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Humanity driving 'unprecedented' marine extinction

Species such as bluefin tuna are being pushed to the brink due to humans’ tendency to fish for larger species more often than smaller ones. Photograph: REX/Shutterstock

Report comparing past mass extinction events warns that hunting and killing of ocean’s largest species will disrupt ecosystems for millions of years

Humanity is driving an unprecedented extinction of sealife unlike any in the fossil record, hunting and killing larger species in a way that will disrupt ocean ecosystems for millions of years, scientists have found.
A new analysis of the five mass extinction events millions of years ago discovered there was either no pattern to which marine species were lost, or smaller species were the ones that disappeared.
But today’s sixth extinction is unique in the way that the largest species, such as great white sharks, blue whales and southern bluefin tuna, are being pushed to the brink, due to humans’ tendency to fish for larger species more often than smaller ones.
The consequences, according to a study published in the journal Science on Wednesday, are devastating for the ecology of the world’s oceans.
“If this pattern goes unchecked, the future oceans would lack many of the largest species in today’s oceans,” said Jonathan Payne, associate professor and chair of geological sciences at Stanford University. “Many large species play critical roles in ecosystems and so their extinctions could lead to ecological cascades that would influence the structure and function of future ecosystems beyond the simple fact of losing those species.”
The danger is disproportionate to the percentage of threatened species, with the authors warning the loss of giants would “disrupt ecosystems for millions of years even at levels of taxonomic loss far below those of previous mass extinctions”.
The loss of larger species in the oceans could have knock-on effects on ecosystems, Payne said, citing the loss of very large predatory seasnails (Triton) from coral reefs, which appears to be one of the reasons behind the explosive growth in numbers of crown of thorns starfish, which eat coral.
Humans would be affected by such trends too, he said, as communities rely on coral reefs to attract tourism. He also pointed to the examples of tuna and cod, whose extinction would deprive people of an important source of income and protein.
To see how the current loss of species compared to previous extinctions, Payne and his team analysed a database of 2,497 groups of marine vertebrate and mollusc over the past 500 years, and compared it to the ancient past.
They found no precedent in the fossil record for today’s trend towards killing off larger-bodied species, with previous mass extinctions marked by either no association with body size or an association with smaller species.
“The link that we found between body size and extinction threat in the modern oceans is quite strong,” Payne told the Guardian.
Co-author Noel Heim, also at Stanford, said: “We see this over and over again. Humans enter into a new ecosystem, and the largest animals are killed off first. Marine systems have been spared up to now, because until relatively recently, humans were restricted to coastal areas and didn’t have the technology to fish in the deep ocean on an industrial scale.”
Fellow author Douglas McCauley said large body size was often linked with the need for larger ocean spaces to range in, so an increasing trend for governments to create very large marine protected areas could hold some hope for species.
“Historically marine protected areas have been small boutique affairs - more like the size of golf courses. In the past five years, however, the world has begun aggressively setting up very large marine protected areas.
“Recently Obama created the world’s largest protected area in Papahānaumokuākea, a protected area just over a million square kilometres in size. This is really good news as parks of this size will indeed provide meaningful protection for large vulnerable animals we highlight as being at risk.”

Humanity driving 'unprecedented' marine extinction Adam Vaughan 14 September 2016

Atlantic bluefin tuna are corralled by fishing nets during the opening of the season in 2011 for tuna fishing off the coast of Barbate, Cadiz province, southern Spain. (AP Photo/Emilio Morenatti)

