Bravo Mahmood!

Mahmood is Prof. Dr. Mahmood Shivji of the Guy Harvey Research Institute and the Save our Seas Shark Center, both at Nova.

He's the guy who gets all of our DNA samples and you may have heard of him in relation to his recent discovery of a forensic tool (the actual paper is here) to pinpoint the geographical origin of the fins of endangered Scalloped Hammerheads from the Hong Kong Shark fin market.
This is how Reuters covered it.



Now Mahmood has posted this brilliant video about what happens in the lab once they have taken a small sample of the fins. Shame that there's no embedding feature.

Anyway, a big Kudos for the discovery and congrats for having produced a compelling piece about GSI and the need for Shark Conservation.
Bravo!

Christmas!

OK OK, here's something real cute!

Click on the reindeers - Enjoy!

MerryHappy!

This year's Xmas message comes from Yao Ming.
Kudos!

Sota Tale Lill!

Very sad!

Lill has just left for her native Norway after one year of diving with us.
Talk about culture-, and above all, climate shock!

It has been a real pleasure, and a privilege hosting her as she is a really nice person and a brilliant underwater photographer on top of that. As anticipated, it will be very hard to ever match her stunning Shark portfolio, the more as she earned herself the right to establish a quasi-permanent residence in the much coveted pit - actually much to the chagrin of your truly who found himself relegated to much less advantageous locations!
But as they say, pretty girls' privileges!

Take good care of yourself and come back soon - you're part of the team now!

Shark Con Review

Andy Murch has reviewed the stupidity here.

As a friend writes
Sounds like a waste of a good opportunity. If all it's going to do is get people to argue over the numbers, that's just annoying.
Indeed - so let's just forget about the whole fiasco!

And if you still think that this or that number is really important, you may want to read this about the demise of big Sharks off the coast of Africa - posted by a game fisherman!

Poor Shark-feeding Operations

People send me the coolest stuff.

Like this op ed (click to read) by David Diley from the British Dive magazine.
It really is an excellent overview and I could not agree more with its conclusions, tho knowing the diverse array of industry actors out there, I very much doubt that the suggested single, global, governing body will eventuate anytime soon - let alone, that anybody would then accept to defer to its rulings! But the concept per se is of course spot on and many of the opinions expressed in that piece dovetail perfectly with what this blog has been advocating all along.
Bravo David!

Talking of which, I finally came across Phil Lobel's Diver Eco-Tourism and the Behavior of Reef Sharks and Rays which you can download right here. Phil dove with us one year ago and I was pleased to read this.

The unifying scientific question in terms of understanding how dive operations may or may not be impacting sharks and rays and the associated diver safety issues is whether the individual sharks and rays are local residents and thus able to learn and habituate to divers. Alternatively, if these sharks and rays rarely reside for long-term in the same areas, then they are much less likely to become accustomed to a site-specific feeding dive.
I base this on my own experiences, especially with the grey reef shark Carcharhinus amblyrhynchos. I have observed that sharks unfamiliar with divers are more aggressive and less predictable than those that have habituated to the presence of divers, such as we now see in numerous marine protected areas such as Blue Corner, Palau, and Shark Reef Marine Reserve, Fiji.

Precisely!

Good to see that at least in some, more enlightened places, the conversation is progressing away from the old, tired and stupid stereotypes!

Great White off Florida!

Got this message from Gary in Florida.

Just got this in....4 days old..... Awesome to see a Great White off Florida.
This is when they are migrating south into the Gulf of Mexico so the time frame fits for a white being in our waters now. They begin returning back north and come by again around May. They are either mating or pupping in the Gulf...and very deep.......1000ft......but I don't think anyone knows for certain yet.

I thought you might be interested in this message posted on the Fl Sportsman message board-

Last week my best friend was coming back in form offshore when they saw a bunch of birds. Curious to see what they were after, they stopped and looked like to be a huge black drum. They videod the rest of a great white having a little snack about 6 to 7 miles outside of the mayport jetties.

Was it really "at least 18 feet" as suggested by the original YouTube clip? Hmmmmm...

