Shark Spotters supporters program

We are proud to announce that we have signed on as official supporters of Shark Spotters. We are Silver partners, and for larger businesses there are higher levels of support on offer. (We are hoping to encourage some of the other dive centres to consider supporting Shark Spotters, too…) Individuals can also sign on to the supporters program, or donate in many different ways. Shark Spotters is part-funded by the City of Cape Town and the Save Our Seas Foundation, and the rest comes from public donations.

One of the Shark Spotters flags at Fish Hoek beachåç
One of the Shark Spotters flags at Fish Hoek beachåç

The Shark Spotters provide beach safety, a world-first environmentally friendly shark exclusion net at Fish Hoek beach, run educational programs at local schools, and conduct shark research in and around False Bay.

All of this work keeps both people and sharks safe, and this is at the heart of what Shark Spotters does.

The shark exclusion net has been around for about five years, and (unlike the gill nets in KZN) is specially designed not to pose a hazard to any marine life. It gets taken in every evening, to eliminate the risk of an animal becoming entangled at night when the spotters are not on duty. It is an extremely successful and popular feature of Fish Hoek beach, and is invariably packed with happy, safe swimmers during the summer months. If you’re curious about it, watch the video above to see what it looks like from underwater, and read more about it here, here and here.

The Shark Spotters info centre at Muizenberg
The Shark Spotters info centre at Muizenberg

Their research continues to illuminate the activities of white sharks in the bay, but is also in the process of shedding light on the interactions between white sharks, sevengill cowsharks and bronze whalers as they share the ecosystem. They have even published a recent paper (open access) on the predation of sevengill cowsharks by orcas in False Bay, which is well worth a read.

The Shark Spotters outpost at Caves (Kogel Bay)
The Shark Spotters outpost at Caves (Kogel Bay)

Currently, they’re partnering with a Swiss firm in a cutting-edge research project to determine how automated shark spotting, making use of cameras and machine learning algorithms, can augment the already impressive skills of the spotting team. By first training a sophisticated algorithm to distinguish between a shark, pieces of kelp, dolphins, wind chop, and all the other visual phenomena that a spotter comes across during the course of a day, it is hoped that a fixed camera system, with some software, could assist the spotters in their work. It is not intended to replace human spotters, but to augment and facilitate their work.

The Shark Spotters hut at Fish Hoek beach
The Shark Spotters hut at Fish Hoek beach

We’re happy to be contributing to the important work of Shark Spotters – if you’d like to as well, visit their website to find out how to lend your support, or drop me an email and I’ll connect you with the right people.

Newsletter: Is that rain?

Hi divers

Weekend dive plans

No diving

Whalebones on Sixteen Mile beach in the West Coast National Park
Whalebones on Sixteen Mile beach in the West Coast National Park
The weather forecasts that I watch the most have cycled through a series of odd updates that have shown alternately shown lots of rain on Saturday and Sunday, and none at all. I have students in the pool on Sunday so I won’t venture out into the ocean, but if you do, be aware they may or may not be surge, rain, or sunshine… Depends on your favourite forecast.
 

regards

Tony Lindeque
076 817 1099
www.learntodivetoday.co.za
www.learntodivetoday.co.za/blog/

Diving is addictive!

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Baby (Smith’s swimming) crabs

Last week we met Smith’s swimming crab (Charybdis smithii), a rare visitor from the tropics that arrived in the southern reaches of False Bay during the third week of January 2019. We found some adult individuals at Long Beach, well inside False Bay, on 3 March.

Juvenile Smith's swimming crabs at Kommetjie
Juvenile Smith’s swimming crabs at Kommetjie

At the same time that fishermen were reporting adult Smith’s swimming crab off Cape Point, a huge number of tiny red crabs washed up on Long Beach, Kommetjie. There were great piles of them, but we only managed to visit a day or two later on Friday 18 January.

