Constantine Alexander's blog

Ocean microbe communities changing, but long-term environmental impact is unclear

As oceans warm due to climate change, water layers will mix less and affect the microbes and plankton that pump carbon out of the atmosphere – but researchers say it's still unclear whether these processes will further increase global warming or decrease it.

The forces at work are enormous and the stakes huge, said Oregon State University scientists in an article to be published Friday in the journal Science.

But inadequate ocean monitoring and lack of agreement on how to assess microbial diversity has made it difficult to reach a consensus on what the future may hold, they said.

"We're just beginning to understand microbial diversity in the oceans and what that may mean to the environment," said Stephen Giovannoni, an OSU professor of microbiology. "However, a large portion of the carbon emitted from human activities ends up in the oceans, which with both their mass of water and biological processes act as a huge buffer against climate change. These are extremely important issues."

The interest is growing, scientists say, because nearly half of the world's photosynthesis is contributed by microbial plankton, and the process of marine carbon production and consumption is much faster than on land. A turnover of terrestrial plant biomass takes 15 years, they say, while marine turnover takes just six days.

As the ocean surface warms, evidence shows that it will become more "stratified," or confined to layers that mix less than they did in the past. This should reduce overall ocean productivity, Giovannoni said, but so little is known about the effect on ocean microbes that the implication for carbon sequestration and global warming is less clear.

Some OSU research on routine seasonal changes of microbes in the Sargasso Sea of the Atlantic Ocean suggests that different and specialized microbial communities can become more dominant when water warms.

As warmer oceans become a more long-term and global phenomenon, researchers need to know more about these microbes, and whether their behavior will amplify or reduce atmospheric carbon and the greenhouse effect.

It could be either, Giovannoni said.

"Some warming of surface waters may reduce carbon sequestration, which could cause a feedback loop to increase global warming," Giovannoni said.

"Other forces, what we call the microbial carbon pump, could cause carbon to sink into the deep ocean and be segregated from the atmosphere for thousands of years," he said. "We know both of these processes exist, but which one will become dominant is unpredictable, because we know so little about ocean microbes."

It was only two decades ago that OSU scientists discovered SAR11, an ocean microbe and the smallest free-living cell known, but one that's now understood to dominate life in the oceans, thrives where most other cells would die and plays a huge role in carbon cycling on Earth.

Microbial action also surprised scientists just recently, Giovannoni noted, when specific microbe populations surged following the Gulf Coast oil spill and cleaned up much of the oil faster than many thought possible. And some plans to "fertilize" the ocean and sequester atmospheric carbon through marine phytoplankton growth have been put on hold, he said, because it just isn't certain what would happen.

To reduce that uncertainty, Giovannoni advocates more aggressive development and implementation of marine microbial monitoring technology around the world, to add to what scientists can already learn from study of satellite images. And the field is so new, he said, that many researchers are not even comparing the same types of data or standardizing the tools they use to assess microbial diversity – a problem that needs to be addressed.

Dramatic advances in DNA sequencing in recent years, Giovannoni said, should also help researchers unravel the ocean microbe mystery.

Contact: Stephen Giovannoni
steve.giovannoni@oregonstate.edu
541-737-1835
Oregon State University

Scared of a younger rival? Not for some male songbirds

		This is a white-crowned sparrow. Photo courtesy of Douglas Nelson, Ohio State University

When mature male white-crowned sparrows duel to win a mate or a nesting territory, a young bird just doesn't get much respect.

Researchers found that older male white-crowned sparrows don't put much of a fight when they hear a young male singing in their territory – probably because the older bird doesn't consider the young rival much of a threat.

But a male sparrow will act much more aggressively if it hears a bird of the same age singing in a territory it claims as its own.

"These male sparrows assess an opponent's fighting ability based on age. And for a mature sparrow, a young male is just not going to scare them," said Angelika Poesel, lead author of the study and curator of Ohio State University's Borror Laboratory of Bioacoustics and the tetrapod division.

Poesel conducted the study with Douglas Nelson, associate professor of evolution, ecology and organismal biology at Ohio State and director of the Borror Lab. Their results appear online in the journal Biology Letters.

This study is one of the first to suggest that some birds use each other's songs – and not just plumage – to help determine a potential rival's age and thus threat level.

The researchers did the study in a migratory population of white-crowned sparrows that nested in a state park in Bandon, Oregon from 2008 to 2011. The researchers have been studying this population since 2005.

