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Eco-labelled fish may be unsustainably fished, or the wrong species

The Chilean seabass is no stranger to being mislabelled. It bears little relation to the various fish that are also known as basses, and it’s more properly referred to as the Patagonian toothfish (a name that is presumably more difficult to market). But the confusion doesn’t end there. While the toothfish is the target for illegal and unsustainable fishing operations, the Marine Stewardship Council (MSC) has certified one fishery as being sustainable. It’s found around the island of South Georgia near the tip of South America.

But some products marked as certified toothfish don’t come from this fishery. Some aren’t even toothfish at all.

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The living toothbrushes that keep coral reefs healthy

The most important fishes on a coral reef aren’t the impressive predatory ones or the flashy colourful ones – they’re just humble cleaners.

The cleaner fish Laborides dimidiatus is cross between a janitor and a medic. It runs special “cleaning stations”, which other fish and ocean animals visit for a regular scrub. The cleaners remove parasites from their clients, even swimming into the open jaws of predators like moray eels and groupers. They’re like living toothbrushes and scrubs. And they work hard – every day, a single cleaner inspects over two thousand clients, and some clients visit the stations more than a hundred times a day.

The cleaners, and their relationships with their clients, make a classic case study for biologists studying the evolution of cooperation. The tiny fish clearly get benefits in the form of a meal, and they enjoy a sort of diplomatic immunity from otherwise hungry hunters. On the face of it, the clients also benefit by getting scrubbed of harmful parasites. Now, Peter Waldie from the University of Queensland has shown how important this hygiene is.

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Satellite pictures reveal “landscape of fear” in Great Barrier Reef

From the ground, Heron Island looks like it has materialised out of a holiday brochure. It’s home to pristine beaches and lazing tourists, all surrounded by the turquoise waters of Australia’s Great Barrier Reef. But there’s an aspect to Heron Island that doesn’t fit with this idyllic vibe. It’s what Elizabeth Madin from the University of Technology, Sydney, has dubbed a “landscape of fear”. To see it, you need to take to the air.

Satellite images of Heron Island, freely available as part of Google Earth, depict the same vibrant colours. But around some of the reefs, there are distinct halos – light blue rings that encircle patches of rock and coral. These rings are caused animals such as fish and sea urchins, which munch on the algae and seaweed that cover the reef floor. These grazers hide from predators within the rocks and dart out to eat the surrounding algae, leaving behind a barren halo among an otherwise green landscape.

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Vegetarian piranhas are the Amazon’s champion gardeners

This monstrous fish is a tambaqui, a close relative of the piranha. Fortunately, it doesn’t share its cousin’s flesh-eating lifestyle. Instead, the 30-kilogram tambaqui (or pacu) is a vegetarian. It swims through the flooded forests of the Amazon, eating fruits that drop from the overhanging trees. In doing so, it acts as an vehicle for the Amazon’s seeds, carrying them to distant parts of the jungle within its gut.

This is a role that we normally associate with birds or monkeys, but Jill Anderson from Cornell University has found that the tambaqui is a champion seed carrier. It can spread seeds over several kilometres, further than almost any other fruit-eating animal on record.

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A warmer ocean is a less green one

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The Earth’s oceans are mysterious and largely unexplored. Many of their inhabitants are familiar to us but their whereabouts and numbers are far less clear. This is starting to change. In two new studies, Boris Worm from Dalhousie University has revealed an unprecedentedly detailed portrait of the planet’s marine life, from tiny plankton to mighty whales. And with that knowledge comes concern, for neither study paints an optimistic picture about the fate of tomorrow’s seas, as changing climate slowly raises their temperature.

Graduate student Daniel Boyce focused on some of oceans’ smallest but most important denizens – the phytoplankton. These tiny creatures are the basis of marine food webs, the foundations upon which these watery ecosystems are built. They produce around half of the Earth’s organic matter and much of its oxygen. And they are disappearing. With a set of data that stretches back 100 years, Boyce found that phytoplankton numbers have fallen by around 1% per year over the last century as the oceans have become warmer, and if anything, their decline is getting faster.  Our blue planet is becoming less green with every year.

Meanwhile, post-doc Derek Tittensor has taken a broader view, looking at the worldwide distributions of over 11,500 seagoing species in 13 groups, from mangroves and seagrasses, to sharks, squids, and corals. His super-census reveals three general trends – coastal species are concentrated around the western Pacific, while ocean-going ones are mostly found at temperate latitudes, in two wide bands on either side of the equator. And the only thing that affected the distribution of all of these groups was temperature.