Juvenile Smith's swimming crab at Kommetjie
Juvenile Smith’s swimming crab at Kommetjie

We had to hunt a little, but after a while we found the crabs – now only a few remaining, but most of them very active and vital. Opinion from George Branch is that these are most likely the final larval stage of Smith’s swimming crab, and the same warm conditions wit anomalous westerlies that brought their adults to the peninsula, brought the juveniles.

Juvenile Smith's swimming crab at Kommetjie
Juvenile Smith’s swimming crab at Kommetjie

This conversation (facebook group, may be closed) suggests that the juvenile Smith’s swimming crabs were also seen on Milnerton Beach around the same time as they appeared on the beach at Kommetjie.

I took a couple of short videos of the tiny crabs, which show them in motion on the wet sand.

Apologies for the loud wave noise and less than perfectly steady camera work. Read more about these pelagic crabs, exceptionally infrequent visitors to our shores, in this post.

Hello, Smith’s swimming crab!

One of the things I love about False Bay, and about Long Beach in particular, is the tendency for creatures from all over South Africa’s coastline to end up here, often tropical marine life that got caught in the warm Agulhas current, and then within the circulation of False Bay, ending up just behind the Simons Town harbour wall.

Smith's swimming crab (Charybdis smithii) Smith’s swimming crab (Charybdis smithii)

Thus it was, early in March, that we discovered several adult specimens of Smith’s swimming crab (Charybdis smithii) at Long Beach when we went for a dive. One or two were already dead, and the rest were struggling either on the sand, or in the shallows, looking unhealthy. The water temperature at the time was about 17 degrees.

The first hint that this unusual and rarely-seen visitor had arrived on our shores was a series of social media posts, from January, in one or two of the fishing groups I follow on facebook. (These are excellent places to keep tabs on what’s happening in parts of the ocean I might not routinely visit, and there’s a wealth of knowledge and experience among the members.) Here’s a conversation between local fishermen about seeing large numbers of adult Smith’s swimming crabs just off Cape Point (also facebook). You can also see some photos of one of the crabs from Sea-Change here (facebook), taken on 22 January in False Bay.

Smith's swimming crab (Charybdis smithii) Smith’s swimming crab (Charybdis smithii)

At the same time as these social media posts, there was an influx of small, red crabs on the other side of the Cape Peninsula, at Long Beach in Kommetjie. (But more on that in another post.) Two Oceans says that Smith’s swimming crabs were first described in False Bay in 1838, and then again in 1978, 1983, and 1993. This facebook thread suggests that they may have been last seen off Muizenberg around 2005-2006.

Smith's swimming crab (Charybdis smithii) Smith’s swimming crab (Charybdis smithii)

I read more about Smith’s swimming crab in two papers: this one (Romanov et al), from 2009, and this one (Van Couwelaar et al) from 1997. The more recent paper updates many of the findings of the earlier one. Both teams of scientists behind these papers used trawl data from pelagic cruises to learn about the distribution and life history of these crabs.

Smith’s swimming crab is a pelagic crab that spends the vast majority of its one year, monsoon-driven life cycle in the water column. They are endemic to the western Indian ocean, and are usually found in the area bounded by the Arabian sea (which is west of India) and the latitude of Dar Es Salaam in Tanzania (about 7 degrees south of the equator), and from the east African coast, across east to the Maldives. They may congregate in huge patches, larger than tens of square kilometres, and may reach a biomass of more than 130 kilograms per square kilometre. These swarms are densest between June and September. During July, their concentration can peak at more than 15,000 individuals per square kilometre.

Smith's swimming crab (Charybdis smithii) Smith’s swimming crab (Charybdis smithii)

The crabs congregate on the seafloor of the continental shelf during the months of September to December, mating late in the year. No adult crabs are usually seen between April and June (Van Couwelaar et al speculate that the adults die after breeding), at which time, after metamorphosis, the swarms again become apparent in the western Indian ocean. The crabs grow to about 7.5 centimetres carapace width.

The crabs seem to perform a diel migration, moving deeper in the water column during the day (down to 350 metres’ depth), and returning to the surface at night. They swim continuously and are voracious predators in order to support the high metabolic demand created by this constant activity. They are able to regenerate all their limbs except for their swimming legs (Van Couwelaar et al deduced this in much the same way as Abraham Wald decided which parts of World War II bombers to reinforce – no crabs with partially grown swimming legs were caught in their trawls).

