Best of our wild blogs: 29 May

Singapore’s Sea Cucumbers: A Dichotomous Key
from Urban Forest

The Singapore Trilobite Larva
from Macro Photography in Singapore

Do you know your Singapore?
from Nature rambles

Final day of the Festival!
from Festival of Biodiversity 2012

Exciting happenings at the Festival of Biodiversity 2012
from Peiyan.Photography

Mega Marine Survey at the Festival of Biodiversity (26-27 May)
from Mega Marine Survey of Singapore

The Crabs at the Festival of Biodiversity (26-27 May)
from Adventures with the Naked Hermit Crabs

TeamSeagrass at the Festival of Biodiversity (26-27 May 2012)
from teamseagrass

2012 Guide to Singapore Government Funding and Incentives for the Environment from Green Business Times

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Bidadari works begin by year end

First launch of build-to-order flats at new town may take place by 2015
Esther Teo Straits Times 29 May 12;

WORK on the latest new town, Bidadari, will start by the end of the year, paving the way for 12,000 new homes to be built in central Singapore.

The site is slated for both private as well as Housing Board (HDB) homes.

Depending on demand, the first HDB build-to-order launch may take place as early as 2015, a National Development Ministry (MND) spokesman said.

This could mean HDB flats completed by 2018 or so, consultants said.

The move to develop Bidadari is part of a twin-pronged strategy to meet ongoing strong housing demand. The other is to use land in existing estates more intensively, the MND spokesman said yesterday in response to queries.

Bidadari, near Potong Pasir, is a former cemetery whose graves were exhumed in 2001 to make way for housing.

It is currently a park, slightly smaller than Punggol estate.

Consultants say interest in homes at Bidadari is likely to be strong as it is relatively close to the city centre. They say Bidadari could be the next Bishan, also a former cemetery, yet one of the choicest HDB estates now.

Bidadari is served by two MRT stations: Woodleigh on the North-east line and Bartley on the Circle line.

In response to queries, the MND spokesman told The Straits Times that infrastructure work there will start by the year end. Site preparation and earthworks for Bidadari will be followed by the building of major roads, drains and sewers.

Mr Tan Kok Keong, OrangeTee's research and consultancy head, brushed aside worries over superstition, given the site's history. The Government's development plans are typically driven by housing demand alone, he said.

'There is no real stigma for fully exhumed sites anyway... But since Bidadari is quite a large site, it will take some time to be fully built,' he added.

Another new town further along the pipeline is Tengah, near Choa Chu Kang and Bukit Batok, which will yield about 56,000 homes over the next decade or so.

There are more than 900,000 HDB flats in Singapore currently.

'We will build infrastructure ahead of demand and start to prepare for new towns at Bidadari and Tengah,' the MND spokesman said in response to queries.

'How fast they are built up depends on the overall demand for housing in Singapore, but we are planning ahead for flexibility.'

Tengah is a large forested area about the size of Choa Chu Kang. Basic infrastructure and land preparation works will take longer.

Another new town down the track is Simpang, though details are not available yet as it will be developed much later, MND said.

Simpang town will be on the coast, bounded by the Strait of Johor to the north, Sembawang town to the west, Yishun town to the south and the mouth of the former Sungei Seletar to the east.

MND said that it is working out the detailed planning for Tengah and Simpang and will make specific announcements when ready.

The ministry also pointed to the need to use existing land in mature estates more intensively.

'Specifically for residential needs, while we can expect to open up relatively undeveloped areas such as Tengah and Bidadari, we will also need to intensify the use of existing land within more mature housing estates.'

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Trees used as gauge for climate shift

Volunteers put plastic bands around 500 trunks to measure their growth
Siau Ming En Straits Times 29 May 12;

EVERY Saturday for the past 18 months, a team of 10 volunteers and researchers has been trekking through the Bukit Kalang forest, armed with plastic strips, springs and crimping tools.

The volunteers - staff from HSBC Bank and researchers from the Smithsonian Tropical Research Institute's Centre for Tropical Forest Science (CTFS) - then proceed to wrap trees with the plastic bands.

