Baboons on the beach

Baboon on the beach Baboon on the beach

A recent low tide visit to the beach at Platboom near Cape Point, on the Atlantic coast of the peninsula, enabled us to watch a troop of Chacma baboons (Papio ursinus)  foraging for limpets, mussels and other marine snacks on the rocks at low tide. The baboons bite the tops off the limpets with their formidable incisors, or pry them from the rocks intact to get at the protein-rich flesh. They also eat mussels.

Baboons foraging for seafood at Platboom Baboons foraging for seafood at Platboom

This foraging behaviour is extremely rare among primates. In baboons, it is only observed on the Cape Peninsula and in one other species in Somalia. Matthew Lewis studied this troop of baboons as they foraged around the Cape Point nature reserve, and his thesis makes for fascinating reading. (Wild Card Magazine also featured Matthew’s research.)

Baboon on the beach Baboon on the beach

The amount of time the baboons are able to spend foraging on the shore is largely determined by the height of the tide, and by weather conditions. As a result, the amount of time the baboons spend seeking marine food sources is small compared with the time they spend looking for roots, bulbs, insects, berries, and small animals.

Low tide at Platboom Low tide at Platboom

These baboons are part of the Kanonkop troop which ranges freely in the Cape of Good Hope section of Table Mountain National Park and whose home range does not bring them into conflict with humans (or, as a rule, allow them access to any anthropogenic food sources). They were completely uninterested in us and our vehicle, unlike the baboons we see further up the peninsula around Millers Point, for example.

Concentrating baboon Concentrating baboon

Goose barnacles on the beach

A (lovely, rain-bringing) onshore wind left great rafts of kelp all over Noordhoek beach one weekend in mid May. Finding anything of substance on this beach is unusual; it’s on an exposed piece of coastline and all but the most robust objects are dashed to pieces before they arrive on the sand. Seeing all the washed up kelp also reminded me that frequenting the beaches inside False Bay, that are daily cleaned of washed up kelp by the City of Cape Town, is liable to give one a skewed idea of just how much kelp naturally washes up on the sand.

Kelp stipe covered in goose barnacles
Kelp stipe covered in goose barnacles

This time, there was kelp, and lots of it. Several of the pieces of kelp had been colonised by goose barnacles. There are several species of goose barnacle that occur off South Africa’s coast, but these ones are Lepas testudinata. They are incredibly strange looking animals, and some of them were still alive and writhing slowly in the drying sun.

In parts of the world (I’m looking at you, Iberian peninsula), goose barnacles are an expensive delicacy. I have nothing to say about that.

Goose barnacles, with my paw for scale
Goose barnacles, with my paw for scale

Lepas testudinata larvae most often attach to free-floating pieces of kelp (Ecklonia maxima) and plastic debris, which is why you have probably never seen these mesmerisingly gross-looking creatures while on a dive. In the picture below, you can see that they’re attached to the bottom of a kelp holdfast, where it would ordinarily attach to the rock. This shows that they attached after the kelp broke off.

A kelp holdfast encrusted with goose barnacles
A kelp holdfast encrusted with goose barnacles

Each barnacle is possessed of a long fleshy peduncle, or stalk, which attaches to the kelp holdfast, stipe or fronds. On the end of the peduncle is a carapace (shell) made up of five separate pieces. The large part of the barnacle on the end of the peduncle (what you’d think of as its body), covered by the carapace, is called the capitulum. The apparatus that the barnacle uses for feeding – essentially six pairs of hairy legs – reside inside the carapace, along with the mouth. There’s some more detail and a nice diagram at this link. If you are familiar with other kinds of barnacles – the volcano-shaped ones that live on rocks, ships, whales and piers for example, then most of this (except the peduncle) should sound familiar to you.

Lepas testudinata goose barnacles
Lepas testudinata goose barnacles

Research done around South Africa’s coast (published here) by Otto Whitehead, Aiden Biccard and Charles Griffiths, identified the marked preference of Lepas testudinata for attaching to kelp. The researchers surveyed a selection of beaches around South Africa’s coast, from the west coast of the Cape Peninsula up to northern KwaZulu Natal, between June and October 2009. When they found goose barnacles washed up, they recorded the species of barnacle, the type of material they were attached to, the dimensions of the object, and its location. They also estimated the number of barnacles in each colony they found.

Lepas testudinata was the species they found most commonly, of the six species in total that they identified along the area of coast that was surveyed. (There’s a nice picture of the six species in their paper, which I used to identify the ones I found.)  This species of goose barnacle was found to prefer kelp, as mentioned, and also tended to colonise large objects compared to the other species (this could, of course, be because pieces of kelp are usually larger than items such as bits of plastic, glass, feathers, and shells that some other species prefer).

Kelp fronds with goose barnacles
Kelp fronds with goose barnacles

Lepas testudinata was the only species of goose barnacle that the researchers regularly found to form colonies comprising more than 1,000 individuals. It is also the only species of goose barnacle recorded by the survey that is only found in temperate (cooler) waters, which happens to be where kelp is found, too.

The researchers note that the goose barnacles of the Lepas testudinata species that they found on kelp seemed to have exceptionally long peduncles, some more than 25 centimetres long, and that this seems to differ from what has been previously known about them (which is that they have “short, spiny” peduncles). They suggest that perhaps the variety of Lepas testudinata that colonises kelp may even be a separate species from the one previously described (more research obviously required to ascertain this). You can see from my photographs that the peduncles of the washed up Noordhoek beach goose barnacle colonies are also quite long, some easily 20 centimetres in length.

Clusters of goose barnacles on a kelp stipe
Clusters of goose barnacles on a kelp stipe

They also found that the increasing prevalence of long-lasting and buoyant plastic marine debris and other anthropogenic objects around our coastline, which some species of goose barnacles preferentially attach to, gives these weird little creatures increased opportunities to form colonies, and to spread to new places. This is one of those interesting phenomena to keep in mind, as humans inexorably alter the environment. Some creatures will benefit in strange ways from warming oceans, and others will find new homes in the garbage we leave lying around.

What causes the brown water at Muizenberg beach?

Capetonians are familiar with the tea-coloured water that runs in our mountain streams. Most people know that the brown colour comes from tannins, leached naturally from the indigenous fynbos vegetation. Perhaps less well known is the reason for the brown water that is sometimes seen in the surf zone along Muizenberg beach, stretching all the way to Strandfontein, Monwabisi and beyond.

Tea-coloured water at Muizenberg
Tea-coloured water at Muizenberg

The most frequent explanations that are offered on social media are, of course, pollution, “raw sewage”, and the like. This is not the reason for the brown water, and it does not necessarily impact the water’s safety or healthfulness for humans to swim in.

Like False Bay’s famous colour fronts, the reason for the brown waves at Muizenberg beach turns out to have much to do with the topography of False Bay, particularly of the kilometres-long beach at its head (Muizenberg-Strandfontein-Macassar-Monwabisi), and something called a diatom.

View of Muizenberg showing patches of brown water
View of Muizenberg showing patches of brown water

Diatoms

Diatoms are a type of phytoplankton (plant plankton or microalgae). They are single celled, usually symmetrically shaped organisms that multiply by dividing in half at a constant rate. Their cell walls are made of silica, SiO2. Chicken keepers and gardeners may be familiar with diatomaceous earth – this is made up of the fossilised shells of ancient diatoms.

Diatoms are what are called primary producers or autotrophs, meaning that they generate organic material from carbon dioxide and other inorganic nutrients (for example nitrates and phosphates), through the process of photosynthesis, which uses light as an energy source. Primary producers sit at the base of the food chain and all life relies on them, directly or indirectly. Everything else produces organic material from other organic material (such as diatoms).

