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Here’s a little something to soothe the nerves of Cape Town’s swimmers – during the 2017/18 summer season, Shark Spotters recorded an all-time low number of great white shark sightings, across the eight beaches on which they operate in Cape Town.

That drop in numbers is especially apparent around False Bay’s Seal Island, with the great whites arriving later than usual this year, with reduced activity.

As an aside – those of who you think that you’ve seen increased media coverage of shark attacks worldwide aren’t wrong, either, but there are a few factors you might want to consider before you get worked up.

Nervous Cape Town beachgoers are probably breathing a sigh of relief right now, and they should, but there has been a rather unexpected result with regards other shark activity in the area.

The Save Our Seas Foundation have more on that front:

Intriguingly, the reduced presence of white sharks at Seal Island seems to have opened up a niche that has quickly been seized by sevengill cowsharks, and for the first time in False Bay history, cage diving charters are advertising “Cowshark cage dives!” at Seal Island. When one looks at the big picture, it most certainly begs the question: what is going on in False Bay?

‘Cowshark cage dives’ doesn’t quite have the same ring as ‘great white cage dives’, but I guess you have to keep business ticking over.

So, what exactly is happening with regards the aquatic ecosystem of False Bay?

…let us begin with the status quo of the shark hierarchy within the bay over the past decade. As top dogs, white sharks were never particularly worried about competition or predation from other shark species, so their movements in the bay were largely driven by prey availability. To paint the picture more clearly, we can label white sharks as the “lions” of the False Bay ecosystem, perched at the top of the food chain, following the juiciest prey without worry of competition.

During winter, when young of the year, freshly weaned and oh-so-ignorant seal pups leave the safety of Seal Island and hop into the sea for the first time, white sharks are known to aggregate in the waters around the island to take advantage of these easy pickings.

As the seals get older and wiser in the summer months, white sharks move inshore to take advantage of easier prey – seasonal shoals of fish such as yellowtail. This resulted in the year round presence of white sharks in False Bay, but different movement patterns between seasons.

The slightly smaller shark species, like the sevengill cowsharks [below] and bronze whalers, are referred to as the “leopards” of the ecosystem. They are middle-order predators, and whilst the sevengills eat the same prey as the great whites, they have developed tactics to minimise conflict with the dominant predator.

As for the bronze whalers, they tend to give great whites a very wide berth.

Now, with the decreased presence of the great whites, things are changing:

…never before has there been such a long period of consistently low activity at both Seal Island and along the inshore. The burning question on everyone’s mind is of course: “Where are the white sharks???” Unfortunately, the answer to this question is still under debate, with fingers being pointed at a range of potential culprits – from fishermen, to orcas, to changing environmental conditions…

But what is truly fascinating about this lull in white shark activity is what is unfolding in False Bay now that the “lions” have left the proverbial pride-lands. The decline in authoritative white shark presence has presented new opportunities for our “leopard” species, which have been quick to fill the gaps left by white sharks within the bay.

Hence, we have seen a sudden increase in the number of bronzies [below] along the inshore during summer, while the cowsharks appear to have taken up residence at Seal Island, making the most of the lack of competition from white sharks…

Furthermore, the well-known safe haven for sevengills, and popular dive site at Miller’s Point on the western border of False Bay, has been largely abandoned for the past year, perhaps due to the fact that the sevengills are now making hay while the sun shines at Seal Island.

When the cat is away, the mice will play – except in this instance, the mice are rather large sharks.

Ecologists are now trying to figure out if this will become the new norm, although they don’t have enough info to fill in all the blanks just yet:

The observed decrease in white shark presence in False Bay does not appear to be mirrored all along the South African coast, with certain areas on the south and east coast actually experiencing increased white shark activity lately.

This is promising as it points to a regional distribution shift, rather than a country-wide population decline, which would have far worse repercussions for our coastal ecosystems. However, what has caused this shift remains unclear, and until further research can be conducted to pinpoint the cause, we are unable to predict if and when white sharks will return en masse to False Bay.

In order to further understand these shifting dynamics, further tagging is now taking place, and Shark Spotters hopes to add bronze whalers to the list of those they tag:

It is hoped that through ongoing research, environmental monitoring and collaboration with other researchers, we can gain a better understanding of what is driving these current changes, and what the future holds for the sharks of False Bay.

I’m going to assume that this has made you feel better about braving the frosty Cape waters this summer.

You’re welcome.

[source:sosf]