Cape Fur seals (Arctocephalus pusillus pusillus) are
an iconic part of Cape Town’s marine life. Charismatic, curious and playful; people have always enjoyed watching them and learning about their behaviour.
So, at the end of September, when these charming animals started washing up dead more regularly onto beaches along the West Coast, it caught people’s attention, and they began asking questions. Now, over two months after the issue was acknowledged, these sad events are still happening, and definitive answers are still required.
I interviewed Jacques Nel, founder of the West Coast Seal Project, to gain more information on recent events and hear his opinion on what is happening.
There are a few facts that have been discovered so far. Cape Fur seals are dying at a faster rate than is typical for this time of year, and signs of malnutrition have been identified. However, the underlying cause of this malnutrition is still being debated, and people have differing opinions behind their deaths.
Local NGO’s, scientists and community members are working hard to understand as much as possible and do what they can to help the distressed seals, but money is a big issue.
One theory behind the current seal crisis is the ongoing, and worsening, impacts of climate change.
Climate change is having a dangerous effect on our oceans and marine life. Globally we are witnessing a changing distribution in species caused by increasing sea temperatures, acidification and salinity.
Cape Town is not exempt from these changes. As a city built around the ocean, its climate, fauna and fauna are defined by two ocean currents: the Benguela and the Agulhas. These currents have created a rich marine ecosystem and are essential to the sea life found beneath the waves.
Cape Fur seals are found in the Benguela marine ecosystem, a cold, nutrient-rich current that runs north along the West Coast of Africa. A Benguela El Niño effect has already been detected, meaning that the waters are getting warmer on average.
Cape Fur seals live in a dynamic and rapidly changing environment, but as with any animal, they have their limits for how quickly they can adapt to new long term conditions. At first the seals will not be directly affected by climate change, but their food sources may change.
Jacques spoke on the subject:
“Fish are very vulnerable to temperature and salinity changes. It will initially affect their breeding, potentially decreasing the number of offspring they produce.”
The mass death of seals along the West Coast could indicate underlying problems with the health of the marine ecosystem, so it is essential to document and investigate the causes.
A second theory thought to be a potential cause of seal deaths is over-fishing and competition from the fishing industry.
The waters around cape town have seen a decline in fish numbers over the last few years. Whether this is a result of over-fishing or rising sea temperature has not been established, although both are likely to be major contributory causes. Whatever the reason, the overall consequences are the same. Seals will struggle to find enough food, and their health will be impacted.
Cape Fur seal’s prey is commercially important, so there is competition between fishermen and the seals. It is a complicated socio-economic concern for Cape Town, and correct boundaries are still trying to be found. Fishermen’s quotas are also being thinned out to protect the valuable marine ecosystems, increasing the competition between the fishing industry and the seals. Fishermen struggle to catch enough to sustain their livelihoods, and seals are being left with scarce prey.
Jacques has worked with seals around Cape Town for many years and has good relationships with many of the local fishermen:
“We all know there is overfishing happening, but I disagree that there are no fish around for the seals to eat and that is the causing their deaths. Even if seals can’t eat their normal prey, they will find something different such as birds and crustaceans.”
“Reports from fishermen say that there are fish around. The Snoek run has had a successful year, and there are massive schools of anchovies, so there is food available for the seals. Fishermen are witnessing seals not wanting to eat. Seals would normally be attracted to the fishing boats and scavenge the scraps that are thrown overboard. However, recently, the seals have been drifting between the boats, but they are not interested. They are just skin and bones.””
There is no doubt that Cape Town struggles with overfishing, but the recent deaths don’t appear to be solely happening due to a lack of fish available.
“The mass death of seals along the West Coast could indicate underlying problems with the health of the marine ecosystem, so it is essential to document and investigate the causes.”
A third reason contributing to the seal die-off is the presence of Avian influenza in the region.
Avian influenza is a highly contagious virus that occurs naturally among wild birds. The Cape Cormorant, which is on the marine endangered list, has been the most affected.
Although tests have confirmed that the dead seals do not have avian influenza, it could still harm them indirectly.
Jacques had a lot to say on this point, and it was interesting to hear how he noticed the link between the birds and the seals:
“I picked up the seal die-off because of avian influenza. I noticed that there was suddenly an increase in seal deaths about two weeks after the initial spike in bird deaths. The bird deaths and seal deaths both continued to escalate, and they were following the same course and spreading south.”
Jacques doesn’t have the results to back him up yet, but he believes that there is a link between avian influenza and this year’s seal deaths:
“This is not tested, but if I have to look at what’s in front of me on the table, there are food possibilities for the seals and the pattern between avian influenza and the seal deaths is undeniable. My theory is that the seals are choosing not to eat, which is why they are malnourished. But what is the cause behind them not wanting to eat? It could be due to bacterial infection, toxicities in the water, poison, heavy metals- but normally, those things are very localised. I think that the seals are either eating sick alive birds, recently dead birds or decomposing birds. Seals are opportunists, so they will eat what they can find. The seals don’t necessarily need to have avian influenza to get sick due to avian influenza by eating an infected bird. This is the only explanation that makes sense to me at this point.”
One final stressor which could be exacerbating the current seal die-off is the time of year. Jacques explained:
“During the breeding season, there is much more action on the rocks, both between the seals and from the weather, which is why you normally get a die-off at this time of year. Colonies come together, so there are more seals concentrated in one area. High tides, rough seas and strong currents are all more common, and they play a role in newborn seal deaths by knocking them off the rocks. However, this current scenario is not just looking at pup deaths, so the time of year is probably not a major contributor.”
Breeding season and rough weather are risk factors that the seals face every year, so it is unlikely to be the main reason for deaths.
All of the above problems are possible reasons behind the Cape Fur seal deaths. However, what also needs to be considered is the danger of cumulative impacts. If the seals were facing just one of these issues in isolation, there is a greater chance that they would overcome it, but when combined with other stressors, they are left in a precarious position.
The answers may not yet be available, but I think it is clear that Cape Fur seals are being bombarded with many life-threatening problems. What we are witnessing should be a wake-up call to address the impacts we have on marine species.
We also must remember that these events are happening a year after 5000 Cape Fur seals were found dead in Namibia. Is it a sign that this is the new normal? Are we to expect the same again next year?