Anyway, it's a cool document - Enjoy!






PS: story here.

Actions speak louder than Words

Fisher and the hook - and still proud of it!

The San Diego Reader has just published this story.

It's a great and well researched piece about the Shark fishing tagging disaster in the Farallones and the outrage it sparked among scientists, divers and the public alike. Kudos to all of them for having spoken up and said it as it is.

Alas, the perpetrators remain completely unfazed.

Not that I would have expected anything else from Fisher.
As amply documented by his public boasting, all he really cared about was to hook and subdue (if that doesn't say it all) a couple of giant Sharks - and the scientific research was just a pretext to do so within two marine sanctuaries, and to subsequently sell the show to Nat Geo. Very savvy indeed, and pretty cynic on top of that - but again, hardly surprising considering his track record.

What however baffles and quite frankly saddens me is that Domeier just doesn't seem to get it.
What is being criticized is the brutal handling of the Sharks, not the fact that this or that tag was deployed. In fact, everybody seems to agree that SPOT tags are the current cat's meow and that the long-term observational data collected would provide valuable and unique information about the GWs life history - but apart from Fisher's obvious requirements: was hooking and subduing really the only possible procedure?

Really?
I may be repeating myself, but just imagine the outcry if anybody dared to state that the level of temporary stress we subject these animals to is unfortunate, but the scientific advancements are well worth the effort, and then proceeded to go and hook and subdue, say, an Orca! And then released it with a huge hook embedded in its throat!

Are we really to believe that Domeier could not have adapted the proven non-invasive techniques for capturing and handling large Cetaceans? That he could not have tagged the Shark by keeping it in a cradle next to a skiff, like everybody else seems to do? That he could not have built some tool like the grabber this guy has invented, or used nets instead of rod and reel? Or re-designed the anchors so that the tags could have been deployed by using pole spears? Or developed some other non-invasive technique?

Did he even try?
Thing is, he just doesn't seem to give a rat's ass about the animals, does he.

Eagerly awaiting news of the Shark you tortured and injured!

We're OK!

Mick has come and gone.

It arrived several hours early (and this in Fiji!) and crossed right overhead, an interesting, albeit scary experience. People have been killed and damages are extensive and still being assessed.

We were very lucky and are back to operating normally.
Thank you to all of you who have written and asked how we're doing.

Florida - excellent News!

Hopefully, soon, no more of this in Florida!

Bravo!

The good people from the Florida Fish and Wildlife Conservation Commission FCW have approved wide-ranging measures aimed at protecting the state's stressed Shark populations, among which a total ban on harvesting Silkies and Sandbars (and Atlantic Sharpnose Sharks which however don't occur in Florida waters).

And the commission has also approved (I hear, unanimously!) draft legislation to fully protect Florida's Lemon Sharks!
Great news and huge Kudos to the impressive coalition of activists, NGOs and scientists that have tirelessly worked towards achieving this goal. I read that a final public hearing on the proposed lemon shark rule will be held during the February FWC meeting in Apalachicola - so there, just one more push and it should hopefully be a done deal!

More info here.

DaWolf!

This is about as brilliant as it gets! Pic by Wolfgang Leander (click to enjoy).

We've met - finally!

And no, don't worry, I'm not about to venture writing a laudatio, well deserved as it may be, after just one short lunch.
The more as all you need to do, is to google "Wolfgang Leander" to discover who he is and what he does - along with the biggest endorsement of them all, a dishonorable mention by the anonymous scumbags over at CDNN!

Thing is, we've had our initial run-ins.

But what became immediately apparent was that the man, on top of being a true gentleman, was passionate, highly intelligent and willing to engage in constructive dialogue instead of resorting to the usual petty bickering which is so typical for our sharkophilic circles. Being short tempered and petty myself, I could not but admire and above all, respect his restraint and eventually, his positions - and I have no doubt that this is also the principal reason why he is so universally revered among Shark lovers, to the point where everything he does and says is inevitably being defined as iconic.
Not bad for a self-professed nutter!

