Newsletter: Pretty perfect

Hi divers

Weekend dive plans

Sunday: Boat dives from False Bay yacht club at 8.30 am to Roman Rock or Photographers Reef / divers’ choice for the second dive

The forecast for the weekend is really good with almost no wind or swell. False Bay is a pleasant colour and temperature.

Our plan is to meet in the False Bay yacht club parking lot in Simons Town at 8.30 am on Sunday. We will most likely dive Roman Rock or Photographers Reef for the first dive and let divers’ choice determine the site for the second dive.

Jetty behind the aloe
Jetty behind the aloe

Handy info

The toilets at the Simons Town jetty are currently closed for renovations as I understand it. They are due to be ready soon but I do not have a date. Also note that the Wharf street parking at the jetty is again a paid parking area for the season.

regards

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

Diving is addictive!

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Newsletter: Mountains

Hi divers

Weekend dive plans

Saturday: Boat dives at 10.00 and 12.30 from Hout Bay or False Bay yacht club

It may seem that given the week-long south easter we are having, it would be a simple matter to decide which side of the peninsula to dive. The picture was taken from Chapmans Peak drive today around lunchtime, and the water is not very clear – there are rocks just below the surface in the little bay below the road, but they are hardly discernible.

View from Chapmans Peak drive
View from Chapmans Peak drive

The water colour in False Bay is not very different but False Bay does seem to recover faster than the Atlantic coast of the peninsula. Sunday’s forecast is for gale force winds, so Saturday is the only decent diving day, but where?

Depending on tomorrow’s wind direction I will make a call late in the afternoon on whether we will launch in False Bay or out of Hout Bay. Either way it will be for dives at 10.00 am an 12.30 pm. I will have mostly Open Water students so the maximum depth will be 18 metres.

Email, text, wolf whistle if you want to dive.

regards

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

Diving is addictive!

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Newsletter: Cocktail weather

Hi divers

Weekend dive plans

No dives

We are in a phase of semi-decent weekday diving and dodgy weekends again. We had fairly good False Bay diving during the week, but the weekend forecast is not ideal for much beyond storm chasing. Strong winds and some significant swell topped off with a dash of rain are hardly a cocktail for diving. Northerly wind is not that great for False Bay and neither is a 5 metre swell, so best you pursue some other form of activity this weekend.

Sightings

One of the guys in the Underwater Cape Town facebook group reported a sighting of a john dory at A Frame this week. These fish are striking, solitary, and seldom seen. Bizarrely for such an exotic-looking fish, they are popularly served wrapped in newsprint with a side of chips. We were lucky to spot one at Long Beach a few years ago. (Go check out the video on Underwater Cape Town for a better idea of what they look like, and keep your eyes open next time you go diving!)

John Dory at Long Beach in January 2010
John Dory at Long Beach in January 2010

Talks talks talks

This Wednesday 17th is the nautical archaeology talk I mentioned in last week’s newsletter. There’s a talk on 23 August about the health of our fish stocks by scientists Colin Atwood and Jock Currie at Bellville Underwater Club – info on facebook. If you have a UCT staff or student card, you can listen to conservation photographer Thomas Peschak speaking on 21 September – info on facebook, too.

regards

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

Diving is addictive!

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Sharks! MOOC videos (part II)

Here is a selection of the videos for weeks three and four of the recent Sharks! MOOC hosted on edX. You can find weeks one and two here. All the videos are available on youtube if you’re really interested – you can check out the channel containing all this year’s videos, or a giant playlist containing all the videos from the 2015 iteration of the course.

Dark shyshark on the sand at Long Beach
Dark shyshark on the sand at Long Beach

Week 3: Thinking like a Shark – Brains and Behavior

Introduction – thinking like a shark

General organisation of the nervous system

Brain regions overview

Brain size

Prey localisation

Seeing underwater

Eyes for deep water

Lateral line system and Ampullae of Lorenzini

Electric snouts

Group hunting – broadnose sevengill sharks – an interview with Dave Ebert on research he did decades ago on the sevengill cowsharks of Millers Point

Week 4: Sharks in the World – Human Interactions, Ecology, and Conservation

Introduction – sharks in the world

What sharks eat

Food webs

What eats sharks?

