The days are getting longer and the daytime temperatures are slowly creeping upwards… Well, on some days. Saturday looks like a better bet for False Bay with Hout Bay being an option on Sunday. The water colour off Dungeons has improved slightly today.
Tomorrow I am shore diving students at Long Beach at 10.00 am. On Saturday we will do an early False Bay double tank dive at 7.00 am. Let me know if you’d like to get wet.
As part of First Thursdays, you can attend the opening of the Birdlife Oceans of Life photographic exhibition at the South African Museum on the evening of Thursday 6 October. There’s information here (facebook) – this year’s exhibition includes a retrospective of the last few years’ best images.
Diversnight is on Saturday 7 November, so start charging your torches!
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 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.
Outside Online describes a recent paper that proposes “acoustic sanctuaries” to protect cetacean populations of marine mammals off the coast of British Columbia in Canada. This is a fascinating idea, and need not be difficult to implement:
These quiet areas could be pain-free places for governments to formally institute quiet zones, the paper argues. Ships wouldn’t have to be rerouted, the authors note, they would simply have to continue avoiding sensitive areas.
Let’s stay with whales for a bit. I love tales of serendipity in science. My favourite Ed Yong writes for The Atlantic about a team using multiple (160, to be exact) hydrophones (underwater microphones) to listen for fish in the Gulf of Maine. They were able to visualise the locations of millions of herring; they also discovered that they could hear thousands of whale calls clustered in specific locations, mostly humpbacks, which are very vocal animals. But this was not all:
Each whale species calls within a certain frequency range and makes its own distinctive repertoire of sounds. Using this information, the team could look at their recordings and extract the locations of five huge filter-feeding species (the blue, fin, humpback, sei, and minke) and three toothed ones (sperm, pilot, and killer).
John Dabiri and his team injected dye into the water around a moon jelly as it swam. Like Gandalf’s smoke rings, the jellies created rings of water behind them, moving down their tentacles as they swam.
The team later showed that the moon jellyfish actually produces two vortex rings for every beat of its bell. While the first one travels backwards, a second one rolls back into the bell itself, speeding up as it goes, and sucking water into the center of the jellyfish. This allows the animal to recapture some of the energy it spends on each swimming “stroke,” and pick up speed even when it’s making no effort. For that reason, the moon jellyfish is the most efficient swimmer in the ocean.
Here are some holiday reading recommendations – not too taxing, not entirely insubstantial – to enjoy while lounging under an umbrella by the pool or waiting for a flight to board. You will probably enjoy them because they’re about marine life, and I assume that if you didn’t have a passing interest in the ocean, you wouldn’t be reading this blog.
Longform is a website that provides reading recommendations – usually (as the name suggests) long form stories, not restricted to a particular range of topics. I am a subscriber to the Longform newsletter, and lately a user of their iPad app.
The Longform guide to sea creatures is a short list of juicy long articles whose common thread is that they focus on marine animals. I’ve shared some of them with you already – Killer in the Pool and Moby Duck being the most notable. Others are about giant squid, octopus, tuna, whales, and the Loch Ness monster. It’s a page worth bookmarking, should you anticipate requiring a couple of hours of thoughtful, fact-checked, well researched reading on the subject of marine life.
You can find the list of Longform sea creature articles here, and a mostly overlapping but slightly different version on Slate.com, here. (The advantage of the Slate list is that you can send the articles to your Kindle, to read later.)
South African legislation has not yet addressed the conflict between customary rights to marine resources by the communities who depend(ed) on them, and environmental law that designates certain areas as reserves and forbids fishing.
In essence, it lays down a proportionality requirement, in terms of which it must be shown that the law in question (the Marine Living Resources Act) serves a constitutionally acceptable purpose and that there is sufficient proportionality between the infringement and the purpose that the law is designed to achieve.
a very clear constitutional duty on the government to ensure that natural resources such as marine resources are managed in a manner which acknowledges the economic interests in fisheries, but at the same time ensures that ecosystems and species are protected to ensure long-term viability.
Feris describes arguments for fisheries management approaches that make use of indigenous communities as custodians, assessors of the fishing stock, and managers and enforcers. The aim of such an approach would be to confer both a right (to harvest) and a duty (to protect) upon the local communities that have traditionally had access to a marine resource. Ensuring that employees at national parks and protected areas are drawn directly from the surrounding communities is one way to enact this type of philosophy.
Can I suggest Feris’s article as some Sunday afternoon reading? This is not a problem that is going to disappear in South Africa any time soon, and as a trying-to-be-compassionate human and conservation-minded ocean person it’s good to familiarise oneself with the grey areas that challenge one’s convictions.
Sustainable Seas Trust is endeavouring to strike the balance that Feris writes about in her article, and – should you be at a loss as to how to proceed – you could consider supporting them.
Here’s a quick read on shark repellents from Smithsonian.com. While it only takes a few paragraphs to explain the different attempts humans have made to avoid encountering sharks while using the ocean, the task of actually developing technology to do this is far more complex. Testing shark repellents is also ethically difficult – in the same way that it’s hard to test medications for use during pregnancy, as one could be causing harm to human subjects.
(It’s worth reading a bit about the Shark Shield device pictured above for more on testing. Testing the efficacy of stripy wetsuits, on the other hand, is almost impossible, and for this reason they can be almost impossibly lucrative – imagine a product where you don’t have to prove whether it works, and when it fails you can (a) throw up your hands and make an excuse along the lines of “it was a freak event”/”the guy must have been wearing it incorrectly” or (b) close the company and disappear.)
The “electronic fence” mentioned at the end of the article is the shark repellent cable that the KwaZulu Natal Sharks Board tested at Glencairn last summer. You can read more about that (also from Smithsonian.com) here.