Article: The Atlantic on how much of the sea is fished

The proportion of the world’s oceans that are fished has recently been the subject of two papers in Science, both of which used the same data set to reach different conclusions. One study concluded that 55% of the ocean is affected by fishing, while a follow up (using the original data set, but at finer resolution) concluded that the number is closer to 4%.

A janbruin emerges from a school of fish at Atlantis
A janbruin emerges from a school of fish at Atlantis

Ed Yong of The Atlantic sets out the disagreement, and explains the subtleties and the points of view on each side of the debate. Far from being an insoluble  scientific crisis, the divergent findings show the iterative nature of the scientific process and the manner in which back and forth between scientists leads to progress. It brings to light important questions worth considering, ones that are more important than simply asking the original question of how much of the ocean is fished.

Instead, you have to ask different and more refined questions. How much of that fishing is sustainable? Which species are being targeted? How are they faring? Can they bounce back?

Read the full article here.

Article: Quartz on octopus cities

I’ve just finished reading another book about octopus (yet to be shared here), and the author talks at length about an octopus “city” off the coast of Australia, discovered in 2009 and dubbed Octopolis. Another, similar location, named Octlantis, has since been found, and scientists have recently published their research on these unusual places. Octopus are not social creatures – at least, they were not thought to be until these two locations, where up to 16 octopus live in close quarters and exhibit complex social behaviours, were discovered.

Octopus at Long Beach
Octopus in his hole at Long Beach. The reddish brown is an angry colour.

Team leader, marine biologist Professor David Scheel, believes that…

… octopus behavior probably hasn’t changed in [the last decade]. Rather, humans’ ability to observe the behavior has. Today more divers are in the water with cameras and better technology to quickly communicate findings amongst divers and scientists.

Once again, the potential for citizen scientists to make discoveries of this nature is highlighted.

Read about the discoveries here. This article, from Citylab, has a map of the most recently discovered octopus aggregation site.

Shrimp news from False Bay

The University of Cape Town has announced that a further three new species of shrimp, all spotted close to shore near Millers Point in False Bay, have been described and named. All three belong to the same genus (Heteromysis), and look similar, with pale bodies marked by red spots and stripes. One of these new (to science) species lives inside octopus dens, and another lives inside the shell of certain types of hermit crab. These three shrimps join the stargazer shrimp that was discovered by and named for Guido Zsilavecz, citizen scientist and author of several books on False Bay’s marine wildlife.

Two of the new species were discovered by local film maker Craig Foster, founder of the Sea-Change project about which we read last week. These types of discoveries are very exciting and should be a great inspiration and encouragement to divers and other water users. Time in the water is rewarded. If you can’t identify something, send an email with its photo to SURG. It is possible to make significant contributions to science while holding down an entirely non-scientific day job!

Read all about the new shrimps here.

Article: Exploring False Bay’s kelp forests

Kelp forest in Sandy Cove
Kelp forest in Sandy Cove

Environmental journalist Pippa Ehrlich writes beautifully for Safarious of diving in the kelp forests of False Bay with Sea-Change founder Craig Foster. You might be familiar with Sea-Change from an exhibition at the Sea Point promenade a couple of years ago.

The idea of getting into this freezing world every day without a wetsuit was daunting. We did some stretching and breathing to warm up. The sky was grey and my feet had gone numb in the shallow water we’d had to walk through. I was not looking forward to being fully submersed in it.

Ehrlich and Foster (and others from the Sea-Change team) dive daily in False Bay, sans wetsuits. It is their mental (spiritual?) approach to the marine environment, however, that sets the project apart. It’s a mindset that may be unfamiliar to many divers, especially those of us who favour scuba, but it is worthy of serious consideration. The article reads like a story of love and healing.

The accompanying photos are beautiful, too. Read it.

Article: Outside on shark repellents

A recurring but seemingly never-resolved question that intrigues shark researchers and management entities is that of whether there exists a reliable, non-lethal shark repellent.

Such a shark repellent would solve all manner of management problems: organisations like Shark Spotters exist partly to navigate that tense, thin line between sharks killing people and people killing sharks.

Furthermore, there would be a significant financial payoff associated with a successful patent of such a product. (I do not mean to suggest that this is the primary motivation for doing this kind of research, but untested, untestable products like this cannot possibly be marketed with anything else in mind.)

Life-size model of a white shark
Life-size model of a white shark

There are several ideas that have been either proposed, tested, or marketed. The SharkShield has been tested (not just by us), with mixed results. A shark repellent wetsuit has certainly been well publicised (there’s even a TED Talk), but, like medicines for pregnant women, I can’t see how it can be properly, ethically tested in order to state with some degree of certainty, in a statistical sense, that it works. The test described here has N=2, and there wasn’t a human in the suit.

I digress. Outside Online has an interesting article this month about the efforts by Eric Stroud, a pharmaceutical consultant, who – after much experimentation – settled on several compounds found in decaying shark flesh, which seem to work well as a repellent of about 30 species of mostly coastal sharks. The compound can also be synthesised, although the real thing, from a dead shark, apparently works better. Stroud’s financial backers travelled to Mossel Bay to visit Oceans Research, a multi-disciplinary research organisation with several shark scientists on its staff, to test the chemical on great white sharks. The article provides an overview of the history of shark repellent technology, and brings us up to date with this new chemical alternative. It’s early days…

Read the full article here. And remember, kids, that while the only thing that will keep you completely safe from a shark is not going into the sea at all, there are a bunch of simple, sensible things you can do to reduce your chances of meeting a man in a grey suit. Do them!

Article: The Atlantic on booming cephalopod populations

Let’s not quit our contemplation of the remarkable octopus just yet. For The Atlantic, the wonderful Ed Yong reports on a long-term (since the 1960s) trend of increasing cephalopod populations in the world’s oceans. Cephalopods are octopus, squid, and cuttlefish. The first paragraph of Yong’s article describes cuttlefish in Australian waters that are “the size and weight of a corgi”. I’m hooked (and slightly alarmed).

Octopus at Long Beach
Octopus at Long Beach

Scientists have found that, while there are short-term fluctuations, the overall trend in all kinds of cephalopod populations is up. The populations for which data was collected – largely from fisheries – live in all parts of the ocean, in both hemispheres, suggesting that a global phenomenon is affecting their breeding and survival success rates. Climate change and our overfishing of the ocean’s other inhabitants, as Yong points out, are obvious potential candidates here.

This issue is particularly relevant given the presence of an octopus fishery in False Bay, but unfortunately no one knows how successful that fishery has been (and I don’t buy anecdotal evidence on this – give me data).

Read the full article here.

Newsletter: Warmer and warmer

Hi divers

Weekend dive plans

Friday: Shore diving at Long Beach at 10.00 am

Saturday: Launching from False Bay Yacht Club at 7.00 am for a double tank dive

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.

 

DAFF octopus fishing gear
DAFF octopus fishing gear

Here’s a little bit of reading on the octopus fishery in False Bay (courtesy of Yvette!). This NSRI blog post, and the comments, are also required reading.

Coming up

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!

regards

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

Diving is addictive!

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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.

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.

Article: National Geographic on great white sharks

The July 2016 issue of National Geographic contains an article entitled “Why Great White Sharks are Still a Mystery to Us“, and luckily for those of us who don’t have approximately $100 to drop on a magazine (I exaggerate, and it’s probably worth it), it’s available online as well. It’s an excellent explanation for why and how technology is being used to study these remarkable creatures.

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.