I am telling you all about diatoms because the brown water at Muizenberg contains an accumulation of a diatom that you can call Anaulus australis Drebes et Schultz the first time you mention it, but usually just Anaulus australis, or Anaulus for short. There are several members of the genus Anaulus, but usually just one tends to be dominant at each beach where these accumulations occur, and Anaulus australis is the main species found along the South African coast.

Analaus are pillow-shaped diatoms. If you wanted to see what an individual Anaulus diatom looked like, you’d use a microscope, but when enough of them are in one place, they can be seen to change the colour of the water. There’s a picture of them under a microscope at the bottom of this webpage (they also occur in Brazil). They occur at beaches with particular topograhical characteristics, which explains why you haven’t seen them at Camps Bay, Kogel Bay, or Scarborough.

At hospitable beaches, the diatoms are always there, spending much of the time lying dormant in the sand behind the surf zone. A proportion of the diatom population is able to survive for relatively long periods (estimated to be more than two months) like this, in the dark on the seabed, not photosynthesising or dividing, until the correct meteorological conditions arise for an accumulation. But first – what sorts of beaches are hospitable to Anaulus?

Brown water in the surf zone at Muizenberg
Brown water in the surf zone at Muizenberg

Topographical conditions

There are five physical features of coasts that are prone to diatom accumulations. They are:

  1. a high-energy sandy – not rocky – shore
  2. a long beach, more than 4 kilometres in extent
  3. the presence of rip currents
  4. a surf zone at least 150 metres wide
  5. a nutrient source close to the surf zone (often an unconfined aquifer overlaid by a dune field)

Muizenberg and Strandfontein beach tick all these boxes. The beach stretches from Surfers Corner all the way across the top of False Bay to Monwabisi, a distance of over 20 kilometres. It is a high energy beach, meaning that it is exposed to large waves and strong winds, and is not protected by any offshore features such as sandbars or headlands that might reduce the force of the waves. Rip currents do occur at the beach, and both these and the exceptionally wide surf zone – wider during south easterly winds in summer – can be observed from the mountainside on Boyes Drive. (A rip current is like a hidden river flowing out to sea from the beach. The Sydney Morning Herald has an excellent visual explainer of rip currents here.)

The head of False Bay where Muizenberg is situated is incredibly nutrient-rich, much of it thanks to urbanisation. The canalised Zandvlei estuary – the only vaguely functional one on False Bay’s coast – is situated a short distance down the beach, and supplies nitrates, phosphates and other nutrients to the surf zone. Many of these nutrients are technically pollutants, added to the river further upstream. The Cape Flats Waste Water Treatment plant at Strandfontein also discharges 200 million litres of treated water per day (under normal, non-drought circumstances) via a canal onto Strandfontein beach. This is essentially an artificial estuary for Zeekoevlei. This waste water has spent some time working its way through the settlement ponds at Strandfontein, but is nevertheless rich in ammonia and other nutrients, and Anaulus accumulations are a very common sight in the surf around this discharge point. The dunes that run along Baden Powell drive overlay a high water table, and groundwater seepage – specially during times of heavy rainfall – may also leach nutrients out of the ground and into the surf zone.

Meteorological conditions

The meteorological conditions required for an Anaulus accumulation involve strong wind and a large swell. These act together to create rough sea conditions, which stir up the dormant diatoms from the ocean floor. The diatoms adhere to air bubbles in the surf zone, staying suspended in the water column, which is when you would notice the water turning brown. Exposed to light, they awaken from their dormant state and start to photosynthesise, take up nutrients, divide and multiply. The presence of rip currents creates an onshore-offshore flow all along the beach. This forms a semi-closed ecosystem, and the diatoms are essentially trapped in gyres in the waves. Longshore currents that run parallel to the beach transport Anaulus cells out of the surf zone at one end, and bring fresh (sea)water in at the other end of the beach.

It may seem surprising that anything manages to accumulate in the waves of a beach, but the surf zone is actually quite retentive, meaning that things that end up there often tend to stay there. (Incidentally, this is why it’s a terrible idea to discharge the byproduct of reverse osmosis seawater desalination –  a super-salty brine – into the surf zone. It must be discharged offshore so that it can disperse and mix with the surrounding water.)

Diatoms in the surf zone at Muizenberg
Diatoms in the surf zone at Muizenberg

You’ll notice that, contrary to what you may have seen when large amounts of plankton are under discussion, I’ve been using the word “accumulation” instead of “bloom” to talk about Anaulus. This is deliberate, because of the constant presence and constant rate of division of the diatoms. When the water goes brown, it doesn’t mean that Anaulus is suddenly multiplying faster than usual. It means that it’s all been gathered together in patches, is exposed to light and therefore photosynthesising (at its usual steady rate), and is thus more visible than it was when it was lying on the ocean floor.

Anaulus at Muizenberg in November 2017
Anaulus at Muizenberg in November 2017

The human factor

You may also be thinking that everything I’ve said about the nutrients that Anaulus requires to survive and thrive points to the fact that humans – and pollution – are ultimately responsible for these brown-water plankton accumulations at Muizenberg. Well yes, in a way. But accumulations of Anaulus australis and related species have been observed and documented for well over 100 years at suitable beaches around the world, and are a natural phenomenon.

Yes, we are providing more nutrients to the False Bay diatom population than they would otherwise have received without human settlement in the greater Cape Town area, but these accumulations would likely occur regardless. They are certainly more intense now than they would have been in the past, but estuaries are nutrient-rich locations even when not surrounded by a large city. Furthermore, the water table is high on the Cape Flats, which would supply nutrients to the surf zone regardless of whether humans lived nearby.

Anaulus is in fact performing a vital and useful function by mopping up the excess nutrients that the city discharges in the ocean. The mass of diatoms – primary producers – also provides a food source to bivalves such as mussels, and other invertebrates. We can be grateful that the excess nutrients that urbanisation directs towards the ocean at the head of False Bay leads only to accumulations of harmless diatoms, rather than to frequent occurrences of harmful algal blooms that can kill marine life and exacerbate respiratory problems in humans.

Muizenberg during a diatom aggregation
Muizenberg during a diatom aggregation

Sources

Most of the original scientific study on surf zone diatoms in South Africa was done by a group of researchers (primarily M Talbot, Eileen Campbell and Guy Bate) from the University of Port Elizabeth, working at the Sundays River Beach in the Eastern Cape. I did quite a bit of reading to research this post, but you can start with this paper for a description of the topographical characteristics of beaches where surf zone diatoms accumulate. The first few chapters of this Masters thesis also provide a good overall survey of what is known about surf zone diatoms.

Putting knowledge into practice

Not every instance of brown, foamy water at the beach will be an Anaulus accumulation. On the west coast of South Africa, for example, there are no beaches where Anaulus occurs, but you may see brownish foam that is the result of heavy wave action frothing up organic matter in the surf (nothing sinister – there is a lot of organic material in the ocean). A clue to help you distinguish diatom accumulations from other brown-water phenomena – apart from running through the checklist of required beach characteristics above – is that an Anaulus accumulation doesn’t stretch much beyond the back of the surf zone. If the brown water stretches beyond the furthest row of waves, it’s probably something else. (And this seems like an apposite time to remind you that sewage looks whitish-grey, not brown, when it’s pumped out into the ocean.)

The number of beaches worldwide where surf zone diatom accumulations occur is so small – less than 100 – that Odebrecht et al could enumerate them in a 2013 paper. I hope this helps to convince you that the brown water at Muizenberg beach (and beyond) is something special and interesting, not to be feared. Go surfing!

