I again have students in the pool on Friday, and we will shore dive on Saturday. No boat dives planned. Sunday sadly looks a little on the windy side.
Sunset over Langebaan lagoon
Yoshi the turtle has made landfall in Australia. She was probably hoping to watch the Formula One. Read all about her incredible journey here. What a girl!
Do you live in a city? Worried about keeping yourself and those you care about healthy? Here’s a helpful article. Look after yourselves and stay safe!
I’ve got students in the pool on Saturday, and Sunday looks too windy for dives, so we’ll have to wait to get in some salt water until conditions improve.
Turtle time
It’s the start of that time of year when turtles strand on the beaches of the Western Cape. What to do if you find one? Don’t throw it back into the sea. The Two Oceans Aquarium explains how you should proceed. Read more here.
Why so quiet? What have we been doing? Working, mostly. Trying to stay alive. And a bit of reading, and some beachcombing. Enter this is marvellous little book from fish fundi Rudy van der Elst (A Field Guide to the Common Sea Fishes of South Africa).
Chapter by chapter, van der Elst describes the types of debris that one might find on a beach. After a brief orientation chapter covering the ocean current regime around South Africa, relevant regulations, safety, beach ecology, tides, pollution and more, we launch into a tour of washed-up treasures.
Predictably, many of the items to be found are organic in nature – plants, invertebrates of various types, eggs and egg cases, fishes, birds, and shells. There are also items such as oceanographic devices, tags from marine animals, fishing equipment, cyalumes, buoys – some of these (such as tags) should be returned to their owners, and others should be removed from the vicinity of the ocean (such as discarded fishing nets and lines).
The chapter on marine animals (resting, nesting and stranded) is exceptionally useful and it is almost for this alone that I’d like to put a copy of this book in every home in every coastal town in the country. Seals, whales, turtles and seabirds can end up on the beach, sometimes in difficulty and at other times not. It can be hard to tell, and well-meaning members of the public can unwittingly cause great harm while trying to assist. A list of useful contacts in this regard appears at the end of the book, such as the Two Oceans Aquarium and the SPCA (region-specific).
The final two chapters cover miscellaneous “treasures” such as fossilised sharks teeth, sea glass, logs, and actual treasure, as well as beachcombing through the ages in South Africa. Here we learn about tidal fish traps, coastal caves, and other historical coastal dwellers who made their living from the sea.
We’ve found some awesome things on the beach, from shipwrecks to goose barnacles to rare crabs. Beachcombing is an accessible hobby that requires nothing but time, observation skills, curiosity, and a beach to stroll on.
This is a beautifully illustrated, comprehensive little volume that deserves to come with you on your beach holiday. It’ll prompt more careful examination of the flotsam and jetsam on your local beach, and, probably, more early morning low-tide visits to find the best pickings!
Neither day of the weekend looks all that promising for diving. The Atlantic is most likely to have the better visibility, however the swell on Friday and early on Saturday is not really my cup of tea. I will take a look at False Bay on Saturday, and possibly launch there on Sunday if it looks decent. If you’d like to dive, let me know!
Salt marsh at Langebaan lagoon
Turtle time!
We are entering into the busiest time for turtle wash-ups on the Western Cape coastline. On Tuesday, 14 (yes, fourteen) baby turtles stranded themselves in Hermanus. These little animals are in a highly compromised state when they end up on the shore, as they can’t cope with the cold waters this far south.
The Two Oceans Aquarium has a sophisticated turtle rehab facility, and, once they’re fattened up and restored to full health, the little turtles are released in the summer months when the warm current is closest to the Cape Peninsula coastline. Read about what to do if you find a baby turtle here. Local drop off points for tiny turtle guests are at the Two Oceans Aquarium (obvs), and the Shark Spotters info centre in Muizenberg.
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.
The forecast for Saturday looks rosy so we will launch from the Simon’s Town jetty at 9.30 and 12.00. Both dives will be shallow, most likely Roman Rock and Photographer’s Reef. False Bay is a little patchy so dive sites might change.