Deep water communities

Shark struck

The problem with shark nets

Why are aquariums important?

Husbandry

Industrial fishing

The art of Ray Troll

Sawfish DNA

Sharks! MOOC videos (part I)

I completed the edX-hosted Sharks! MOOC, presented by Cornell University and the University of Queensland, and it was excellent. The content was clear and for me, who stupidly quit high school biology at the age of 14 for the sake of a more classical (less useful) education, filled in a large number of gaps in my understanding of sharks and rays.

The course format was a mix of video lectures and interviews, notes, diagrams and multiple choice questions for grading purposes. The videos are available on youtube – you can check out the channel containing all this year’s videos, or a giant playlist containing all the videos from the 2015 iteration of the course.

I’m going to link to some of the most interesting videos below, so you can get a taster of what the course was like. Please sign up next time it gets offered, if you didn’t do so this time!

Broadnose sevengill cowshark at Shark Alley
Broadnose sevengill cowshark at Shark Alley

Week 1: The Big Shark Picture – Biodiversity and Evolution

Intro – the big shark picture

Shark tracking

Light, depth and landforms

Habitat dive

Hotspots

Origins of taxonomy

Start with the fins

Skeletal anatomy

14 living orders

Species discovery

A walk through deep time

Bear Gulch – a golden age of sharks

Megatooths of Maryland

Week 2: Miracles of Evolution – Functional Morphology and Physiology

Introduction – miracles of evolution

Why a hammerhead?

How shark tails work

Drag

Oil and water

Edged weapons

Blue shark vs white shark

Pursue or ambush?

Manta ray feeding and migration

Shark vs mammal circulation

Breathing water

Countercurrent gas exchange

Osmoregulation in the bull shark

Greenland sharks

Reproduction in the sand tiger (ragged tooth) shark

Modes of reproduction

Week 3 (shark brains and behaviour) and 4 (sharks in the world) videos will follow in a separate post.

Newsletter: Testing 123

Hi divers

Weekend dive plans

Saturday: Two launches from False Bay Yacht Club, meeting at 8.00 am

A long period 3 metre swell arrives tomorrow, drops on Saturday and then builds again on Sunday. I am planning two launches early on Saturday morning as I have several students to certify. We will meet in the car park at False Bay Yacht Club at 8.00 am. Destination unknown and weather dependent. If you’re keen on a magical mystery tour, drop me an email, text or Whatsapp.

The boat from underwater
The boat from underwater

Keeping busy

In case you missed it on the blog this week, we tested one of our self-inflating life jackets in the pool, to see what would happen when it got wet. It works!

Maritime archaeologist John Gribble is speaking at the auditorium of the South African Astronomical Observatory on Wednesday 17 August, 4.30 for 5.00 pm. His talk is entitled “From Shipwrecks to Hand Axes: An Introduction to South Africa’s Maritime and Underwater Cultural Heritage” and is described as follows:

South Africa’s maritime and underwater cultural heritage is surprisingly diverse and extremely rich. Although shipwrecks are the most obvious elements of this rich heritage resource, there are a range of pre-colonial maritime heritage resources that are less well known. This talk will introduce South Africa’s maritime and underwater cultural heritage, highlight the archaeological importance of this resource, and touch on a few examples of interesting, local historical wrecks.

There is no need to book, the event is free to the public.

regards

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

Diving is addictive!

To subscribe to receive this newsletter by email, use the form on this page!

Testing a self-inflating life jacket

If you’ve been on our boat, you may have noticed that I always wear a life vest. It’s a slimline one that we purchased in Denmark a few years ago. The vest contains a small gas cannister with a pellet (looks like a headache pill) that releases the gas in the cannister and inflates the jacket when the pellet gets wet enough to dissolve.