Colour fronts in False Bay

Colour front seen from Sunny Cove on 27 November 2015
Colour front seen from Sunny Cove on 27 November 2015

Perhaps you have wondered what causes the patterns of strange coloured water in False Bay during the summer months. Perhaps you have dived in it, and wondered why sometimes you can’t see your hand in front of your face! Wonder no more – I am here to help.

Colour fronts

Frequent visitors to and residents of the shores of False Bay will observe that at certain times of the year, the ocean is marked by bands and arcs of sharply contrasting coloured water. This phenomenon is known as a colour front. In oceanography, a front is the interface or boundary between two separate masses of water. In this case, the water masses are easy to discern, because they are of different colours. There are usually other characteristics of the water on each side of the front that differ, too. Fronts are either convergent (the water masses are moving towards each other) or divergent. The presence of marine debris (like pieces of kelp) at the front boundary suggests that it is convergent.

Causes of colour fronts in False Bay

Prior to 2005, there was much conjecture about the causes of these fronts (including the usual pollution bugbear), but little evidence to support any of the theories. By sampling, the fronts were found not to be caused by pollution, or by plankton blooms in the surf zone. It was known that a colour front was most likely to occur in False Bay after a period of southerly or south easterly wind lasting a few days. October and November seem to be prime months for the phenomenon.

When a large, obvious colour front arose near Simon’s Town in November 2005 with milky green water on one side, and darker blue-green water on the other, researchers from UCT and IMT sprang into action, sampling the water on each side of the boundary so that they could measure its characteristics. Speed is of the essence in these situations; colour fronts can disappear quickly. The one in the picture below is busy decaying – notice the smudged boundary.

Colour front in north western False Bay on 13 November 2014
Colour front in north western False Bay on 13 November 2014

Measurements revealed that the milky green water overlaid the clearer, bluer water, down to a depth of 11-12 metres (this will vary from front to front). The milky water did not extend to the ocean floor.  Scuba divers around the Cape Peninsula will be familiar with the experience of diving through two or more layers of water, with varying turbidity (clarity) and temperature! (Here is picture of Tony and Christo diving near Oudekraal in the Atlantic that shows what the boundary between two layers of water can look like.)

The researchers found that the milky coloured greenish water was full of fine, almost neutrally buoyant particles of calcium-rich sediment. The green-blue water contained much less calcium, but relatively more silicon, which would suggest the presence of diatoms (a kind of phytoplankton – you can think of them as teeny tiny plant-like organisms) or sand in the water. The origins of the calcium-enriched sediment in the milky water are interesting: one source is from the shallows (less than 30 metres deep) of north western corner of False Bay, where the ocean floor is made up of rocks that are rich in calcium carbonate (such calcrete and limestone), some areas covered by a thin layer of sand.

Milky-white water near Swartklip on 29 November 2014
Milky-white water near Swartklip on 29 November 2014

The second probable origin for the particles of calcium-rich material is the interface between the sea and the land at the northern end of False Bay. The cliffs at Wolfgat/Swartklip at the head of the bay are made of calcrete, and at Swartklip the beach narrows to the extent that the cliffs erode directly into the water when the sea is high. Strong southerly winds create a wide (of the order of one kilometre) surf zone at Muizenberg and Strandfontein; a spring tide also adds to ideal conditions for the generation of a colour front.

The temperature of the milky water was found to be slightly (0.4 degrees Celcius) higher than the green-blue water. This measurement will also vary from front to front. The researchers speculate that the temperature difference could be because the milky water originated in the surf zone, which is shallower and therefore warmer, or because the high concentration of suspended particles in the milky water caused greater absorption of heat from the sun.

Colour front at Smitswinkel Bay on 24 October 2014
Colour front at Smitswinkel Bay on 24 October 2014

Summary

Here’s the tl;dr: strong southerly and/or south easterly winds, perhaps coupled with spring tide conditions, set up a very wide surf zone along the northern end of False Bay, which disturbs the sediment on the ocean bottom and drives the waves further up the beach than usual. Particles of buoyant calcium carbonate from the sea floor and eroded from the cliffs at Swartklip are lifted up into the water column, changing its colour to a milky-green shade. Wind-driven circulation patterns in the bay push the front from its original location in a southerly direction, towards Simon’s Town.

What to do?

Contrary to what your friends on social media may claim, not all colour changes in the ocean around Cape Town can be attributed to a giant sewerage plume. Hardly any of them can, in fact. In summer, the reason for the ocean looking green, red or even brown is likely to do with a plankton bloom of some description, or related to suspended sediments (as in this case) or other naturally arising material in the water. Instead of using this as an opportunity to become hysterical on the internet, how about celebrating the incredibly dynamic system that we can observe, living near the ocean? Drive up a mountain next to the ocean and take in the spectacle from on high. Dip your face in the water and see what it does to the viz. Take some pictures for posterity. And – if you don’t know what’s causing it – try to find and question someone who does know, like a scientist, or consult a good non-fiction book, to find out some facts.

If you’d like to read more about colour fronts in False Bay, take a look at this scientific paper (pdf), which I used as source material for most of this post. The paper is called A Prominent Colour Front in False Bay: Cross-frontal structure, composition and origin

Southern African Shark & Ray Symposium 2015 – first day

The view from the top of Red Hill, over SImon's Town
The view from the top of Red Hill, over Simon’s Town

Earlier this week I had the great privilege of attending the 3rd Southern African Shark and Ray Symposium, which was held from 7-9 September at the Blue Horizon Estate above Simon’s Town. I am not a shark scientist (these days I am probably best described as a lapsed mathematician) but have an interest in the subject so I went to listen. If I had to provide some bite-sized takeaways from the first day of the symposium, jotted down without applying any of the science communication principles I learned at the workshop yesterday, it would be these:

  • Shark mitigation – avoiding negative interactions between humans and sharks – is HARD and a lot of smart people are working on the problem.
  • The City of Cape Town is a world leader in shark mitigation efforts, along with Shark Spotters. They really think about the problem, and care about both people and sharks.
  • If you are not blessed with high coastal terrain and surface-swimming sharks (which would permit a shark spotting program like Cape Town’s one), other shark mitigation measures are in the pipeline… From orca-patterned surfboards (and wetsuits?) to shark exclusion nets to large-scale electrical repellent cables.
  • The KZN Sharks Board catches a lot of sharks, rays and other animals in their gill nets and drum lines, and this is upsetting and far from ideal. But they facilitate an incredible amount of scientific study, too – their catches do not go to waste.
  • The KZN Sharks Board is committed to finding measures other than gill nets and drum lines to keep bathers safe, and they are actively working on the problem (refer to the electrical shark repellent cable I mentioned above).
  • Sometimes scientific research doesn’t look the way you expect or imagine. Ruth Leeney of Protect Africa’s Sawfishes spent months on the ground interviewing Mozambican villagers in the far north of the country to assess the population status of sawfish in Mozambique. She collected data that no one else could have obtained by other means!
  • Smaller, less charismatic sharks, like catsharks, need more love. There are also whole families of sharks that divers don’t see (such as dogfish) and hence aren’t really aware of. They are caught prolifically as by-catch and not much is known about them. But some smart people are working on this!
  • There are motivated, talented scientists working hard in South African government departments to protect our marine resources and making recommendations to manage them sustainably. (There’s also many a slip ‘twixt cup and lip, but they are trying very hard.)
  • Technology – be it cameras, software, or tags – is enabling great leaps in our understanding of what’s out there, which will enable us to protect and conserve things better.
  • Ocean acidification as a result of climate change could affect sharks directly, by actually wearing away their denticles (tooth-like structures on their skin). Denticles protect sharks and help them to swim faster.

