The seas’ most sought-after fish are swimming between a rock and a hard place: the fisherman’s net and an encroaching mass of suffocating water.

A recent study has uncovered a new dose of bad news for ocean fish and the fishing industry. Areas of the deep ocean with little dissolved oxygen, called dead zones, are expanding and, thus, shrinking many fishes’ watery homes.

One driving force behind the predicament is none other than that pesky climate problem.

“Climate change is actually working in tandem with overexploitation of the animals to push these populations into a real dangerous place in terms of population collapse,” said Eric Prince, a fisheries biologist with the National Oceanic and Atmospheric Administration’s Southeast Fisheries Science Center and co-author of the study.

For example, Prince and his colleagues calculated that the Atlantic blue marlin, an economically valuable fish that was a focus of their study, has lost about 15 percent of its habitat from expanding dead zones since 1960. Dwindling habitat threatens not only the lives of fishes, but also the sustainability of the already ailing fishing industry.

Breathing room

Like their above-water brethren, fish need oxygen, which is dissolved in the water. Big, predatory fish, such as the blue marlin, need more dissolved oxygen than most, because they require lots of energy to grow and survive. Without sufficient oxygen, they’ll suffocate.

The level of oxygen in the water thus partly delineates fish habitat boundaries. Dead zones often draw these borders.

As climate change causes open ocean dead zones to balloon, fish habitat deflates.

Diagram modified from one originally published in Deep Sea Research Part I: Oceanographic Research Papers, Vol 57, Issue 4, Lothar Stramma, Sunke Schmidtko, Lisa A. Levin, & Gregory C. Johnson. Ocean oxygen minima expansions and their biological impacts, 587-595, Copyright Elsevier (2010).

Technically known as oxygen minimum zones, dead zones are actually a natural occurrence. Found at depths of between 200 and 1000 meters, they are caused partly by seawater circulation and partly by the decomposition of organic matter, namely deceased sea critters that sink from surface waters.

As aerobic bacteria nosh on the organic matter, they use up the oxygen in the water. Eventually, hypoxia happens—the water becomes so depleted of oxygen that many creatures can’t survive.

Since deep-sea dead zones are insulated from the ocean’s surface, where the water borrows oxygen from the atmosphere, they can only reload with oxygen if currents make a long-distance delivery, according to Sunke Schmidtko, an oceanographer at the University of East Anglia, the other co-author of the study.

Deep-sea dead zones are different from their coastal cousins like the one in the Gulf of Mexico. Coastal dead zones form due to a buildup of agricultural fertilizer that rivers, such as the Mississippi, collect and then flush out to sea, causing abnormal blooms of plant life.

De-fizzing the ocean

But climate change is turning what Mother Nature does normally into a big problem. As the air is getting hotter, so is the water, and warmer water can hold less oxygen than colder water.

This is similar to what happens to a soft drink on a hot day. After sitting in the heat and sun, the fizz fizzles, and you are left with a flat, carbon dioxide-depleted beverage.

Also, warmer surface waters are less likely to sink to the ocean’s lower layers, because warm water is lighter than the colder water below, Schmidtko explained. In other words, as the oxygen-rich surface layers heat up, they could have a harder time delivering oxygen to the deeper ocean.

Schmidtko clarified that oceanographers are still trying to determine how exactly climate change is affecting the ocean, but with their knowledge of how water works, these represent their current speculations.

The rock below

With less oxygen to go around, oxygen minimum zones are swelling and intruding on many fishes’ living zones.

For example, marlins often dive deep to feed, sometimes as far down as 800 meters. However, in the eastern Atlantic’s growing dead zone, which is already one of the largest in the world, Prince found that marlins can’t dive as deep as their west-side counterparts.

“They need to go where the food is and where they can breathe,” he said.

With less breathing room below, the floor of their habitat rises, and they are pinned to the surface layers. With nowhere to go but up, marlins become squished into tighter, testier quarters with other predatory fish and their prey. They also find it harder to dodge a waiting fishing hook or net.

“Concentrating them makes it much easier for overexploitation by [humans],” said Prince.

