Global erosion of ecosystem services

14 09 2010

A few months ago I was asked to give a lecture about erosion of ecosystem services to students in the University of Adelaide‘s Issues in Sustainable Environments unit. I gave that lecture last week and just uploaded a slidecast of the presentation (with audio) today.

I’ve reproduced the lecture here for your viewing pleasure. I hope you find the 45-minute presentation useful. Note that the first few minutes cover me referring to the Biodiversity film short that I posted not too long ago.

CJA Bradshaw





Classics: Mesopredator Release

17 03 2010

© J. Short

Although popularised by Crooks & Soulé (1999), Soulé et al. (1988) first gave us the term that described how entire ecosystems can become unbalanced by a reduction of a higher trophic-level predator exerting so-called ‘top-down’ control on the abundance of species occupying lower trophic levels.

The idea had theoretical support in ecology (Wright et al. 1994; Litvaitis & Villafuerte 1996), but it was not until Soulé and colleagues described how the decline of dominant predators combines with habitat fragmentation to release top-down pressure on smaller predators, thereby increasing predation rates on prey lower down the trophic web.

Crooks & Soulé (1999) described an example where the decline in coyotes (Canis latrans) in combination with urbanisation-driven habitat fragmentation led to an increase in cat (Felis catus) densities and the subsequent decline in scrub-breeding birds. More recent examples attest to the importance of the mesopredator release phenomenon: Myers et al. (2007) described how the decline in large coastal shark species has allowed mesopredator cownose rays (Rhinoptera bonasus) to increase, leading to a reduction in commercially important shellfish densities; and Johnson et al. (2007) showed how dingoes (Canis lupus dingo) in Australia suppress populations of exotic predators such as cats and foxes, leading to more locally abundant populations of native marsupials (see previous post).

Conservation biologists have benefited from this knowledge because we’ve realised that top-order predators affect far more than their immediate prey. These examples really hit home how a fully functional community is required for ecosystem stability, so we should strive to preserve complete complements of communities, not just our favourite species.

CJA Bradshaw

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Susceptibility of sharks, rays and chimaeras to global extinction

10 11 2009
tiger shark

© R. Harcourt

Quite some time ago my colleague and (now former) postdoctoral fellow, Iain Field, and I sat down to examine in gory detail the extent of the threat to global populations of sharks, rays and chimaeras (chondrichthyans). I don’t think we quite realised the mammoth task we had set ourselves. Several years and nearly a hundred pages later, we have finally achieved our goal.

Introducing the new paper in Advances in Marine Biology entitled Susceptibility of sharks, rays and chimaeras to global extinction by Iain Field, Mark Meekan, Rik Buckworth and Corey Bradshaw.

The paper covers the following topics:

  • Chondrichthyan Life Historyangel shark
  • Niche breadth
  • Age and growth
  • Reproduction and survival
  • Past and Present Threats
  • Fishing
  • Beach meshing
  • Habitat loss
  • Pollution and non-indigenous species
  • Chondrichthyan Extinction Risk
  • Drivers of threat risk in chondrichthyans and teleosts
  • Global distribution of threatened chondrichthyan taxa
  • Ecological, life history and human-relationship attributes
  • Threat risk analysis
  • Relative threat risk of chondrichthyans and teleosts
  • Implications of Chondrichthyan Species Loss on Ecosystem Structure, Function and Stability
  • Ecosystem roles of predators
  • Predator loss in the marine realm
  • Ecosystem roles of chondrichthyans
  • Synthesis and Knowledge Gaps
  • Role of fisheries in future chondrichthyan extinctions
  • Climate change
  • Extinction synergies
  • Research needs

common skateAs mentioned, quite a long analysis of the state of sharks worldwide. Bottom line? Well, as most of you might already know sharks aren’t doing too well worldwide, with around 52 % listed on the IUCN’s Red List of Threatened Species. This compares interestingly to bony fishes (teleosts) that, although having only 8 % of all species Red-Listed, are generally in higher-threat Red List categories. We found that body size (positively) and geographic range (negatively) correlated with threat risk in both groups, but Red-Listed bony fishes were still more likely to be categorised as threatened after controlling for these effects.

blue sharkIn some ways this sort of goes against the notion that sharks are inherently more extinction-prone than other fish – a common motherhood statement seen at the beginning of almost all papers dealing with shark threats. What it does say though is that because sharks are on average larger and less fecund than your average fish, they tend to bounce back from declines more slowly, so they are more susceptible to rapid environmental change than your average fish. Guess what? We’re changing the environment pretty rapidly.