Last weekend, they marked a milestone by banding their 500th tree.

This tree-banding exercise is a joint effort by the CTFS and HSBC. The objective: To study tree growth in response to climate changes.

'It turns out that measuring tree growth enables us to also calculate carbon uptake because roughly one-half of the mass of a tree is made up of carbon,' explained Dr Shawn Lum, 49, principal investigator of the research team, who is also a lecturer at the National Institute of Education, a partner of the CTFS.

Dr Lum is also president of the Nature Society Singapore.

The volunteers have been working on a 2ha site - the size of two football fields - and can band 15 to 25 trees in a span of four hours each time.

The plastic strips that go around the girth of the trees come with inserted springs to take in the trees' expansion, which indicates carbon uptake over a six-month period.

Typically, the trees are measured at the 1.3m height, but volunteers have to ensure the point of measurement is not at a malformed or bumpy part of the trunk. Because trees absorb carbon dioxide as they grow, they are able to offset the population's carbon footprint - the amount of carbon dioxide emitted from people's urban lifestyles.

Dr Lum said a longer-term use of these tree-banding results is that it can 'help us determine which species and type of trees can help us efficiently offset our carbon footprint'.

This is not the first time a tree-banding survey has been conducted here.

In 2008, a similar project of 1,000 trees was carried out at the Bukit Timah Nature Reserve.

The team studied Bukit Kalang this time because it needed to compare the carbon uptake by the coastal hill land in Bukit Timah with the low-lying land in Bukit Kalang.

While the Bukit Kalang project is still in its early stages, preliminary findings are similar to those from the Bukit Timah study.

That study had shown that primary forests can store more carbon than secondary forests.

Trees in primary forests are bigger and taller, have a lower propensity to regenerate, and take a longer time to grow.

Tree-banding has been carried out by researchers in some 20 countries under the respective CTFS internationally, said Dr Lum.

There are plans to extend the project to a new area - either to another patch of forest or to study the existing site in greater detail.

'Or we can do both, which is what we currently aim to do,' added Dr Lum.

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Malaysia: 46 pangolins rescued from car boot

The Star 29 May 12;

ALOR SETAR: An attempt to smuggle 46 pangolins out of the country by hiding them inside a car boot was foiled by the Kedah Department of Wildlife and National Parks (Perhilitan).

The pangolins worth RM43,000 were found in a car in Simpang Empat, Changlun, said its director Rahim Ahmad.

Authorities released the animals in a protected area in Kedah.

“A Kedah Perhilitan team, assisted by our counterparts from Penang, trailed the car for about 30km from the North-South Expressway Hutan Kampung toll plaza until Simpang Empat,” Rahim said.

“We stopped the car but the driver escaped,” he said yesterday.

Saved from the cooking pot
New Straits Times 29 May 12;

ALOR STAR: Forty-six pangolins, worth RM43,000, were saved from the cooking pot yesterday.

The animals, which were bound for exotic food restaurants in a neighbouring country, were found in the boot of a Toyota Camry at a traffic light in Changlun near here at 8.30am.

Kedah and Penang Wildlife and National Parks Department (Perhilitan) officers had trailed the car for about 30km from the Hutan Kampung Toll Plaza near here.

The car driver pushed the officers away and fled the scene on foot when the Perhilitan team approached his vehicle.

State Perhilitan director Rahim Ahmad said four of the pangolins were juveniles.

Rahim said he believed that the pangolins were to be supplied to Thailand.

"Prior to the discovery, we conducted an investigation to locate the poacher following a tip-off from the public."

Rahim said the department had lodged a report to seek the police's help in locating the suspect.

Pangolins are much sought after as exotic meat and it is believed the consignment was being smuggled to Thailand.

Rahim said the pangolins would be released in the forest reserves of Pedu, Padang Terap and Ulu Muda.

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Malaysia: Saving Sungai Klang

Tan Cheng Li The Star 29 May 12;

Long treated like a sewer rather than a river, can Sungai Klang be revived?

