Southern African Shark & Ray Symposium 2015 – second day

View from the top of Red Hill, over Simon's Town
View from the top of Red Hill, over Simon’s Town

Overall impressions from the second day of the Southern African Shark and Ray Symposium, which was held from 7-9 September at the Blue Horizon Estate above Simon’s Town, are these nuggets of sharky goodness:

  • Collaboration between scientists leads to amazing things, like the massive acoustic tracking system that covers the entire south and east coasts of South Africa.
  • You can tell a lot about what an animal is doing, without necessarily being right next to the animal all the time, with some clever technology and mathematics (yay maths!)
  • There are tiger sharks that are partially resident off Ponta do Ouro, Mozambique. They are being tracked and studied. Something to bear in mind next time you visit!
  • Sharks that cross borders (e.g. tiger sharks, great white sharks) are hard to conserve and face huge risks when they move out of protected areas.
  • False Bay’s great white sharks are incredibly well understood (great work has been done in the last 5-10 years), and at the same time the more we know, the more questions there are!
  • We are beginning to get a better understanding of sevengill cowsharks in False Bay and research is ongoing. Plus, did you know there’s a huge sevengill population around Robben Island?
  • Many of the shark and ray populations around South Africa’s talks are not comprised of separate groups of animals (e.g False Bay’s white sharks, Gansbaai’s white sharks and so on), but interbreed all along their range. This means you can’t protect one aggregation site and expect the species to survive and thrive – you have to think about threats along the entire range of the animal. This was a common theme in the genetics talks (which is a difficult subject to explain to peasants like me).
  • Juvenile hammerhead sharks aggregate in Mossel Bay at certain times of year! (This wasn’t the point of what was an excellent talk, but I was excited to hear it.)

You can read a summary of all the day two talks in this quite large pdf – Storify died.

Panorama of Checkers, Ponta do Ouro (southern Mozambique)

Plate coral at Checkers
Plate coral at Checkers

The dive site Checkers, that I visited for the first time on our most recent trip to Ponta do Ouro in southern Mozambique, is notable for the amount of plate coral that can be seen there. Unlike many of the other sites in the area, Checkers has quite dramatic topography, changing depth over relatively short areas. Here’s a short panorama video I shot at one point during the dive. There weren’t many fish around at this point, but you can see the plate coral and the slope of the reef.

You can also see, right at the end, one way of diving with your main squeeze!

Dive sites (Southern Mozambique): Checkers

There are a lot of reefs around Ponta do Ouro and Ponta Malongane, and it was great to dive two new ones (Checkers and Steve’s Ledge) on our visit there in June-July. I did this dive with Christo and Laurine. Esther and Tony were feeling a bit under the weather with mild colds, so they sat out the first dive of the day on the Thursday of our trip. Checkers is a short boat ride from the launch site at Ponta.

Giant cushion star
Giant cushion star

The first thing I noticed at Checkers was the abundance of plate coral, which is beautiful but requires divers’ buoyancy to be impeccable to avoid crunching it. (It is surprisingly strong, though – on two separate Sodwana trips, owing to poor buoyancy control and body awareness, I have witnessed divers reclining on huge plate corals like overdressed burlesque dancers in giant martini glasses, and the plate corals survived without breaking. The divers almost didn’t, though! Grr!) There are plate (or table) corals of all sizes, some of them growing across gaps in the reef. This provides excellent habitat for marine life.

Soldiers hiding under plate coral
Soldiers hiding under plate coral

The reef has more interesting topography than a place like Doodles, even though it is relatively close to Doodles with no other reef in between. It slopes quite dramatically in some places. Christo suggested swimming back and forth across it in both directions so as to be able to have maximum opportunity to see into all the crevices and under the overhangs. The reef is relatively small and round rather than long, meaning that it’s probably not ideal to dive in a strong current, because doubling back will be tricky.

A porcupinefish on the move
A porcupinefish on the move

There are sand channels running through the reef in places, and as we swam over one of these we were passed by a beautiful porcupinefish with sad eyes, making his way somewhere. He swam right between us without batting an eyelid. I spent quite a lot of time trying to photograph this juvenile batfish, but he was far too busy demarcating his personal space among clouds of other fish under an overhang to turn sideways to the camera.

A juvenile batfish under an overhang
A juvenile batfish under an overhang

This is a great dive site for spotting hidden, interesting animals. There is enough life in the form of schooling fish over the reef to keep divers who don’t like sticking their heads under overhangs busy too! Photographic opportunities abound (despite the evidence I have presented here), but it isn’t possible to get to everything in an ethical manner (i.e. without lying on the reef like a plonker) because of the delicate structure of the coral.