The increasing concentration of animals at the top could also lead to a boost in the amount of sinking organic matter, which would further worsen the oxygen shortage below.

Softening the hard place above

As a prized catch, Atlantic blue marlins are already victims of overharvesting. In fact, their populations have dropped 60-64 percent over the past three fish generations (14-18 years).

But the growing dead zones can actually fool scientists and fishermen into thinking fish populations are doing just fine, since more fish are squeezed into a smaller area. Thus, to ensure the dead zone-fishing vise does not become their demise, Prince said scientists must more carefully monitor fish populations, as well as the expansion of the dead zones.

While fish stock assessments are starting to incorporate this information, Prince warned the pace needs to quicken.

And if the Earth is to continue warming, as most scientists predict, Schmidtko added that humans should chill out on fishing.

After all, we will never be capable of “ventilating the ocean,” he said.

Among all animals, amphibians are in the worst shape; fully 30 percent are classified as threatened or endangered. Amphibians – including frogs, toads and salamanders — are under attack by a deadly fungus. They are losing habitat to farms and cities, and collected as food or pets. Amphibians are suffering from chemical pollution and the warming climate.

The present is harsh enough, but the future seems worse.

This week, Nature publishes the first global attempt to forecast the impact of three big threats to amphibians by 2080 – a year chosen to be one century after the study’s baseline data.

By comparing areas with plenty of amphibian species with projections of climate change, land use change and the chytridiomycosis fungus, the researchers forecast a grim future for these cold-blooded, four-legged vertebrates. “The bad news is that more than two-thirds of all high-richness regions will probably be affected, to a high intensity, by one of these three threats,” said lead author Christian Hof, who did the work as a Ph.D. student and post-doctoral fellow at the University of Copenhagen.

The geographic study of data on 5,527 amphibian species found little overlap between the cool, moist areas afflicted by fungal serial killer chytridiomycosis, and the places likely to suffer the worst effects of changes in climate and land use.

And the losers win!

In forecasting the future of amphibians, the study coined two technical terms: “losers” — species that are expected to suffer due to disease or changes in climate or land use, and the less numerous “winners,” which are expected to prosper by 2080.

The projection hinged on whether an expected change would make a habitat more or less suitable to the species, says Hof, who’s now at the Biodiversity and Climate Research Center in Frankfurt, Germany. “We ran a number of climate-change models and based on them, calculated a change in climate suitability for each region across the globe.”

Based on these changes in suitability due to climate, land use and disease, Hof adds, “We calculated the number of species that would probably decline due to a decline in habitat suitability. We classify the species as a loser in a particular region, but that does not mean it will decline across its whole range.”

Overall, the researchers found an increasingly dire future for amphibians. For example, 54 percent of frogs are likely to be “climate losers” in the average grid cell of their model. And heavy impacts are projected for about two-thirds of the regions with the highest species richness in frogs and salamanders.

In fact, the future could be even worse, since the study ignored a number of potentially damaging factors, including chemical pollution from cities, factories and agriculture.

Photo: Robert Fletcher, Ohlone Preserve Conservation Bank

Tougher times might await this prowling California tiger salamander, an endangered California native.

Going down!

It’s frustrating but understandable that the study could not predict rates of decline among amphibians. “For many species, we are not sure about the actual distribution, many have tiny ranges and we don’t know where they occur, so we can’t relate historic changes to, say, climate change. We were very careful not to predict extinctions, based on these uncertainties.”

Data are scarce in the study of amphibians, agrees Anna Pidgeon, an assistant professor of forest and wildlife ecology at University of Wisconsin-Madison. “It’s frustrating, amphibians are out at night, often in remote areas, they are small and many are cryptic, so it’s a huge challenge” to understand their populations and ecologies. “We work with the best data we have all the time … and try to make inferences from what we know about close relatives.”

Pidgeon, an expert on habitat needs of vertebrates, says predicting 70 years into the future is always dicey, but that the study’s analysis of multiple threats and global scope are major accomplishments. “They did a lot of things to make sure they were using consensus data, and that makes it a pretty solid approach.”