A male white-crowned sparrow, like many bird species, uses its songs to claim a nesting territory, win an appropriate mate, and sometimes to find additional females to mate with. Males will often attack and attempt to chase away other birds of the same species that sing in their territories.

In some species of birds, second-year males differ in their plumage and/or their songs from older, more mature birds. In white-crowned sparrows, second-year males have some plumage differences from older males. But this study focused on another difference: second-year males will often sing two or more versions of their species' song before they settle on the one that they will use the rest of their lives.

That means older white-crowned sparrows can tell a youngster by the fact that it will sing more than one version of the species song.

In this study, the researchers mapped out territories of 16 male white-crowned sparrows – eight of which had held territories at the park in previous years (identified by bands placed on their legs in previous years) and eight second-year males that had never held a territory there before.

The researchers placed a loudspeaker within the birds' territories and played recordings that suggested either a second-year bird or an older, mature bird had invaded their territory.

Several measures determined how threatened the birds were by what they perceived as an incursion into their territories.

If the male perceives the bird they hear as a greater threat, it will approach the loudspeaker more closely (to confront the rival), take more flights toward the speaker, and sing more songs.

Results showed that older birds didn't react as strongly when they heard a recording of a second-year bird than they did to one of an older male. In other words, when they heard the second-year male, they didn't approach the loudspeaker as closely, they didn't fly to the speaker as many times, and they didn't sing as often in response.

"Other research suggests that younger male birds are less successful at attracting females than older males. That means older males see these young birds as little threat to them and not worth a lot of attention," Poesel said.

But the study did show that second-year males that had established a territory did respond aggressively when they heard the recordings of other second-year males within their area.

"Another young male that is likely in search of a territory is seen as a strong threat and an equal competitor," she said. "They will elicit a strong, aggressive response from another young bird."

These findings suggest that some male songbirds use each other's song as a way to conduct a "mutual assessment" of each other as a potential rival.

"There's more likely to be a conflict when both of the birds see themselves as equal competitors," Poesel said.

"White-crowned sparrows aren't interested in picking a fight with another bird that is much stronger or weaker than themselves."

The research was supported by a grant from the National Science Foundation.

Contact: Angelika Poesel
Poesel.1@osu.edu
614-292-2176
Ohio State University

Researchers study parenting behaviors of stressed-out birds

Tachycineta bicolor. Credit: John Benson, Madison WI

Imagine an environment filled with wind, storms, predators, noise, and limited food and shelter. Then imagine providing and caring for a tiny egg or peeping baby bird in those conditions. The tree swallow and most other wild birds face these stressful challenges on a day-to-day basis.

Virginia Tech biologists recently received a $705,000 National Science Foundation grant to study how these birds respond to stress as well as the behaviors that stress produces. The question driving the research: do stressed out birds make good parents?

Fran Bonier, research scientist in biological sciences, and Ignacio Moore, associate professor of biological sciences, study stress hormones known as glucocorticoids. These hormones are present in most living organisms, including humans, and levels become elevated when a stressful life event occurs, such as danger, injury, reproduction, or parenting.

Glucocorticoids are used to provide the temporary energy boost needed to outrun a bear, dodge a falling limb, or rescue a baby from danger, Moore explained. But he and Bonier are interested in what happens when organisms sustain longer periods of elevated glucocorticoids, such as when a soldier is deployed for six months in dangerous territory, or a tree swallow lives with limited resources for a long period of time.

For their experiment looking at tree swallows, Moore and Bonier partnered with Queens University in Kingston, Ontario, Canada, which operates a biological station that is home to many types of birds. The station provides boxes for the cavity-dwelling swallows to nest in, but otherwise, the birds live in a wild, natural habitat.

Bonier, stationed at Queens, takes blood samples from tree swallow mothers, which must be done within three minutes of human contact to get an accurate, base-line reading. During the next four years, she will compare the glucocorticoid levels in the birds' blood with their observable behaviors as parents. For example, at what level of stress will a bird abandon her young and focus on meeting her own needs? She will also conduct experiments in which she changes the birds' hormone levels, brood sizes, and blood parasite loads and then measures the effects on parenting behaviors.