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Bearded goby munches jellyfish, ignores toxic gases, is generally very hard

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The Benguela region, off the coast of Namibia, is a shadow of its former self. In the first half of the 20th century, it was one of the world’s most productive ocean areas and supported a thriving fishing community. Today, the plentiful stocks of sardines and anchovies, and the industries that overexploited them, are gone. The water is choked of oxygen and swarming with jellyfish. Plumes of toxic gas frequently erupt from the ocean floor. But one fish, the bearded goby, is positively thriving in this inhospitable ecosystem. It’s a critical link in a food web that’s on the verge of collapse.

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Overfishing gives toxic seaweeds an edge in their competition with corals

Coral_reefThe world’s coral reefs are disappearing. At least a third of the world’s reef-building species face extinction and in the Caribbean, the average cover of hard corals has fallen by around 80% in the last thirty years. The rich habitats they create are giving way to simpler, less vibrant communities, dominated by seaweeds. But seaweeds aren’t just opportunistic colonisers of waters abandoned by corals – they are coral-killers themselves.

Douglas Rasher and Mark Hay from the Georgia Institute of Technology have found that grazing fish typically keep seaweeds in check. If those fish start disappearing, as they often do because of human hooks, the seaweeds run rampant and corals suffer. Anywhere between 40-70% of the most common seaweed species release compounds that drive away the algae that allow corals to derive energy from the sun. Bereft of energy, the corals ‘bleach’ and die. The message is clear – through overfishing, we are accomplices in seaweed-mediated coralcide.

Seaweed” is a loose colloquial term for a wide variety of algae, which hail from a few different kingdoms of life. For a while, it’s been clear that they can compete with corals for the same patches of ocean, but the exact nature of that competition has been controversial. To settle the debate, Rasher and Hay set up field experiments in two different reefs, one in Fiji and one in Panama. In both cases, they pit the common coral Porites porites against seven common species of local seaweed. The competitors were lashed against one another using a grid and some rope and left in place for 20 days.

At such prolonged close quarters, the corals became heavily bleached compared to others that were seaweed-free. Their ability to photosynthesise was shot by anywhere from 52 to 90%. Only the parts that actually touched the seaweeds were harmed; the areas on the sides stayed healthy.

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Restoring predator numbers by culling their prey

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Helping out a threatened predator by culling their prey seems like a really stupid idea. But Scandinavian scientists have found that it might be the best strategy for helping some of our ailing fish stocks.

The brown trout increases the numbers of its prey by eating it!Lennart Persson and colleagues from Umeå University came up with this counterintuitive concept by running a 26-year natural experiment with the fish of Lake Takvatn, Norway. At the turn of the 20th century, the top predator in Lake Takvatn was the brown trout. Over-fishing sent its numbers crashing, and it was virtually gone by 1980.

In its place, a smaller fish – the Arctic char ­- was introduced in 1930. Char should make a good meal for trout, so it was surprising that when the trout were reintroduced they failed to flourish despite an abundance of food.

It was only in the 1980s, when the researchers removed over 666,000 char from the lake that the trout started bouncing back. While their prey population fell by 80%, the trout have increased in number by 30 times. The lake’s temperature and nutrient levels were mostly constant during this time, so why did the trout do better when they prey was culled?

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What makes 250,000,000 fish gather in the same place?

Blogging on Peer-Reviewed ResearchOn the 3rd of October, 2006, Nicolas Makris watched a quarter of a billion fish gather in the same place. They were Atlantic herring, one of the most abundant fishes in the ocean and one prone to gathering in massive schools. This was the first time that anyone had watched the full scope of the event, much less capture it on video.

The first signs of the amassing herring appeared around 5pm and by sunset, the gathering had begun in earnest. Once a critical level of fish was reached, the shoal expanded at a breakneck pace, suddenly growing to cover tens of kilometres within the hour. By midnight, the shoal contained about 250,000,000 individuals – 50,000 tonnes of fish gathered in one place.

The ability of fish to congregate in gigantic schools may be familiar but until now, we’ve known remarkably little about the things that set off these gatherings. Without Facebook as a coordinator, what causes small groups of herring to take sociability to an extreme? Scientists have tried to follow gathering fish aboard research vessels but these can usually only see a small fraction of the massive schools are any one time.