BY NOW, many people would have noticed that something is up in several rivers within the Klang Valley. In Ulu Klang, shady trees that line Sungai Klang have been sacrificed for slope protection works. Where Sungai Kerayong flows through Cheras, a water treatment plant is under construction. In Selayang, the banks of Sungai Gombak have been beautified.

We are cleaning up Sungai Klang – again. These works are all part of the mega River of Life (ROL) project to mop up Sungai Klang in its upper reaches and where it passes through Kuala Lumpur. Once the river runs clear, beautification schemes and commercial development will come up along 10.7km of the river in the city centre, in areas like Titiwangsa, Masjid Jamek and the Putra World Trade Centre.

It is a bid to emulate successful riverfront developments seen in cities the world over. However, one question persists in the minds of many: Will the river rehabilitation work this time?

The past 30 years have seen billions of ringgit spent on numerous projects to revive Sungai Klang.

Yet, the river remains as murky as ever. Needless to say, scepticism is rife that the latest project will be like its predecessors – so-called clean-ups which focused on river beautification rather than the crucial task of improving water quality.

Department of Drainage and Irrigation (DID) director Datuk Lim Chow Hock, however, brushes aside such doubts, asserting that things are being done differently this time around.

“In the past, most of the attempts to clean up the Klang River systems have been in an ad hoc manner by different agencies and municipalities. There was a lack of high-level (ministerial level) co-ordination and no regular follow-up monitoring. Previous projects were not on such a big scale. We’re looking at a wider area now, and not just one stream,” says the head of the river basin and coastal zone management division.

The ROL project area covers Sungai Klang from its upstream until its confluence with Sungai Kerayong, as well as its tributaries, the Gombak, Batu, Bunus, Jinjang and Kerayong rivers – altogether totalling 110km. The clean-up effort will target pollution sources in Kuala Lumpur and the municipalities of Selayang and Ampang Jaya.

Early, proper planning also sets the latest river clean-up endeavour apart from past schemes, adds Lim. “We identified what the pollutants are and where they’re from, and zero down to the agencies responsible. That’s how we came out with the 12 initiatives to clean up the rivers.”

The main culprits which are fouling Sungai Klang are: effluent from sewerage treatment plants (80%); commercial and residential centres (9%); industries and workshops (5%); food industries, restaurants and wet markets (4.2%); and squatters and others (1.8%).

The clean-up initiatives aim to tackle the problem at the source – that is, curb pollution from entering the river in the first place.

So, the plan is to: better-treat sewage; handle wastewater from wet markets; install gross pollutant traps in main drains; treat the water in flood retention ponds before releasing downstream; build facilities to filter and treat river water; trap greasy waste in food courts; reduce pollution from squatters; prevent industrial discharges; upgrade drainage and stormwater systems; check erosion from urban development; improve rubbish disposal; and study on other pollutants.

The Government has allocated RM3bil for the task of raising the river water quality from the current Class III and Class IV (not suitable for body contact) to Class IIb (suitable for body contact and recreational usage) by 2020. The project kicked off a year ago and different parcels are in various stages of completion.

“When completed, the bulk of the contaminants in Sungai Klang will be captured. The river will be transformed into a vibrant and liveable waterfront with high economic value,” says Lim.

He says some 77,000 tonnes of rubbish end up in Sungai Klang annually and currently, only a third of that is trapped. Under the ROL project, more trash rakes, trash screens and floating booms are being placed along rivers and in flood detention ponds. Also, gross pollutant traps (GPT) will be installed in major drains to prevent trash, silt and grease from ending up in rivers.

While only a few drains had GPTs in previous clean-ups, the ROL project will have some 300 units. Lim, however, hopes to see less of such devices in future. “They will not be necessary if people stop littering. We would have failed if we need to add GPTs.”

To improve the city’s drainage and stormwater management system, river banks are being shored up to prevent erosion, which clouds up waterways. To maintain a natural riverine habitat, DID is moving away from concrete linings of river banks. At Kampung Sungai Mulia in Gombak, stacks of Green Terramesh (which are made from coconut husk fibres sandwiched between layers of wire mesh) protect the banks of Sungai Gombak.

“These slow down the water flow and allow natural filtration,” explains Anita Ainan, chief assistant director at DID Kuala Lumpur.

