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Marine Resources


October 2012 Issue

DNA Method Tracks Fish, Whales With Half-Liter Seawater Samples
Researchers at the University of Copenhagen have developed a method to account for marine fish biodiversity that uses metabarcoding of environmental DNA obtained directly from seawater samples. This approach, which can detect species based on water samples of a half liter, has been used in freshwater environments but not marine settings.

Today, marine fish are often surveyed using selective and invasive methods mostly limited to commercial species and restricted to areas with favorable conditions. The method presented in the scientists' two studies, which were published in PLoS One, could be used for estimating fish stocks.

By isolating DNA from half-liter seawater samples collected in Denmark and using DNA sequencing of polymerase chain reaction amplicons, the researchers detected 15 fish species, including detected cod, herring, eel, plaice and pilchard. A variation of this method has also detected harbor porpoises.

When comparing the DNA method to existing practices traditionally used for monitoring fish, such as trawl and pots, it proved as good as or mostly better than existing approaches. The study authors noted further studies are needed to validate the DNA approach in varying environmental conditions.

Farmed Escaped Salmon Change Wild Salmon Stocks, Study Finds
Farmed escaped salmon affect both the genetic composition of wild salmon and their geographic population structure, according to a study published in August in PLoS One. However, a direct relationship has not been established between the frequency of escaped salmon in a given river and the extent of the genetic impact on that specific population, study co-author Beate Hoddevik Sunnset of the Institute of Marine Research in Norway wrote.

Each year, hundreds of thousands of salmon escape from commercial farms, but until now the extent to which the genetic composition of wild salmon is affected has not been known. Escapees enter rivers, outnumber wild fish in some years and have been documented to spawn.

The researchers conducted a spatiotemporal analysis of more than 3,000 salmon collected from 21 distinct populations in Norway between 1970 to 2010. The analysis of 22 microsatellites, individual admixture, divergence at neutral microsatellite markers and increased allelic richness revealed genetic changes in six of the populations. Results indicated a reduction in genetic differences among salmon populations.

In four of Norway's rivers (the Opo, Vosso and Lone in Hordaland, and the Western Jakobselv in Finnmark) the changes were significant. A majority of the historical population genetic structure throughout Norway appeared to have been retained, suggesting a low to modest success of farmed escapees in the wild. In areas where a robust wild population lives, it is likely that the escapees do not manage to interbreed as effectively as in rivers, where there is less competition.

One surprising result from the study was the inability to detect genetic changes in 15 of the populations surveyed. This suggests that in many places escapees have a reduced likelihood to genetically mix with the native populations, and therefore, the effects of escapement are unpredictable.

Sea Life 'Facing Major Shock,' Researchers Report
Life in the world's oceans faces far greater change and risk of large-scale extinctions than at any previous time in human history, marine scientists reported in a Trends in Ecology and Evolution paper in August.

The researchers searched historical and fossil records to establish the main causes of previous marine extinctions and the risk of their recurring today.

Three of the five largest extinctions of the past 500 million years were associated with global warming and acidification of the oceans—trends the scientists found also apply today. Other extinctions were driven by a combination of loss of oxygen from seawaters, pollution, habitat loss, and pressure from human hunting and fishing.

These factors are presently observed in the seas and oceans, in addition to added drivers of human pollution from chemicals, plastics and nutrients, the scientists said. The authors recommend curbing carbon-dioxide releases, managing the run-off that triggers ocean 'dead zones,' and better fisheries management to help prevent mass-exctintion events.

Australia Bans Super Trawlers From Fishing in its Waters
Australia's lower house in September passed legislation to prohibit the super trawler FV Abel Tasman from fishing in the country's waters for up to two years. The law, introduced by Environment Minister Tony Burke, will apply to all super trawlers and new forms of fishing.

The legislation will establish a panel to further assess the environmental impact of the Abel Tasman before permitting the vessel to fish. The panel will report directly to Burke and present its findings to the parliament.

'There has never been a fishing vessel of this capacity in Australia before and the EPBC [Environment Protection and Biodiversity Conservation] Act needs to be updated so that it can deal with it,' Burke said. He stated concerns over the potential for harmful by-catch of dolphins, seals, seabirds and threatened or protected species.

The EPBC Act had not contained provisions for preventing new fishing vessels such as the FV Abel Tasman from fishing while environmental assessments are underway.

The 142-meter super trawler, owned by Seafish Tasmania (Triabunna, Australia), was docked at Port Lincoln in South Australia. Seafish Tasmania had planned to fish in waters from Western Australia to southern Queensland, the BBC reported. It had obtained approval from the Australian Fisheries Management Authority for a quota of two types of fish.

'The science has been done,' said Gerry Geen, director of Seafish Tasmania, in an interview on Radio Australia. 'The scientists say very, very clearly that this fishery is sustainable, that the impacts on by-catch species are minimal and that we have the best world practice, world-class techniques in place to minimize by-catch.'

Environmental activist groups such as Greenpeace celebrated the ban.

'This decision will put pressure on the European Union to withdraw its subsidies from the super trawler fleet and is a step towards more sustainable fishing,' said Ben Pearson, head of Greenpeace campaigns.


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