For my part, I just sensed that we were kindred spirits and was eagerly awaiting the chance to meet face-to-face in order to die Paar kleineren Missverstaendnisse auszuraeumen, which is German for kiss and make up, or the like.
And I'm happy to report that we have made up and that ever since, we've been kissing like crazy!

But as I said, this is not a laudatio.
This is personal, and all I wanted to say that I'm deeply impressed by the person I'm starting to discover, and that I like him very much. Yes he may indeed be iconic - but above all, to me, he is a true Mensch - culture, passion, quirks and all.

The lone Wolf travels farther, faster.
In diesem Sinne mein Lieber - Machetjut!

The Numbers - revisited

Ever heard of the Monty Hall problem?

Me neither, until the silly con-troversy about the correct Shark numbers exploded in the blogosphere.
I stumbled across this prime example of counter-intuitive numbers crunching (try it, you'll be surprised!) after researching the Bayesian Inference, a method of data analysis that is based on Baye's Theorem and promises to deliver better results than its more conventional counterpart. Having once studied the latter, I can now attest to the fact that they will both trigger equally severe migraines.

The reason for my digression into the arcane realm of advanced statistics is that I've finally managed to read the relevant paper dealing with those controversial numbers, and that the researchers pride themselves in having applied Bayesian statistical methods when analyzing their data.
Its title is Global estimates of shark catches using trade records from commercial markets and you can download it right here.

In a nutshell, it comes to the conclusion that based on the Shark fin market, as of 2000, the global annual number of Sharks killed was between 26 and 73 million, with a median value of 38 million (you can find this at the bottom of page 1119).

That's certainly useful information as it attributes an order of magnitude, tens of millions, to that specific problem.

What I found more interesting are the numbers on page 1121 that attribute orders of magnitude, and consequently, relative values, to the trade in fins of the 11 identifiable species, i.e. Blue, Silky, Oceanic Whitetip, Sandbar, Shortfin Mako, Great Hammerhead, Bull, Dusky and Tiger , plus unspecified Hammerheads and the Threshers - which if you run the numbers, incidentally means that approx. half of the inspected fins were of unknown origin.

Still, and I'm repeating myself, the whole thing is nothing more than an erudite crapshoot.
You may want to scroll to page 1117 and the chapter Extrapolation to global trade volumes where an attempt is made to estimate the global trade figures based on the hard data available, i.e. the number of fins traded in Hong Kong. You will undoubtedly notice that there's a formula which is undoubtedly theoretically impeccable and, one would think, should thus yield impeccable results.

But only in theory.
The practical problem is of course that every single one of its variables is based on assumptions.
Plausible as those may be, that sure is a lot of cumulative speculation and the end result is accordingly rather fuzzy, a fact that the researchers themselves are more than willing to concede.

Also, please keep in mind that the paper only investigates the number of Sharks killed and then traded for fins.Granted, those may indeed be the majority (or maybe not if one considers the waste of discarded bycatch) and thus a strong indication for the scope of all global catches and granted, the latter numbers would be obviously higher - but claiming anything beyond that would just be utter speculation and of little help to the cause of Shark conservation where we need to advance credible, fact-based and verifiable arguments.

I've said it before, the numbers per se are rather irrelevant.
To be of any use, they must be put into context, by comparing them to what is known about the status of individual species in individual habitats - as in page 1122 where the researchers have applied their findings to the situation of the Blue Sharks, the species which is yielding the largest amount of fins.
These are their conclusions.

Acknowledging the margins of error, and the likely downward bias of trade-based estimates, our evaluation,using a Pacific numbers-based reference, suggests that blue sharks globally are being harvested at levels close to or possibly exceeding MSY (Maximum Sustainable Yield).
In contrast, our comparison with an Atlantic, biomass-based MSY reference point suggests catch levels may be less problematic.

But then, this.

Given that we have no population estimate, we are not able to evaluate the actual sustainability of our estimated catch levels. The MSY reference point is the highest possible catch that could theoretically be sustainable, and thus any catch that approaches or exceeds this level is of concern.

And this.

