Lecture: Alison Kock on Shark Spotters

The Save Our Seas Shark Centre in Kalk Bay held another marine speaker series this November, and Tony and I attended a couple of the talks. One which we enjoyed was given by Alison Kock, research manager at Shark Spotters. Shark Spotters is a beach safety program that Capetonians are rightly very proud of – there’s more about it on the Shark Spotters website, here and here. Alison’s talk focused on some updates as to the research that is going on in False Bay, and extensions of the spotting program.

Updates on the shark spotting program

Between 2004 and 2012 the shark spotters have made more than 1,400 sightings of white sharks, 60% of which resulted in beach closures. The sharks are either resting, passing by, or searching for prey (other sharks, rays, fish) when they come inshore in summer. For spotting to be effective, at least 40 metres of elevation is required from which to observe the beach. The beaches in False Bay differ, in that sightings at Muizenberg resulted in a beach closure only 30% of the time, while at Fish Hoek the beach was closed 80% of the time. This is because of the nature of the surf and sharks’ behaviour at the different beaches.

At Muizenberg, the backline is some 300 metres off the beach, and the majority of the time sharks are cruising along behind the backline or further off the beach. The beach is only closed when sharks enter the surf zone – 74% of the time they are simply swimming past the beach. When a shark is behind the surf zone, the red flag is raised (for High Shark Alert) but the beach remains open.

At Fish Hoek, 61% of the sharks remain behind the breakers, but this is a mere 50-100 metres from the beach. 68% of the sharks are swimming past, but their proxmity to the beach means that more beach closures take place than at Muizenberg. The lookout location at Fish Hoek is on the mountainside, 110 metres above the beach.

Shark exclusion net at Fish Hoek

Fish Hoek is to be the site of a trial shark exclusion net that will be tested in the next month or two, all going well. It’s important to understand that this is an exclusion net, not a gill net, and the team in charge of the trial have been mandated to design and construct a net that will not lead to bycatch of any marine species. The aim is not to kill sharks and reduce the population, thus reducing the chance of interactions with people (this is what the Durban nets do), but rather to build a “wall” in the sea to keep them out of a specific area of Fish Hoek Bay in order to make it safe for swimming.

The other important thing to remember is that nothing like this has ever been done before. Owing to the strength of the wind and swells that we experience in Cape Town’s summer, and the presence of large amounts of kelp in False Bay which can foul the net, the net will only be deployed on calm days and will be removed overnight. The net has been designed and is being constructed at the moment, but the process of deploying and removing it (to be handled by the trek fishermen) will be a learning experience initially. If the initial prototype has flaws, the City of Cape Town is determined to iron them out and make it work. It would be courteous and generous of the media and other observers to recognise that this is a world first, and to allow for an initial period of change and possible disruption as the net is tested and refined.

New spotting locations

Earlier this year, Caves at Kogel Bay (on the eastern side of False Bay beyond Gordon’s Bay) was added as a spotting beach. This is a popular surfing location and the water is relatively deep as much of the coastline in that location is rocky cliffs. There have been numerous sightings there since spotting commenced, confirming that this site seems to be on a route that white sharks take in and out of False Bay.

Monwabisi Beach on the northern end of False Bay is the site of up to 10 drownings per year, owing to dangerous rip currents that are, in part, a result of artificial structures constructed for swimming (see the satellite image below). Shark Spotters is adding Monwabisi Beach to the list of regular beaches that have spotters on duty. This is an exciting development and will be particularly important if the proposed oceanfront development along Baden Powell Drive takes place.

[googlemaps https://maps.google.com/?ie=UTF8&ll=-34.074071,18.687294&spn=0.006185,0.009645&t=h&z=17&output=embed&w=425&h=350]

SharkShield research

South African researchers collaborated with scientists in Australia to test the effectiveness of SharkShield, a portable device for use by surfers and divers and intended to repel sharks with a magnetic field. The South Africa researchers towed a seal decoy at Seal Island with the SharkShield attached, while the Australians tested it in natural predation situations. They found that the device does not attract sharks (this I imagine would be the absolute minimum functionality required before one even considered using it!). The device repelled some sharks, but not all of them, and its effectiveness depended on the shark’s state of mind. The range of its effectiveness was found to be about 2 metres diameter from the object. The full research study is available here.

Safety tips

Alison concluded her talk with some shark safety tips, of which it’s good to remind oneself of once in a while (specially in summer):

Be aware of your surroundings. The presence of dolphins, bird activity, or fishing may indicate that white sharks will be in the area. Don’t let the cute dolphins distract you and get your guard down!
Check out recent sightings. Visit the Shark Spotters facebook page, and make sure you understand the flag system and read the signs at the beaches you visit.
Don’t swim at night, in low light (sunrise and sunset), or in murky water (such as at a river mouth) or poor visibility.
Stay in shallow water. Three quarters of shark activity at our beaches is behind the backline.
Avoid high risk times and areas when you go swimming.
Stay in groups – don’t get separated or swim out far beyond the other water users.