Although the study looked at overlapping threats, it did not actually look at interactions between those threats, Hof says. “What needs to be done, and we could not do that with our model, is to look at, for example, how climate change would affect susceptibility to the fungus. How would habitat fragmentation affect susceptibility to climate change?”

Although the study does not suggest practical changes that could sustain amphibians in the short run, “The general conclusion is that it’s very important, when thinking about the future for amphibians, to consider different threats together,” says Hof. “Just looking at one threat will not give us the whole picture.”

– David J. Tenenbaum

Humans and cats go way back. The relationship sprouted around 2000 BC in Egypt, where humans first domesticated felines. Today, more than 90 million cats in the United States alone enjoy the companionship of humans, while another estimated 90 million are stray or feral.

As in most relationships, there are still secrets between humans and their feline friends. But a recent study published in the Journal of Wildlife Management shed light on one secret that may have been nagging cat owners: what do outdoor cats, otherwise known as “free-roaming,” do all day?

Since there are several cat enthusiasts at The Why Files, we, too, wondered about the answer to that question. And the answer belies a few thorny predicaments peculiar to the cat-human relationship.

A day in the life of a free-roaming cat

Decked with radio collars that tracked their every move, 42 free-roaming cats (18 of them pets, 24 of them owner-less) were the stars of the two-year University of Illinois study. The researchers’ goals were to compare what owned versus un-owned cats did all day, where and how far they wandered, and how likely they were to survive in the often risky outdoors.

Certainly, to no cat owner’s surprise, the felines spent much of their time lounging or sleeping, just like their strictly-indoor counterparts. However, the amount of time pet cats versus owner-less cats spent snoozing differed significantly. Pet cats lazed about for 80 percent of their days, while un-owned cats loafed for “only” 62 percent of the time.

“That alone is very interesting. It could be associated with their requirements. It’s possible that the cats without owners have to spend more time looking for resources to take care of themselves,” speculated Nohra Mateus-Pinilla, study co-author and wildlife veterinary epidemiologist at the Illinois Natural History Survey.

Another important finding, according to Mateus-Pinilla, were the differences in the cats’ ranges. While, not surprisingly, un-owned cats roamed further afield than owned cats, Mateus-Pinilla and her co-authors were surprised by how far the stray cats strayed and by the diversity of habitats they skulked in, as compared to pet cats. While most of the pet cats stuck close to home, the most itinerant stray cat wandered around a 547-hectare (1,351-acre) area.

From original map by Jeff Horn

Despite range differences, un-owned and owned cats’ territories can overlap. The red outline shows the largest range tracked for an un-owned cat in the study, and the yellow dot indicates one pet cat’s range.

“Because of the large home range sizes in the evidence of both cats without ownership and cats that are owned, their home ranges are overlapping. And because of the mortality evidence, these animals could be facing a certain amount of risks that we are unable to measure,” said Mateus-Pinilla.

Indeed, the risks of being a free-range cat are much higher than those of indoor cats, and if the cat has no owner, its fate is almost always bleak. In their study, six stray cats died, while only one owned cat died.

Mateus-Pinilla said their study raises many new questions. To The Why Files, however, it seems that living in the company of humans has its advantages for cats. But keeping this relationship indoors may have advantages for wildlife and people too—-implications that drive the otherwise curious research on free-roaming cats.

Too many kitties on the range

While the indoor-outdoor debate lives on in the cat owner community, and regardless of whether or not cats enjoy the out-of-doors, their secret lives outside entail some dirty secrets that are alarming scientists and laypeople alike.

The sheer number of free-range cats, owned or not, has become a conservation and health concern, some scientists say. Like any species, too many can spell trouble.

Cats, by nature, are superb predators. A cat stalking a bird or squirrel is simply doing what cats do. However, their prowess as hunters, combined with their overpopulation, has wildlife biologists and enthusiasts biting their nails over the potential endangerment or extinction of some prey species.

“There are a growing number of landscapes in which free-ranging cats are not only the most abundant mid-sized mammalian predator, but they can outnumber all of the native mammalian mid-sized predators combined. So they really do become the dominant mid-sized predator in many landscapes,” said Stanley Temple, an emeritus professor of forest and wildlife ecology at the University of Wisconsin-Madison, who was among the first to study the ecological impacts of free-roaming cats.

