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At least it should reduce the attacks

09 Dec 2020 | News Roundup

We noted last month CNN’s claim that global warming was making shark attacks worse in Australia even though they had not increased even slightly in half a century. But since climate change ruins everything, even a good shark attack, we now read that climate change is going to wipe out Australia’s sharks. And everything else: “Rapid climate change represents an existential threat to all life on Earth”. So presumably we won’t miss the sharks, or celebrate being able to go back in the water, because we’ll be as dead as the dodo and the Port Jackson shark. Unless somebody is exaggerating.

The authors of this piece in The Conversation, and of the study on which it is based, have some news for the settled science. Namely the same old same old that it’s not settled. “Port Jackson sharks from cooler waters in the Great Australian Bight found it harder to cope with rising temperatures than those living in the warmer water from Jervis Bay in New South Wales. This is important because it goes against the general assumption that species in warmer, tropical waters are at the greatest risk of climate change.” Ah, so we’re going to get some welcome humility about the state of our knowledge?

Alas no. We get howling at the moon instead. “In Australia, the grim reality of climate change is already upon us: we’re seeing intense marine heat waves and coral bleaching events, the disappearance of entire kelp forests, mangrove forest dieback and the continent-wide shifting of marine life. The southeast of Australia is a global change hotspot, with water temperatures rising at three to four times the global average. In addition to rising water temperatures, oceans are becoming more acidic and the amount of oxygen is declining. Any one of these factors is cause for concern, but all three may also be acting together.”

In the first place, the normal claim is that where you live is warming at twice the average. If you’re going to say southeast Australia is going at three to four times, we’d like to see the measurements and check if they’ve been cherry-picked. And since it would mean somewhere else is warming more slowly than the average, we’d like to know where.

In the second, that “may be acting together” is a bit odd. Surely you looked. And how could they not be. But perhaps it is no time to quibble as our finny friends with the big teeth vanish thanks to CO2.

The authors assure us the crisis is upon them, and us. “One may argue sharks have been around for millions of years and survived multiple climate catastrophes, including several global mass extinctions events. To that, we say life in the anthropocene is characterised by changes in temperature and levels of carbon dioxide on a scale not seen for more than three million years.”

That last part might be interesting if true. But it isn’t, on the temperature front. And anyway, as they note, sharks have been around for over 400 million years so what happened three million years ago is basically current events to them. They’ve seen it all and survived it all.

They went through the K-T mass extinction that took out an estimated three quarters of all species on Earth including the non-avian dinosaurs and indeed every four-legged land beast weighing over 25 kgs. Though to be fair that extinction seems to have been less lethal to sea-dwellers.

Sharks also, of course, went through the earlier Triassic-Jurassic extinction that, again, took down about three quarters of all species some 200 million years ago. And the Permian-Triassic disaster 50 million years before that one, in which at least 90% of species are thought to have perished. Which we think worth emphasizing because the authors’ explanation of why sharks are now about to get the chop is that “sharks can’t evolve fast enough to keep up because they tend to be long-lived with low reproductive output (they don’t have many pups). The time between generations is just too long to respond via natural selection.”

Ha ha. Dumb sharks. You thought you’d outlived the great amphibians, the dinosaurs, the Paleocene and Eocene giant mammals and most hominids because you were adaptable. (Oh, and the Late Devonian extinction that went on for about 20 million years c. 375-55 mya.) But these scientists found you out. You’re not adaptable. You’re slow and clunky.

The way they tested the adaptability of sharks to temperature change was they “collected Port Jackson sharks from cold water around Adelaide” while from the “warm water in Jervis Bay” they collected… Port Jackson sharks (which by the way have some of the weirdest-looking eggs you could ever hope to see). So it’s the same species flourishing in warmer and colder water that proves sharks can’t cope with temperature changes?

Yes. And as you can imagine, it’s all bad news. Fewer sharks means more sea urchins as all life perishes, and more sea urchins means more sore feet. No, wait, it means decimated kelp forests. Again, the authors seem not to have heard of those famous boom-and-bust cycles of prey then predators. Or the dynamic adaptability of nature.

The piece ends by saying the settled science needs a lot of work. Including “We also need a better handle on how a wide range of species will respond to a changing climate. This will help us understand how communities and ecosystems might fragment, as each ecosystem component responds to warming in different ways and at different speeds.” But notice that they have their verdict already (“how communities and ecosystems might fragment”, not “whether”) and just need a quick show trial. Of how, for instance, those famously vulnerable sharks swam blithely through the Paleocene-Eocene thermal maximum, the warm Cretaceous and the Holocene Climatic Optimum, not to mention the chilly Pleistocene, but are now going to vanish beneath the waves rather than swim somewhere nicer where other members of the same species already live.

4 comments on “At least it should reduce the attacks”

  1. Ocean acidification: It is worth noting that 500 million years ago, the atmosphere contained 15 times the concentration of CO2 as it does at present. Were the oceans a pool of acid then? No. In fact, that was the age of the biggest explosion of life the Earth has ever known: the Cambrian Explosion. Most of this explosion of life took place - you guessed it - in the oceans, and among species with shells.

  2. Mangrove die back??? My boat is moored in long and narrow estuary in Port Adelaide. Both shores are covered in mangroves . Not one has died in the past 40 years I have been boating there. They are slowly expanding into the marina waters. Top of the estuary is a power station that lets the cooling water in so the area of marina has no swimming allowed due to high temperature of water. Does not seem to bother the fish or the dolphins that hunt there every day.

  3. We should EXPECT more shark attacks in Australian waters, especially in Queensland (my home state) and New South Wales. In response to a spate of shark attacks in the 1950s, a programme of netting was introduced. Since the turn of the millenium, many environmentalists objected to the netting programme as it harmed sharks (and other species of fish, animal and mammals), so there is less netting.
    Less netting and shark capture, means more sharks able to get close to shore so more attacks should be expected; nothing to do with climate change but due to the decline of netting.

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