Tony's "don't take my photo" face
Tony’s “don’t take my photo” face

When we went back to Copenhagen between Christmas and New Year, we purchased replacement cannisters, thinking that for safety’s sake it would be wise to service our life jackets to ensure that when we need them, they’re in tip top condition.

The question then arose as to what to do with the existing, unused cannisters in the life vests. Since you can repack the vest with a new gas cannister and dry pellet after deployment, and neither Clare nor I had seen one of these life jackets in action before, we decided to let it fire off in the swimming pool. Here are the results:

It definitely renewed my confidence in the life jacket, an important component of our safety gear, and (as you can hear in the video) provided some significant entertainment for my camera person Clare.

Article: The New York Times Magazine on animal tagging

Staying with our informal theme of the last few weeks’ (admittedly sporadic) posts, let’s look at a recent article from the New York Times Magazine. Not solely focused on marine animal studies, the article explains how technology has enabled even the general public to directly observe and learn about the migrations of birds, sharks and other animals. The utility of this kind of information is obvious:

By discovering the precise routes animals take during migration, scientists can assess the threats they face, like environments altered by habitat loss and overhunting.

A white shark with a satellite tag
A white shark with a satellite tag

The article’s author is brilliant nature writer Helen MacDonald, who wrote H is for Hawk, and she goes on to muse about the meaning of the relatively few individually tagged and named animals which become icons of their species as they appear to transverse a simplified, borderless planet in solitude. (The OCEARCH sharks on their satellite map refer!) It is easy to lose sight of the rigours of the environments they move through, but easy to become invested in the future of particular individuals.

Erik Vance’s article on great white sharks for National Geographic covers tagging, and he elaborates on his blog about how tags can facilitate population estimates. You can also read about whale tagging, tuna tagging, and the tagging study taking place on False Bay’s cowsharks.

What a time to be alive. Read the full New York Times Magazine article here.

Newsletter: Swell weather

Hi divers

After a few days of rain and southerly swell False Bay does not look that great. This swell direction is set to stay for a few more days and in fact changes only on Monday. There is some south easterly wind on Friday and Saturday but not really strong enough to clean up the Atlantic enough for decent visibility.

Storm clouds at Zeekoevlei
Storm clouds at Zeekoevlei

I think it may well be a dry weekend as far as diving is concerned, however if things start to look more promising than they currently do, I will be in touch. Let me know if you’d like me to message you if we go diving.

regards

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

Diving is addictive!

To subscribe to receive this newsletter by email, use the form on this page!

Two ways to count sharks

Did you pick up the July edition of National Geographic to read about great white sharks, or read the article online? (Pro tip: you should.)

The article’s author, science writer Erik Vance, contributes to a blog that I follow called The Last Word on NothingI was delighted to read a follow-up he posted to his National Geographic feature, explaining how scientists count sharks. At the heart of the method is a beautiful piece of statistics (a model) that allows scientists to draw conclusions about the size of a population – some of whom are tagged or marked  – based on only a sample of the individuals, and what proportion of those sampled individuals is tagged.

A dorsal fin breaks the surface
A dorsal fin breaks the surface

Why is it important to know how many great white sharks (or cowsharks, or whale sharks, or or or…) there are? The most obvious answer relates to conservation: if we have a baseline population estimate, we can then determine whether it is increasing or decreasing over time. What is the status of the population? Are these animals endangered, or flourishing? Are conservation measures necessary? Are they effective?

Go and read about counting sharks here. An important thing to pay attention to when you are reading any scientific model is what the underlying assumptions are, because they will show you the circumstances under which the model will fail.

And for some hot off the press South African research on a related subject but taking a different (genetic) approach, check out this press release. The study’s author, Sara Andreotti, spoke on the topic at the SA Shark and Ray Symposium in 2015.