The scientists predict that they will find one of several competing hypotheses to be true. One possible scenario is that there is no connection between glucocorticoid levels and bird parenting behaviors. In a second scenario, a mother's decision to cut and run will be based on the offspring's age and health—if it's older and healthy, the mother will sacrifice her own needs to increase her young's chance of surviving. A last possible scenario is that the mother will choose to invest in herself when conditions worsen.

The experiments could provide groundbreaking insight into the effects of stress on organisms, as well as the evolution of biological systems. The Tech researchers share the total $800,000 grant with Mark Haussmann, assistant professor of biology at Bucknell University, who will be measuring molecular markers of stress in the birds.

"The grant is going to dramatically change the scope or our research project, increasing our ability to answer important questions," Bonier said. Meanwhile, as part of the grant's outreach component she will offer annual public workshops on box-nesting birds in Ontario. Participants will learn how to build and maintain a nest box as well as identify nesting species.

Contact: Lindsay Key
ltkey@vt.edu
540-231-6594
Virginia Tech

Ocean warming causes elephant seals to dive deeper

Global warming is having an effect on the dive behaviour and search for food of southern elephant seals. Researchers from the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association cooperating in a joint study with biologists and oceanographers from the Universities of Pretoria and Cape Town have discovered that the seals dive deeper for food when in warmer water. The scientists attribute this behaviour to the migration of prey to greater depths and now wish to check this theory using a new sensor which registers the feeding of the animals below water.

The southern elephant seals from Marion Island, located in the south western part of the Indian Ocean, are extreme divers in the truest sense of the word. The animals spend more than 65 per cent of their lives in depths of over 100 metres, diving far deeper than their fellow species in southern areas. The maximum dive depth of these seals is over 2000 metres. However, the water masses through which the elephant seals from Marion Island swim in search of food are becoming increasingly warmer due to climate change and are forcing the animals to dive deeper. The Southern Ocean is warmed primarily in the water levels up to a depth of 1000 metres and therefore in those areas in which squid and fish ought to be found. "This prey is moving down to greater depths presumably due to the increasing water temperatures and this is forcing the seals to follow them", explains Dr. Horst Bornemann from the Alfred Wegener Institute.

Over the course of several years he and his colleague Dr. Joachim Plötz together with Dr. Trevor McIntyre and other seal researchers from the Mammal Research Institute (MRI) in South Africa have fitted over 30 elephant seals with satellite transmitters. These transmitters, the size of a fist, are attached to the head of the seals using artificial resin immediately after moulting and measure the dive depth, water temperature and salinity every time the animals dive. When the animal resurfaces to breathe the transmitters send their data to the respective research institutes via satellite. The results show that the elephant seals need to dive deeper in warmer water so that they ultimately have less time to actually search for food. "We therefore assume that the animals will find less prey in warmer water masses", explains Joachim Plötz.

The scientists from Bremerhaven will be going back to Marion Island in April of this year to collect evidence for their theory. This time they wish to equip the animals with a "jaw movement" sensor which has been developed by Japanese biologists at the National Institute of Polar Research in Tokyo. It is not much larger than a small finger and notices when the seal opens its mouth. "So far we can only derive from the dive profile whether an elephant seal was probably following a fish swarm. With this new measuring device we learn whether he has actually eaten", says Joachim Plötz.

Using this forage data the AWI biologists wish to draw conclusions as to the spatial and temporal distribution of particularly productive zones in the South Polar Sea. "The food in the sea is unevenly distributed. It is not worth the seals fishing anywhere and at any time. With the new data we hope to see the routes taken by the elephant seals of Marion Island and the water levels in which they find food", says Horst Bornemann.

The scientists also take days of walking over the "island of horizontal rain" into the bargain to achieve their research goal. "The elephant seals of Marion Island are very loyal to their location. They return to this island time and again to moult and mate. This behaviour gives us the opportunity to consistently fit measuring devices to the same animals thereby gaining an insight into the movement patterns of individual animals. Their movement and dive routes help us to find out where the oceanic food grounds of the Marion Island elephant seals are located", explains Joachim Plötz.

The extent to which the animals of this rather northerly elephant seal colony are able to adapt to the warming of the ocean remains to be seen. The scientists from Germany and South Africa see only two alternatives for the animals: either the seals extend their hunting grounds to the colder water masses of the Antarctic or they must dive even deeper in future. The elephant seals from Marion Island are very close to reaching their physiological limits even in their dive behaviour today. This leads the biologists to assume that this may reduce the survival rate of the seals in the long term.

