Mon, 17 September 2012

A significant link between lunar phase and water temperatures and shark sightings has been shown in the latest research by the Shark Spotting programme in conjunction with the University of Cape Town, writes Spike.


Sitting in the Empire Cafe overlooking the crumbling surf of Muizenberg Corner, we discuss sharks, the ocean and surfers.

Alison Kock, the shark scientist from Shark Spotters, looks forward to her first surfing lesson immediately after our meeting.

She's keen to get in the water, although from where I sit with a few more years surfing experience, the sea looks murky. But beginners seldom worry about conditions.

We're talking sharks. That's Alison’s language, and she’s fluent in it.

She's excited about significant trends that have been output from statistical models they have been working on with UCT, and in particular the work on the relationship between white shark sightings and environmental variables to be published in a Masters dissertation by Applied Marine Science (AMS) student Kay Weltz.

The starting point was shark sightings data recorded by their spotters at Muizenberg Corner, Fish Hoek and Saint James over almost a decade, including also the time of the day, name of spotter, and rough daily weather conditions. The second step was combining this data with specific environmental variables including lunar phase, water temperature, cloud cover, tides, and details on wind (data provided by the South Africa Weather Service, and the SA Navy Hydrographic Unit).

This study was investigated by AMS Masters student Weltz in collaboration with Professor Colin Attwood, Dr. Henning Winker and Alison Kock, using statistical models.

The most basic output of the model, and that recorded by the press this week, shows that June and July have the least shark sightings, and that by September they're steadily increasing into summer, when activity is high. These are trends we have come to know. They're a common part of the seasonal ebb and flow as the resident white sharks of False Bay move more inshore during summer.

White sharks look for easy prey, and their movements are specific to that. False Bay white sharks are mostly juveniles and sub adults that are sexually immature.

As Alison says, white sharks look for easy prey, and their movements are specific to that. False Bay white sharks are mostly juveniles and sub adults that are sexually immature.

The media has overlooked aspects of the survey that are much more significant than the known fact that more white sharks are seen in summer. One that jumps out like a breaching animal is water temperature. How's this: according to the data recorded by the spotters, there are four times more chance of spotting a white shark in 18 degree water than there is in 14 degree water. It makes sense. Bait fish are more active in warm water.

Another is lunar phase. Though slightly less significant, there is still a trend showing almost twice the chance of a sighting during a New Moon than a Full Moon. The speculation here is that bait fish are more active under cover of darkness, and therefore so are predators.

The problem of course, Alison says, is to find a practical use for this information.

Immediate steps are underway to place water temperature and lunar phase data on information boards at the beaches. The more knowledge and information, the better for people to make up their own minds.

"But we also need to digest this information and think about it a bit more. We need to consider what needs to happen."

She already has some ideas, around how water users assess conditions. Alison urges surfers to look for shark cues when sussing out the surf. Not only should we be checking out the wind, the swell and tides, but let’s expand the ritual to include shark probability. In essence, surf forecasting with a bit of shark forecasting.

Does the spot fall within a high shark area? Are there shark spotters there? What time of the year is it? What is the water temperature? What is the moon doing? Is there a lot of activity in the water, such as birds, bait fish, dolphins and seals?  Are you near a river mouth? Is the water murky?

It's about probability of spotting a shark given certain conditions. If numerous 'red flag' signals converge, surfers need to make a call, just as you might if an onshore is blowing, or the surf is too big at the spot you're checking out.

Shark sightings on the Cape Pensinsula are increasing. Like it or not, that is inevitable. The way we deal with it is up to us. Finger pointing and acrimony will not resolve a thing.

Our challenge is to keep the balance between hype and risk, and taking calcuated risks to enjoy our passion when we feel the time is right. We need to get past the hype, but without losing respect for an apex predator - a tightrope balancing act.

Science is inexact. Scientists are the first to admit it. They do not provide the answers. But they do arm us with information that is critical to our understanding, and if we approach the issues as a collective, as a community, this information is invaluable.

"We are not trying to foster fear. For us it's about giving people information they can use."

Oh and by the way, she stood up on her first wave. On the second, she rode all the way to the beach.


Craig Warlow
0 #17 Craig Warlow 2012-12-27 21:47
I am a great believer in studying statistics and data when it comes to predicting marine life behaviour. I was a sea angler for many years and kept detailed diaries of my fishing trips. I did this for several years and it gave me great insight into whether a prospective trip would prove fruitful or not. There were certain venues that fished better on small tides, others on big or medium, others at low water, others at high. Water temperature, time of day, water clarity, wind, cloud cover etc all played their part. I am convinced that shark behaviour / possibility of attack is also governed by the same sort of details, and others too. It never became an exact and 100% accurate prediction of the day ahead, but more than often the predictions were generally correct, and let me know whether it was worth venturing our or not... Surely that is very important when swimming in shark infested waters?
-1 #16 JamiiH 2012-11-13 13:51
Great insight Spike....what are the chance of you doing a "shark" forecast along with the wave predictions?
0 #15 Karel 2012-11-07 00:50
Puff: reply to question whether anyone has mapped attacks on surfers with reference to whether the victims were paddling into waves, out to the lineup, sitting on their boards, feet up or feet down etc?..... I found this website very informative too http://sharkattacksurvivors.com/
-1 #14 MIchel 2012-11-05 21:15
1. In the '50s and '60s people said that the risk was higher in warmer water. The scientists dismissed it as an old wives tale. Statistics show it is true.

2. New moon spring tides bring the most flow of water over the rocks and are more likely to dislodge shellfish and other critters that fish like to eat, so GW seals will arrive, and GW Sharks will follow.
Rudi Coetzee
0 #13 Rudi Coetzee 2012-10-09 06:45
Shark sightings are scarce this year compared to last year. I agree that the water temperature is also at least 2 - 3 degrees down on last year the same time. We should also check the influence of the South Easter (major change took place yesterday, 8 Oct 12.
+1 #12 Puff 2012-09-28 17:13
Great article, thank you. I have a healthy respect (read fear) for sharks. The more scientifically driven articles I read re sharks the better I understand how to manage my fear.
Quick question, any idea whether anyone has mapped attacks on surfers with reference to whether the victims were paddling into waves, out to the lineup, sitting on their boards, feet up or feet down etc?
Rob Mousley
0 #11 Rob Mousley 2012-09-21 17:03
Great article... Great information. Thanks Spikey!
The more we know about these animals, the better our chances of reducing unfortunate interactions with them.
Anton L
-1 #10 Anton L 2012-09-21 09:22
yeah - go Alison!

shot for this one, spike. Its always an interesting topic and it's great to learn more.
Andrew Macgregor
-1 #9 Andrew Macgregor 2012-09-18 10:30
Thanks Spike, Alison and Shark Spotters for sharing very interesting, would be interesting to see how these different locations tie in with ocean currents in the bay. Do the sharks tend to swim with the current or against it??
Were there more sightings at high or low tide? What influence did swell height have?
-1 #8 rob1610 2012-09-17 13:36
Quoting RobMobius:
With reference to the graph,

Are there really 80 sightings on avg during the month of Dec at Muizenberg?

when i attended the talk at the save our seas foundation that question was also asked. the speaker mentioned that out of all the sightings, the shark alarm is not raised all of the time. in certain cases the shark is cruising past the back line 150m off going away form the beach in other instances the shark is on a tracjectory straight
for the line up, for example that is. i think its based on the fact that not all sightings pose an immediate threat while other most certainly do.
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