We also determined the spatial distribution of threat, and found that Red-Listed species are clustered mainly in (1) south-eastern South America; (2) western Europe and the Mediterranean; (3) western Africa; (4) South China Sea and South East Asia and (5) south-eastern Australia.

shark market, Indonesia

© W. White

Now, what are the implications for the loss of these species? As I’ve blogged recently, the reduction in predators in general can be a bad thing for ecosystems, and sharks are probably some of the best examples of ecosystem structural engineers we know (i.e., eating herbivores; ‘controlling’ prey densities, etc.). So, we should be worried when sharks start to disappear. One thing we also discovered is that we still have a rudimentary understanding of how climate change will affect sharks, the ways in which they structure ecosystems, and how they respond to coastal development. Suffice it to say though that generally speaking, things are not rosy if you’re a shark.

We end off with a recommendation we’ve been promoting elsewhere – we should be managing populations using the minimum viable population (MVP) size concept. Making sure that there are a lot of large, well-connected populations around will be the best insurance against extinction.

CJA Bradshaw

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ResearchBlogging.orgI.C. Field, M.G. Meekan, R.C. Buckworth, & C.J.A. Bradshaw (2009). Susceptibility of Sharks, Rays and Chimaeras to Global Extinction Advances in Marine Biology, 56, 275-363 : 10.1016/S0065-2881(09)56004-X





Shark tags

19 05 2009

I have no real reason for posting this, other than I found it amusing. I do not know to whom I should attribute the cartoon, so apologies to the author. Click for a larger version if you find this too small to read.





Cartoon guide to biodiversity loss IV

15 04 2009

And the most degraded and self-flagellating humour on Earth continues (see also previous instalments here, here and here) …

cartoonenvironment_cartoon_7030

hourglass-earth

5765_shark_cartoon

CJA Bradshaw

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Protein mining the world’s oceans

31 03 2009

Last month David Agnew and colleagues published a paper in PLoS One examining the global extent of illegal, unreported and unregulated (IUU) fishing (Estimating the worldwide extent of illegal fishing), estimating its value from US$10-23.5 billion and representing between 11 and 26 million tonnes of fish annually. The value is roughly the same as that lost from illegal logging each year. Wow.

Of perhaps most interest is that Agnew and colleagues found evidence for a negative relationship between IUU fishing as a proportion of total catch and an international (World Bank) governance quality index. This suggests that improving governance and eradicating corruption may be the best way to curtail the extent of the illegal harvest.

We have just published a paper online in Fish and Fisheries about the extent and impact of IUU fishing in northern Australia. Entitled Protein mining the world’s oceans: Australasia as an example of illegal expansion-and-displacement fishing, the paper by Iain Field and colleagues advocates a multi-lateral response to a problem that has grown out of control in recent decades.

IUU fishing is devastating delicate ecosystems and fish breeding grounds in waters to Australia’s north, and can no longer be managed effectively by individual nations. The problem now requires an urgent regional solution if food security into the future is to be maintained.

The paper is the first big-picture account of the problem from Australia’s perspective. Although there had been a decline in IUU fishing in Australian waters over the past two years, possibly linked to large Australian government expenditure on enforcement and rising fuel prices, the forces driving illegal fishing have not gone away and are likely to resurface in our waters.

We expect that the small-scale illegal fishers will be back to prey on other species such as snapper, trochus and trepang as soon as it is economically viable for them to do so. To date, these IUU fishers have focused mostly on high-value sharks mainly for the fin trade, to the extent that the abundance of some shark species has dropped precipitously. IUU fishing, which has devastated fish resources and their associated ecosystems throughout Southeast Asian waters, is driven by deep economic and societal forces. For example, the Asian economic crisis in the late 1990s drove a large number of people out of cities and into illegal fishing.

It is not enough to maintain just a national response as the problem crosses national maritime zones, and it poses one of the biggest threats known to marine ecosystems throughout the region. These IUU fishers are mining protein, and there is no suggestion of sustainability or factoring in fish breeding or ecosystem protection into the equation. They just come into a fishing area and strip-mine it, leaving it bare.

Illegal fishing in Australian waters started increasing steeply about 10 years ago, largely because of over-exploitation of waters farther north, peaking in 2005-06 then falling away just as steeply. There are three factors behind the recent downturn: Australian government enforcement measures estimated to have cost at least AU$240 million since 2006; the high price of fuel for the fishing boats; and, most importantly, the fact that the high-value species may have been fished out and are now economically and ecologically extinct.

The $240 million has funded surveillance, apprehension, transportation, processing and accommodation of the several thousand illegal foreign fishermen detained each year since 2006. These activities have been successful, but it is doubtful whether they can hold back the IUU tide indefinitely – the benefits to the illegal fishers of their activities far outweigh the penalties if caught.

With increasing human populations in the region, the pressure to fish illegally is likely to increase. Regional responses are required to deter and monitor the illegal over-exploitation of fisheries resources, which is critical to secure ecosystem stability as climate change and other destructive human activities threaten food security.