These crabs are important prey for yellowtail, as for other pelagic fish species such as blue sharks, yellowfin tuna and bigeye tuna. The fishermen of False Bay observed that they made excellent bait.

Smith's swimming crab (Charybdis smithii) Smith’s swimming crab (Charybdis smithii)

So what brings Smith’s swimming crab this far south? False Bay is way out of their range. This paper (Chapman, 1988) suggests that prior arrivals of these crabs on our shores have co-incided with weaker than usual summer south easterly winds (which has definitely been a feature of late 2018 and the start of 2019 – we had a gloriously wind-still summer for the most part) and the westward movement of warm water containing the crabs. We did have a spell of unusual westerly wind just prior to these crabs’ arrival.

A fascinating 1984 paper by George Branch describes a temperature anomaly during the summer of 1982-83. This particular Cape summer was characterised by very little of the typical south easterly winds, leading to reduced upwelling, and relatively high sea temperatures (Duffy et al, Effects of the 1982-3 Warm Water Event on the Breeding of South African Seabirds, 1984). The exceptionally warm water on the south and west coasts of South Africa caused mass strandings of some tropical animals (such as portuguese man ‘o war), mortalities of others (such as black mussels), changes in abundance of some species, and extensions of some species’ geographic range. For example, an exceptional number of juvenile turtles washed up on the beaches of False Bay, several months before the usual start of the usual turtle stranding season (which is, very loosely speaking, March-July). Prof Branch records that large numbers of healthy, adult Smith’s swimming crab washed up at Cape Hangklip, and smaller numbers at Boulders Beach, Strand, Milnerton and Blouberg. About 62% of the crabs were female, and many of them survived in aquaria for some time after stranding.

In short, it seems that we had our own little temperature anomlay, however brief, in early 2019, and the pulse of warm water brought with it these rarely seen (in Cape Town) crabs. What luck to spot this unusual visitor!

There are some lovely pictures of Smith’s swimming crab, healthy and in mid water, taken off Tanzania, here.

Newsletter: Turning tides

Hi divers

Weekend dive plans

Sunday: Shore dives in False Bay, or boat dives from False Bay Yacht Club

There are large patches of red tide in False Bay, and no wind to clear them up. For this reason I’ll decide on Saturday whether we’ll be boat or shore diving on Sunday. I have students, so we’ll keep it relatively shallow either way. Let me know if you want to keep in the loop for the weekend dives. There’s been bioluminescence at the Strand beach this week, so keep an eye out for it around Fish Hoek beach during the evenings if the red tide persists.

Spring high tide at Fish Hoek beach
Spring high tide at Fish Hoek beach

Tidal documentary

Don’t forget the screening of Tidal at St James beach on Thursday 7 March. RSVP here.

regards

Tony Lindeque
076 817 1099
www.learntodivetoday.co.za
www.learntodivetoday.co.za/blog/

Diving is addictive!

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Newsletter: Signs of the times

Hi divers

Weekend dive plans

Sunday: Shore dives at Windmill or A Frame

Sewage spill at Long Beach
Sewage spill at Long Beach

Wildly different forecasts for this weekend make me inclined to go with the safest option, namely Sunday, as the best dive day. I have students to dive so will be shore diving, most likely from Windmill or A Frame, as when I checked earlier this week, the “stay out of the water” sign remains at Long Beach.

regards

Tony Lindeque
076 817 1099
www.learntodivetoday.co.za
www.learntodivetoday.co.za/blog/

Diving is addictive!

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Newsletter: From the heart

Hi divers

Weekend dive plans

Saturday: Boat dives from Hout Bay or shore dives at Long Beach

Weekend conditions don’t look all that great. Saturday will most likely be best for launching from Hout Bay , or there may be a slight chance of shore dive from Long Beach for students. I will make this decision late tomorrow depending on sea conditions. Let me know if you’re keen to dive.

