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Ecological concerns - genetic and evolutionary
We humans are seriously fucking with the planet. No, I am not talking about pollution here. Its even more serious - there are some serious evolutionary and genetic changes going on. Against the natural evolutionary system. It used to be that the bigger, stronger animals that prospered, and smaller animals were targeted. Most if not all wild species that humans are targeting for food are not only evolving - often with negative consequences - but are affecting other species too. Smaller in size, they are actually a bigger threat to their own survival as species.
http://news.yahoo.com/s/nm/20090112...nters_evolution
As humans hunt, their prey gets smaller: study
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WASHINGTON (Reuters) – Hunting and gathering has a profound impact on animals and plants, driving an evolutionary process that makes them become smaller and reproduce earlier, U.S. researchers reported on Monday.
Their study of hunting, fishing and collecting of 29 different species shows that under human pressure, creatures on average become 20 percent smaller and their reproductive age advances by 25 percent.
The human tendency to seek large "trophies" appears to drive evolution much faster than hunting by other predators, which pick off the small and the weak, the researchers report in the Proceedings of the National Academy of Sciences.
"As predators, humans are a dominant evolutionary force," said Chris Darimont of the University of California, Santa Cruz. "It's an ideal recipe for rapid trait change."
Darimont and colleagues calculated the rates of trait change with a metric called the "Darwin," after Charles Darwin, who developed the theory of natural selection to help explain evolution.
They studied changes in the size of fish, limpets, snails, bighorn sheep and caribou, as well as two plants -- the Himalayan snow lotus and American ginseng.
In virtually all cases, human-targeted species got smaller and smaller and started reproducing at younger ages -- making populations more vulnerable.
"Earlier breeders often produce far fewer offspring. If we take so much and reduce their ability to reproduce successfully, we reduce their resilience and ability to recover," Darimont said.
The findings fit in with other studies that suggest many fish are over-harvested.
"The public knows we often harvest far too many fish, but the threat goes above and beyond numbers," Darimont said in a statement. "We're changing the very essence of what remains, sometimes within the span of only two decades. We are the planet's super-predator."
Regulations meant to protect the young may in fact be helping drive this unnatural process, Darimont said.
"Hunters are instructed not to take smaller animals or those with smaller horns. This is counter to patterns of natural predation, and now we're seeing the consequences of this management," he said. |
http://news.bbc.co.uk/2/hi/science/nature/4281171.stm
Fish shrinkage threatens survival
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The shrinking size of fish due to their overexploitation has dire consequences for the recovery of depleted stocks, scientists have claimed.
Fishing drives natural selection for smaller fish that grow more slowly and have reduced reproductive potential.
These changes are genetic and therefore hard to reverse, scuttling the renewal of dwindling fish populations.
Details of the research were discussed on Saturday at a major science conference in Washington DC.
"Most fisheries are collapsing and many are on the brink of potentially irreversible loss," said Jeremy Jackson, of the Scripps Institution of Oceanography in California.
"There are massive evolutionary shifts going on in the remnant populations of fish. Large fish with huge reproductive potential are being replaced by smaller fish with diminished reproductive potential," he told the annual meeting of the American Association for the Advancement of Science (AAAS).
No reverse
David Conover, of Stony Brook University in New York found a two-fold change in productivity in Atlantic silversides within just four generations of fish.
"By selectively harvesting the largest fish, we end up changing the whole biology - not only growth rates, but egg size, fecundity, feeding behaviour," he said.
"The scary part is that when we stopped size-selective harvest, the biology didn't change back, it was permanent."
Research by Dr Conover and other groups in Norway, Canada and Austria also found declines in the reproductive potential of fish populations.
Work by Steven Berkeley, of the University of California-Santa Cruz, shows that older and therefore bigger female Pacific rockfish produce exponentially more eggs than younger, smaller females and their larvae have a greatly increased chance of survival.