Contact: Sina Löschke
medien@awi.de
49-047-148-312-008
Helmholtz Association of German Research Centres

Piranha vs. Arapaima: Engineers find inspiration for new materials in piranha-proof armor

It's a matchup worthy of a late-night cable movie: put a school of starving piranha and a 300-pound fish together, and who comes out the winner?

The surprising answer—given the notorious guillotine-like bite of the piranha—is Brazil's massive Arapaima fish. The secret to Arapaima's success lie in its intricately designed scales, which could provide "bioinspiration" for engineers looking to develop flexible ceramics.

The inspiration for this study came from an expedition in the Amazon basin that Marc Meyers, a professor at the Jacobs School of Engineering at UC San Diego, took years ago. The mechanical and aerospace engineering professor immediately wondered at the Arapaima's armor-like protective scales. How could it live in piranha-infested lakes, where no other animals could survive?

 

It's a matchup worthy of a late-night cable movie: put a school of starving piranha and a 300-pound fish together, and who comes out the winner? The surprising answer -- given the notorious guillotine-like bite of the piranha -- is Brazil's massive Arapaima fish. The secret to Arapaima’s success lie in its intricately designed scales, which could provide "bioinspiration" for engineers looking to develop flexible ceramics. Credit: Jacobs School of Engineering, University of California, San Diego

Meyers and colleagues set up a lab experiment that pits piranha against Arapaima by using a machine that resembles an industrial-strength hole punch. Piranha teeth were attached to the top "punch," which was pressed down into Arapaima scales embedded in a soft rubber surface (which mimics the soft underlying muscle on the fish) on the lower "punch." The teeth can partially penetrate the scale, but crack before they can puncture the muscle, Meyers and colleagues demonstrate in the journal Advanced Biomaterials.

The Arapaima scale combines a heavily mineralized outer layer with an internal design that helps the scale resist the pirahna's razor-like bite. The mix of materials is similar to the hard enamel of a tooth deposited over softer dentin, said Meyers, who also teaches nanoengineering at the Jacobs School of Engineering "You often find this in nature, where you have something hard on the outside, but it rides on something softer that gives it toughness."

It's a combination that engineers would like to reproduce for applications such as soldiers' body armor, which needs to be both tough and flexible. Other applications might include fuel cells, insulation and aerospace designs.

		This is a close-up of two Arapaima scales, overlapping as they would in nature. Credit: Jacobs School of Engineering, University of California, San Diego

Meyers is an expert in biomimetics, the study of natural materials from living organisms and the processes that produce them. He says that engineers are pursuing biomimetics because "we are hitting a wall, so to speak" with conventional materials and syntheses.

"We have used our ingenuity to the maximum, but one way to overcome that is to look at nature," Meyers suggested. "The materials that nature has at its disposal are not very strong, but nature combines them in a very ingenious way to produce strong components and strong designs."

Lessons from the Arapaima's scales

In the case of the Arapaima, the ingeniously designed scales serve as peace through strength, allowing them to coexist with piranha when the two are crowded into Amazon basin lakes during the region's dry season.

The Arapaima experiments, some of which were also published in The Journal of the Mechanical Behavior of Biomedical Materials, suggest a few lessons for bio-inspired engineers:

Mix it up: The combination of hard and soft materials, the researchers note, give the scales several ways to repel the bite. The scales overlap like shingles on the fish, and each scale has a "very hefty mineralized layer on top of it," Meyers said. Underneath, each scale is composed of much softer collagen fibers stacked in alternating directions like a pile of plywood.

The external surface is twice as hard as the internal layer, giving the fish a layer of dense armor. At the same time, the structure of the internal layer lends toughness to the scale. "As you stack the layers of fibers in this way," Meyers explained, "they have different orientations, which gives strength that is the same in all directions."

		Arapaima gigas scales have a highly mineralized outside layer, and an internal layer of collagen fibers stacked in a "plywood " formation for maximum toughness. Credit: Jacobs School of Engineering, University of California, San Diego. Arapaima picture courtesy of William Fink, Curator of Fishes, Professor, University of Michigan

Texture is key: People living in the Amazon sometimes use the ridged Arapaima scales (which can be nearly four inches in length) as nail files. The corrugated surface keeps the scales' thick mineralized surface intact while the fish flexes as it swims. Ceramic surfaces of constant thickness are strained when forced to follow a curved surface, but the corrugations allow the scales to "be bent more easily without cracking," Meyers said.

