters occur, researchers are hoping necropsy data will help them understand the alarming pattern, first observed in late 2021. The researchers are calling for empathy towards these seals: as marine biologist Dr Tess Gridley, founding director of Sea Search Research and Conservation, puts it, these seals are sick. Their behaviour is not their fault.

If — as seems likely — there is a link between anthropogenic ecosystem disturbance and the seals’ illness, the fault may even be ours.

Scientists believe these seals are not vicious, but confused; they suspect a toxin called domoic acid is to blame for overstimulating certain neurons

In the lab, the seal is cut open; her organs are lifted out and examined, photographed. Bits of them go into small plastic jars: a slice of spongy liver; the heart, dark and vivid. The heart must be extracted last, I learn, because once you remove it blood pools so rapidly in the body cavity that other organs are obscured. You could get lost in it.

Dogs yap in the background and a fly buzzes. There is the squelching sound of flesh and blubber. Now that the heart is in its jar, each small prod of the seal’s body makes blood slosh. When load-shedding begins the electrical silence amplifies the fingernails-on-a-chalkboard sound made by a thin saw scraping along the seal’s skull.

I have come to Cape Town as a researcher in anthropology, volunteering with Sea Search to learn about the inner workings of marine biology. My role now is to steady this seal’s body as Nicole Kieswetter, who wields the saw, works to extract the brain. Kieswetter is the field data collection lead for Sea Search’s seal project. Her steady fingers belie the fact she is newly trained in the art of necropsy. Under the long strokes of her blade I think I can smell bone burning away.

Once Kieswetter has cut a sufficient opening — triangular, about the size of her small palm — she slides her fingers into it and wraps them around the brain, trying very hard to make sure it holds its form. When the brains loosen, she says, it is difficult to forestall total unravelling. She separates from the skull the membrane that contains the brain. Each of her movements is slower than the last. Finally she lifts the brain out, cupping it in both hands so that a photo can be taken by the other Sea Search volunteer present.

The pile of squiggly grey matter goes into a plastic jar of formalin. We clean the room and discard what remains of the seal’s body — back into the same black bag she arrived in. We drive back to the Sea Search office in Muizenberg, bearing one more fleshy data set to add to their overflowing storage spaces until such time as they have the resources to properly test and process the hearts, brains, whiskers, slices of liver and kidney they have been collecting for more than a year.

We necropsied that particular seal in early November 2022. Pupping season was beginning, and the team at Sea Search expected, as in the 2021 season, that in the next weeks and months they would be kept busy collecting carcasses. The years 2020 and 2021 had brought what they call mass abortion events, with an estimated 5,000 not-quite-gestated foetuses scattered dead around the beaches of Namibia in 2020, and the Western Cape in 2021. Sea Search researchers witnessed females giving birth to dead pups, then dying shortly afterward, often with “indications of neurological effects, with animals showing disturbing convulsions as they lie dying”. ⁠ 

There are an estimated 2-million Cape fur seals. The species is not considered to be in any danger. The birth rate and the mortality rate are naturally high, the latter in both newborns (20% in the first month of life) and yearlings, some of which fail to thrive when their mothers’ milk is redirected to younger siblings. It is normal to see some dead seals at this time of year. In 2022, as it turned out, there was fewer deaths overall than in the year before.

But so many deaths, especially abortions — preterm stillbirths — are not normal. Nor is the seals’ strange behaviour, which includes anomalies such as convulsions, twitching and random lunging as well as increasing aggression — the latter directed not only towards humans but also dogs, garbage, boats and other seals. These animals are normally placid, sometimes downright playful with humans. The attacks have sent some people to hospital and created serious concerns for those whose livelihoods depend on proximity to the seals — on the seals’ forbearance, if not their goodwill; on them being, if not always peaceful, predictable enough to trust.

Gridley says that for those who work with and around the seals, until now there has never been reason to fear them. She describes walking through seal colonies where the ground pulses with the dark brown, furred bodies, where the seals arched their backs and called out, going about their business as she went about hers. Sometimes, she says, you might have to wait until a large male moves out of your way; once in a while one might send a small warning nip in your direction. But the attacks of the past couple of years have been entirely different. Those who have experienced them have felt targeted, and the worst of the aggressive seals have been relentless, returning to bite the unfortunate human or boat again and again and again. Strips of wetsuits or flesh have been torn away by these bites.