Because of their impacts on both native predators and prey, conservation scientists consider free-roaming cats invasive species. While not the greatest threat to wildlife, they add to the increasingly complex web of existing threats.

Species most at risk of death-by-kitty are birds that spend a lot of time on the ground, small mammals and reptiles, according to Temple. In fact, cats are second to habitat destruction as the cause of bird extinction. Thirty-three bird species have met their fate to the paws of cats since the 1600s.

The world’s ever-shrinking “islands” of wildlife habitat are hotspots of conservation concern over free-roaming cat populations, since the native species in these areas are the hardest hit by invading cats. For example, birds that live in America’s dwindling grasslands or on the increasingly crowded seashore are finding themselves in a precarious situation.

Open and fragmented landscapes, which also include forest outskirts and farmland, are the territories of choice for cats. And, except in subtropical locales, they tend to stick close to humans. Even if un-owned, most cats are still dependent on people for either food or shelter, or both.

“They are remarkably resourceful at taking advantages of the opportunities that we present,” said Temple, who clarified that free-roaming cats are only truly “feral” if they are completely independent of humans.

Their dependency on humans highlights another dilemma: free-range cats can easily spread diseases and parasites that can jump from cat to cat, cat to wildlife, and even cat to human. The list of contagions includes feline leukemia, feline immunodeficiency virus, worms, rabies and toxoplasmosis, a parasite-caused disease that can damage the developing brains of unborn human babies, if their mothers are infected.

Free-roaming cats’ close proximity to both humans and other animals thus creates a potentially strong reservoir for these diseases. While vaccinating both owned and un-owned cats can help reduce the spread of disease, vaccines are not 100 percent effective and the logistics of vaccinating every single cat may be impossible, especially since many vaccinations are annual.

Photo: Rodrigo Basaure

These street cats certainly benefit from a human handout, but do humans benefit from the cats’ potential disease threat?

It’s complicated

Indeed, solutions to these predicaments aren’t easy. While the science may seem to imply that rounding up every cat on the range may be the best solution, the ubiquity of free-roaming cats and the emotions wrapped up in some people’s relationship with felines complicate the matter.

Studies suggest that many free-range cats are people’s beloved pets that are allowed outside, said Temple. But, while keeping every pet cat indoors would significantly and immediately cut the number of free-range cats, not every cat owner agrees that indoor life is best for kitty.

To further complicate things, one of the often promoted “humane” methods of attempting to reduce un-owned cat populations — trap, treat, neuter, release — repeatedly fails. Not only are there always the cats that get away, but releasing the cats back into the “wild” still does not eliminate the risks to wildlife.

Temple believes that for a cat-control method to work, three criteria must be met: the strategy must actually control cat numbers over large areas, it can’t harm any other part of the ecosystem, and it is socially acceptable. The last criteria can be the trickiest to meet and often creates tension between humans.

Photo: Flickr

Is this outdoor kitty taunting his indoor pal? But who has the better life?

“The divide over how to deal with cat overpopulation, in one way, can be simplified as the group of people who are really concerned about ecological impacts of cats versus those that are really concerned about the welfare of individual animals,” said Temple, based on his years of experience conducting public outreach on the issue. He clarified that he likes cats and is actually the owner of a 21-year-old feline.

Temple believes solutions that meet both factions on common ground do exist. Keeping pet cats inside and trapping, treating, neutering and confining un-owned, free-roaming cats are two strategies that meet his criteria. Though, for some people, it will take some convincing.

Mateus-Pinilla was careful to emphasize that their study did not seek to evaluate management options. They were focused on adding to the science and remaining neutral in the debate about solutions to the issue of free-roaming cats.

– Jenny Seifert

For controlling agricultural insects, bats are worth at least $3 billion a year to U.S. agriculture, according to a 2011 study from Boston University. “People often ask why we should care about bats,” said study co-author Paul Cryan, a research scientist with the U.S. Geological Survey in Fort Collins, Colo. “This analysis suggests that bats are saving us big bucks by gobbling up insects that eat or damage our crops. It is obviously beneficial that insectivorous bats are patrolling the skies at night above our fields and forests—these bats deserve help.”