Freedom to move: The corrugations, the soft but tough internal layer and the hydration of the scales all contribute to their ability to flex while remaining strong. It's an engineering solution that lets the fish remain mobile while heavily armored, and also allows the scales to bend and deform considerably before breaking.

What's next?

From the abalone shell to the toucan's beak, Meyers said, the natural world is replete with inspiration for 21st century materials scientists. One of his next projects will involve the scales of the alligator gar, a huge fish from the American South whose scales were used by Native Americans as arrow tips. He recently received some samples from Louisiana artist Dianne Ulery, who makes jewelry from the ivory-colored, arrowhead-shaped scales. Students in his lab also are working on abalone shells and samples of leatherback turtle skin obtained from the National History Museum in San Diego, among other species.

In some respects, the field of biomimetics is a return to the roots of manufacturing, Meyers suggested, when early humans crafted from leather, bone and wood. "We've produced materials with much higher performance, but we're reaching the limit with synthetic materials," he noted. "Now we are looking back at those natural materials and asking, 'how does nature put these things together'?"

When he is not conducting research or teaching, Meyers also is a successful fiction author. He has published two novels so far, "Mayan Mars" and "Chechnya Jihad." He is currently looking for a publisher for his third work of fiction, which takes place in the Amazon. Piranhas are featured in that work in a spectacular manner, he said.

Additional researchers include Y.S. Lin, C.T. Wei and P-Y Chen at the Jacobs School of Engineering and E.A. Olevsky at San Diego State University. Funding was provided from the National Science Foundation DMR Biomaterials Program.

Contact: Ioana Patringenaru
ipatrin@ucsd.edu
858-822-0899
University of California - San Diego

Mike deGruy will be missed.

Mike deGruy was a graduate student in marine biology when he first picked up a 16mm film camera. Thirty-plus years on, his company, the Film Crew Inc., travels the oceans making underwater films for the BBC, PBS, National Geographic and Discovery Channel. He dived beneath both poles and visited the hydrothermal vents in both the Atlantic and the Pacific. And as you can imagine, he collected many stories along the way.

An accomplished diver and underwater cinematographer, deGruy also became a go-to host and expedition member on shows like the recent Mysteries of the Shark Coast with Céline Cousteau and Richard Fitzpatrick. (He was a regular on Shark Week -- and a shark attack survivor himelf.) But his first passion was cephalopods, and in fact deGruy and his team were the first to film two rarely seen cephalopods, the nautilus and the vampire squid, in their home ocean.

He had worked extensively on epic series for Sir David Attenborough and the BBC Natural History Unit, producing incredible underwater footage. This includes The Living Planet, in 1984, Life in the Freezer, in 1993, Blue Planet in 2000 and Life of Mammals in 2002. His work on Trials of Life in 1990, won him international acclaim, and he continues to work in the wildlife filming community today, specialising in shark behaviour.

Mike deGruy, an Emmy Award-winning documentary filmmaker and marine biologist who through the lens of his submersible cameras transported viewers to the deepest parts of the oceans died on February 4, 2012, in a helicopter crash in Australia. He was 60.

 

Big boost for wildlife conservation: 23 new SOS projects

Tiger photographed by camera-trap in Hua Kha Khaeng Wildlife Sanctuary, Thailand

Beginning in January 2012, top species conservation experts from around the world have determined the allocation of $US 3.3 million to 23 species conservation projects. Gorillas, cockatoos, and frogs are just a few of the multitude of threatened species that are receiving a helping hand from SOS (Save Our Species), a global species conservation fund initiated by IUCN (International Union for Conservation of Nature), the World Bank and the GEF (Global Environment Facility).

Drawing on species conservation knowledge accrued over decades by IUCN, for the first call for proposals SOS focused on species groups that were completely assessed on IUCN’s Red List of Threatened Species™ and already had specific conservation action plans in place. According to IUCN’s Red List, one in three amphibians, one in eight birds, and one in four mammals are at risk of extinction in the wild. Nineteen different organizations will use these funds to conserve threatened animal and plant species and their habitats.  