A heart for you on Valentines day
A heart for you on Valentines day

Sunday is the Cape Peninsula marathon, starting in Green Point and finishing in Simon’s Town, so expect some road closures.

Film screening on the beach

There’s a free screening of the documentary Tidal at St James beach on Thursday 7 March. Read about the film here, and RSVP on Quicket. There’s no charge.

Tony Lindeque

076 817 1099
www.learntodivetoday.co.za
www.learntodivetoday.co.za/blog/

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Newsletter: Seal the deal

Hi divers

Weekend dive plans

No diving This weekend’s wind is forecast to be between 30 and 50 km/h, which, in my book, renders the weekend not suitable for diving. Sorry, kids.

Elephant seal on Fish Hoek beach
Elephant seal on Fish Hoek beach

See a seal instead

If you feel like a natural exfoliation, the visiting elephant seal is still on Fish Hoek beach, just after the little yellow and white mini lighthouse half way down the beach. He’ll be leaving soonish, so don’t delay. Read more about elephant seals here.

Tony Lindeque
076 817 1099
www.learntodivetoday.co.za
www.learntodivetoday.co.za/blog/

Diving is addictive!

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Visible shipwrecks: the barge Margaret

One of the most spectacular shipwrecks I’ve ever seen was that of the 100 metre long unmanned barge Margaret, which ran aground at Jacobsbaai on the West Coast on 24 June 2009. Margaret was carrying two halves of a floating dry dock and twelve river barges (positioned atop each other in side by side pairs, with two rows of three at the bottom). She was under tow by the tug Salvaliant from the Chinese shipyard where everything was manufactured, to Rotterdam. The barges were destined to transport cargo up and down the navigable rivers in Europe. During a winter storm, the tow parted, and Margaret and her cargo ran hard aground on the rocky reef just outside Jacobsbaai.

The eight storey pile of barges in December 2009
The eight storey pile of barges in December 2009

Salvaging the barges proved to be an almost intractable problem, so Margaret was still sitting firmly a couple of hundred metres off the beach when Tony and I visited six months after her grounding, in late December 2009. The stack of barges and two halves of a floating dry dock (the blue parts of the structure in the images) was clearly visible from a great distance. The sight was even more incongruous than that of the Eihatsu Maru aground on Clifton beach, which was  a wreck-lover’s dream (but unfortunately not a permanent arrangement).

View of the barge Margaret from atop the sand dunes at Jacobsbaai
View of the barge Margaret from atop the sand dunes at Jacobsbaai

I wish I’d taken a picture of what the wreck looked like as we drove down the hill into Jacobsbaai, but you can see one here if you scroll around a bit. It looked like an office block rising out of the ocean. The wreck was so large that it was visible from almost every point in the sleepy town, and the brain struggled to make sense of the sight. It’s clear from the images what a challenge it must have been to tow the barge in the wind, as the forty to fifty metre high, perfectly flat sides of the stack must have provided tremendous resistance in a gale.

Portion of the barge wreck at Jacobsbaai
Portion of the barge wreck at Jacobsbaai

The owner ran out of money to continue salvage in February 2010, and Margaret was becoming increasingly damaged and unstable as time passed. The risk of the upper barges coming loose during another storm, and drifting away to cause a hazard to other ships or coming ashore on the beach, was great. It was decided by SAMSA to persist with an attempt to reduce the wreck, at taxpayers’ expense. Any money obtained by selling off the salvageable barges would go towards defraying costs.

During the salvage work on the barge Margaret
During the salvage work on the barge Margaret

Salvage

Tony and I visited the wreck again in April 2010, after the demolition that freed six of the topmost barges. The seaward wall of the upper piece of floating dry dock, weighing 91 tonnes, had been cut away to allow the barges to slide off freely.

The remains of the barge Margaret in April 2010
The remains of the barge Margaret in April 2010

Over two tons of explosives were used in total.  Small (125 kilogram) explosive charges were set off one after the other to create a ripple effect that dislodged the top six barges. These were towed to Saldanha, and then sold.

