Last Friday while diving out of Hout Bay we were visited by what felt like an overwhelming number – but was approximately fifty – whales. Most of them seemed intent on staying close to the boat and in fact a few rubbed themselves on the boat’s keel strip, which was slightly alarming. I stood dead still, wearing my life jacket, with the engines off and the boat stopped right next to the divers, hoping that they wouldn’t get too rowdy (the whales, not the divers). The divers had the amazing experience of whales at the safety stop.
We have been experimenting with early (6.00 am) and late (3.00 pm) launches for quick double tank dives to slot in as part of a well-planned work day. We’ve had lovely conditions and we’ve enjoyed seeing familiar places in a different light!
We are starting to have fewer days of howling south easterly winds and it is a sign of good things to come, especially for those who prefer diving in False Bay. There is nothing spectacular in the weekend forecast: no howling wind, no huge swell and maybe a spot of rain. I think False Bay will be the place as the temperature of the Atlantic hit 19 degrees celsius today.
I have a backlog of students currently so we will try to shore dive and boat dive on both days. Once I have confirmed numbers I will text those on the “ready to dive” list. You know what to do!
DAN Divers Day
If you aren’t diving this coming Saturday afternoon (13 February), consider the DAN Divers Day at False Bay Underwater Club in Wynberg. It’ll be an afternoon of talks about dive safety and research, with local and international speakers. Register here – if you want to see the full program drop me an email and I’ll forward it to you.
After foraging on the sea shore for edible seaweeds and mussels under the guidance of Roushanna and Gael from Good Hope Gardens, we returned to Gael’s house in Scarborough to prepare a meal with our finds. The group divided into four, and we worked together to prepare the food using recipes provided by Roushanna.
Sushi rice mixed with finely chopped sea lettuce (Ulva spp) formed the base of vegetarian sushi rolls, which were decorated with kelp, tongue weed, radishes, avocado, mayonnaise, and a secret sauce (recipe for the rolls here). Sea lettuce was also the seaweed of choice for a couscous and rocket salad, decorated with hibiscus flowers and miniature tomatoes (recipe for the salad here).
I worked on the coleslaw, made from finely sliced red cabbage, carrots, and hanging wrack (Brassicophycus brassicaeformis) – a seaweed I found so tasty and crunchy I could have sat right there in a rock pool and eaten it directly off the rocks. The mussels were picked over, scrubbed, and prepared with white wine, cream, onion, and garlic. Crusty ciabatta soaked up the sauce. Once we were done, it looked as though we had enough mussel shells for our own personal shell midden!
Roushanna prepared nori (purple laver, Porphyra capensis) crips for us (like kale chips, but with a crispier texture and more flavour), and chocolate nori ice cream for dessert. We supplied our own drinks. During breaks in the lunch preparation some of the group enjoyed a face (and hand) mask made from seaweed ingredients. Others of Roushanna’s recipes you can explore for yourself are for sea biscuits (scones made with sea lettuce), fruity vegan jelly, and kelp and avo salad.
Lunch was a collaboration, and a tasty culinary adventure. I found it marvelous to discover what is available on the sea shore, and to get a small hint of how our strandloper ancestors foraged on the Cape Peninsula.
(Puzzled what this is all about? Read my first post about coastal foraging here.)
As I get older I am finding it increasingly difficult to suppress a wildly eccentric streak that frequently finds me – consciously or unconsciously – making small preparations for some kind of apocalypse (zombie or otherwise). This might be related to living on the South African roller coaster for too long, but whatever the origin of this latent anxiety, it has served to make our home life more sustainable and – little bit by little bit – more independent of the electricity grid, the municipal water system, and grocery stores. The idea of coastal foraging dovetails nicely with my desire to learn how to live a little bit more off the land than off the shelves at Woolworths!
It is important to respect some simple rules to ensure that your foraging is sustainable, safe, kind to the environment, and legal. Each of us had purchased a mollusk permit allowing us to harvest mussels, obtainable from the post office (available for R94 using the same form as the scuba diving in marine protected areas permit), and these were inspected by fisheries officials quite early on in our forage. You don’t need a permit to harvest seaweed (however if you wanted to do it on an industrial scale you might need to go through official channels).
There are three types of mussels found on South Africa shores: the ribbed mussel and black mussel are indigenous, and the Mediterranean mussel is introduced. Unfortunately Mediterranean mussels out-compete the indigenous varieties, and we only saw one or two black mussels while we were out. The mussels we harvested were the Mediterranean variety, distinguishable from black mussels by the thick, flat edge to their shells. Black mussels have pointy edges all around their shells, making them more streamlined.
There is only one type of seaweed growing along our coast that is harmful to eat (acid weed – Desmarestia firma, which has sulphuric acid in its fronds). This brown algae species does not grow on the rocky shore but only further out in the surf zone. This gives rise to the simple rule of only harvesting seaweed that is growing on the rocks, and never collecting seaweed that is floating free.
When harvesting seaweed, we used a pair of scissors to avoid pulling the entire plant off the rocks, and cut no more than a third of the leaves. Seaweed is full of vitamins and minerals, particularly iodine and potassium. It isn’t something you’d make a whole meal of, but it is a healthful addition to many dishes and – once you know how to prepare it – tastes pretty good!
You can read more about the Good Hope Gardens coastal foraging experience here and here. Watch this space for more about what we prepared with our seaweed spoils…
Cats are useful when it comes to boats. Despite using them to sleep, play and look at the world from, they can also perform useful inspection duties, making sure everything is in order. Here, showing unusual devotion to duty given that both the boat cover AND the console cover are on, Junior inspects the interior of the console to make sure that I didn’t forget to tell him there are sardines there, or something.