 

“The dire situation facing the world’s biodiversity calls for an action and response. SOS is seeking to bring knowledge, expertise and funding together in order to address the plight of threatened species,” says Julia Marton-Lefèvre, IUCN’s Director General. “Through these exciting projects we hope to show that, if properly implemented, conservation works.” 

 

A high variety of different species is crucial for ecosystem health and SOS aims to conserve a multitude of threatened creatures, focusing on Asian and African mammals, amphibians and birds with the new round of funds. SOS supports a variety of mammal projects such as conservation programmes targeting the critically endangered Cross River Gorilla (Gorilla gorilla diehli) and Black Rhino (Diceros bicornis) in Africa, in addition to the endangered Snow Leopard (Panthera uncia) in Pakistan. 

 

Mammals represent the largest portion of the SOS portfolio, but they are not the only species at risk. SOS also supports bird and amphibian projects, protecting the critically endangered Spoon-billed Sandpiper (Eurynorhynchus pygmeus) in Asia; a project to re-introduce the Philippine Cockatoo (Cacatua haematuropygia); and an initiative preserving the Golden Mantella Frog (Mantella aurantiaca) in Madagascar.

 

“Ignoring species conservation means ignoring a world in which species are currently disappearing at a rate 100 to 1,000 times higher than normal. The loss of wild plant and animal species is a real threat to human well-being, sustainable development and poverty reduction. In these times of economic turmoil, it would be wise not to further damage nature—our ultimate safety net,” says Jean-Christophe Vié, Deputy Director of IUCN’s Global Species Programme and SOS Director. “By implementing on the ground conservation action, the projects SOS select help protect entire habitats which both people and wildlife depend on.”

 

In October 2010, SOS was established with more than $US10 million in financing commitments in order to build a global coalition to protect threatened species and their habitats. This unique international alliance aims to raise awareness of biodiversity conservation and looks for participation from innovative companies across all industries. Nokia was the first company to join SOS.

 

“SOS was established to use the charisma of wild animals to explain the role of nature, generate interest in the plight of threatened species, and shed light on the complexity of conservation work,” says Monique Barbut, CEO and Chairperson of the GEF and Chair of the SOS Donor Council. “Today, with our core funding we are adding 23 new projects covering a large number of threatened species, including around 60 that will be closely monitored. So far we are on track. The only thing missing now is the private sector’s commitment to join our endeavour to save the planet’s captivating wildlife before it is too late.”

 

This decade has been declared by the United Nations as the Decade of Biodiversity. Issues surrounding species survival will be discussed at the IUCN World Conservation Congress in Jeju, Republic of Korea, from 6 to 15 September 2012.

 

 

For more information:

• Elke Blodau, SOS Marketing and Communications Officer
• Maggie Roth, IUCN Media Relations

Ocean fish farms identified by Google Earth images

Ocean fish farming is a growing industry that may need increased monitoring and regulation, and Google Earth can be a powerful tool to that end, according to a study published in the Feb. 8 issue of the online journal PLoS ONE.

The researchers, led by Pablo Trujillo of the University of British Columbia, used Google Earth satellite images of the Mediterranean to identify sites and sizes of fish farms. They examined 91% of the Mediterranean coast and counted over 21,000 fish cages, the majority of which were off the coast of Greece and Turkey. They were then able to estimate the total amount of ocean fish farmed in a given year, and found that although there were some discrepancies within individual countries, their overall calculations were in agreement with the United Nations Food and Agriculture Organization reports. These results highlight the research and monitoring potential of Google Earth.

Citation: Trujillo P, Piroddi C, Jacquet J (2012) Fish Farms at Sea: The Ground Truth from Google Earth. PLoS ONE 7(2): e30546. doi:10.1371/journal.pone.0030546

Contact: Yael Franco
yfranco@plos.org
415-568-3169
Public Library of Science

Hatchery fish mask the decline of wild salmon populations

Scientists have found that only about ten percent of the fall-run Chinook salmon spawning in California's Mokelumne River are naturally produced wild salmon. A massive influx of hatchery-raised fish that return to spawn in the wild is masking the fact that too few wild fish are returning to sustain a natural population in the river.

The study, published in the online journal PLoS ONE, highlights the danger of relying on census techniques to evaluate the health of wild salmon populations and their habitats. Most hatchery fish in California are unmarked and therefore undetectable in population surveys. For this study, the researchers were able to identify hatchery fish by using a novel technique to detect traces of a hatchery diet preserved in the ear bones of adult fish.