I was tweeting from the symposium twitter account, and along with some of the other attendees we produced a fairly comprehensive summary of each talk, along with some visual media. Here’s a link to the day one compendium as a pdf (quite large).

Lecture: Adam Barnett on broadnose sevengill cowsharks

I’ve been appallingly tardy in writing about this talk, but recent events in False Bay have reminded me that my notes have been sitting waiting for me to attend to them for several (ahem) months. My diary indicates that the series of talks that it was part of was held in November 2012. Dr Barnett has in fact left South Africa and returned during the time it’s taken me to get to this task. Sorry.

Broadnose sevengill cowshark at Shark Alley
Broadnose sevengill cowshark at Shark Alley

Dr Adam Barnett, a visiting researcher from Deakin University (Australia) and the University of Tasmania, spoke at the Save Our Seas Shark Centre in Kalk Bay, on the same evening that we listened to Alison Kock and Kay Welz speak about white sharks in False Bay. He has been conducting research on broadnose sevengill cowsharks (viewable in frequently clean, shallow water at our local dive site Shark Alley), in Tasmania.

Broadnose sevengill cowsharks (Notorynchus cepedianus) are part of the order Hexanchiformes, which comprises six species. This is  a primitive order of modern sharks with six or seven paired gill openings (most sharks have five). Four species are cowsharks, and the others are deep water sharks.

Surprisingly little is known about sevengill cowsharks, but Dr Barnett contends that they should be an extremely important apex predator. They are found worldwide, but not (so far) in the north Atlantic. There are far more of them than there are white sharks, and they eat the same sort of things: fish, rays, seals, and other sharks. Their role in coastal ecosystems is very important.

They are found in coastal waters of countries including (but not limited to) Australia, South Africa, Argentina, and California. There are known nursery areas at the latter two locations. Only one pregnant female has been dissected. She was carrying 82 pups (for context, white sharks bear 2-10 young, hammerheads about 50, whale sharks up to 300, and most other shark species 2-40). Their reproductive cycle is thought to be about two years in length. It is not known at what age these sharks reach sexual maturity.

Video still of the hooked cowshark
Video still of the hooked cowshark

Sevengill cowsharks are on the IUCN Red List as data deficient (not enough is known about their conservation status). The IUCN Red List website page about the sevengill is informative. They are a target species for recreational fisheries (we often see specimens with hooks stuck in their mouths when we dive at Shark Alley), and a low value bycatch species for commercial fisheries in South Africa. There are several semi-commercial fisheries elsewhere that target them. There is some evidence that the fisheries in California and Namibia are not sustainable.

Tasmania study


View Larger Map
For some time, Dr Barnett has been studying the sevengill cowshark population found in the south eastern corner of Tasmania, in the system of bays that makes up the Derwent River estuary. The water here is turbid and there is a wedge of salt water that moves up and down the river with the tide. The river is at most 40 metres deep, and Norfolk Bay is about 20 metres deep. The winter water temperature in the area is 8-13 degrees, and in summer the maximum water temperature is 21-22 degrees. Much like False Bay (except for the river)!

The estuary is a shark refuge area and also includes populations of soupfin and smoothhound sharks, which pup there. The aim of the study has been to determing the population structure, abundance, diet, habitat use, and predator-prey relationships of the cowsharks.

Barnett fished for sharks using long lines with 50 hooks per line, deploying four lines per night. He tagged and released 457 sharks in total, took biological samples and measurements, determined their sex, and flushed their stomachs to see what they’d been eating. Sixteen percent of the females had mating scars (bite marks). He found more sharks each year in summer, and fewer in winter. Do they leave? Or do they not get caught in winter? Of the 457 sharks tagged, 68 (15%) were recaptured, in the same bay as where they were first caught.

Cowsharks are about 50 centimetres at birth, and after a year they are 70-80 centimetres long. The Derwent estuary is not a pupping or nursery ground, based on the measurement distribution that Barnett observed. He caught 60-100% female sharks (depending on what time of year he fished), averaging about 60% females. In winter he found no males, with a few showing up by spring.

Barnett also set an array of 74 VR2 acoustic receivers 800 metres apart, during the period December 2007 to June 2009. He set them along the boundary of the protected area and at entrances to bays and inlets. For the movement study he tagged 43 animals (31 female) with acoustic tags that communicate with the receivers. The process to implant the tag is a three minute surgery. He found that no Norfolk Bay shark moved to the upper Derwent estuary, and no estuary shark moved to Norfolk Bay. This suggests strong site fidelity. There is some overlap between the populations in late autumn, and by winter most of the sharks (including all the males) left the area. After winter the animals returned to where they were tagged.

Pop up archival tags attached to five males and five females located the makes 1000 kilometres north in Jervis Bay, south of Sydney, and the females closer – slightly offshore, with one visiting a depth of 300 metres. The sharks are more active and in shallower water at night, spreading out more. During the day they spend a lot of time close to the seabed, moving up and down in the water column at night.

Barnett tagged several of the sevengill sharks’ prey species, and determined that the sevengills were only in the bay when their prey items could be found there. The fact that the sharks are not breeding in the area suggests that their habitat use is indeed diet related.

False Bay study (ongoing)

Excitingly, broadnose sevengill cowsharks are the subject of a current study in False Bay involving Dr Barnett and local scientists, making use of the array of acoustic receivers that was originally set to study white shark residency patterns. There are also compatible receivers in Algoa Bay, Mossel Bay, Gansbaai, Port Alfred, Port St Johns and on Aliwal Shoal. At least nine sharks have already been fitted with acoustic tags at Miller’s Point, and a hook was incidentally removed from one shark’s mouth.

Miller’s Point is a unique aggregation site: the researchers aim to determine why. Female sharks that look very pregnant are often observed by divers there. The researchers will use the data from the acoustic receivers to try to determine the sharks’ habitat use in False Bay, their seasonal movements, the population structure and the effects of fishing. This will assisst in managing the species. They will also study their interaction with white sharks (with whom they compete for food), and the cowsharks’ predator-prey interactions with other species. This is important for ecosystem management.

Sevengill sharks have been seen and caught at Robben Island in Table Bay, in Betty’s Bay, and in Gordon’s Bay (at night). It is possible to dive with the Betty’s Bay sharks, if you know where they are! It isn’t known whether there are any at Seal Island, perhaps closely sharing that habitat with the white sharks.

Dr Barnett’s results from his work in Tasmania are fascinating because they shed light on broadnose sevengill cowsharks as a species as well as their specific behaviour in the Derwent estuary. So little is known about our local population that the temptation to try to generalise some ideas from his Tasmanian research is irresistible. I hope that the tagging study currently taking place will increase our understanding of these local celebrity sharks, and that it will assist in managing the species and the places they live so as to ensure that the population continues to thrive. Yay science!

Lecture: Ryan Johnson on whether science can save sharks

Tony and I attended a talk by television presenter and shark scientist Ryan Johnson at the Save Our Seas Shark Centre in Kalk Bay one evening in mid-July, as part of their series of marine-related talks. We were very interested to hear this talk because Johnson worked on the recent Ocearch project in South Africa, which tagged 42 great white sharks in South African waters earlier this year and caused intense controversy for a variety of reasons. The sharks were removed from the water for up to 15 minutes, and biological samples (blood, parasites, muscle biopsies) were taken for 12 reasearch projects as well as fitting a satellite tag to the shark’s fin.

The topic Johnson chose to speak about was “can shark science save sharks?” By his account, the three month long Ocearch expedition, and the criticisms levelled at the project, caused him to question some very fundamental aspects of what he was doing as a scientist. If scientists cannot help sharks, then of what use is their work? Johnson listed some of the criticisms that were levelled at the Ocearch project, and responded to them one by one.