Safe haven
"What we need to provide is some refuge from fishing so that the genes for larger, faster-growing fish have some sanctuary from fishing," said Dr Berkeley.
Andy Rosenberg, of the University of New Hampshire, said that the way fish resources were currently being managed was prolonging the period of recovery for stocks.
"The longer we ignore these fine-scale processes, the longer it will take for that recovery. And it's not a simple linear relationship - you can cause massive damage in a very short period of time and it can take them much longer to recover," he said.
Cod off the coast of Newfoundland - once one of the largest fish populations in the world - have suffered a 99% decline since the 1960s.
Research shows that changes in size and age at maturity caused by just 30-50 years of fishing have reduced the chance of cod's recovery by 25-30%. |
http://news.bbc.co.uk/2/hi/science/nature/4620960.stm
World's biggest fish 'shrinking'
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Whale sharks spotted off the coast of Australia are getting smaller, researchers have said.
In a decade the average size recorded by observers has shrunk from 7m to 5m.
Whale sharks, the world's largest fish, are caught for food in some east Asian countries and Australian researchers suspect this is causing a decline.
The fish is listed as "vulnerable", and one of the authors of the new study has described the new finding as "a very worrying sign".
The data comes from ecotourism companies which run expeditions to watch whale sharks and swim with them in Ningaloo Marine Park off the north-west coast.
"The eco-tourism industry logs the position and size and sex of every shark it swims with," said Mark Meekan, of the Australian Institute of Marine Science (Aims).
"We have obtained those datasets and analysed them over time," he told the BBC News website, "and essentially what we have seen in the last decade is a decline in average size of shark from 7m to 5m.
"Now, if you consider that the sharks probably aren't sexually reproductive or mature until they're 6 or 7m long - that's a very worrying sign."
Looking for options
Whale sharks (Rhincodon typus) are filter feeders, eating small marine organisms such as krill.
They can live for up to 150 years, attaining lengths of more than 15m, and are believed to reach sexual maturity around the age of 30.
Whale shark, Image: Rachel T Graham
The fish are placid filter-feeders
Under the IUCN Red List of threatened species, they are categorised as "vulnerable" to extinction.
"Whale sharks, like many other shark species, are highly vulnerable to over-exploitation due to their long lifespan and low reproductive rate," commented Callum Roberts, of York University in the UK, who has researched whale sharks extensively in the Caribbean.
"They have been added to CITES' list of species threatened by international trade," he told the BBC News website, "but this will not protect them if they are caught by, for example, Taiwanese vessels and then consumed in Taiwan.
"So whale sharks are at risk, and the decline in size might be due to capture of large sharks."
There are also indications that the number of sharks visiting Australian waters may be decreasing, which would be additional evidence for a decline prompted by over-fishing.
Playing tag
Aims researchers are running a tagging programme in an attempt to plot whale shark migration routes between Australia, Asia and the eastern coast of Africa.
Specimens tagged in Australia have swum to Asian waters; last month a tag transmitted for days from the same location in Indonesia, apparently on land, leading researchers to suspect that the shark had been caught and the tag removed.
Either the meat is eaten, or the giant fins used as advertising boards for restaurants serving shark fin soup; livers are used for oil, and cartilage in traditional Chinese medicine.
Finding migration routes could help pinpoint areas where they are being caught.
"Many of the people doing the fishing are just local villagers with no other option," said Mark Meekan.
"If we know who they are, we can give them another option, and that option is very lucrative; the ecotourism industry in Ningaloo generates AU$70m (£28m; US$50m) a year, enough to support an entire town."
Longer term objectives of the Aims programme include finding out more about the life cycle of the whale shark.
The biggest mystery concerns breeding and reproduction; males and females live in largely segregated communities, but must come together somewhere to breed.
They are believed to bear live young, but sightings of pups are extremely rare. |
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Last edited by Magnetonium on Feb-21-2009 at 05:31
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