As a result of the global nature of our assessment we cannot evaluate the exploitation status of individual populations.
Furthermore, the blue shark is one of the most prolific and resilient of shark species (Smith et al. 1998; Corte´s 2002) and thus our blue shark results cannot be used to make inferences about other shark species. Conclusions regarding the sustainable or unsustainable use of other species, and thus the shark fin trade as a whole, will require more detailed species-based stock assessment reference points.
However, given the lower productivity of the other species common in the fin trade (Smith et al. 1998; Corte´s 2002), the large difference between trade-derived estimates of exploitation and the catch estimates reported to the FAO adds to growing concerns about the overexploitation of sharks.

Alas, we don't seem to have those data.
Plus, and that's one of the recurring threads of this blog, time is running out and we must stop procrastinating.
Collecting and analyzing the required data is difficult and tedious, sometimes impossible, and whilst this happens, the stocks may well decline below their Minimum Viable Population size and be irrevocably doomed for extinction.

Until we know more about the parameters that determine the MSY, and thus, the extent at which each species can be harvested sustainably given its current numbers, its life history and the attributes of its individual habitat, it is imperative that we apply the precautionary principle and pre-emptively halt, or at least severely curtail any further harvesting whenever, and as soon (!) as we perceive that the animals are being overexploited.
On a happy note, that's what I understand just happened in Florida, which is great!

With that in mind, the current debate may be intellectually stimulating - but other than generating a lot of incestuous and superfluous sound bites about the pathetically trivial imperative that we need to get the facts right before opening our mouth, it is of little practical use.

May I thus humbly suggest that we, yours truly included, stop vociferating and revert back to the mission at hand, to try and protect the animals we all profess to love.

Scanning the Horizon

Caribbean Lionfish Hunter (yup this is a link)

A large group of smart people have gotten together this September and defined some nascent conservation issues for 2010, both threats and opportunities.

The resulting paper is called A Horizon Scan of Global Conservation Issues for 2010 and you can download it here, and yes, as you should, you would have to pay for that. Or, you may want to consult the useful synopses posted on Conservation Bytes and Planet Earth Online.

It spans a list of 15 topics, some of which surprising like International Farmland Acquisitions by foreign governments, some somewhat obscure and eclectic like the effects of Nanosilver in Wastewater, some visionary as in Synthetic Meat or releasing Aerosols into the Stratosphere to combat Global Warming to outright scary as in Artificial Life.
In very general terms, they all illustrate the complexity of our environment and the vast, and often totally unexpected ramifications of our actions upon it.

As in the case of the Lionfish invasion of the Western Atlantic.
Likely the progeny of aquarium pets that escaped or were discarded in Florida during the early nineties, they have completely overrun the Caribbean and are inexorably threatening South America.

You can check out the progression here.

This what the paper says (links are mine).

Invasive Indo-Pacific Lionfish.
Small numbers of predatory Indo-Pacific lionfish (mainly Pterois volitans) were first recorded in waters along the eastern coast of the United States in 1992 .
The source of introduction is uncertain. The rate of lionfish range expansion was initially slow, but increased markedly after the colonisation of Bahamian coral reefs in 2004.
Lionfish are now established throughout most of the northern Caribbean and have been recorded as far north as Rhode Island and south to Colombia. Where they are established, lionfish are found at densities far exceeding those reported for their native range (e.g. > 390 lionfish/ha in the Bahamas compared to about 80/ha in the Red Sea).
Lionfish grow to a maximum length of about 45 cm, and prey on a wide variety of fish and invertebrates. On experimental reefs in the Bahamas, young lionfish reduced the recruitment of native coral reef fish by nearly 80%; the effects of lionfish on natural reefs are still unmeasured.
Lionfish are protected by venomous spines, and while small lionfish can be eaten by large groupers, such predators are rare throughout the Caribbean.
Lionfish are, however, now being fished and offered on the menu of some Bahamian restaurants.