  • Why must Americans come and do this work? Why can’t South Africans do it themselves? There were 30 South African and 12 international scientists on the project, showing that we do certainly have the scientific capacity to do research on this scale. Funding, however, was never going to be found from local sources.
  • The scientists weren’t using the best methods. Alternative tagging methods for large marine creatures include the pop-up archival tags (PAT) tags used by the Breede River bull shark project, and acoustic tags, which have been used in False Bay and involve placing transponders on the ocean floor which record a signal when a tagged shark swims past. PAT tags have a life of only three months in Southern African waters because of the rate of algae growth, so no multi-year data would be obtained. They also are only accurate to within 300 kilometres, so no fine scale data would be available either. Acoustic tags require a network of transponders to be placed at locations past which the shark is likely to swim (and at this stage we don’t know what those locations are, for white sharks), and provide no detailed directional information unless the transponders are very close together. Satellite tags (SPOT tags) are by far the best option as they have a life of about five years, and work all over the world.
  • White sharks are already protected in South Africa, so what’s the point of doing research on them? This is true, but as Johnson later pointed out, they are not protected in any neighbouring countries other than Namibia, and certainly not on the high seas.
  • It was all done for television sensationalism. I can’t actually remember what Johnson said about this one (I wrote nothing down, so he may have pooh-poohed it briefly and moved on), but I can say that while the visuals of a white shark being wrestled by a fisherman and hoisted onto a platform may be arresting, there was no other way to get the biological samples and apply the satellite tags on an animal this size. Johnson acknowledged that this aspect of the research was not pretty, but that the alternative – no more sharks – is far worse. In response to a question he also acknowledged that deformity of the tagged sharks’ dorsal fins will take place, but that improvements in the positioning of the tags (higher up) and the anti fouling substance used to prevent algae growth will hopefully reduce the deformities from the levels observed during similar research in 2003-2004. The tags will fall off after about five years.Again, it is a trade off between being able to better protect sharks with the knowledge gained from harming a minority of them, or simply not being able to protect any sharks at all. I haven’t seen the show yet, so I’m not sure how much “ocean posturing” went on (it was probably too cold to get the speedos and bikinis out), but there’s no escaping the fact that a lot of science was taking place at the same time. Perhaps we must overlook the human frailty that causes some of us to seek the limelight, and focus on the very exciting research that is taking place now, long after the cameras have stopped rolling.
  • The idea of a “caring fisherman” is an oxymoron. According to Johnson, the professional fishermen working with Chris Fischer to hook the sharks and bring them on board the Ocearch boat have for years been adherents of the “only keep what you’re going to eat” viewpoint. (I’m not sure you should even take it out the water if you’re not going to eat or tag it, though, but we’ll let that one go.)
  • There was no public participation or information provided. Shark cage diving operators in Mossel Bay were only informed two hours before the Ocearch crew started work in the area that they were going to be operating nearby, and we are all familiar with the complete PR debacle that took place when the project came to Cape Town. Johnson admitted several times that they “dropped the ball significantly” on this, and said that while public participation is not necessary (I agree – it’s a ridiculous idea to ask a generally uninformed public whether they think science should be done), keeping the public informed absolutely is both courteous and necessary.
  • The participants took part in the research for financial gain. According to Johnson, none of the scientists got paid a cent, and Chris Fischer himself is not very financially flush either. There is no way for me to know anything about this, and I have no opinion on it.
  • The government has no ability to enforce whatever recommendations the scientists make based on the research, so why do it? This is a poor argument – the mandate of science is to provide research regardless of whether the will or means to act on it exists. At some future time the government may remove its head from the sand on these issues, and at that time scientists will be ready with data and analysis.
  • The project had no academic credibility. There were 30 local shark scientists involved (the majority of the community), and during the course of several workshops and discussions the project was discussed with academics in order to determine whether everyone would be involved. The consensus was a fairly resounding yes, by all accounts.

Johnson acknowledged that several of the criticisms of the project, especially regarding the complete absence of communication on what was planned and what the scientists were doing, were valid, but reiterated that the opportunity to do research like this, with funding provided by the History Channel (over $5 million), is simply a once in a lifetime event. It seems that everyone has learned something about bridging the apparent disconnect between scientists and the general public in South Africa. Hopefully these lessons are taken to heart!

As pointed out earlier, the criticism that bothered Johnson the most was that the research was purely academic and couldn’t contribute to the conservation of the animal. This prompted him to ask several questions, which he shared with us.

White sharks have been protected in South Africa since 1991 on the basis of a “precautionary principle”. What can this research add apart from simply satisfying academic curiosity? Will it have tangible benefits to the conservation status of white sharks in South Africa?

White shark capture rates in the KZN “bather protection” nets between 1978 and 2008 suggest that the population is stable. The average size of captured sharks, however, is dropping significantly, indicating that the breeding stock is being depleted. Female white sharks take 15 years to reach sexual maturity (the age at which they will start to breed), and a rapid, sudden population decline is possible if these mature females have mostly been fished out (by whatever means).

Dorien
Dorien

Moreover, while white sharks are protected here and in neighbouring Namibia, protection simply on a national scale is not effective. Dorien and Lyla Grace are examples of tagged sharks that have ventured far out of South Africa’s EEZ (territorial waters) and are thus exposed to uncontrolled fishing, longlining and finning by foreign vessels. Perseverance, another of the Ocearch sharks, has ventured to the edge of the continental shelf into waters patrolled by longliners.

Luis Antonio
Luis Antonio

Regarding the question of whether white sharks are targeted in South Africa, Johnson observed that the KZN nets take about 30 white sharks per year. (Stop and think about that number. It’s enormous.) Three tagged sharks have already extensively utilised this coast: Edna, Nico, and Luis Antonio, who spent almost three months chilling just off Richard’s Bay in what might be an as yet unidentified aggregation area. Very large white sharks have been caught in the shark nets there (over 4 metres in length), and this has potential consequences for the entire white shark population.

The role of the recreational fishing community was raised in the question of whether white sharks are captured incidentally in South Africa, but I think also ought to be examined in terms of whether it targets white sharks deliberately. Fisherman Leon Bekker of George, who was photographed (by Ryan Johnson, in fact) hauling a white shark out of the water by the gills and posing for photos with it for 15 minutes claimed he had caught the fish by accident and it was washed ashore, but much evidence indicates that a minority of recreational anglers deliberately seek out white sharks, using heavy tackle and special hooks, in order to feel more manly by subjugating another living creature, one presumes. Classy guys.

Johnson did point out (and Meaghen McCord has echoed this point in talks I’ve heard her give) that the majority of recreational anglers are keen to be legal and to operate on the side of the law and of conservation data. I hope this is true and that the local fishermen who use the internet and post in angling forums are a minority. That’s all I’m saying.

Regarding incidental capture of white sharks, in the last 10 years there have been about five white sharks voluntarily surrendered to authorities after accidental capture by fishermen. No one is under any illusion that these are the only sharks that have been captured by accident in the past decade – fishermen are generally afraid to hand over a protected species if it’s caught by accident and most will toss it overboard, or the fins and jaws are valuable enough to tempt many people to hang onto their catch. We have no idea of the impact of long lining, purse seine fishing and trawling, and accidental entanglement. The white shark killed by whelk farming gear (warning – horrible photo) earlier this year is a case in point.

Johnson also questioned whether our Marine Protected Areas (MPAs) are effective. He showed a map of the De Hoop MPA, with a large white shark aggregation area stradding the boundary as these creatures took advantage of the massive fish stocks in the area. Clearly the MPAs are of benefit to fish that don’t range very far (as Colin Attwood pointed out), but white sharks have enormous migratory paths and may spend very little time in protected waters.