One person described being pulled down by a seal, over and over. He described the seal’s wide-open jaws; he described it shaking him. He was hospitalised because of his wounds. He has since healed physically, and showed me large, jagged scars on his leg. But months after his experience, when he closes his eyes he can still see that seal’s wild face. For most of his life this man has been in the water of Hout Bay, which often pulses with seals, every day. He had never witnessed or heard of anything like what he experienced. It was so extraordinary he wondered if someone might have dumped cocaine into the water.

When he described the seal’s movements, his eyes shifted, and when his body was not mimicking the seal’s odd, jerky movements, it often shook, like he was still trying to shake off the experience of the seal relentlessly shaking him. He told me he still, months later, relived it in his sleep.

More testing, specifically of the seals’ hearts and brains, must be completed before scientists can be absolutely confident that domoic acid is the culprit in Cape fur seals’ plight

Sea Search’s preliminary testing of their collection of seal parts correlates with the seals’ behaviour to suggest domoic acid toxicity, colloquially known as shellfish poisoning, as the most likely cause. Many of the seals they necropsy are thin. Most of their stomachs are either empty or full of exoskeletons from various shellfish — according to Sea Search scientists, an apparent change from their habitual diet of fin fish, populations of which have dwindled under heavy human fishing. The seals don’t seem to mind eating shellfish. But, as bottom feeders and scavengers who directly consume algae, shellfish bioaccumulate neurotoxins like domoic acid in far higher proportion to their own mass than fin fish. This can have tragic, even fatal results for those who consume them, including humans, in whom deaths have been recorded as recently as a case in Alaska in 2020.

More testing, specifically of the seals’ hearts and brains, must be completed before scientists can be absolutely confident that domoic acid is the culprit in Cape fur seals’ plight. Several other possible explanations include an increase in human water use and human-seal interaction, reduced food supply, another illness like distemper, or more gear entanglements.

But the seals’ symptoms and diet are consistent with that of sea lions in California who were proven to be experiencing domoic acid poisoning, and where there was a similar shift in prey populations.

Domoic acid has been consistently present in the Cape fur seals that scientists have been able to test, including those who were behaving abnormally; and, according to Gridley, seasonal increases in domoic acid documented by plant scientists coincide with the timing of Cape fur seals’ various, troubling afflictions.

Domoic acid occurs in particular types of algal blooms which are becoming more prominent as ocean waters warm. We cannot cool the ocean. Nor can we return to it the fish the seals would prefer to be consuming, at least not without much stronger political and popular will than now exists — and possibly not even then.

Tess Gridley and Aaron next to a line of dead seals.
Tess Gridley and Aaron next to a line of dead seals.
Image: Sea Search Research and Conservation

WHAT CAN WE DO?

Two women were attacked in late September 2022, a few hours apart, by what is believed to be the same seal on Fish Hoek Beach. There is a video of one of these incidents. Debbie Hendrikz, who was on the beach after her early morning swim group, is kneeling on the sand when a seal runs towards her and begins to bite her. She tries to run away, she stumbles, the seal pursues her, bites her again and again.

Finally, she runs away and the seal, briefly, collapses. The video went viral and the social media response was fierce, as it has been with multiple incidences of seal aggression. Commenters decried Hendrikz’s proximity to the seal — a wild animal — suggesting it was her fault she was attacked; that she should have known better. Yet Hendrikz was several metres away, looking at a starfish. Most people who frequent Fish Hoek or other nearby beaches have been at least as close as she was to Cape fur seals. Many people, like Gridley, the other Sea Search researchers, and myself when I was with them, have safely moved in much closer proximity.

Hendrikz says she had seen that seal before; that it had swum peaceably near her and other swimmers. She calls what came over it “madness.” She write⁠s:

“Neither of us provoked the seal. There have been other incidents too. I stand corrected but apparently there have been more seal attacks in the last six months than in 20 years. Why? We need to ask this for the sake of safe beaches and for the sake of ecology in our oceans. What are we putting into it? Is it really a natural phenomenon? We need to ask ourselves these questions and be part of the solution.”

What is a “natural phenomenon”? During my time with Sea Search, I interviewed a number of people who had experienced or witnessed seal-human aggression. All had extensive experience around Cape fur seals, and echoed Gridley’s assertion that normally the seals do not mind when humans are around. While these people’s specific experiences differed, one thing all agreed on was that something about the aggressive seals was not normal. It was in their eyes, their bearing, their strange jerky movements. It was hard to pinpoint, but it was palpable.