The pests obviously have no "natural" predators in the Caribbean and the local predators that could fulfill the role of regulating their population, like the larger Groupers and the Sharks, are severely depleted. I fear that despite of the valiant efforts of those who promote fishing and eating them (nice collection of recipes here), they are there for good, like, say, the cane toad in Oz (and alas, in Fiji as well).
Maybe, eventually, the Lionfish populations will somewhat balance out, the more as there is evidence that all individuals are the descendants of very few females and that, at least in theory, after experiencing such a severe population bottleneck, they would eventually have to crash back to their effective population size, like the Cheetahs. Maybe, some local predators, parasites or pathogens will learn to exploit the new resource and thus keep the numbers in check.
But it sure is a very very long bet and not likely to happen anytime soon, at least not soon enough to be of real practical use.

Thing is that ever since we've "evolved" to become a global nuisance, these migrations and infestations have become so frequent to constitute the norm rather than the exception.
Just think about our animal baggage, be it domesticates, many of which have gone lethally feral, stupidly introduced species like Fiji's ubiquitous and invasive Minah and Mongoose, or unwanted followers like the Norvegian Rat or the Bedbug. Or the plants, be it agricultural or ornamental, like the Traveller's Palm I'm looking at whilst writing this is Fiji - originally, endemic to Madagascar!

And recently and as always, mostly unwittingly, we've started meddling on a truly epic scale.
By building canals we've created highways for marine invasions between the Med and the Red Sea and between the Pacific and the Caribbean. By heating up the planet, tropical pests like disease-bearing Mosquitoes, Rodents and Fire Ants and pathogens are ever expanding (and check out this example of how anthropogenic marine invasions are affecting Great Britain) and according to the above mentioned paper, there's a risk that as the Arctic melts, it will lose its function as a barrier between the Atlantic and Pacific Oceans, with unknown consequences for those two ecosystems - as in: adios Deadliest Catch!

Anyway, I'm ranting as usual.
All I wanted to say is that it sure is complicated and always interconnected - and that we should never forget that Marine, and Shark Conservation are but one facet of a much bigger and alas, equally bleak picture.

OK, back to the Sharks.

Crunchtime!

Walt Stearns is a good guy (and brilliant photographer) and Doc is obviously a Shark God.

Both have put their weight behind trying to save the endangered Florida Lemon Sharks and for once, it looks like their lobbying and that of the good people over at the Shark Safe Network, and of many many others, are really having a positive effect.
So far so good.

But now, it's crunch time.
The Sun Sentinel has published this excellent overview of the current situation and if you're intrigued by the Lemon Shark aggregations it mentions, you can watch a short video of this amazing phenomenon right here, along with explanations by the Lemon Shark God himself here.

It is unique and also, highly vulnerable and needs to be preserved, as these may well be the breeding stocks of the entire Atlantic coast. They have also become a valuable resource for tourism, meaning that the Sharks are so much more valuable alive (as in 150,000 bucks per Shark over its lifetime) than dead.
Whichever way you choose to slice it, it is really imperative to see this through - and we are so close!

This is what's at stake.

The wildlife commission will decide whether to approve a draft ban (please read it, it amply explains why this needs to happen) on lemon shark catches at its Dec. 10 meeting in Clewiston.
The commission's ban would apply only to state waters, which extend three miles off the east coast and nine miles off the west coast. But the federal government, which regulates fishing up to 200 miles off the coast — except where that zone would run into the Bahamas — may follow Florida's lead if the state requests it. Karyl Brewster-Geisz, fishery management specialist for the National Marine Fisheries Service, said states normally request comparable regulations in federal waters for consistency.

Being my usual pessimistic self, I fully expect the fishermen to make a last stand in an effort to ditch, or delay the legislation. The way I see it, this is not a done deal quite yet.
For them, it's obviously about their livelihood and their families and for some, it's probably also about their penis size, at least for sociopaths like that sharkman, or whatever, I've just blogged about (and yes I'm being polite!).
In brief, expect backlash.

Please please please take the time to attend that hearing and to lobby for the conservation of Lemon Sharks in Florida.
This is not about being anti-fishing, it is about being pro-Shark and everybody is invited to remain polite (yes, like me!) and fact based. The Shark Safe Network has done and continues to do an excellent job in coordinating the effort and you should contact them and refer to their judgment when it comes to formulating common arguments and pursuing a common strategy.