Towards the end of his talk, Johnson touched on something that has bothered me about shark conservation in South Africa, but also internationally. There seems to be a disproportionate amount of rivalry, posturing, jockeying for media coverage, and misguided competition between individuals who SUPPOSEDLY have only sharks’ best interests at heart. Johnson observed sadly that this type of infighting “makes shark killers smile”.

In response to questions Johnson shared a bit of insight around the tension that existed between cage diving operators (some of whom bizarrely objected to television coverage of the very “product” they are selling – at high prices – to visitors from around the globe, and have failed to recognise what a boon the real-time tracks of the tagged sharks are to their presentations to guests prior to embarking on a trip), the conditions attached to the permit granted by the Department of Environmental Affairs (DEA), the presence of very professional government observers and vets on board the Ocearch vessel, and the ridiculous controversy over the “five tons of chum“, which was drummed up by an uninformed (or deliberately obstructive) local cage diving operator.

We found this interesting, as it provided much colour and understanding about the events of the torrid couple of weeks when the DEA revoked and then reinstated the Ocearch permit, but at the same time I must observe how saddening and disappointing it is to find such a complete lack of co-operation and open communication between all parties concerned: the DEA, Ocearch, conservationists, scientists, and eco-tourism operators. What is it about sharks that seems to bring out the worst, most self-interested aspects of the personalities involved?

Having depressed myself thinking about this topic again, I’ll close with a quote from an Ocearch press release in which the names of the scientists working on the project were released for the first time (only after a fire storm of controversy erupted when a bodyboarder was bitten by a white shark in False Bay):

Knowledge generated in this way can capacitate resource managers to effectively mitigate threats to this species by developing effective conservation and management measures. Such knowledge may, for example, include identification of areas where white sharks are vulnerable to exploitation, identification of habitats that are critical for mating, birthing, and feeding, and insight as to whether our white shark stock can adequately be conserved locally or whether regional or international cooperation will be necessary.

Let’s obtain that knowledge, analyse it, and act on it. Please, thank you.

Lecture: Colin Attwood on the effectiveness of South Africa’s Marine Protected Areas

Colin Attwood is a professor in the zoology department at the University of Cape Town with a special interest in Marine Protected Areas. Tony and I attended a talk by him at the Save Our Seas Foundation Shark Centre on the same evening as the talk about Baited Remote Underwater Video Stations (BRUVS) in False Bay. The two talks dovetailed nicely, since the aim of the BRUVS project is to enable more effective monitoring of our Marine Protected Areas.

The South African coastal waters are under threat from a number of directions. Resource extraction (mining, oil drilling and the like) carries a danger of catastrophic pollution and spills, and the craft used for these activities are often vectors for alien species. Aquaculture, which may seem like a good idea, also threatens to introduce alien species to sensitive areas of the coast, and generates huge amounts of pollution too. Municipal failures such as sewerage spills, plastic pollution, and most of all fishing are the other big threats to the integrity of the ocean habitat. A future threat to our coastline is phosphate mining (the phosphate would be shipped to China and Australia to rehabilitate farmland), and demersal trawl fishing is a constant threat to large areas of the coastline.

The scale of fishing in South Africa’s coastal waters is terrifying: 800,000 tonnes of marine life is harvested annually. About 300 species (including invertebrates such as abalone and rock lobster) are targeted, but about 550 are impacted, many as bycatch. To put that in perspective, there are about 2,200 fish species found around our coastline.

South Africa has a fairly extensive network of MPAs, covering 19% of our coastline. 9% of the coast falls within no-take zones, where nothing is to be removed by fishing or other methods. If one rather measures the extent of our MPAs as a percentage of our exclusive economic zone (EEZ) which extends 200 nautical miles off our coastline, they cover only 0.4% of South Africa’s territorial waters, and only 0.16% of our EEZ is a no-take zone. The west coast of the country is largely neglected, but other than that the MPAs are distributed quite evenly around the coastline.

Marine protected areas protect habitats and ecosystems, as well as commercially important fish populations. They do this by preventing fishing in nursery areas and locations where spawning takes place, as well as by preserving the genetic structure of the population. They allow research into the effects of fishing to take place by providing areas that aren’t fished to compare with areas that are. They also enable non-consumptive activities such as scuba diving, whale, seal and seabird viewing, and coastal tourism to take place.

One interesting aspect of MPAs that Prof Attwood pointed out is that they are used for crowd control. Anyone who has seen the number of vehicles on the beach at Sodwana during high season might think that this is terribly destructive and not what an MPA should look like. What is in fact taking place is that 95% of the people are being funnelled through 5% of the MPA, constraining the damage done by human activities to a very restricted area.

Redundancy in Marine Protected Areas, as in engineering, is a good thing. If a species exists in more than one MPA, it is less vulnerable to habitat destruction and catastrophic events such as oil spills. One of Prof Attwood’s students has done work on whether all our marine species are adequately protected (i.e. appear in at least one, and preferably more than one MPA). The results are sobering – of the 225 shore species surveyed, 26% of them do not live in any of our MPAs and 85 species only exist in one MPA. Of the inshore species surveyed (230), 33% are not in an MPA. 25% of the 145 estuarine species surveyed do not live in any of our MPAs, and of the 446 species found out in up to 500 metres on the deep continental shelf, 78% of them are not in an MPA. Only two MPAs (Pondoland is one) cover any of these species at all!

Prof Attwood then gave us a rapid tour through the important scientific studies that have been conducted in South African MPAS. It was only in the last 20 years that the scientific community shook off its skepticism that Marine Protected Areas – underwater, without fences – would actually work. The results are very heartening, and numerous studies have confirmed MPAs efficacy. Fish are more abundant, and populations of heavily exploited fish recover remarkably rapidly and thoroughly when fishing pressure is removed. I first read about this in Charles Clover’s book End of the Line, where he describes an MPA in New Zealand, at Goat Island, and what a delight and amazement it is to the locals and tourists who get to encounter abundant fish in knee deep water.

Giant roman at Photographer's Reef
Giant roman at Photographer’s Reef

Roman inside the Goukamma MPA (8 x 1 nautical miles in dimension, along the coast near Knysna) are on average larger, and change sex later. Roman change from female to male at a certain age, but fishing pressure outside the MPA has forced a physiological change in the fish: their sex-change takes place at age 8 instead of the usual 10 years. The roman inside the MPA are thinner and in poorer condition than those outside the reserve, where fewer fish means less competition for prey. This is at first blush a strange result, but makes complete sense given the higher density of fish inside the MPA – and perhaps these “thinner” roman are fit, compared to the chubby, overfed ones outside the MPA! Prof Attwood pointed out that MPAs are not good for all species – the example here is the crinoids (feather stars) that romans love to eat. Inside the MPA there is a significantly lower density of feather stars than outside, where fewer roman prey on them.

The talk concluded with a map showing analysis of where South Africa’s next MPA should be located. It’s possible to identify critical locations where species that are not widespread live or breed, and these are the areas that should be protected. Tony and I both found this talk extremely inspiring and encouraging, as Prof Attwood does not do the kind of science that gets shelved somewhere and forgotten about. The results of his work are useful in policy making, legislation and decisions about the protection and use of our common marine resource, and he is active and willing to participate in that aspect of marine conservation.

Effects of chumming in False Bay

Following on from my post on Saturday regarding the scientific studies done on the effects of chumming elsewhere in the world, a study done in False Bay in 2004 has been brought to my attention by the team at Shark Spotters (thank you!). Much more should be made of this work!