Yoshi the loggerhead turtle
Turtles
Amazingly, we still meet people who don’t realise that baby sea turtles – and even big ones, if they’re poorly – can’t survive for long in the cold waters around the Western Cape. Luckily the Two Oceans Aquarium has a well-developed turtle rehab facility, where they look after turtle hatchlings and older turtles brought in by members of the public.
The turtles receive veterinary treatment, vitamin supplements, a healthy diet, and excellent care from a dedicated team of aquarists. The aim is to return all the turtles that regain sufficient health to survive independently, to the wild, as most sea turtle species are vulnerable. These turtles are released in each year in December, when the warm Agulhas current is at its closest to Cape Point, giving the turtles their best chance of survival. The most famous release story is Yoshi, who swam all the way to Angolan waters, and is now off Namibia again, heading south. Maybe she misses us.
If you find a stranded sea turtle, keep it safe and dry, and notify the aquarium as soon as possible. The NSRI can assist with large turtles, and know how to help. There’s more information on what to do here.
Like turtles? Want to read about turtle science in South Africa? We have just the book for you.
Diversnight 2018
This year, Diversnight is on Saturday 3 November. The aim is for as many divers to be underwater at 20h18 as possible. More details to follow closer to the time!
I would love to be writing to you, claiming a weekend ahead with stunning dive conditions…. But I am not. The week has had some looooong period large (i.e. Dungeons) sized swell. Although the swell drops off for the weekend, the wind (mostly northerly) and its strength (strong), don’t look all that great.
Heart-shaped sea star
I am out on the boat tomorrow and the conditions should be the same for Saturday so if it’s good… I will change my plans, otherwise it is most likely going to be a dry weekend. If you want the option of diving based on tomorrow’s conditions, let me know.
What to do if you find a stranded sea turtle?
A tiny little chap was found at Kommetjie this past week. If you find a stranded turtle, keep it dry, and transport it as soon as possible to your nearest turtle rescue point. If you’re in Cape Town, this is most likely the Two Oceans Aquarium directly, or the Shark Spotters info centre at Muizenberg, who will make sure the turtle gets to the aquarium for rehabilitation and future release. Read more about what to do on the Two Oceans Aquarium website, here.
Between the Tides: In Search of Sea Turtles – George Hughes
I have been late in coming to this book, which was published about five years ago. George Hughes is a world-renowned, South African turtle scientist whose work has done much to ensure protection for sea turtles in the southern Indian Ocean. He was the guest speaker at an event held at the Two Oceans Aquarium to celebrate the release of Yoshi, the loggerhead turtle who spent over 20 years at the aquarium and is now powering along the Namibian coastline in rude health.
Between the Tides
Dr Hughes was CEO of the Natal Parks Board and then Ezemvelo KZN Wildlife, but Between the Tides relates his early career as a student looking for turtles along South Africa’s wild north east coast, in places that today support thriving dive and fishing charters. His legacy of turtle research continues.
Turtle surveys were conducted around Madagascar, the Comores, Reunion, the Seychelles, and on the Mozambique coast. The fact that the iSimangaliso Wetland Park now exists, offering a protected and well-regulated breeding environment for three species of turtles (loggerhead, leatherback and green – discovered there in 2014) is thanks to the early and persistent work of Dr Hughes and his colleagues. Turtles were first found nesting on this piece of coast in 1963, when it was still completely wild and mostly neglected by the authorities. In this book Dr Hughes recounts the development of the tagging program that he started, in which over 350,000 hatchlings were flipper tagged and/or marked over a period of 31 years.
Only about two out of every 1,000 hatchlings survive to return to the area in which they hatched, to breed. Female loggerheads are estimated to reach maturity around the age of 36 years, during which time they navigate an ocean of threats. This makes every surviving hatchling incredibly valuable.
The recovery of the number of loggerheads, in particular, has been quite spectacular, with more modest but noticeable gains in the leatherback population. More recently, as technology has allowed it, satellite tagging has shown their movements around the Indian ocean
If you find a baby sea turtle on the beach (this is the time of year when they start washing up), here is what you should do. The most important thing is to keep it dry, and to contact the aquarium as soon as possible.