Makris wasn’t so hampered. He used a new technique called Ocean Acoustic Waveguide Remote Sensing (OAWRS) that can visualise fish populations over vast distances in real-time. It needs two ships, one to send out sound waves in all directions and a second to pick up their echoes as they bounce off fish and floor alike.

In an instant, it can scan an area of ocean 100km in diameter, and it can update its images every 75 seconds, providing an unprecedented view of the genesis of herring shoals. The location was Georges Bank off the coast of Maine, where herring migrate to spawn in early autumn. Makris pointed his instruments at an area where herring historically gather, and waited.

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Human-induced evolution reverses for shrunken fish once fishing stops

Blogging on Peer-Reviewed ResearchEarlier this year, I wrote about how the human obsession with size is reshaping the bodies of other species at an incredible pace. Unlike natural predators that cull the sick, weak and unfit, human fishermen prize the biggest catches and throw the smallest ones back in.

Silverside.jpgAs a result, fish and other species harvested by humans are shrinking, often within a few generations, and are becoming sexually mature at an earlier stage. These changes are bad news for populations as a whole, for smaller individuals often have lower odds of survival and produce fewer offspring.

But David Conover from Stony Brook University has found a silver lining in this tale – selectively harvesting fish can lead to dramatic changes in body size, but these changes are reversible. Release them from the pressure of constant hunting, and some of the animals start to rebound to their previous state.

Conover spent ten years raising a commonly harvested species called the Atlantic silverside in six captive populations, each containing about 100 individuals. Every year, the fish produced a new generation and for five years, Conover would remove 90% of the fish, either by taking the largest ones, the smallest ones or randomly selected individuals. In every other way, the fish were all reared under exactly the same conditions. This constant upbringing ensured that any changes to their bodies would be the result of genetic influences rather than environmental ones.

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Male and female mako sharks separated by invisible line in the sea

Blogging on Peer-Reviewed ResearchIn the middle of the Pacific Ocean, Gonzalo Mucientes has discovered an invisible line in the sea that separates male mako sharks from females. The line runs from north to south with the Pitcairn Islands to its west and Easter Island to its east. On the western side, a fisherman that snags a mako will most probably have caught a male. Travel 10 degrees of longitude east and odds are they’d catch a female. This is a shark that takes segregation of the sexes to new heights.

Mucientes and colleagues from Spain, Portugal and the UK spent four months aboard a Spanish longline fishing vessel.  Amid more typical catches, the boat often snagged shortfin makos and blue sharks. When they did, the researchers meticulously noted the boat’s position, and analysed the shark carcasses on board.

Their results showed a clear “line in the sea”. All in all, the fishermen captured 264 male makos, mostly towards the west of the line and 132 females predominantly in the east. Makos are found all over the world, but this study shows that at a more regional level, their populations are structured to an astonishing degree. 

This segregation is even more surprising when you consider that makos are the world’s fastest sharks. They can clock speeds of up to 45 miles per hour, about eight times as fast as Michael Phelps at his peak. They really shouldn’t have any problems in covering vast tracts of water.

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Human hunters unwittingly shrink their prey species at incredible rates

Blogging on Peer-Reviewed ResearchAs a species, our unflinching obsession with size is just as apparent in our dealings with other animals as it is in our personal lives. Fishermen prize the biggest catches and they’re are obliged to throw the smallest specimens back in. Hunters also value the biggest kills; they provide the most food and make the flashiest trophies. This fixation isn’t just a harmless one – by acting as a size-obsessed super-predator, humans are reshaping the bodies of the species we hunt, at a remarkable pace and to a dramatic degree.

Big_Horn_Sheep.jpgPredators already put a lot of pressure on their prey to evolve new ways of escaping untimely death. But humans are predators like no other. Not only do we target an uncommonly wide range of species, but we also tend to focus on larger and older specimens, ignoring the sick, weak and unfit individuals that fall prey to most other hunters. In doing so, we have become a leading evolutionary force, setting off some of the most abrupt physical changes ever observed in wild populations.

Chris Darimont from the University of California has exposed the scope of these changes by analysing the results of 34 earlier studies that looked at 29 different species, all harvested by humans. From mighty bighorn sheep to innocuous limpets, Darimont found that almost all of the harvested species had shrunk in some way, becoming about 20% smaller within a few generations. The vast majority also became sexually mature about 25% earlier.