Dive date: 2 July 2015

Air temperature: 21 degrees

Water temperature:  23 degrees

Maximum depth:  16.8 metres

Visibility: 12-15 metres

Dive duration: 57 minutes

Potato bass at Doodles, Ponta do Ouro (southern Mozambique)

Potato bass at Doodles
Potato bass at Doodles

We had amazing experiences with potato bass last time we dived in Ponta do Ouro, encountering them most notably at reefs called Texas and Doodles. This time, Doodles did not disappoint us. There is a one-eyed potato bass (his eye was caught on a fishing hook) who is very comfortable around divers, and when we met him this time he calmly swam through the group. Check how large he is compared to Laurine!

He was accompanied by a school of juvenile kingfish – the yellow and black ones – that will grow into amazing silver swimming machines similar to these queenfish. He also had a remora in his entourage (visible in the picture above), which could not seem to get a grip on him but was sticking around anyway and doing a lot of swimming in the process.

After the other divers moved on, I stuck around and watched him for a bit. He swam towards me slowly, like a cowshark, and I regretfully and respectfully made tracks.

Snappers at Steps, Ponta do Ouro (southern Mozambique)

I hope you don’t get tired of snappers, because I haven’t yet. Here’s a wonderful school of them at Steps, a dive site in southern Mozambique that we visited during our July trip to Ponta do Ouro.

Snappers at Creche, Ponta do Ouro (southern Mozambique)

Above the coral reef at Creche, a dive site in southern Mozambique, hang huge and colourful schools of fish. A quiet, calm diver may approach them quite closely. Here’s Tony filming some yellow snapper:

I love this close up of snappers:

And here’s another school of snappers making shapes in the water:

I find them quite hypnotic!

Swimming with the fish at Creche, Ponta do Ouro (southern Mozambique)

The reef called Creche, which we dived twice during our June-July trip to Ponta do Ouro in southern Mozambique, is full of fish life. The water above and around the reef is usually so dense with fish that divers drift among schools of snapper, fusiliers, goatfish and other fry of species I can’t recognise because they’re still too small.

Here are some fusiliers with us at Creche:

And here’s a mixed school of mostly yellow snappers:

Being this close to wildlife (which is how you should think about fish) is an almost miraculous experience.

Suunto D6 in full panic mode (part II)

Yesterday I told you about a dive on Doodles, a reef in southern Mozambique, during our trip to Ponta do Ouro last month. Doodles has a maximum depth of about 14 metres. After forty five minutes’ dive time, my Suunto D6 began to register extreme depths (89 metres maximum), and to give various instructions about decompression ceilings and times, accompanied by strident warnings about exceeding my PPO2.

Suunto D6 after missed decompression
Suunto D6 after missed decompression

While annoying and potentially dangerous to lose the services of my dive computer mid-dive, it was also an excellent learning opportunity. Because I usually try quite hard to be safe and not to upset my computer, and dive within the conservative, recreational limits that I am trained for, I never get to see any of this behaviour from the instrument. (Fortunately the dive was shallow and I still had plenty of no-decompression time left so it was far from an emergency situation.)

After the dive, I soaked the computer in warm fresh water, and it gradually came out of dive mode over a period of about ninety minutes. During the course of this simulated ascent, the required decompression times and depths calculated by the algorithm were not adhered to, so the computer entered an error mode, which, according to the manual, indicates that “the risk of DCI has greatly increased.” (In fact, from all the beeping and flashing, I suspect the computer thought I was dead or close to it.) This error mode does two things: it disables the dive planning capabilities of the computer, and it locks you out of dive mode for 48 hours.

The D6 in gauge mode
The D6 in gauge mode

I had never gotten the computer into this state before, so I was keen to see how it behaved when I took it on a dive in error mode. You can see in the photo above that I am wearing Tony’s Mares Nemo Wide (aka the flatscreen TV) to give me actual information about my no-decompression time, depth and dive time, but I took my D6 along for the ride. It is in gauge mode; this means it gives you only measurements, and is the setting a free diver might use.

The measurements available in gauge mode are: depth (18.4 metres in the photo above), the maximum depth you’ve been to on this dive (19.9 metres), an elapsed dive time (17 minutes), and water temperature (not shown) but it refuses to calculate a no-decompression limit for you. This would usually appear where the Er appears in the picture above.

Depth profile (with warnings)
Depth profile (with warnings)

For your enjoyment, here’s another screen shot of the dive profile from MacDive, with the warnings expanded. Click on the image to see it full size. It is clear that the first warning beeps I heard during the dive were because of elevated PPO2 levels. At 89 metres the device immediately put me in deco, and then as it “ascended” fairly rapidly, it gave a warning about oxygen toxicity (OLF or oxygen limit fraction as used in the Suunto algorithm) and an ascent rate warning. On the right, at about 10 metres, a warning is given that the depth is still below the required level to complete the decompression.