Along Sungai Kerayong, the “soft rock” is used. These are heavy-duty geo-textile bags filled with sand to a weight of two tonnes each. Arranged in stacks along the riverside, they protect the waterway and offer a substrate for vegetation to take root. Anita says the choice of river bank protection technique depends on the flow velocity and availability of riverside land.

“We are going towards more eco-friendly methods but for areas with space constrain, we still have to use concrete walls,” says Anita.

Filtering the dirt

As raw or partially treated sewage is a major culprit, the ROL project emphasises the upgrading of sewage treatment plants (see story on P4). It will also see an approach to river clean-up that is new to Malaysia – treatment of raw river water. Fourteen river water treatment plants will be built to cleanse the Gombak, Batu, Klang and Kerayong rivers.

One RM10mil plant is under construction for Sungai Kerayong in Taman Yu Lik, Cheras Baru.

Nazri Yasmin, chief assistant director at DID Kuala Lumpur, says river water will be diverted to the plant and run through filters consisting of various microbe-enriched media, to remove pollutants.

The cleansed water is then released back into the river. The type of filtration system will depend on how badly polluted the river is. DID is also planning such water treatment facilities for the Puah and Benteng flood detention ponds.

Most of the foul waste of wet markets end up in streams. The newer ones of Kuala Lumpur’s 28 wet markets are connected to public sewers but not the older ones. Under the ROL project, Kuala Lumpur City Hall (DBKL) will build wastewater treatment plants at markets in Selayang, Old Klang Road, Air Panas, Sentul and Pudu.

Hew See Seng, senior deputy director (drainage) at DBKL, says there are no sewer lines near enough to the five markets. Furthermore, Indah Water Konsortium prefers not to have raw effluent flowing into public sewers as this will burden sewage treatment plants.

“Laying long sewer lines and upgrading treatment plants might end up being more costly and time-consuming (than building the treatment plants),” says Hew.

DBKL deputy director-general (project implementation and maintenance) Mohd Najib Mohd says construction will start within the next two months for the plants in the Selayang and Old Klang Road markets, with completion due for early next year. He says due to space constrains, DBKL has chosen a membrane bio-reactor which is a compact treatment system. The plant in Selayang market along Jalan Ipoh, for instance, will sit on a 100sqm space. The Korean technology is being provided by Buditranz Consult.

Hew says designing the plant for the Pudu market, however, will be challenging as the over 1,000 stalls there are spread all over, and there is hardly any space for a treatment plant.

DBKL has received RM3.5mil this year alone for the plants but with one costing between RM2mil and RM4mil, Najib fears that funds might run short.

Not widespread enough

The ROL project might have zeroed in on many pollution sources but many others have been omitted. Communal oil and grease traps have been installed in 26 food courts in Kuala Lumpur and 20 each in Ampang Jaya and Selayang but there are thousands of other restaurants and hawker centres that still discharge waste straight into drains.

Off the Middle Ring Road II in Ulu Klang, scores of polluting businesses such as car workshops line the banks of Sungai Klang. These premises have drains that discharge directly into the river. By right, these businesses have no place sitting on the river reserve – but do the Ampang Jaya Municipal Council or Selangor Government have plans to relocate them?

Likewise, riverine squatter settlements often foul up streams with trash and raw sewage but the ROL project only has plans for stormwater treatment plants at Taman Melawati and Kampung Fajar in Ulu Klang. Lim says this is an interim measure to handle the pollution as relocation of squatters will be a long-term effort.

Each time it rains, Sungai Klang turns the colour of teh tarik because of land-clearing for residential development in the upstream areas such as Taman Melawati, Kemensah and Ukay Perdana. The siltation not only starves the river of oxygen but makes the river shallow, raising the possibility of flooding. The ROL project will only upgrade two sediment ponds, in Taman Bukit Mulia, Bukit Antarabangsa and Bukit Botak, Selayang – which does little to stop eroded soil from fouling up Sungai Klang,

There are concerns that the ROL project focuses too strongly on hard engineering measures – such as treatment plants for river water and wet markets effluent and GPTs – which are costly and work only with proper operation and maintenance. And treating river water is an “end-of-pipeline” solution. It does nothing to prevent pollution. Also, GPTs need regular removal of the trapped trash and silt if they are to perform their role. Same goes for oil and grease traps.