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Shark-hunting harms animals at bottom of the food chain

Blogging on Peer-Reviewed ResearchOn the surface, plummeting populations of sharks do not seem like much cause for concern for humans or, for that matter, other sea life. But this simple viewpoint relies on splitting animals into two groups – predators and prey. In practice, this distinction is far too crude. Too put it bluntly, there are predators and there are predators. Those at the top kill those in the middle, and stop them in turn, from killing those at the bottom. As the old saying goes, the enemy of my enemy is my friend.

Tigershark.jpgThe rise in shark fishing is mainly driven by a growing market for their fins. Shark fins soup is a delicacy in China, which is utterly ludicrous given that the fins themselves are tasteless and merely add texture. China’s strong economy has put this expensive treat in the range of the expanding middle classes and the world’s sharks are paying the price for it.

Ransom Myers from Dalhousie University, Halifax, decided to study the effects of declining shark numbers by analysing a uniquely comprehensive shark census taken over the last 30 years on the American eastern seaboard. In these waters, several shark species have all but vanished since 1972, including 99% of the bull, dusky and smooth hammerhead populations. And because fishing expeditions tend to catch larger individuals, the average size of the survivors has plummeted. Mighty animals like the tiger and black-tip sharks are now up to half as long as they used to be.

Unsuprisingly, as the sharks declined, their prey benefited. Great sharks mainly hunt smaller predators, including their close relatives skates, rays, and indeed, smaller sharks, whose numbers surged in their absence. The cownose ray, for example, is now ten times more common than it was in the mid-70s. And here’s where the domino effects begin.

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Farmed salmon decimate wild populations by exposing them to parasites

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Blogging on Peer-Reviewed ResearchThe next time you buy salmon from your local supermarket, think about the hidden costs in each succulent fillet. Compared to wild fish, farmed salmon is far less likely to burden your wallet. But by buying it, you may be placing a much larger burden on the environment. Fish stocks around the world are declining due to over-fishing and ‘aquaculture’ – the farming of fish – was originally thought to help. But farming brings with it a host of ecological problems.

If the farmed fish are meat-eaters, as salmon are, they must be fed on the proteins and oils of wild fish, which does nothing to alleviate the stress on wild populations. Domesticated farmed fish are also genetically different to their free counterparts, and escapees risk spreading their genes and replacing local genetic diversity.

Sealice.jpgBut the biggest and most immediate problem may be to do with the spread of parasites. Large, crowded and trapped animal populations are an easy target for parasites, and salmon farms are no exception. Farmed salmon are often infested with sea lice, parasitic relatives of prawns and shrimp, that cause direct damage, starve their host and increase vulnerability to disease. But the real problem comes when infected farmed salmon pass their parasites onto wild fish.

Martin Krkošek and colleagues from the University of Alberta believe that salmon farming may be disrupting behaviour that evolved in salmon to protect their young from parasites.

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Fishing bans protect coral reefs from devastating predatory starfish

CrownofThornsStarfish.jpgBlogging on Peer-Reviewed ResearchA complete ban on fishing can save coral reef communities in more ways than one. A few weeks ago, I blogged about a study which found that the coral trout, a victim of severe overfishing, was bouncing back in the small regions of the Great Barrier Reef where fishing has been totally forbidden. It certainly makes sense that fish will rebound when fishing ceases, but a new study reveals that the bans have had more indirect benefits – they have protected the corals from a predatory starfish.

The crown-of-thorns starfish (Acanthaster planci) is a voracious hunter of corals and a massive problem for reef conservationists. It’s bad practice for any science writer to anthropomorphise an animal, but the crown-of-thorns really does look incredibly, well, evil. Its arms (and it can have as many as 20) are covered in sharp, venomous spines. As it crawls over the reef, it digests the underlying coral by extruding its stomach out through its underside.

From time to time, their numbers swell into plagues of thousands that leave behind the dead, white skeletons of corals in their wake. These outbreaks eventually die off as the starfish eat themselves out of food supplies, but not before seeding downstream reefs with their tiny larvae that drift along the southern currents. During their peak, they destroy far more coral than other disturbances such as bleaching events or hurricanes.

Now, Hugh Sweatman at the Australian Institute of Marine Science has found that these outbreaks are much less frequent in the “no-take marine reserves”, where fishing is absolutely forbidden. Every year between 1994 and 2004, Sweatman carried out a census of starfish numbers in up to 137 areas across the Great Barrier Reef’s massive length.

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