As conservation officials scramble to respond to white nose, they are enacting quarantines to prevent people – cavers, bat-lovers and scientists alike – from transporting the fungus between caves. Last year, for example, the National Wildlife Refuge System halted public access to all caves and mines on its refuges, and set protocols to prevent scientists from spreading the infection.

In May, 2011, the Fish and Wildlife Service rolled out a national plan for confronting and controlling white nose syndrome.

But bats can do plenty of transportation on their own. Even non-migratory bats may fly 200 miles between their hibernation site and their summer range, says David Blehert, a microbiologist at the U.S. Geological Survey National Wildlife Health Center in Madison, Wis., and a leader of white nose studies. “They can move large distances, across state lines, so there is potential for significant disease spread based on bat-to-bat interactions.”

What is the white nose syndrome situation now? Why is it so deadly? What bright ideas are afoot to preserve insect-eating bats, and what is the likely end game?

Why deadly?

In the short time since white nose syndrome appeared in 2006, scientists have pinpointed a fungus called G. destructans as the killer. But how does G. destructans do its work? One clue comes from the fact that it only kills during hibernation, when bats live in mines and caves at a rather chilly 7°C. “The fungus only grows in the cold, and when insectivorous bats hibernate in a temperate region, they drop their core body temperature to the ambient level,” says Blehert.

(The fungus is not likely to attack fruit-eating bats, says Blehert, because they do not have long periods of “torpor,” the slow-metabolism hibernation state that is conducive to the white-nose fungus.)

A low body temperature allows the bats to survive winter without eating, but it could also curtail the immune system, Blehert says. “Studies of bat immunology are in their infancy, but based on what is known about the physiology of other hibernating mammals, especially the 13-lined ground squirrel it’s likely that the immune system becomes suppressed, and that leaves them particularly vulnerable” to the fungus.

How does the fungus kill? It apparently does not enter systemic circulation, as internal organs are not damaged. All mammals awaken from hibernation occasionally, but Craig Willis of the University of Manitoba has speculated that infected bats have more waking hours, causing them to run out of energy during a period when they neither eat nor drink.

Blehert and his colleagues favor a second explanation: dehydration. Despite the “white nose” name, Blehert says, the most significant infection occurs on the wings. “The wings of a bat have eight times as much skin as the trunk; it’s a massive, very delicate and exposed membrane” with a single layer of epidermis surrounding a thin layer of connective tissue and some muscles and glands. “The fungus selectively invades the wing skin, and destroys everything in its path,” Blehert says.

Beyond their role in flight, bat wings are also needed to regulate temperature, fluids and electrolytes. “The wings may be the Achilles heel that exposes them to such significant infection,” Blehert says.

Indeed, an emerging disease that is devastating amphibians, the chytrid fungus, also affects the skin, and is thought to kill by causing an electrolyte imbalance. “The amphibian’s skin is very important for the balance of water and electrolytes, which has been the basis for our hypothesis about why white nose syndrome is so deadly. There was a paper¹ in 2009 that demonstrated that a superficial chytrid infection causes an ion imbalance in frogs, causing a disruption of the potassium gradient that causes the heart to stop. A superficial fungal infection causes a cardiac arrest! This is a very different concept than getting athlete’s foot and having an itchy foot.”

Stopping the wave of death

As dead bats pile up in caves, what can be done to stop the spread of G. destructans? The first step, trying to slow dispersal, is already under way in affected states, with restrictions on cave entry, and new protocols for disinfecting equipment and people who have a legitimate reason to visit hibernation spots.

The fungus does respond to common anti-fungal agents, according to a 2011 study, which found, unexpectedly, that the meds worked at the low cave temperatures that the fungus prefers. “The challenge is, how could you use pharmaceuticals to manage a disease in free-ranging wildlife?” says Blehert. “They don’t go to the doctor, and they inhabit environments that are likely contaminated with fungus. Say you could treat bats and cure them of the infection. If you can’t remediate their hibernation sites, they will become reinfected when they re-enter the cave.”