We mostly can’t see it around us, and too few of us seem to care — but nonetheless, scientists are increasingly convinced that the world is barreling towards what has been called a sixth mass extinction” event. Simply put, species are going extinct at a rate that far exceeds what you would expect to see naturally, as a result of a major perturbation to the system.
In this case, the perturbation is us — rather than, say, an asteroid. As such, you might expect to see some patterns to extinctions that reflect our particular way of causing ecological destruction. And indeed, a new study published Wednesday in Science magazine confirms this. For the world’s oceans, it finds, threats of extinction aren’t apportioned equally among all species — rather, the larger ones, in terms of body size and mass, are uniquely imperiled right now.
From sharks to whales, giant clams, sea turtles, and tuna, the disproportionate threat to larger marine organisms reflects the “unique human propensity to cull the largest members of a population,” the authors write.
“What to us was surprising was that we did not see a similar kind of pattern in any of the previous mass extinction events that we studied,” said geoscientist Jonathan Payne of Stanford University, the study’s lead author. “So that indicated that there really is no good ecological analogue…this pattern has not happened before in the half billion years of the animal fossil record.”
The researchers conducted the work through a statistical analysis of 2,497 different marine animal groups at one taxonomic level higher than the level of species — called “genera.” And they found that increases in an organism’s body size were strongly linked to an increased risk of extinction in the present period — but that this was not the case in the Earth’s distant past.
Indeed, during the past 66 million years, there was actually a small link between smaller body sizes and going extinct, marking the present as a strong reversal. “The extreme bias against large-bodied animals distinguishes the modern diversity crisis from all potential deep-time analogs,” the researchers write.
The study also notes that on land, we’ve already seen the same pattern — and in fact, we saw it first. “Human hunting has been extensive for many thousands of years on land, whereas it’s been extensive for a couple of hundred years in the oceans,” says Payne.
Thus, humans already drove to extinction many land-based large animal species in what has been dubbed the Late Quaternary extinction event as the most recent ice age came to a close.
“These losses in the ocean are paralleling what humans did to land animals some 50,000 to 10,000 years ago, when we wiped out around half of the big-bodied mammal species on Earth, like mammoths, mastodons, saber-tooth cats and the like,” said Anthony Barnosky, executive director of Stanford Jasper Ridge Biological Preserve, who was not involved in the study but reviewed it for the Post. “As a result, terrestrial ecosystems were locked into a new trajectory that included local biodiversity loss over and above the loss of the large animals themselves, and changes in which kinds of plants dominated.”
Barnosky was the co-author of a study published last year that found an “exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way.”
A particular problem, says Payne, is that if you take out all the top predators, then the species they used to prey upon can run amok and explode in population, having large reverberating effects on the entire ecosystem.
“The preferential removal of the largest animals from the modern oceans, unprecedented in the history of animal life, may disrupt ecosystems for millions of years even at levels of taxonomic loss far below those of previous mass extinctions,” the authors write.
Interestingly, if climate change was the key driver of species losses, you’d expect to see a more evenly distributed set of risks to organisms.
“I’ve worked on the Permian mass extinction quite a bit, it shows environmental evidence of ocean warming, ocean acidification, and deoxygenation, the loss of oxygen from seawater,” says Payne. These are the very same threats to the oceans that we’re worried about now due to ongoing climate change. But the Permian extinction, some 250 million years ago, did not feature a selective disappearance of large-bodied organisms, Payne says.
Thus, as previous work has also suggested, the current study underscores that ecosystem risks are not being principally driven by a changing climate — yet. Rather, they’re being driven more directly by which species humans hunt and fish, and where they destroy ecosystems to build homes, farms, cities, and much more. But as climate change worsens, it will compound what’s already happening.
“The losses the authors describe in the oceans do not include the extinctions expected from business-as-usual climate change,” said Barnosky. “Adding those human-triggered losses onto those we’re already causing from over-fishing, pollution, and so on is very likely to put the human race in the same class as an asteroid strike–like the one that killed the dinosaurs–as an extinction driver.”
The study emerges even as the U.S. State Department prepares to open its third annual Our Ocean conference, where heads of state and ocean advocates convene to try to protect more and more of the oceans’ area from over-fishing and other forms of despoilment (and climate change). The study should only heighten the focus at that event.
But Payne says that, in a way, the research is heartening for those who care about ocean conservation – precisely because human-driven large animal extinctions in the sea are not as advanced as they are on land, there is still a huge amount of biological life that we can save.
“I talked to a couple of people who said they found this a very discouraging result,” Payne says. “I tend not to look at it that way. I think there are a lot of reasons to be optimistic about the oceans, because we haven’t impacted them much yet.”

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