Some amount of domoic acid in ocean ecosystems is natural, but it seems something about this situation is not. If domoic acid is causing the seals’ unusual behaviour, there must be more of it now, or they must be consuming more of it with their changing diet. It is possible both factors are at play. In any case, what is going on with the seals signals an ocean ecosystem in disarray. This is cause for alarm, not just for the seals and those humans whose lives bring them near seals, but for all of us who depend on the health of the ocean. That is, all of us.

Little mitigation is possible until a fully-fledged scientific investigation can be undertaken. For this, more funding is badly needed.

The carcass I helped necropsy a year ago was one of hundreds which have been collected over the past three years on beaches all along the Western Cape. People have been injured by aggressive seals in locations including Fisk Hoek, Kommetjie, Clifton, Strand and in the waters off Hout Bay’s Duiker Island. There have been several incidents in the past few weeks, and more than 50 recorded since 2021. Gridley notes that patterns have begun to emerge in Sea Search’s documentation of these incidents, confirming the apparent increase in seal aggression is not merely a matter of increased reporting.

Gregg Oelofse, City of Cape Town coastal manager, says that most of the time, when we give wildlife adequate space, incidences of aggression or biting will be “absolutely minimal and very rare”. He recommends that anyone going into the water must be highly aware of their surroundings: if there is a lot of activity — birds and seals feeding, lots of fish around — go elsewhere. If a seal is coming towards you, move away slowly and do not harass the animal further; do not fight back unless you have no other choice. Most seals you see on land, Gridley says, are resting and will ignore you; if you encounter a resting seal, no action is necessary besides giving the seal space and not approaching it for photos or any other reason.

The carcass I helped necropsy a year ago was one of hundreds which have been collected over the past three years on beaches all along the Western Cape

Oelofse emphasises: “We want to advocate very strongly that if you are unfortunate enough to be bitten by a seal, that you seek appropriate medical care and that you make sure that the person who treats you is aware that you’ve been bitten by a seal, and that there is risk of infection and that it’s taken very seriously and treated properly.”

There is no cut-and-dried rule about how to know when a particular seal is apt to behave aggressively. Those I spoke with who had experienced such behaviour noticed a few abnormalities: some aggressive seals had bloodshot eyes; all looked wild and “off” from their normal disposition, like they had lost their senses. Some people had the sense that the seals who attacked them were close to death. 

Still, this direct aggression is uncommon. Of the estimated 2-million seals, several dozen have been reported to behave in this way. The impetus here is not to fear the water: it is to remember that we share it with others, who depend on the ocean as much as or more than we do — for sustenance and shelter; for a home; for joy. If domoic acid poisoning is the cause of Cape fur seals’ aggression and unusual mortality, human activity is in part responsible for it, and while there is no easy solution nor is there any going back. What we can do in the present is attempt to gain scientific confidence about what is going on with the seals, as a first step in trying to find a way to help them.

If domoic acid is proven to be sickening Cape fur seals, there are steps we may take. Monitoring and treatment programmes have been effective elsewhere in the world; perhaps some seals can be saved before they come to the point of aggression and death. With time, we might discern more conclusive behavioural or physical clues about which seals are sick. Officials and NGOs are working together on documentation, observational assessments and response, including capture, when sick seals can be identified.

As members of the public, we can exercise more caution around all seals. We can be alert and prepared, we can make better decisions about how, how often and how closely we travel among them. We can be attentive to their dispositions. We can stay further from their territory, though so many of us have become accustomed to sharing it with them, and they with us.

Even if nothing can be done about these seal deaths, these seal illnesses; even if we will someday have no choice but to begin to think of seals not as benign coastal residents but as potential predators to be feared and avoided, it is possible their suffering — and ours — could help engender change. Perhaps the seals’ plight could help us understand that the resources of the ocean are limited, and at present, brutally stretched; that pelagic ecosystems and those who inhabit them are both precarious and precious. Perhaps the seals could drive us to act on this understanding. Perhaps these dying, violent seals could convince us, if we have not yet convinced ourselves, that among the many finite and life-sustaining resources the Earth and its non-human inhabitants provide, what remains of their beneficence is too often taken for granted — and it is a privilege we can ill afford to lose.

If you come upon a dead seal, Sea Search scientists are asking that you upload a photo to the free citizen science app iNaturalist. Each carcass collected for necropsy costs around R2000 - donate to help at https://seasearch.co.za/support. If you encounter an aggressive seal or one otherwise in need, you can contact the Cape of Good Hope SPCA’s wildlife department at 021 700 4158/9 or after hours 083 326 1604


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