Lim asserts that the structural measures are necessary, but have to be completed by non-structural measures such as beefing up enforcement and raising public awareness.

“We can’t be cleaning the river and on the other hand, people continue throwing rubbish into the river.” To prevent river siltation, he says municipal councils will have to enforce earthworks bylaws requiring development sites to have sediment ponds.

To ensure smooth implementation, he says the ROL projects are being closely monitored by three committees right from the planning stage to the implementation, operation and maintenance stages, according to Key Performance Indexes.

But one contentious point remains: the ROL’s scope of only the upper catchment tributaries and the stretch of Sungai Klang which flows through Kuala Lumpur, which is where the lucrative riverfront development will be sited. So beyond the city centre, Sungai Klang will again be fouled by nasty discharges as it passes through other highly developed areas of Selangor.

Lim says clean-up of the rest of the Klang river basin will be in future phases but there have been no official announcements on this. Without similar efforts, Sungai Klang will never be truly clean. So now, we are cleaning up the river – only to mess it up again downstream.

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Indonesia: Dugongs in Balikpapan gulf face extinction

Nurni Sulaiman, The Jakarta Post 28 May 12;

The endangered dugong (Dugong dugon), or seacow, which is found in the Balikpapan gulf, East Kalimantan, Indonesia, is at risk of extinction as its numbers have continued to decrease due to industrial expansion, a researcher says.

Stanislav Lhota, a researcher from the Czech Republic, said “Massive industrial expansion, which includes waste and land expansions, has caused sedimentation in Balikpapan gulf waters. Heavy metals and other pollutants, such as those from vessels’ lubricants, also threaten seagrass — the seacows’ food,” Lhota said recently.

Lhota cited noise pollution from vessels traveling in and out of the harbor as another factor worsening the dugongs’ habitat.

“[The busy traffic] is scaring the dugongs and forcing them to go far away,” he said.

The downstream area of Balikpapan gulf has witnessed rapid industrial expansion; the Balikpapan administration plans to broaden the expansion to the upstream area also.

“If this happens, sea grass along the Balikpapan coastline will disappear due to sedimentation and chemical pollution from industrial activities,” he said, adding that if the local administration turns the west side of the city into an industrial area, “Balikpapan will no longer have a healthy coast”.

In the long run, the planned expansion will also affect the habitats of coral, green turtles and irrawaddy dolphins, he added.

Dugong, one of the rarest animals in Indonesia, can be found from Madagascar and East Africa to India and Australia.

An estimated 1,000 to 10,000 dugongs survive in Indonesian waters; however, that number is believed to have decreased significantly over the past few years.

In Kalimantan, dugongs can be found in five locations: Balikpapan gulf; Berau regency, East Kalimantan; Derawan island; Karimata island, West Kalimantan; Kotawaringin, South Kalimantan; and Kumai gulf in Central Kalimantan.

Dugongs were declared extinct in 1996, but the Indonesia Rare Aquatic Species (RASI) spotted dugongs in 2000 in Balikpapan gulf. (swd)

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Warming may wipe out seagrass

The University of Western Australia Science Alert 29 May 12;

A study involving the collaboration between researchers at The University of Western Australia and the Spanish National Research Council has shown that warming of Mediterranean seawater over this century, under a moderately optimistic scenario of greenhouse gas emissions, is likely to cause the functional extinction of these seagrass meadows.

The international study examined the trajectory of the density of seagrass (Posidonia oceanica) meadows in the western Mediterranean during the 21st century under estimated warming based on ten global climate models and two regional models. Researchers used the relationships between the annual mortality rate of P. oceanica and the maximum annual temperature to predict annual seagrass mortality rates. The result was a decrease in shoot density by 90 per cent at mid-century.