Also, if you haven't already done so, sign the petition as the decision makers do certainly care about the public's opinion.

Thank you.

Shark Con???

Is this even for real???

Tragically, I fear it is.
It features this asshole and it also features stupid sound bites by Mr. No-PhD, the inevitable token expert, and then the heroic feats of "somebody" who believes that it's cool, no: EPIC!, to feed Sharks whilst wearing a baseball cap put on in reverse. Gee, talk about an EPIC! lineup! Oh and did I mention that the footage is from Tiger Beach?
Galatians 6 : 7-9 indeed!

It's all so bad I that I'm really at a loss here.
Anyway, have a look at this shit.

Hat tip: Wolfgang (but I frankly dunno if I should thank you for this buddy).

PS good reaction by the smart people over at Underwater Thrills here.

Shark Divers and RTSea Productions - spawning excellent pro-Shark media

Fantastic pic by Chip Scarlett

This is what Sharks need.

Shark Divers and RTSea Productions have helped the good people of Wildcoast/Costasalvaje produce a brilliant piece about Isla Guadalupe, one, if not the world's most iconic Great White dive site. This is but the latest in a long lineup of pro-Shark media spawned by this successful cooperative venture.

I've found (yes I speak Spanish) the mini-series highly informative and entertaining whilst clearly promoting a pro-Shark, pro-Industry, pro-research and conservation oriented message - as it should be.
Big Kudos and Thank You to everybody involved - and may many more such excellent productions follow!

Original stories here and here.
Enjoy!

Shifting Baselines

Do you know what this is?

If so, you must be older - like, for example, yours truly.
When I was a kid, I would visit my granddad in Northern Germany and we would rig up a disgusting slimy knot of earth worms and go catch European Eels, one of Europe's most fascinating, albeit equally wriggly and slimy Fishes. This used to be one of the region's most abundant Fishes and staple diets, either fresh as grüner Aal or as Räucheraal, the smoked version that would end up in dishes like the iconic Hamburger Aalsuppe.

I've called the Eel fascinating because of its life history.
All of Europe's Eels are born thousands of miles away in the Sargassum Sea, from where they gradually migrate to the European rivers (and by crawling on land, to remote lakes and ponds, too!), only to return back to the Sea as "yellow", and then "silver" Eels in order to mate and then perish, truly a titanic endeavor. This makes them diadromous catadromous, as opposed to Salmon which are anadromous and our Bull Sharks which are amphidromous (but are they philopatric? Or may they even display natal philopatry? Now that sure would be questions worth exploring! Juerg?).
Yes it sounds complicated but it's actually easy - and fascinating!

Thing is, whilst I was busy doing things with Sharks, the Eels have all but vanished (also read this) and are now classified as Critically Endangered. Shocking!
And they're not alone: according to a new study, 95% (yes, again one of those numbers...) of many of the North Atlantic's migratory Fishes have been wiped out. And yes, the culprits once again would be us:

Limburg and Dr. John Waldman, of Queens College of the City University of New York, report that a complex combination of habitat loss (caused largely by the construction of dams that prevent fish access to traditional spawning areas), urban sprawl, overfishing, pollution and climate change have led to the precipitous decline. Compounding the problem, they say, is the evolving knowledge of the humans who make decisions about how natural resources are managed.

"We're looking at shifting baselines here," Limburg said. "Every human generation gains knowledge about the world and establishes a baseline for what's normal. But there is no institutional memory about how things used to be."

No shifting baseline here.
I remember - and lemme tell you, this really sucks big time!

Please, read this, watch this and explore the website!

What everybody needs to know

I stand corrected.

I was intuitively of the opinion that oceanic Sharks are most likely doomed for extinction, a hypothesis that reverberates in some of my posts like this one.
I was obviously influenced by the fact that I live in the South Pacific where fishing for coastal Sharks, compared to the killing of Sharks by the Tuna fleets, appears to be a relatively minor threat. But CJA Bradshaw is of course right when he says that globally, the threats to coastal species are higher as they don't only have to contend with fishing pressure, but with habitat degradation and climate change on top of that, likely most of it anthropogenic (the latter being a comment by me, not him).