The authors of the anti-fungal study did raise the possibility of using meds to decontaminate caves, but this process is not being done, Blehert says. “Going into a cave with a general fungicide would be like dropping a nuclear bomb on a city. Caves are full of bacteria, fungi, invertebrates and vertebrates that may only exist in that unique ecosystem, and getting rid of such an important group of organisms [fungi] could risk significant unintended consequences.”

Willis has proposed using little heaters, since bats seem to fare better in warmer regions of caves, perhaps because that sustains immune function. Small heaters are being tested as bat refuges in some New York State caves, says Lisa Warnecke, a post-doctoral fellow at Manitoba.

Lessons from Europe

G. destructans is an “emerging exotic disease,” and to investigate such diseases, scientists always want to know how the pathogen interacts with hosts in its land of origin, which seems to be Europe:

In 2009, the fungus was found in a greater mouse-eared bat in France²;

ENLARGE

Photo: Gabrielle Graeter, NCWRC

Is this bat unhappy about the tufts of fungus on its muzzle — or the researcher’s big hands?

During the winter of 2009-2010, infected bats were found in 76 of 98 sites in the Czech Republic; and

A 2010 study³ in Europe found a white nose pathogen in 21 of 23 suspected bats that was “100% identical” to the U.S. pathogen.

Although the fungus been found in at least five bat species in Europe, die-offs have not been seen there, suggesting that something is different about how the pathogen, host and environment interact. Pathogens and hosts co-evolve through time in a complex dance:

The pathogen may become milder, improving its own survival (and that of its host);

hosts may evolve immune resistance; and

hosts can change their behavior to reduce exposure to the disease.

In the lab in Manitoba, Willis and Warnecke are studying how long little brown bats are awake during hibernation, whether the fungus is a necessary and sufficient cause of death, and if the North American or European strains of fungus have different effects on the bats. “If both isolates show the same severity for North American bats, that may mean that bats in Europe have co-evolved with the fungus and are resistant to it,” says Warnecke. “On the other hand, if the European isolate does not cause trouble for North American bats, then the fungus in North America is a mutant that has gotten really aggressive.”

Other factors could explain the lack of disease in Europe, says Blehert. “European bats are larger, which may provide them with more of a buffer against a physical insult like a fungal infection.” The little brown bat, the preeminent victim of white nose, weighs about 6 grams – about the weight of two pennies, Blehert says.

European bats also tend to hibernate in small groups. “They don’t have those 100,000-plus hibernacula like we see in the United States. With fewer animals, the disease transmission dynamic is likely to be reduced, with less amplification of the fungus, and lower rates of bat-to-bat transmission.”

In the long run, Blehert says, American bats may evolve some resistance. “In general, the population decline in caves and mines comes to about 78 percent, but the bats have not disappeared. We would expect something that gets into population to cause high mortality and a steep drop-off in population. Then, with fewer animals around, disease transmission could moderate.”

Although the regional extinction of the brown bat has been predicted to occur 16 years from now, “our bats may ultimately develop population dynamics more like Europe, with fewer animals and moderated disease transmission and progression,” Blehert says.

Evolution, in other words, could select for animals that, for behavioral or immune reasons, are less susceptible to white-nose.

But letting the situation play out without trying to help the bats, Blehert says, amounts to a high-stakes gamble with one of the wonders of the night sky.

Hoping to avert a biological infestation that could eventually stretch across a band of southern states, the U.S. Fish and Wildlife Service has proposed to ban the import and interstate transport of nine giant constrictor snakes. After the comment period expires May 11, the agency will review its options and consider whether to push forward with regulations.

The proposal was not popular with snake enthusiasts and the pet trade, but these giant constrictors are big, fearsome predators that can even kill alligators and panthers.

In short, these snakes (including the boa constrictor, four pythons and four anacondas) seem more suited to Tarzan movies than Florida travel brochures.