All models predict a rapid warming of surface seawater along the 21st century, leading to an increase in the frequency and intensity of heat waves. The models predict the average surface temperature of seawater during the summer would be 3.4 °C warmer by the end of this century compared to now. The models predict that from 2050 onwards, seawater temperature will exceed 28 °C, the threshold temperature triggering mortality of P. oceanica, every summer.

Posidonia meadows in the Mediterranean are in decline not only because of higher temperatures but also due to local disturbances, such as pollution and destruction of the prairie for anchors.

Co-author and Director of the UWA Oceans Institute Winthrop Professor Carlos Duarte says that the paper, Mediterranean seagrass vulnerable to regional climate warming, published online in the journal Nature Climate Change, reveals actions to mitigate local impacts, while beneficial, are not enough to increase seagrass resistance to warming.

"To assess whether local disturbances could increase the vulnerability of P. oceanica to warming, the researchers examined the trajectory of the abundance of P. oceanica under three scenarios of mitigation of local stresses; the immediate removal of local stresses, the mitigation of local perturbations by 2030, and ‘business as usual.'

"The most swift action - the mitigation of local disturbances by 2010 - delayed the functional extinction of the meadow by a decade, but only two years if mitigation of local stresses is only achieved by 2030.

"Therefore, measures to mitigate local stresses, while beneficial, increase the resistance of P. oceanica to ocean warming only modestly," Winthrop Professor Duarte said.

The researchers concluded the study demonstrates that rapid international action to reduce emissions of greenhouse gases at levels well below those considered in this study is the only solution capable of ensuring that this ancient ecosystem persists throughout the twenty-first century.

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Radioactive bluefin tuna crossed the Pacific to US

Alicia Chang Associated Press Yahoo News 29 May 12;

LOS ANGELES (AP) — Across the vast Pacific, the mighty bluefin tuna carried radioactive contamination that leaked from Japan's crippled nuclear plant to the shores of the United States 6,000 miles away — the first time a huge migrating fish has been shown to carry radioactivity such a distance.

"We were frankly kind of startled," said Nicholas Fisher, one of the researchers reporting the findings online Monday in the Proceedings of the National Academy of Sciences.

The levels of radioactive cesium were 10 times higher than the amount measured in tuna off the California coast in previous years. But even so, that's still far below safe-to-eat limits set by the U.S. and Japanese governments.

Previously, smaller fish and plankton were found with elevated levels of radiation in Japanese waters after a magnitude-9 earthquake in March 2011 triggered a tsunami that badly damaged the Fukushima Dai-ichi reactors.

But scientists did not expect the nuclear fallout to linger in huge fish that sail the world because such fish can metabolize and shed radioactive substances.

One of the largest and speediest fish, Pacific bluefin tuna can grow to 10 feet and weigh more than 1,000 pounds. They spawn off the Japan coast and swim east at breakneck speed to school in waters off California and the tip of Baja California, Mexico.

Five months after the Fukushima disaster, Fisher of Stony Brook University in New York and a team decided to test Pacific bluefin that were caught off the coast of San Diego. To their surprise, tissue samples from all 15 tuna captured contained levels of two radioactive substances — ceisum-134 and cesium-137 — that were higher than in previous catches.

To rule out the possibility that the radiation was carried by ocean currents or deposited in the sea through the atmosphere, the team also analyzed yellowfin tuna, found in the eastern Pacific, and bluefin that migrated to Southern California before the nuclear crisis. They found no trace of cesium-134 and only background levels of cesium-137 left over from nuclear weapons testing in the 1960s.

The results "are unequivocal. Fukushima was the source," said Ken Buesseler of the Woods Hole Oceanographic Institution, who had no role in the research.

Bluefin tuna absorbed radioactive cesium from swimming in contaminated waters and feeding on contaminated prey such as krill and squid, the scientists said. As the predators made the journey east, they shed some of the radiation through metabolism and as they grew larger. Even so, they weren't able to completely flush out all the contamination from their system.

"That's a big ocean. To swim across it and still retain these radionuclides is pretty amazing," Fisher said.

Pacific bluefin tuna are prized in Japan where a thin slice of the tender red meat prepared as sushi can fetch $24 per piece at top Tokyo restaurants. Japanese consume 80 percent of the world's Pacific and Atlantic bluefin tuna.