All the green circular icons appearing around the middle of my dive, where the computer thought I was at 35 metres, indicate that the computer registered that I surfaced, but not for long enough to show on the dive profile. Weird!

My D6 remained angry for 48 hours after the dive at Doodles; by this time, we had finished our diving for the week. I’m not sure whether the problem with the pressure sensor is a permanent one (requiring repairs, a service or a new dive computer), or whether it was just dirty or stuck and will have resolved itself next time I dive with the instrument. I’ll be wearing a spare dive computer when I do, just in case.

Suunto D6 in full panic mode (part I)

On the second dive we did at Doodles during our trip to Ponta do Ouro, something happened that caused my dive profile to look like this (click on the image to embiggen):

Profile (from MacDive) of a dive at Doodles
Profile (from MacDive) of a dive at Doodles

Fortunately that something was not me falling down an 89 metre deep hole in the ocean floor whilst breathing off a 12 litre cylinder of air, 45 minutes into a dive. It was something going wrong with (we think) the pressure sensor of my Suunto D6 dive computer. I have had the computer for a few years, and apart from the compass appearing to have packed up, it has been a fantastic device.

The first inkling of trouble that I had was when the computer started beeping at me, and when I looked down to see what was up, it said we were at 89 metres. Sunlight was falling on me, so I thought this unlikely. I checked with Christo, and he didn’t think we were that deep either. Nor did his computer. Fortunately I had been diving with a group for a few days, and we were well within our decompression limits at a depth of 14-15 metres. Losing the computer three quarters of the way through a dive wasn’t the disaster it could have been.

I took this picture shortly after the beeping started. The display at the top of the screen shows that the computer is reading 76.7 metres. The maximum depth of 89.0 metres shows at the bottom left. The bottom right shows the oxygen partial pressure, at 1.9. This is greater than the 1.2 limit that I have set for myself inside the computer. The computer thinking that I had rapidly exceeded the maximum PPO2 is probably the initial cause of the beeping I heard.

Suunto D6 showing 76.7 metres' depth
Suunto D6 showing 76.7 metres’ depth

In the middle of the screen you can see a large number 8.0, which is the depth to which the computer wants me to ascend in order to do a decompression stop. Next to that number is an arrow below two horizontal lines, and the number 35. This is how long I should stop at 8 metres in order to fulfil the calculated decompression obligation.

The D6 thinks we have ascended to 47 metres now
The D6 thinks we have ascended to 47 metres now

After a few minutes (I was actually busy ending my dive with a 5 metre safety stop) the computer believed I had ascended to 47.3 metres. By that stage it wanted me to go to 11 metres for a 45 minute stop. When I surfaced after about 60 minutes of dive time, the computer stayed in dive mode, thinking that I was still at a depth of about 35 metres. It continued registering a slow, quite smooth ascent for another hour and a half, as seen in the dive profile above.

The computer was still very grumpy when it took itself out of dive mode in a mug of warm water in the bathroom of Planet Scuba, while we were eating a post-dive lunch. The ascent profile it registered did not fulfil the calculated decompression obligations, and it showed that I had violated my decompression ceiling (either by taking too long to ascend to start the stops, or by not spending enough time at the stop depth).

I have put myself briefly into deco a few times (usually during days of repetitive diving during dive trips, and once or twice in Cape Town with two relatively deep and long dives in a day), so the readouts from the D6 on this dive are not unfamiliar to me. I have never before, however, seen such large numbers or heard so much beeping! I have always corrected the situation by ascending a little way, which removed the decompression obligation and returned the display to what I am familiar with as a religiously recreational, no-decompression diver. In this case, the D6 was doing its own thing and nothing I did seemed to influence the depth reading it gave.

I found this to be an excellent opportunity to re-familiarise myself with the behaviour of the Suunto D6, and also to see what all the error messages look like on the dive profile when I downloaded the computer into the MacDive software I use for electronic dive logging. The story does not end here – if the computer did not think I was dead from DCI, it wasn’t going to let me dive any time soon – check back tomorrow (or the day after).

Twinstripe fusiliers at Creche, Ponta do Ouro (southern Mozambique)

Twinstripe fusiliers over the reef at Creche
Twinstripe fusiliers over the reef at Creche

Unlike the large, distinctive schools of mostly yellow-coloured snappers that we saw on several of the reefs that we dived while in Ponta do Ouro, twinstripe fusiliers tended not to hang around as long, or as densely grouped. These beautiful blue fish with yellow stripes tended to stream past us in huge, spread out schools, passing for minutes at a time like passenger pigeons, and then disappearing.

I found the experience captured  in this video, filmed at the reef called Creche, to be almost transcendental – I felt as though I was in a blue cathedral, with the fish streaming past me towards the light of a distant stained-glass window. Or something – it was quite moving, anyway.