The wreckage of Margaret and her cargo in April 2010
The wreckage of Margaret and her cargo in April 2010

If you like reading court judgments, here’s one in which the owners of the barges attempt to claim damages (massive ones) from the owners of the tug Salvaliant. There’s also a great collection of photos of the wreck in her various incarnations here.

The wreckage of Margaret in late April 2010
The wreckage of Margaret in late April 2010

In late April 2012, Tony snapped this lucky shot of two of the barges leaving Simons Town harbour under tow. They’d been moored against the harbour wall for at least a month, to the consternation and fascination of the local paddling community.

Two of the salvaged barges leaving Simons Town harbour in April 2012
Two of the salvaged barges leaving Simons Town harbour in April 2012

The remains of Margaret and her cargo were further demolished down to sea level and below, and now comprise an artificial reef. Fortunately there was no fuel or other pollutants in the stack of barges, which made the process significantly less polluting than it might otherwise have been.

The barge Margaret today

Tony and I visited Jacobsbaai to check out what remains of Margaret and her cargo in September 2018. The path to the wreck, which was formerly blocked off by hazard tape and “salvage in progress” signs, is wide and easily walkable. One can go right up to the rocks and view the wreckage from reasonably close up. Watch your foothold here, as it can be slippery and the rocks aren’t all firmly packed.

The remains of the barge Margaret and her cargo
The remains of the barge Margaret and her cargo

Look out for a small memorial to one of the salvors, who passed away in an accident on the wreck during the course of the salvage operation.

Sharp wreckage sticking out of the sea
Sharp wreckage sticking out of the sea

Parts of the wreck look like shark fins in the water, and it is possible that even more of it is visible at low tide.

The remains of the barge Margaret in 2018
The remains of the barge Margaret in 2018

You can find the wreck by turning off the R399 towards Jacobsbaai, and continuing towards the coast until the road becomes gravel. Carry on this road, and when you reach a T junction take a right turn to circle around the tiny, sheltered bay in front of you. When you can’t drive any more – there will be a small housing development in front of you – park the car and either walk up the steps on the dune to get onto the beach, or, preferably, through the houses. The paved area will give way to a wide gravel path that the salvors used to access the wreck. Continue straight along it and you’ll soon spot the wreckage on the rocks ahead and to your right. Co-ordinates are approximately -32.964140, 17.881612.

Path to what remains of the barge Margaret
Path to what remains of the barge Margaret

If you’re interested in visible shipwrecks, check out my ebook Cape Town’s Visible Shipwrecks, and this post.

Stompneuspunt beacon

View of Stompneuspunt beacon from inside Shelly Point
View of Stompneuspunt beacon from inside Shelly Point

During the course of a West Coast road trip late last year, we stopped at the unmanned Stompneuspunt beacon. This striking, squat structure sits at the southern end of St Helena Bay. To get there, we had to drive through the eerie, deserted, badly laid out Shelley Point golf estate development (tell the guard at the gate that you want to visit the lighthouse). Persistence through the maze of narrow roads turning in upon each other is well rewarded.

Stompneuspunt beacon
Stompneuspunt beacon

The green-painted lantern house atop the structure looks like a minaret, and the whole building looks like an exotic transplant from the Middle East. The beacon is situated on a beach of coarse sand covered with thousands of empty mussel shells and inhabited by flocks of cormorants. The mussel shells wash up after winter storms and red tides, and because of predation by rock lobsters and other shellfish.

Stompneuspunt beacon
Stompneuspunt beacon

The beacon was commissioned in 1934, at which time it was a pyramid-shaped wooden structure. The present building was completed in 2001. The tower is 8 metres high, and the focal plane of the light is 12 metres above sea level. The intensity of the light is a modest 1,403 candelas, but this beacon doesn’t have to compete with much in the way of onshore light pollution. It’s visible from 10 nautical miles away.

Stompneuspunt beacon
Stompneuspunt beacon

Hit up Lighthouses of South Africa for more information on this charming light.