Today we took a load of surfers out to Dungeons. Amongst them were a few first timers at Dungeons and the happy cheers and bear hugs when they caught their first serious Dungeons roller was a sight worth seeing. Dungeons is a spectacular sight so if you haven’t been there do so at least once in your life.
Back to diving… We dived the Atlantic last weekend. Maori Bay was cold and clean-ish. Visibility was around 10 metres but then the temperature was also in the single digits. Die Josie was a lot cleaner and just as cold.
On Sunday we dived in False Bay – doing Search and Recovery for an Advanced course in 2 m visibility makes it a little more realistic!
Well… There is swell and wind in the forecast. The swell was not all that noticeable in False Bay today but was very surf-worthy at Dungeons and Muizenberg today. The wind is forecast at around 30 km/h for both days and for students doing their first boat dives I think it’s not that good an idea. So I have no launches planned for this weekend.
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.
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.
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.
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.
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.
These photos were taken on a day when I was trying my best to work on the boat, but cats were swarming all over it as though it was the Jolly Roger pirate party boat at the Waterfront.
Size is not an obstacle when you have determination. Here is Junior demonstrating that the opening of the inspection hatches under the bench at the back of the boat is almost exactly the size of his upper body.
The Cape Agulhas lighthouse is the most visually pleasing lighthouse that I’ve visited so far. Tony and I visited it while we were staying at De Hoop last September.
Cape Agulhas was named by the Portuguese from their word for needle. During the 1500s, when they were plying Southern Africa’s coastline, the magnetic declination in the area was approximately zero, meaning that there was no deviation between true and magnetic north, and the compass needle pointed to true north.
(Technical sidebar: Cape Agulhas lay on an agonic line during the 1500s. An agonic line is a line on the earth’s surface along which the magnetic declination or variation is zero. Earth’s magnetic field slowly changes, and with it the positions of the north and south magnetic poles. For this reason, the variation between true and magnetic north at a point on the earth changes slowly over time. You can examine a map of historic declination over the last 400-odd years here – if you scroll it back to 1590 you can see the green line through Cape Agulhas.)
The lighthouse is within walking distance of the southernmost tip of Africa inside the Agulhas National Park, and was built on land donated by Michiel van Breda, a local landowner (for whom Bredasdorp was named). Van Breda had experienced the trauma of shipwrecks along the stretch of coastline on his farm, with hundreds of dead bodies washing up after ships foundered on the rocky shores in rough seas. The shipwreck museum at Bredasdorp commemorates many of these wrecks.
The lighthouse was commissioned on 1 March 1849. It has a 7.5 million candela light that emits one flash every 5 seconds and has a range of 31 nautical miles. The lighthouse tower is 27 metres high, with a focal plane 31 metres above sea level. The tower is made of limestone with a white lantern house. By the 1960s the tower had deteriorated to such an extent that the lighthouse was temporarily decommissioned (its job performed in the interim by an aluminium tower), and restoration was undertaken. It was recommissioned in 1988.
The lighthouse is open to the public (also on weekends, which is unusual for a South African lighthouse) and contains a museum and a gift shop on the ground floor. The view from the top is well worth the climb.
A juvenile southern elephant seal (Mirounga leonina) has been seen around the Cape Peninsula for a couple of months. Almost every year solitary individuals are spotted resting on our shores, but they remain uncommon visitors and always cause a bit of excitement. Their usual habitat is subantarctic and Antarctic waters, including the islands belonging to South Africa and New Zealand, the Falkland Islands, and select parts of continental South America. They feed in Antarctic waters and spend winter down by the pack ice, insulated by tremendous layers of blubber. They are expert divers and can hold their breaths for two hours at a stretch.
Southern elephant seals are the largest seals, with the males (which can weigh up to 4,000 kilograms and grow to six metres in length) as much as six times larger than the females, which weigh 400-900 kilograms and grow to between 2.5 and 3 metres in length. At sexual maturity the males develop a big, inflatable rubbery snout (more correctly called a proboscis). This gives them their name, thanks to its rudimentary resemblance to an elephant’s trunk.
Juvenile seals are weaned and leave their mothers when they weigh about 120 kilograms. At this point they are just under a month old. This particular seal, which we saw hauled out near Cape Point, was at least two metres long already, and was busy moulting. During this time, the seal loses (as you can see in the top image) and regrows its fur. Some of its blood supply is diverted towards its skin to facilitate hair growth. Moulting happens during summer, and takes about a month (because it happens so suddenly, it is called a “catastrophic moult”). During this time the seals stay out of the water and possibly do not eat. Lying on the beach, well insulated with blubber, can cause them to overheat, so the seal we saw was flicking damp sand over his (or her) back to cool down.
As far as their conservation status goes, they are listed as of least concern on the IUCN Red List. They are probably helped by living so far from human activity, although they are still affected by plastic pollution, boat strikes and the like.
If you do see one of these animals, don’t be a jerk. Keep your distance (at least 20 metres) and don’t completely surround the seal. This ensures the animal stays happy and calm, and sets an example for others who may not have your good attitude, excellent education and experience with animals. Also, seals can move surprisingly fast on land, and an elephant seal is almost certainly going to weigh a lot more than you do. Tony took these pictures from a respectful distance, with his 150-500 zoom lens.