The relevant paper he has co-authored is called Susceptibility of Sharks, Rays and Chimaeras to Global Extinction and I invite anybody who wants to talk about Shark conservation with any degree of authority to download it here. Yes you will have to pay for it - but it's a must-read and must-have and the authors need to be compensated for their hard work.

Please, take the time to read it in its entirety.
But for those in a hurry, here's a synopsis on Bradshaw's own excellent conservation blog. The authors have also published the following FOC abstract (highlights in italic are mine).

Abstract Marine biodiversity worldwide is under increasing threat, primarily as a result of over-harvesting, pollution and climate change.
Chondrichthyan fishes (sharks, rays and chimaeras) have a perceived higher intrinsic risk of extinction compared to other fish. Direct fishing mortality has driven many declines, even though some smaller fisheries persist without associated declines. Mixed-species fisheries are of particular concern, as is illegal, unreported and unregulated (IUU) fishing. The lack of specific management and reporting mechanisms for the latter means that many chondrichthyans might already be susceptible to extinction from stochastic processes entirely unrelated to fishing pressure itself.

Chondrichthyans might also suffer relatively more than other marine taxa from the effects of fishing and habitat loss and degradation given coastal habitat use for specific life stages.
The effects of invasive species and pollution are as yet too poorly understood to predict their long-term role in affecting chondrichthyan population sizes. The spatial distribution of threatened chondrichthyan species under World Conservation Union (IUCN) Red List criteria are clustered mainly in (1) south-eastern South America; (2) western Europe and the Mediterranean; (3) western Africa; (4) South China Sea and Southeast Asia and (5) south-eastern Australia. To determine which ecological and life history traits predispose chondrichthyans to being IUCN Red-Listed, and to examine the role of particular human activities in exacerbating threat risk, we correlated extant marine species' Red List categorisation with available ecological (habitat type, temperature preference), life history (body length, range size) and human-relationship (whether commercially or game-fished, considered dangerous to humans) variables. Threat risk correlations were constructed using generalised linear mixed-effect models to account for phylogenetic relatedness. We also contrasted results for chondrichthyans to marine teleosts to test explicitly whether the former group is intrinsically more susceptible to extinction than fishes in general. Around 52% of chondrichthyans have been Red-Listed compared to only 8% of all marine teleosts; however, listed teleosts were in general placed more frequently into the higher-risk categories relative to chondrichthyans. IUCN threat risk in both taxa was positively correlated with body size and negatively correlated albeit weakly, with geographic range size. Even after accounting for the positive influence of size, Red-Listed teleosts were still more likely than chondrichthyans to be classified as threatened.

We suggest that while sharks might not have necessarily experienced the same magnitude of deterministic decline as Red-Listed teleosts, their larger size and lower fecundity (not included in the analysis) predispose chondrichthyans to a higher risk of extinction overall.

Removal of these large predators can elicit trophic cascades and destabilise the relative abundance of smaller species.
Predator depletions can lead to permanent shifts in marine communities and alternate equilibrium states. Climate change might influence the phenology and physiology of some species, with the most probable response being changes in the timing of migrations and shifts in distribution.

The synergistic effects among harvesting, habitat changes and climate-induced forcings are greatest for coastal chondrichthyans with specific habitat requirements and these are currently the most likely candidates for extinction.
Management of shark populations must take into account the rate at which drivers of decline affect specific species. Only through the detailed collection of data describing demographic rates, habitat affinities, trophic linkages and geographic ranges, and how environmental stressors modify these, can extinction risk be more precisely estimated and reduced. The estimation of minimum viable population sizes, below which rapid extinction is more likely due to stochastic processes, is an important component of this endeavour and should accompany many of the current approaches used in shark management worldwide.

I find this paper so important that I've taken the liberty of posting its conclusions below.
They tie in beautifully with some of this blog's principal threads, among which the requirement to push for sustainable fisheries. What I however miss is the call for applying the precautionary principle (much called for and rarely heeded, especially in Fisheries management) until the necessary data have been collected and evaluated - but then again, this is a paper dealing with facts and not a conservation manifesto.