The major existing threat comes from thousands of Burmese pythons living in and around Everglades National Park, where the 2006 discovery of a nest confirmed that the python is breeding. It’s uncertain far north the snake is established, but Art Roybal, a Fish and Wildlife Service biologist in Florida, says they are “most likely” breeding in the Myakka River drainage in Sarasota County, but “Future events will determine whether that likely population can persist, spread, or extend to additional animals.” (Here’s a map of Burmese python sightings in Florida).

Although Burmese pythons seldom attack humans, some have killed their owners in captivity.
Fish and Wildlife is also proposing to ban the import and interstate transport of eight other giant constrictors, including the boa constrictor, which has been established for decades west of Miami, and the northern African python, which may be reproducing in South Florida. The agency hopes to designate the snakes as “injurious wildlife” under the Lacey Act.

Over the last 10 years, more than 1.8 million live constrictor snakes, including 12 species, were imported into the United States. Most, however, are ball pythons, which are not included in the Lacey-act proposal.

The snake problem arises almost entirely from pet owners, says the wildlife agency. Some of the invaders (or their ancestors) are escaped pets. Others came from pets that grew big and were dumped into the wild by owners who did not know, or did not care, that these animals could start to play house in the hospitable southern clime.

Although snake dealers generally disdain these proposed restrictions, Gordon Rodda, a U.S. Geological Survey invasive snake expert, says “there already are tens of thousands of these snakes in captivity in the United States, and no-one is proposing any restrictions on that. Private possession of pets is a state responsibility. These proposed rules would affect only the import of new stock and transport across state lines, not the keeping of existing stock or their progeny.”

The art of the invader

Invasive species, whether plants, mammals, insects or reptiles, have inherent advantages over natives: they often lack diseases or predators, and native wildlife and vegetation cannot counter their competitive tactics. “We are talking about non-native predators that our native species have not evolved to cope with,” says Roybal. “They get so large, up to 200 pounds and up to 20 to 23 feet long. They are a sit-and-wait predator. The native species are not used to animals of that sort, and haven’t developed behaviors to avoid them.”

The large constrictors are especially dangerous to threatened and endangered species, says Roybal. “The thing that really opened our eyes was the consumption of three key largo woodrats [by the python] in the Florida keys. This is a very imperiled species, there probably are only 200 to 300 left in the wild. If a large constrictor got established in the keys, it could mean severe impacts and possibly extinction.”

The Burmese python could occupy all of Florida, experts say, and even spread far beyond, according to a U.S. Geological Survey study of the snake’s climate requirements.

Roybal adds that the boa constrictor, and possibly the reticulated and Burmese pythons, recently started breeding in the forests of Puerto Rico, where officials has already removed more than 100 boas. “This is not just a Florida problem,” he says.

Photo: Guam DOA

The last wild Guam flycatcher was seen in 1985; the bird is extinct due to the brown tree snake.

Unimpressed with the threat of invasive snakes? Then check out Guam, where the brown tree snake has eliminated 10 native birds since arriving in about 1950. As many as 13,000 brown tree snakes occupy a square mile on the island.

This venomous snake does not shy away from housing, so it also poses a safety threat.

Brown tree snakes have since hitchhiked from Guam to several Pacific islands, yet there are finally signs of progress in controlling the repellent reptile, says Gordon Rodda, brown tree snake guru for the U.S. Geological Survey. To halt further invasions, Rodda says, “The first and most intense effort was getting them away from the port and airport; that’s been very successful.”

The next step, Rodda adds, is to “expand the defensive perimeter and clear the whole island” with poison bait. Because Guam has no native snakes, “We can put out bait and only the brown tree snake will eat it. In Florida, they have a large number of native snakes and … you can’t go and poison them willy nilly.”

Photo: U.S. Geological Museum

After the brown tree snake invaded the Pacific island of Guam, 10 of 12 native birds disappeared.

If the brown tree snake can be eradicated, it would be logical to restore native birds from other islands, but Rodda says most of Guam’s suitable habitat is owned by the U.S. military, which is unreceptive to the idea.

