Friday, April 22, 2011

Sharks and Oxygen - again?


Check this out, it's great.



Kudos to filmmaker Jonathan Ali Khan.
His Sharkquest Arabia is a highly important project that focuses on an important, difficult to access and thus largely overlooked region where millions of Sharks are being killed for the Asian Shark fin market. I've dived the Red Sea extensively in the late seventies and early eighties and have been fortunate to witness it in all it splendor, and have had a profusion of Shark encounters with the ubiquitous Whitetips, Grey Reefs, Silvertips and Scalloped Hammerheads all the way the more unusual Silkies and Threshers.
Especially the Sudan with iconic sites like Sanganeb and Sha'ab Rumi but also Angarosh and Dungonab Bay was once one of the global hot spots of Shark diving. Yes even then the local fishermen were already targeting Sharks, mainly further south in Yemen where we came across several boats with dead Hammerheads - but seeing the obvious dramatic depletion is never the less simply heartbreaking.
This project is really a great undertaking!

But then, I stumble onto this interview.
Among many good statements, I unfortunately find this.

With 92% of our living biosphere being aquatic, almost 80% of our planet’s air is generated by the algae and microscopic phytoplankton that are found in the sea.
Many thousands of fish species and other marine organisms feed on phytoplankton and algae. Sharks on the other hand prey on the fish that feed on plankton; right up through to the top of the food chain. So if we remove the sharks, as we are systematically doing at an unsustainable rate of over 70 million sharks a year, then it leaves the plankton feeders free of predation and free to gobble up the main source of our planet’s main oxygen supply! Therefore, it is in our interest to maintain a healthy source of oxygen and air, if we want to keep on breathing!

Some seas, such as around Japan, are already struggling with harmful algae blooms, forming red tides and anaerobic conditions that are causing explosions of super-jellyfish populations that are creating havoc with marine diversity, dominating and taking over what were once rich fishing grounds. Those same areas were once managed by a wide range of shark species that controlled the ecosystem effectively by feeding largely on the fish that preyed on the plankton feeders. Ever since those sharks were fished out from around the coast of Japan, the resulting imbalance has proven catastrophic. To a lesser degree, we have already seen similar results in the Red Sea and Arabian Gulf with red tides and toxic algae blooms.

This is just total bullshit.
There are so many wrong assertions here that I'm quite at a loss at where to begin.
Maybe re-read this as a first fact check.

Algal Blooms, harmful and not?
Apart from the fact that red tides consist of oxygen-producing phytoplanktonic algae (!), the causes for their occurrence are varied, ranging from anthropogenic water eutrophication (the likely cause in Japan) to Climate Change to totally natural occurrences like iron dust influx from large desertic areas, the likely cause in the Arabian Seas.
Nothing whatsoever to do with Sharks!

Jellyfish Explosion?
Causes? Probably primarily Climate Change and pollution, to a lesser extent overfishing of their natural predators.
Nothing to do with Shark fishing!

Trophic Cascades
?
Food webs are exceedingly complex, and pseudo-scientific intellectual shortcuts attributing causal top down-effects from the apex predators all the way down to the lowest trophic levels are inevitably destined to be fallacious, the more as in food webs as opposed to proper food chains that are rare, there's ample scope for substitution both of prey and of predators. Plus, we don't target only the predators but also their prey and we fish down the food web once we have dispatched the higher trophic levels, and are thus unwittingly assuming the regulatory role of apex predators as a consequence. Yes it's complicated!
Anyway, the principal predator of Phytoplankton is Zooplankton, an incredible array of animal organisms spanning the whole gamut of taxonomic groups, from the unicellular all the way to complex Fish larvae. But whereas Zooplankton can certainly quickly respond to increases in Phytoplankton abundance, it is equally certainly NOT the principal determining factor for that abundance! The abundance of Phytoplankton is principally correlated to physical factors like ambient nutrient concentrations, temperature and light - not predator abundance and even less so abundance of Sharks!

Yes the theory of correlations between trophic levels is sound - but much more when viewed bottom up.
Top down - not so much!

Long story short?
Like many other Shark activists, Mr. Khan is a seriously good bloke doing seriously good, important stuff. But like all of us, if he wants to be taken seriously, he's got to get his facts right and not make up things on the fly - especially when addressing himself to the media!
Simple - right?

End of rant!

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