"We expected to find hatchery fish, but the sheer number of hatchery fish returning to spawn in the wild is surprising," said first author Rachel Johnson, a fishery biologist affiliated with the Institute of Marine Sciences at UC Santa Cruz and with the Bay-Delta Office of the U.S. Bureau of Reclamation.

"It looked like a healthy population of fish returning to spawn, but the reality is that without the hatchery fish the wild stocks are not sustaining themselves."

The Mokelumne River is one of the major salmon producing rivers for fall-run Chinook salmon in California. Throughout the Central Valley rivers, returning fall-run Chinook salmon numbers have rebounded since a disastrous year in 2007, which led to the unprecedented closure of the commercial salmon fishing season for consecutive years in 2008 and 2009.

In the Mokelumne, the number of returning adult salmon has grown from just 418 in 2008 to more than 18,000 in 2011.

But relying on the census numbers alone provides a false sense of the productivity of the river, Johnson said. The discrepancy between the numbers of fish spawning in the river and the actual survival and productivity of wild fish is a serious issue for conservation efforts aiming to restore the wild populations.

"We might not be monitoring the right thing to evaluate the effectiveness of recovery efforts," Johnson said.

The new study reveals just how thoroughly the system is dominated by hatchery fish. The Mokelumne River Fish Hatchery releases several million juvenile Chinook salmon every year.

The hatchery fish are protected from many of the hazards that cause mortality among wild fish during the initial freshwater phase of their life cycle. There is growing evidence that the different selective pressures on hatchery fish lead to genetic differences, so that the offspring of hatchery fish may be less fit for life in the wild than naturally produced fish.

This is especially worrisome if, as the new study suggests, hatchery fish are gradually replacing the wild population.

"We could be doing more harm than we recognize," Johnson said. "Humans are influencing the wild stocks, but we have not been adequately measuring that in our monitoring of endangered species." This concern applies globally to several species of salmon and steelhead, from Japan to the U.S. west coast, she said.

"We used the Mokelumne River as a case study to highlight the implications of not monitoring hatchery fish in the wild. But the practice of releasing enormous numbers of unmarked hatchery-produced fish to enhance salmon stocks remains the cornerstone of salmon conservation and harvest management worldwide."

The researchers based their findings on an analysis of ear bones, called otoliths, from fish collected after spawning in fall 2004. Coauthor Peter Weber of Lawrence Livermore National Laboratory led the development of the technique for analyzing chemical signatures in the otoliths. These bones grow in increments over the life of the fish and incorporate elements from the fish's diet. Hatchery feed is largely derived from marine fish meal, which leaves a chemical signature distinctly different from that found in wild fish.

This signature from a fish's early diet can be detected even several years after it has left the hatchery.

Nearly 12,000 fish returned and spawned in the Mokelumne watershed in 2004. Most were hatchery fish that returned to the hatchery, but about 1,500 fish spawned in the river. The otolith analysis showed that only ten percent of those spawning in the river were produced there, and only 4 percent of the total spawning population were of natural origin.

"When you use the raw fish counts, it looks like the population is doing well. But if you look at the number of fish that are produced in the wild and return to spawn in the wild, and you follow them through the cycle, you see that the wild fish don't survive at a high enough rate to replace their parents.

So the habitat is not supporting a sustainable wild population," Johnson said.

Mass marking of all hatchery fish would make it easier to distinguish between hatchery and natural-origin fish in population surveys and to actively manage for the recovery of wild populations, she said. Currently, most California hatcheries mark a fixed proportion of the salmon they produce, which helps researchers track them.

"In the Pacific Northwest, many hatcheries mark all of their fish by clipping off the adipose fin. They operate segregation weirs to create 'salmon sanctuaries,' so that hatchery fish can be managed separately to reduce the risk of them spawning with wild fish, competing for habitat, or potentially reducing the fitness of wild populations," Johnson said.

In addition to Johnson and Weber, the coauthors of the paper include John Wikert and Michelle Workman of the U.S. Fish and Wildlife Service, Bruce MacFarlane of the National Marine Fisheries Service, and Marty Grove and Axel Schmitt of UCLA. This research was funded through a grant from the U.S. Fish and Wildlife Service.