Effects of provisioning ecotourism activity on the behaviour of white sharks Carcharodon carchariasLaRoche, Kock et al (Marine Ecology Progress Series, May 2007)

This paper (summary here, full text here) describes a study done in June-October 2004, using acoustic tags and receivers on the sharks and sea floor around Seal Island. Over the five month period, the researchers were at sea for an average of 15 days per month, ten hours per day. Despite this their sample was too limited to draw conclusions about certain things – this is an excellent demonstration of how hard it is to do science in an ecosystem.

The findings are similar to those of the Australian study I mentioned on Saturday in that it was observed that the chum had an effect on shark behaviour, but that it was fairly minimal. The authors estimate that 10-20 sharks are present around Seal Island at any one time during the winter (May – September), but only a small fraction of these approach to investigate the material placed in the water to attract them to the boats.

Moreover, the sharks’ response to the presence of chum decreases with time – during the first hour that a shark was recorded on one of the acoustic receivers, the chumming appeared to have a significant effect on its location at the island. In subsequent hours, however, the sharks seemed to lose interest and resume ordinary behaviour. This effect was also observed on a larger time scale, with decreasing interest over a number of days.

No effect was observed on their predation rate (how many seals they caught) suggesting that (even when they got hold of the bait being used) the chum didn’t cause the sharks to substitute their usual diet with the bait or with some other source. Sharks were seen at the boat only 36% of the time that they were actually at the island. Sharks did swim closer to the surface when the researchers were chumming in the area, but resumed their normal swimming depth elsewhere around the island.

These results are the exact opposite to what one would expect if the sharks were becoming conditioned by the presence of tourist boats chumming at Seal Island. Conditioning refers to changing behaviour by means of some sort of stimulus, in this case by rewarding the shark with a smell or taste of chum (the stimulus) each time it approaches a tourist boat, and thus causing it to approach all boats (for example – the response). If sharks were becoming conditioned by the chumming, one would expect the time they spend around the boat to increase over time, and that they might even approach boats that were not placing any attractant in the water.

There is still work to be done, however:

Unfortunately, conditioning is not the only way that chumming can directly affect the sharks. Extra provisioning could potentially alter residency times at the island, in either a positive or negative direction. It could also theoretically affect shark population structure around the island, if dominant and subordinate individuals react to the chum in different ways. However, despite the fact that it would seem reasonable to surmise that the patterns observed in our data would not translate into changes in shark residency times at the island, nor could the impacts of sparse provisioning have substantial effects on population structure, the short-term nature of the present study makes it impossible to draw any inferences regarding these topics.

I’d suggest you read the original paper if this kind of thing interests you. Even if the statistical jargon (Komolgorov-Smirnov tests, t-tests and the like!) is mysterious to you, it’ll give you a good idea of how arduous it is to conduct a study of this nature (750 hours at sea, in winter, anyone?), how frustrating it can be (the presence of cage diving operators at times meant that their observations had to be discarded in the interests of statistical rigor), and what goes into analysing the data. There is no real place for “gut feel” – it can lead your enquiries in a particular direction, but the final analysis is a statistical, evidence-based one.

Thinking about shark bites (and attending a meeting)

I currently work in investments, and the investment team at the company I work for pays a lot of attention to what are known as cognitive (or behavioural) biases. Many of these biases make humans poor investors; the team I work with try actively to identify these biases when we encounter them in our own thinking about investments, and to counter them. Cognitive biases are patterns of poor judgment, hard-wired in our brains, that were once useful to us – perhaps when our ancestors were running around on the African grasslands – as they enabled quick decision making with limited information. Today, however, countless generations later and faced with survival in a concrete rather than a literal jungle, we are saddled with these brain short circuits that can in fact impair our performance in certain aspects of life, particularly in circumstances where emotions and knee-jerk reactions threaten to overwhelm logic.

Tony and I attended a meeting on on Monday 24 October 2011, held at the Fish Hoek Civic Centre. It was organised by Mark Wiley, the Western Cape Parliamentary Chair of the Committee for Culture and Sport, and was open to business owners who operate in the South Peninsula area. The focus of the meeting was to determine:

  • How the increased presence of shark sightings and the incident had affected business, sport and recreational activity in the Far South area – either positively or negatively
  • How the shark phenomenon was having an impact on the community as a whole from a perception point of view
  • If there was a need for an impact assessment
  • To advise or ask the authorities, City or otherwise, to investigate options to minimise risk to the public and for them to explore options in this regard

(I quote from the minutes – let me know if you want a copy and I will email them to you.)

Attendees included several local business owners, including Dawid Mocke of the Varsity College Surf Ski School and The Paddling Centre, Andrew Brouckaert of Fish Hoek Surf Lifesaving, some local guest house owners, Paul Botha of the Kahuna Surf Academy and a few other local surfers, Kim Kruyshaar from the Scenic South website, and a small group of ocean and/or nature lovers some of whom also have business interests in the area (we count ourselves in this group) such as Steve Benjamin of Animal Ocean, freediver Hanli Prinsloo, Jean Tresfon, Morne Hardenberg of Shark Explorers, Jenny Trethowan of Baboon Matters, and of course Sarah Titley of Shark Spotters.

During the course of the meeting I observed several of the cognitive biases I mentioned above, and realised that it’s very hard to have a conversation about an emotive topic such as shark bites on humans, without a whole host of these biases cropping up. The challenge when it comes to an issue like the shark bite one, is to remain rational and to listen to the statistics – not to the fearful, reptilian part of our brains. We need to form judgments and decisions based on evidence, and not our gut. In choosing what to have for lunch, you can listen to your gut – but not here.

What follows is a selection of statements heard (and sentiments expressed) at the meeting, and the behavioural bias inherent in each. The behavioural bias definitions are from the cognitive biases wikipedia page.

There never used to be any sharks in False Bay

“My family has lived on the mountain in Fish Hoek for sixty years and until recently no one ever saw a shark.”

Anchoring – the common human tendency to rely too heavily, or “anchor,” on one trait or piece of information when making decisions or forming thoughts.

Just because you’ve never heard of Oprah Winfrey doesn’t mean she doesn’t exist.

Just because your family never saw a shark, it doesn’t mean they weren’t there. Did they watch the sea all day, every day? Does your grandmother even know what a shark looks like when seen from an elevated point, when the sun is shining?

Your family wasn’t looking specifically for sharks, and didn’t know what to look for. The Shark Spotters undergo extensive training to distinguish between dolphins, kelp, shadows, and sharks. A lot of the time it’s not as straightforward as looking down the hill and – eureka – seeing a shark!

Sharks have only recently come to live in False Bay (and probably for sinister reasons, like to eat old people swimming at Fish Hoek)

Recency effect – the tendency to weigh recent events more than earlier events

Massive population growth and increased leisure time has given many more people access to beaches and recreational activities in the ocean. Just because they’ve only recently been drawn to our attention, it doesn’t mean sharks haven’t always been here. Sharks have been living in False Bay for longer than we have been in the area, but it’s only recently that we’ve been looking out for them – and more people in the water means more human-shark interactions.

Furthermore, as Anton Louw pointed out, evidence suggests that False Bay has been getting colder – and hence cleaner, enabling sharks to be seen more easily from above. One factor pointing in this direction is the fact that kelp, which likes cold water, never used to be found north of Miller’s Point but now proliferates off Jaggers Walk in Fish Hoek, and colder water implies cleaner water.

If there were fewer sharks in the recent past, it’s possibly because:

  • White sharks were fished aggressively until fairly recently (they became a protected species in the mid-1990’s in South Africa)
  • At one point there were only 35 seals left on seal island after aggressive culling – that means no food to support a population of white sharks, which would send them elsewhere for food in winter.

