It feels very much as though winter has arrived (minus the rain), mostly in the early mornings. When daytime temperatures rise into the twenties, it’s not totally unpleasant! Sunday is one of those days, and we will launch from Simons Town jetty at 9.30 and 12.30. Both sites will be a maximum depth of 18 metres as I have a bunch of Open Water students to qualify.
Sunday: shore or boat dives, depending where the viz is!
A cold front arrives tonight and will make itself felt until Saturday evening. Sunday will be best for diving. I have student dives to complete; if the inshore conditions are good, we’ll shore dive. If the visibility is only to be found further out, we’ll launch Seahorse. If you’re keen to get wet, let me know and I’ll update you on Saturday afternoon.
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.
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!)
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.
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.
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.
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.
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 Nothing. I 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.
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.
The cold front seems to have passed by and the second one that was meant to arrive tomorrow seems now to be giving us a miss. We had 40 mm of rain at home on Thursday, for which we are grateful. The break in the weather means there is a good chance some diving might happen this weekend!
I am going to shore dive on Saturday at Long Beach and launch on Sunday, the first dive being to the Brunswick, meeting on the jetty in Simon’s Town at 10.00am. The second dive will be at 12.30, the location weather and viz dependent.
I know we are barely past the halfway mark of winter, but the last few warm and pleasant days have got me wishing summer was here.
Some swell and lots of south easterly wind are in the forecast for Saturday, so Sunday will be the better option for diving. We will aim for a later start to see how well False Bay fares during Saturday’s onslaught. If we decide to launch the boat it will be from the Simon’s Town Jetty at 9.30 and 12.00 and the most likely sites will be Photographer’s Reef and Roman Rock.
If the conditions aren’t boat-worthy on Sunday, we’ll shore dive at Long Beach.
The great white shark is the ocean’s iconic fish, yet we know little about it—and much of what we think we know simply isn’t true. White sharks aren’t merciless hunters (if anything, attacks are cautious), they aren’t always loners, and they may be smarter than experts have thought. Even the 1916 Jersey Shore attacks famously mentioned in Jaws may have been perpetrated by a bull shark, not a great white.
We don’t know for sure how long they live, how many months they gestate, when they reach maturity. No one has seen great whites mate or give birth. We don’t really know how many there are or where, exactly, they spend most of their lives. Imagine that a land animal the size of a pickup truck hunted along the coasts of California, South Africa, and Australia. Scientists would know every detail of its mating habits, migrations, and behavior after observing it in zoos, research facilities, perhaps even circuses. But the rules are different underwater. Great whites appear and disappear at will, making it nearly impossible to follow them in deep water. They refuse to live behind glass—in captivity some have starved themselves or slammed their heads against walls.
The photographs are by Brian Skerry. It’s worth checking out. Read the article here, or pick up a copy of the magazine when you see it on the shelves.
And for the inveterate shark fans and those who want to pursue some further education, it’s not too late to sign up for the Shark MOOC on edX that started on 28 June. Click here to join in.