Dr Hughes also discusses the sustainable use of sea turtles (for example, for food), something which I’d never thought about and which for that reason is fascinating – and very challenging to come at with an open mind, and appreciating the viewpoints of a scientist who has been steeped in turtle research for most of his life. This is an excellent, proudly South African marine science book, written to be accessible even to those who aren’t turtle fanatics a priori. Highly recommended.
Get a copy of the book here (South Africa), here or here.
We launched yesterday and had pretty good conditions in False Bay at Fan Reef and the northern pinnacles of Roman Rock. It was grey and rainy, but great to be out on the bay.
I’m going to count on the strong south easterly wind tomorrow cleaning up the Atlantic. The very southerly swell on Saturday will not be felt as strongly in Hout Bay, so we will most likely go there for dives. I’ll check the water colour tomorrow afternoon and confirm the final destination. If you want to be on the boat, let me know.
A grey day out on False Bay
Diversnight
Don’t forget that Diversnight is coming up next weekend, on Saturday 4 November. There is no charge for the dive, and the more the merrier. If you need to rent a cylinder or any other gear, please let me know in advance (i.e. not next Saturday)!
Farewell to Yoshi
Yoshi, the loggerhead turtle and undisputed star of the I&J Ocean Exhibit at the Two Oceans Aquarium, will be released soon. The aquarium is hosting a farewell event for her in November, with turtle experts and aquarists as guest speakers. More information here.
The I&J Ocean Exhibit is the largest tank at the Two Oceans Aquarium, and has been open since mid-2016. It features a full 10 metre long tunnel, and is home to Yoshi the turtle, two green turtles, bonito, musselcracker, a guitarfish, some rays, and several other species. Watching the animals being fed at 12pm on a Sunday is a highlight of my monthly shift at the aquarium.
Yoshi the loggerhead turtle
I needed to dive in the tank, and Tony and I were lucky to be escorted by the wonderful Angie, who has been a Divemaster at the aquarium for several years. The dive is easy: the tank is shallow, warm, and the visibility is to all intents and purposes limitless. Angie pointed out that in an out of air situation, we’d just do a CESA to the surface. (This makes the aquarium perhaps the only location you’d use this skill in its pure form…) The animals aren’t dangerous, but they need to be respected, and the soft acrylic windows pose a particular challenge as a careless bump with some dive gear would scratch them from the inside.
Angie and Bob the green turtle
The green turtles are special. Bob was found in poor shape on the beach at De Hoop when he was the size of a dinner plate, and after several months in intensive care, regurgitated a quantity of plastic, including ribbons and balloons. Now, he is friendly and very attached to humans – he especially loves to have his shell tickled, and wriggles from side to side in appreciation. As a result of the amount of time he spent in veterinary care, he will stay at the aquarium for his own safety.
Tony and Sandy the green turtle
Sandy was most likely struck by a boat propellor near Witsand at the mouth of the Breede river. The scars are visible on her carapace in the photo above. She was recently discovered to be definitely female (turtles are tricky). She’s not quite as interested in humans as Bob is, but she was mesmerised by her tiny reflection in Tony’s camera lens, and approached closer and closer to examine it.
The giant guitarfish
In addition to the turtles, Tony enjoyed the fantastic giant guitarfish, and spent much of the dive looking for it. The rays are like puppies, full of youthful exuberance and energy. The schooling fish mostly keep out of the way of the divers, near the surface of the tank, but are a treat to be close to.
Yellow belly rock cod in a cave
Schooling near the surface
What?
We last dived in the aquarium a couple of years ago. The kelp forest, which was an enormously enjoyable dive, is currently closed for renovations but will be re-opening soon. The new shark exhibit will also be open for dives soon (it is already open for looking at, with nine ragged tooth sharks in residence). Meanwhile, the Ocean Exhibit provides more than enough diversion on a day that doesn’t offer good enough weather for a sea dive.