The real test of how radioactivity affects tuna populations comes this summer when researchers planned to repeat the study with a larger number of samples. Bluefin tuna that journeyed last year were exposed to radiation for about a month. The upcoming travelers have been swimming in radioactive waters for a longer period. How this will affect concentrations of contamination remains to be seen.

Now that scientists know that bluefin tuna can transport radiation, they also want to track the movements of other migratory species including sea turtles, sharks and seabirds.


Fukushima Radiation Seen In Tuna Off California
Deborah Zabarenko PlanetArk 29 May 12;

Low levels of nuclear radiation from the tsunami-damaged Fukushima power plant have turned up in bluefin tuna off the California coast, suggesting that these fish carried radioactive compounds across the Pacific Ocean faster than wind or water can.

Small amounts of cesium-137 and cesium-134 were detected in 15 tuna caught near San Diego in August 2011, about four months after these chemicals were released into the water off Japan's east coast, scientists reported on Monday.

That is months earlier than wind and water currents brought debris from the plant to waters off Alaska and the U.S. Pacific Northwest.

The amount of radioactive cesium in the fish is not thought to be damaging to people if consumed, the researchers said in a study published in the journal Proceedings of the National Academy of Sciences.

Without making a definitive judgment on the safety of the fish, lead author Daniel Madigan of Stanford University's Hopkins Marine Station noted that the amount of radioactive material detected was far less than the Japanese safety limit.

"I wouldn't tell anyone what's safe to eat or what's not safe to eat," Madigan said in a telephone interview. "It's become clear that some people feel that any amount of radioactivity, in their minds, is bad and they'd like to avoid it. But compared to what's there naturally ... and what's established as safety limits, it's not a large amount at all."

He said the scientists found elevated levels of two radioactive isotopes of the element cesium: cesium 137, which was present in the eastern Pacific before the Fukushima Daiichi disaster in the spring of 2011; and cesium 134, which is produced only by human activities and was not present before the earthquake and tsunami hit the Japanese plant.

Because cesium 134 is generated only by human activities - nuclear power plants and weapons - and there was none in the Pacific for several years before the Fukushima accident, they reckoned that any cesium 134 they found in tuna off California had to come from Fukushima.


There was about five times the background amount of cesium 137 in the bluefin tuna they tested, but that is still a tiny quantity, Madigan said: 5 becquerels instead of 1 becquerel. (It takes 37 billion becquerels to equal 1 curie; for context, a pound of uranium-238 has 0.00015 curies of radioactivity, so one becquerel would be a truly miniscule proportion.)

The researchers figured that the elevated levels of cesium 137 and all of the cesium 134 they detected came from Fukushima because of the way bluefin tuna migrate across the Pacific.

Bluefin tuna spawn only in the western Pacific, off the coasts of Japan and the Philippines. As young fish, some migrate east to the California coast, where upwelling ocean water brings lots of food for them and their prey. They get to these waters as juveniles or adolescents, and remain there, fattening up.

Judging by the size of the bluefin tuna they sampled - they averaged about 15 pounds (6 kg) - the researchers knew these were young fish that had left Japanese water about a month after the accident.

Most of the radiation was released over a few days in April 2011, and unlike some other compounds, radioactive cesium does not quickly sink to the sea bottom but remains dispersed in the water column, from the surface to the ocean floor.

Fish can swim right through it, ingesting it through their gills, by taking in seawater or by eating organisms that have already taken it in, Madigan said.

Bluefin tuna typically have low levels of naturally occurring radioactive material, such as potassium 40, which was present in the world's oceans long before human beings walked the Earth.

Compared to these natural levels of radioactivity, the amount contributed by Fukushima raised the level about 3 percent, Madigan said.

He said there were probably much higher levels of cesium 134 present in bluefin tuna off Japan soon after the accident, as much as 40 to 50 percent higher than normal. Cesium 134 decays quickly, with a half-life of two years. Bluefin tuna excrete it on a daily basis and it also gets diluted in their bodies as they grow.

(Editing by Philip Barbara)

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