Required reading and kudos to the authors for having written an excellent, informative, exhaustive and in so may ways, seminal paper for Shark conservation!

7. Concluding Remarks

We are still in the fortunate situation that there are no recorded cases of chondrichthyan extinction in modern times.
However, we have identified that the largest, most range-restricted and heavily harvested species might be easily pushed below their MVP sizes, which could be much larger than those estimated under stable environmental conditions. Fishing, at all scales, represents one of the largest mortality sources for many chondrichthyan species, but there are some examples of small local fisheries that have operated without clear declines in population size of targeted species. However, mixed-species fisheries that harvest poorly measured, but presumably large quantities of chondrichthyans are of particular concern, as is IUU fishing.

The lack of specific management and reporting mechanisms for the latter types means that many species might already be reduced to densities where extinction risk is unacceptably high.
It is almost universally recognised now that so-called ‘sustainable’ fisheries will have to be the norm if they are to survive economically, and that they will have to demonstrate negligible or minimal impacts to ecosystems through careful management and stewardship (Hilborn, 2007). IUU fishing can affect shark populations and community structure, and this might be a far greater challenge to control. Recreational fishing and beach meshing can also contribute to local declines. Climate change and habitat degradation will further erode certain populations to the point where extinction risk rises appreciably.

The idea that chondrichthyans have life history characteristics that might predispose them to extinction in a rapidly changing world (e.g. relatively low reproductive potential, growth and capacity for population recovery; Pratt and Casey, 1990) is generally upheld by our results. Furthermore, because chondrichthyans tend to occupy the highest trophic levels, it is arguable that degradation of marine communities might limit the prey quality and quantity available to chondrichthyan predators, further exacerbating population reductions. We found no strong evidence, from admittedly simple models with few parameters, that chondrichthyans are intrinsically more susceptible to extinction than other marine fishes in relation to their evolved niches and life history characteristics. However, chondrichthyans tend to be larger than many other marine fish taxa, and large body size generally correlates with slower growth and lower reproductive capacity. As such, it is the rapid pace of environmental change and harvesting that have the greatest potential to impede certain species from maintaining large population sizes. Any species can withstand moderate to even extreme exploitation if it does not outpace intrinsic replacement rates and adaptation potential (Brook et al., 2008).

We were unable to examine all plausible correlates of threat risk due to data paucity.
Many studies have examined age at maturity and growth rates in terms of vulnerability to extinction, with late-maturing and slow-growing species apparently at greater risk (Reynolds et al., 2005). Therefore, a better compilation of data incorporating these and other possible correlates could reveal further subtleties in the drivers of threat risk in this taxon and other marine fishes. Another caveat is that predictors of threat risk indicate a species’ sensitivity to the largely systematic (deterministic) drivers of population decline (declining population paradigm) (Cardillo, 2003; Sodhi et al., 2008a), whereas actual extinction appears to correlate poorly with ecological and life history traits given that the final coup de grâce tends to result from largely stochastic processes that act independently of a species’ evolutionary history (Brook et al., 2006, 2008; Sodhi et al., 2008b; Traill et al., 2007)

There are many examples of how large predators influence communities and ecosystems via top-down (and in some cases, bottom-up) control of species occupying lower trophic levels.
Thus, the removal of large predators can elicit trophic cascades and destabilise the relative abundance of smaller prey and non-prey species. However, these effects are still poorly understood, especially for large, complex trophic webs where interactions are largely unquantified. Specifically, chondrichthyans can alter prey diversity and size distributions, and their mere presence can affect the foraging behaviour of prey that alters ecosystem functions such as nutrient recycling and structural habitat complexity.

Severe predator depletions can lead to permanent shifts in marine communities and alternate equilibria.
Management of shark populations must therefore take into account the rate at which drivers of decline affect specific species. Only through detailed collection of data describing demographic rates, habitat affinities, trophic linkages and geographic ranges, and how environmental stressors modify these, can extinction risk be estimated and reduced. The estimation of MVP sizes is an essential component of this endeavour and should, in our view, eventually accompany the current approaches used to manage sharks worldwide.