We have south easterly winds of between 30 and 60 km/h spread out over the next few days, and as a result I am not planning any dives for this weekend.
SAS Somerset at the V&A Waterfront
Diver24
Join UCT Underwater Club and the Two Oceans Aquarium for their annual Diver24 event. This year you can enjoy diving-related talks, snacks, and the vibe of the aquarium at night. More info here (facebook).
On your way, you can check out SAS Somerset, pictured above, as she lists slightly in her berth behind the aquarium. She’s the sister ship of SAS Fleur, a deep dive not too far from Seal Island in False Bay.
Sunday: Boat or shore dives in False Bay (conditions dependent)
Apologies for the lateness of this week’s newsletter… Blame a very delayed Safair flight from Johannesburg last night!
Lighthouse at Kalk Bay
We have three windless days coming up and hopefully some sun to go with that. There has been a lot of swell in False Bay, and coupled with the rain and run off the visibility is not all that great. If anything, Sunday will be the best diving option so based on what we see Saturday, we will plan for Sunday. Let me know if you want to join in.
There is a fair amount of swell around right now, combined with strong winds. Although False Bay looks a little scrappy, the water colour remains good. Sunday looks like the best, or only, option for diving, but we will most likely shore dive. I will wait until Saturday mid afternoon to make the call. Get in touch if you wish to join.
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)
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-Changehere (facebook), taken on 22 January in False Bay.
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)
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)
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)
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.
A visit to Port Elizabeth can be very rewarding for the lighthouse enthusiast, with no less than three lights in close proximity. The Hill lighthouse is the oldest, and is almost in the centre of the town. It was commissioned in 1861, at which time it was seven metres high, and retired in 1973 when the competition from surrounding city lights became too intense.
The Hill lighthouse in Port Elizabeth
It is a brick structure, and was originally stone coloured. In 1903 the eight panels of the tower were painted alternate bands of white and red, and in 1907 the entire tower was painted white (as it is today). In about 1921 a red band was painted half way up the tower.
The old lighthouse keeper’s house (now home to NMB Tourism)
The lighthouse keeper’s cottage below the tower was built in 1865 for Charles Hammond, the first lighthouse keeper, who served until 1881.
The lantern room of the Hill lighthouse
The Hill lighthouse was raised by nine metres during 1929-1930 in an attempt to distinguish it from the lights of Port Elizabeth, and was finally replaced by the Deal light, a short distance out of town, when it became apparent that as the city got larger and brighter, the Hill light was being overwhelmed.
The lens of the Hill lighthouse
There isn’t a lot of information available about the optics of this lighthouse, given that it hasn’t been in use for 45 years. It appears that a Chance Brothers lamp apparatus was installed in 1903, with a German-built optic, but more than that I haven’t found. Chance Brothers were glassmakers, who pioneered surrounding lighthouse lamps with a cage of fresnel lenses to make the light visible over greater distances.
The lantern room of the Hill lighthouse
The Hill lighthouse is situated in the Donkin Reserve, a surprising open space high on a hill overlooking the city and the harbour. The area is planted with indigenous vegetation, and boasts beautiful open spaces and a magnificent 470 square metre mosaic (the Piazza Mosaic) showing elements of the history and natural attributes of the city and surrounds.
A detail from the mosaic at the Donkin Reserve
Also on the Donkin Reserve, and right next to the lighthouse, is a ten metre high stone pyramid erected by Sir Rufane Donkin in memory of his wife, Elizabeth, after whom the city was named. Donkin was acting Governor General of the Cape Colony from 1820-1821, sent here to recover from the death of his young wife.
View of Port Elizabeth harbour from the Hill lighthouse
It’s possible for the public to visit and climb the lighthouse, from which beautiful views of the city are visible. As with most lighthouses, the climb is narrow and vertiginous, but recommended! You can find more information about visiting hours here. There’s a nominal fee but the opening hours are far more favourable than most lighthouses I’ve visited. You just need to go into the tourism office under the lighthouse, tell the person on duty you want to climb the tower, and get further instructions there.
Sunday: Boat or shore dives in False Bay, meeting at 0900
Norwegian fishing vessel Nordervon in drydock at the Waterfront
According to our weather station this week, the south easterly winds have arrived, and hopefully this is a signal for warmer weather to move in.
False Bay has been on and off this week with some swell, however the colour is not too shabby. I am launching tomorrow, and depending on what we find, on Sunday I’ll shore dive at Long Beach or boat dive from False Bay Yacht Club. If you’d like to dive, let me know.
Our boat is booked this weekend so I won’t be running any dives. The weekend weather does look good for a dive, however, specially on Saturday.
The NSRI pink rescue buoy in Simons Town
Tales of Surf Rescue
The Two Oceans Aquarium is hosting a fundraiser for the NSRI pink rescue buoy campaign on Wednesday 30 May, at which comedian (and surfer) Nik Rabinowitz will interview a posse of big wave surfers. Event details are on facebook, and tickets are from Quicket.
The forecasts are conflicted as to whether the weekend’s wind will be manageable or hectic. Saturday looks like the better option and it is too early to rule out the Atlantic. Currently it is green off Long Beach in Noordhoek and the CSIR buoy shows the temperature climbing – not good prospects – but if the south easter picks up it will change.
Heron in the Simon’s Town yacht basin
My plan is to launch early on Saturday as I have a Junior Open Water diver who needs to get a handle on backward rolls before vacation time. I will most likely hide in the yacht basin for that. Thereafter we can go anywhere we choose… If the weather permits. So, if you are on the list you will get an update from me at around 7.30am on Saturday, and if its a go, we will leave from the Jetty at 10.00am. Want to get on the list? Let me know!
We came across this small biscuit skate (Raja straeleni) while doing a night dive at the jetty in Simon’s Town, on the occasion of Diversnight 2017. They are found in the eastern Atlantic ocean all the way down to 700 metres depth, grow really slowly, and are frequent bycatch from hake trawling operations off the South African coastline. SASSI says don’t buy it. The species is data deficient on the IUCN Red List.
These skates have thorn-like stings along part of their tails, and this one seems to have a whole lot else going on in the tail region which looks as though it would help him camouflage among seaweed. (None of the biscuit skates pictured in our fish identification books have quite such fancy tail-gear.) Also watch how he flicks sand over himself for additional disguise when he stops moving.
Also, they can jump – perhaps a little known talent… Once, while Clare was on duty at the aquarium, a small one leaped right out of the shallow ray pool that used to be next to the touch pool, and landed on the floor. It was a quiet Sunday afternoon. A quick manhandle and he was replaced in his pool (and that exhibit was moved soon after)!
False Bay is rather pleasant at the moment and Saturday looks to be an ideal day for student dives at Long Beach. We will start at 9.30 am. Sunday has some south easterly wind but I doubt it will be enough to spoil the conditions, so we will launch at 9.30 am from the jetty in Simons Town. Let me know if you want to dive.
CV24 (team Greenings), one of the yachts participating in the Clipper Race, aground at Olifantsbos
Diversnight
Diversnight is this Saturday evening. It’s a night dive, free of charge (unless you need gear), and we are diving at the jetty in Simons Town. We’ll meet at 7.30 pm and get into the water at about 8.00 pm, as the aim is for divers around the world to be underwater at 20:17 (get it?). This year, so far, there are 135 dive sites registered, in 22 countries. Clare might even bake something for when we get out of the water. Join us!