CJA Bradshaw (with IC Field, MG Meekan and RC Buckworth)

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Man bites shark

7 01 2009

cut-shark-finYesterday I had a comment piece of the same title posted on the ABC‘s Unleashed site. I have permission to reproduce it here on ConservationBytes.com.

The silly season is upon us again, and I don’t mean the commercial frenzy, the bizarre fascination with a white-bearded man or a Middle-Eastern baby, the over-indulgence at the barbie or hangovers persisting several days into the New Year. I mean it’s the time of year when beach-goers, surfers, and municipal and state policy makers go a bit ga-ga over sharks.

There are few more polite pleasures than heading down to the beach during the holidays for a surf, quick dip or just a laze under the brolly. Some would argue it’s an inalienable Australian right and that anything getting in our way should be condemned to no less than severe retribution. Well, in the case of sharks, that’s exactly what’s happened.

Apart from a good number of adrenalin-addicted surfers and mad marine scientists, most people are scared shitless by the prospect of even seeing a shark near the beach, let alone being bitten or eaten by one. I won’t bore you with some ill-advised, pseudo-psycho-analytical rant about how it’s all the fault of some dodgy 1970s film featuring a hypertrophied American shark; the simple fact is that putative prey don’t relish the thought of becoming a predator’s dinner.

So, Australia is famous for its nearly 100-year-old pioneering attempt to protect marine bathers from shark attack by setting an elaborate array of shark nets around the country’s more frequented beaches. Great, you say? Well, it’s actually not that nice.

Between December 1990 and April 2005, nearly 3500 sharks and rays were caught in NSW beach nets alone, of which 72 per cent were found dead. Shark spearing was a favourite past-time in the 1960s and 1970s, with at least one high-profile species, the grey nurse shark, gaining the dubious classification of Critically Endangered as a result. Over-fishing of reef sharks has absolutely hammered two formerly common species in the Great Barrier Reef, the whitetip and grey reef sharks (See the Ongoing Collapse of Coral-Reef Shark Populations report). And illegal Indonesian fishing in northern Australia is slowly depleting many shark species in a wave of protein mining that has now penetrated the Australian Exclusive Economic Zone.

Despite the gloomy outlook for sharks, I’m happy to say today that we are a little more aware of their plight and are making baby steps toward addressing the problems. Australia has generally fared better in shark conservation than most other parts of the world, even though we still have a lot of educating to do at home. Over 50 per cent of all chondrichthyans (i.e., sharks, rays and chimaeras) are threatened worldwide, with some of the largest and most wide-ranging species being hardest hit, including white sharks. The most common threat is over-fishing, but this is largely seen by the lay person as of little import simply because of the persistent attitude that “the only good shark is a dead shark”.

The attitude is, however, based on a complete furphy. I’m sure many readers would have seen some statistics like the following before, but let’s go through the motions just to be clear. Dying from or even being injured by a shark is utterly negligible. Based on the International Shark Attack File data for Australia, there were 110 confirmed (unprovoked) shark attacks in Australian waters between 1990 and 2007, of which 19 were fatal. Using Australian Bureau of Statistics human population data over the same period, this equates to an average of 0.032 attacks and 0.006 fatalities per 100,000 people, with no apparent trend over the last two decades.

Now let’s contrast. I won’t patronise you with strange comparative statistics like the probability of being killed by a (provoked) vending machine or by being hit by a bus, they are both substantially greater, but I will relate these figures to water-based activities. Drowning statistics for Australia (1992-1997) show that there were around 1.44 deaths per 100,000 people per year, or approximately 0.95 if just marine-related drownings are considered. These values are 240 (158 for marine-only) times higher than those arising from shark attack.

It’s just plainly, and mathematically, ridiculous to be worried about being eaten by a shark when swimming in Australia, whether or not there’s a beach net in place. The effort made, money spent and anxiety arising from the illogical fear that a shark will consider your sunburnt flesh a tasty alternative to its fishier sustenance is not only regrettable, it’s an outright crime against marine biodiversity. Of course, if you see a big shark lurking around your favourite beach, I wouldn’t recommend swimming over and giving it a friendly pat on the dorsal fin, but I wouldn’t recommend screaming that the marine equivalent of the apocalypse has just arrived either.

You may not be fussed either way, but consider this – the massive reduction in sharks worldwide is having a cascading effect on many of the ocean’s complex marine ecosystems. Being largely carnivorous, sharks are the ecological equivalent of community planners. Without them, herbivorous or coral-eating fish can quickly get out of control and literally destroy the food web. A great example comes from the Gulf of Mexico where the serial depletion of 14 species of large sharks has caused an explosion of the smaller cownose ray that formerly was kept in check by its bigger and hungrier cousins. The result: commercially harvested scallops in the region have now collapsed because of the hordes of shellfish-eating rays.

The day you fail to find sharks cruising your favourite beach is the day you should really start to worry.

CJA Bradshaw

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