There are more sharks now that there have ever been before, and they are coming closer inshore

“I and all the surfers I know see sharks in the surf zone almost every day when we go surfing.”

Attentional Bias – implicit cognitive bias defined as the tendency of emotionally dominant stimuli in one’s environment to preferentially draw and hold attention.

Your buddy is more likely to share with you that he saw a shark while he was surfing than, say, a child’s kite or a peaked cap that got blown into the sea – although they are both equally likely. Sighting a shark carries far more emotional charge than almost anything else. It’s emotionally dominant, to say the least.

Chumming activities are teaching sharks to associate humans with food and drawing them inshore

Availability cascade – a self-reinforcing process in which a collective belief gains more and more plausibility through its increasing repetition in public discourse (or “repeat something long enough and it will become true”).

There’s no evidence for this, even though it’s a popular belief among surfers. Do some reading please. Or buy this book (and read it).

The shark population is exploding

“Just look at how many sharks have been sighted at Fish Hoek beach this spring! The population is out of control!”

Confirmation bias – the tendency to search for or interpret information in a way that confirms one’s preconceptions.

The population of an apex predator cannot explode – it simply cannot happen. Such predators are typically are slow growing, slow reproducing creatures that produce few young, with high energy requirements. The population of everything else lower in the food web – EVERYTHING – would have to explode first, before the shark population could “explode”. And then it probably wouldn’t be a population explosion – it’d be the plot of a science fiction movie.

The Shark Spotters program doesn’t work

Outcome bias – the tendency to judge a decision by its eventual outcome instead of based on the quality of the decision at the time it was made.

Cape Town’s Shark Spotters program is a world leader in approaches that combine both beach safety and conservation awareness. The spotters cannot force people to obey the flags, however, and the actions of a single selfish, irresponsible, immature individual who endangered not only his own life but that of his eventual rescuers cannot be used to tarnish the reputation of this program. This article gives a good summary of just how impressive the Shark Spotters program is.

I thought it was absolutely shameful (and an outright lie) to suggest that the Shark Spotters have somehow failed, or – as one of the attendees who has “surfed in 30 countries in the world” stated – that the spotters are poorly trained and fall asleep at their posts. Unfortunately this comment was not censured.

A rogue shark or group of sharks is responsible for biting humans and coming inshore to the beaches

Clustering illusion – the tendency to see patterns where actually none exist.

You’ve got to choose: you can’t claim that “ALL sharks are maneaters” and in the next breath claim that a single rogue shark keeps coming into Fish Hoek bay to eat swimmers. If sharks actively sought people as prey we’d see several fatalities a day – at any one time there are about 50 white sharks in False Bay, and if they each wanted a human or three for lunch (a white shark can eat four seals on the trot, no problem), I’d fancy the shark’s chances over yours.

Return Jaws to the video shop and read some proper science writing instead. The Rogue Maneater theory has long been discredited.

The business downturn in the South Peninsula is entirely due to the fear of sharks

Negativity bias – the tendency to pay more attention and give more weight to negative than positive experiences or other kinds of information.

I don’t know if you’ve noticed, but the last few years have been tough. When I fill my car with petrol and hand over R550 for a full tank, it feels as if Armageddon is nigh. As Jenny Trethowan pointed out, we’re still making our way through an economic downturn of note, and businesses everywhere have struggled. Blaming this entirely on sharks is disingenuous.

This statement also ignores the eco-tourism value of sharks. Hundreds of people joined the shark spotter on Boyes drive every day during this recent peak of sightings, scanning the bay and excitedly discussing the possiblity of seeing a shark. Do you think they all went home without having a coffee somewhere, or buying a sandwich?

The large number of sharks currently being spotted inshore is going to persist FOREVER

Disregard of regression toward the mean – the tendency to expect extreme performance to continue.

Shark sightings in False Bay (Jan-Nov 2011)
Shark sightings in False Bay (Jan-Nov 2011)

Source: Shark Spotters recent sightings

Year after year a seasonal peak of inshore sightings of white sharks is observed. Sightings typically peak in October, and then decline somewhat for the rest of the summer. During winter, the white sharks hang out at Seal Island and are hardly ever seen inshore. This same sequence occurs year after year after year. It is driven by the sharks’ search for food (they eat seal pups at the island; when the seal pups get too old, fast and wily they eat the fish that come into False Bay with the warmer water in summer), and possibly by socialising activities and the opportunity to rest in the highly oxygenated waters close to shore. There is no reason to state that THIS year the sharks are going to stay in the surf zone, set up homes there and harrass swimmers year-round.

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Having listed the statements above, I realise that there was a disturbing mindset among many of the meeting participants, who seemed opposed to scientific thinking and statistical or evidence-based reasoning. Instead they attached great importance to anecdotes, personal experience (only valuable to the individual unless recorded and shared in an objective manner that recognises shortcomings of perception, memory and understanding) and uninformed generalisations. This kind of thinking is also prevalent in media reports of shark bites, and almost all the conversations I have had with friends and family on the subject (and let me quickly add, I have also been prone to it!).

Unfortunately, as humans we actually can’t help thinking in those ways. We have to actively work against the part of our brain that wants to leap to conclusions based on stories told around the bar or in the elevator, and give it some hard facts to chew on instead. These three cognitive biases capture some of the attitudes I am talking about:

  • Bias blind spot – the tendency to see oneself as less biased than other people.
  • Confirmation bias – the tendency to search for or interpret information in a way that confirms one’s preconceptions.
  • Base rate neglect or Base rate fallacy – the tendency to base judgments on specifics, ignoring general statistical information.

Contrary to my initial expectations the meeting was conducted in a civilised manner, and despite the flawed thinking on display, for the most part the attendees agreed (or claimed to agree) that a solution to the issue of perceived increased risk owing to shark attacks in False Bay must make sense both from a conservation point of view (not killing sharks) and from a human safety perspective. (As an aside, a topic that was skipped over was the possible role of trek net fishermen in attracting sharks to the beaches… A bit of a political hot potato, methinks!)

Tony has experienced a slight dip in business as a result of the recent shark bite incident at Fish Hoek. Experienced divers aren’t generally fussed, but new and prospective diving students are frequently nervous about sharks and ask a lot of questions. I think that no matter how much income Tony lost, however, he’d be very hard pressed to suggest that killing some of the fauna of False Bay was a valid solution to the problem.

However, at least two of the participants at the meeting – both gentlemen of a certain age who claimed vast knowledge about the world’s oceans and Fish Hoek in particular – clearly favour shark nets, culling, hunting down and shooting the “rogue” sharks who persist in coming into the bay or a similar solution. To say so, however, would have been unpopular once it became clear which direction the consensus was moving.

Some of those with a purely financial interest in the public perceiving Fish Hoek beach and False Bay waters as safe also would have jumped at the idea of a solution that removed sharks from the waters around Fish Hoek – whether that involved killing them or not. Fortunately thinking like this is no longer socially acceptable as it smacks of arrogance about humans’ role on earth, and ignorance about the functioning of ecosystems. Fear of saying something socially unacceptable is a tenuous reason to hold back on expressing a favourable opinion towards a shark cull – it by no means signals or causes a change of mind on the subject – but fortunately it was sufficient of a restraint for the meeting participants to reach an agreement that was in favour of the sharks’ continued existence in False Bay, hopefully in harmony with ours.

I was relieved when the meeting concluded with Mr Wiley stating that the evening’s contributions were sufficient to request the Cape Town Sub-Council in Fish Hoek to allocate funds for a research project to making False Bay, specifically Fish Hoek coastline safer for beach users. I believe that this will take the form of a safe swimming area, but we’ll have to wait (hopefully not too long) and see.