Citation: Johnson RC, Weber PK, Wikert JD, Workman ML, MacFarlane RB, et al. (2012) Managed Metapopulations: Do Salmon Hatchery 'Sources' Lead to In-River 'Sinks' in Conservation? PLoS ONE 7(2): e28880. doi:10.1371/journal.pone.0028880

Contact: Yael Franco
yfranco@plos.org
415-568-3169
Public Library of Science

Skin deep

Teeth-like denticles play key role in helping sharks swim, research shows

For swimmers looking to gain an edge on the competition, the notion that simply donning a different swimsuit – like a Speedo Fastskin II suit, with a surface purportedly designed to mimic by shark skin – can be the difference between first and last place is a powerful one.

It's also one that's almost completely misplaced, said George Lauder, the Henry Bryant Bigelow Professor of Ichthyology.

Experiments conducted in Lauder's lab, and described in the Feb. 2 issue of The Journal of Experimental Biology, reveal that, while sharks' sandpaper-like skin does allow the animals to swim faster and more efficiently, the surface of the high-tech swimsuits has no effect when it comes to reducing drag as swimmers move through the water.

"In fact, it's nothing like shark skin at all," Lauder said, of the swimsuit material. "What we have shown conclusively is that the surface properties themselves, which the manufacturer has in the past claimed to be bio-mimetic, don't do anything for propulsion."

That's not to say that the suits as a whole do nothing to improve performance.

"There are all sorts of effects at work that aren't due to the surface," Lauder said. "Swimmers who wear these suits are squeezed into them extremely tightly, so they are very streamlined. They're so tight could actually change your circulation, and increase the venous return to the body, and they are tailored to make it easier to maintain proper posture even when tired. I'm convinced they work, but it's not because of the surface."

By comparison, Lauder said, the research showed that the millions of denticles – tiny, tooth-like structures – that make up shark skin have a dramatic effect on how the animals swim by both reducing drag and increasing thrust.

"What we found is that as the shark skin membrane moves, there is a separation of flow – the denticles create a low-pressure zone, called a leading-edge vortex, as the water moves over the skin," he said. "You can imagine this low-pressure area as sucking you forward. The denticles enhance this leading-edge vortex, so my hypothesis is that these structures that make up shark skin reduce drag, but I also believe them to be thrust enhancing."

Importantly, however, the phenomenon was only found when the skin was attached to a flexible membrane. When placed on a rigid structure, no increases in swimming speed were seen.

"In life, sharks are very flexible. Even hammerheads and large ocean sharks are quite flexible," Lauder said. "If you watch a shark swim, the head does not move very much, so it could be that the denticles on the head are mostly reducing drag, but those on the tail are enhancing thrust, but we don't know what that balance may be. Ultimately, though, one of the key messages of this paper is that shark skin needs to be studied when they're moving, which hadn't been done before."

Studying how shark's skin helps them move through the water, however, is no easy proposition, and one that, for obvious reasons, can't be done using live animals.

To perform the tests, Lauder and his team obtained samples of the skin of two different shark species – mako and porbeagle sharks – and tested them alongside two other materials, the high-tech swimsuits and a material that featured tiny grooves, or "riblets", which has been explored as a way to cut fuel consumption on aircraft and reduce drag on sailboats.

To conduct the tests, each of the materials was mounted on two forms – one a rigid, wing-like structure and the other a flexible membrane. Each was then attached to a robotic arm mounted on a low-friction device suspended over a recirculating tank. To measure the speed at which the apparatus "swims," researchers turned up the flow in the tank until the device returned to its starting point.

Understanding how water flowed over each material, however, was trickier.

To get at the problem, Lauder and his team relied on a technique called particle image velocimetry which uses a laser to illuminate millions of reflective particles in the water. Using a high speed camera that records at up to 1,000 frames per second, researchers can observe how the particles move and observe where and when vortices form.

"I've thought for years that the literature on shark skin needed an upgrade," Lauder said, explaining his motivation for the research. "Once we got going, I thought it would be fun to look at the Speedo materials because we don't have a lot of quantitative information on the effect of surface structure.

"Going forward, we want to try to image the flow as close to the surface as we can reasonably get," he continued. "The other direction we are exploring is to make an artificial shark skin and then manipulate it – delete every other denticle, make them twice as large, or change the spacing – and see what effects that may have."

Funding for the research was provided by the National Science Foundation.

Contact: Peter Reuell
preuell@fas.harvard.edu
617-496-8070
Harvard University