Controlling giant constrictors

GRNAME IMG_0572.JPG
CAPT The art of camouflage. A python basks near a canal in the Everglades. Pythons are hard to see, and most of the Everglades is inaccessible to people, so even removing pythons from roads and levees will barely dent the population.
ATTRIB Photo by R.N. Reed/USGS
ALTTX

Why not just trap these invading snakes?

When it comes to invasive species, and especially snakes, experts agree that prevention trumps eradication. The Burmese python is extremely difficult to find, as it “lives in the middle of the Everglades, the largest wilderness east of the Mississippi River, and in national wildlife refuges,” says Frank Mazzotti, an associate professor wildlife ecology at the University of Florida.

“People don’t really appreciate how hard it is to catch a Burmese python,” says Mazzotti, an expert on snakes in South Florida. In studies of other snakes, he adds, “when people knew the snake population and had well-developed methods for finding and catching them, if they catch 10 percent of them, they feel extremely lucky. It’s not unusual to catch more than 50 percent of a mammal population.”

In an effort to contain the invasion in Florida, federal agents have already trapped a Burmese python on Key Largo, the first major link in the chain of fragile islands called the Florida Keys.

GRNAME Rozar 2009 Goetz MEDIUM-BIG
CAPT A biologist removes a trapped Burmese python on Key Largo. How many evaded the traps?
ATTRIB Photo by R. Rozar, USGS.
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Snakes in general are camouflage experts, says Art Roybal of the Fish and Wildlife Service. “We are told by scientists that for every one snake that you do see, there are 1,000 that you don’t see. … Large constrictor snakes are notoriously cryptic and often hidden and immobile and are therefore difficult to detect.”

“You have to understand the difficulty of finding an animal that looks like a vine that is spread over 10,000 square kilometers of woody swamps,” adds Gordon Rodda of the U.S. Geological Survey. “There is no track record of success in controlling invasive reptiles and snakes. There are reasons to be pessimistic that the Florida population [of Burmese pythons] will ever be controlled.”

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CAPT To slow the invasions, agencies in South Florida are imploring pet owners to find a responsible way to get rid of their pets. Florida now stages periodic “amnesty days” where owners can safely dispose of unwanted snakes.
ATTRIB Army Corps of Engineers
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Along with many other biologists, Rodda, who heads the USGS response to the brown tree snake on Guam, says, “Prevention is way better than fighting the crisis once it’s occurred. Once the snake is established, your chances of eradication are virtually gone.”

Meager options for control and eradication

When the USGS looked at predators and diseases for controlling snakes, it saw no good options. Predators are futile against snakes that can fight back against the big teeth: Burmese python can eat leopards and panthers, and Mazzotti says a captured 16-foot Burmese python threw up a 6-foot, 30-pound alligator. “‘Wow!’ doesn’t even do it justice. It was amazing!”

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TITLE World Wildlife Wrestling FOLLOW WITH A TRADEMARK SYMBOL?
CAPT An American alligator wrestles for keeps with a Burmese python in Everglades National Park. Although the gator seems to have the upper hand (upper fang?), pythons are powerful enough to eat gators.
ATTRIB USGS
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In these struggles, “Probably more often than not, the alligator win, but that doesn’t mean their numbers will be significantly be depressed by alligators,” says Rodda. The death-tangle between a giant snake and a big toothy gator may be eye candy for TV, “but if a small alligator gets pulled from the water at night and swallowed, you are never going to see that. If the alligator was sufficient to control the Burmese python, the snake would not have spread.”

When experts examined 57 potential predators to control the brown tree snake on Guam, none were deemed acceptable. Indeed, introduced predators are not much good for controlling invasive animals, according to the USGS:

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“The record of successes is small, and the number of catastrophic failures (non-target species decimated or even driven extinct by the predator) is large. As a result, it is against U.S. Fish and Wildlife Service policy to introduce predator-based biocontrol agents for vertebrates (there is also a question as to which higher order predator would qualify for preying on giant constrictors!), and we will not entertain that notion further.”
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CAPT Researchers implant a radio transmitter in a 16-foot, 155-pound female Burmese python at Everglades National Park. Radio-tracking shows the snake’s movement, helping guide control efforts.
ATTRIB USGS
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Could bugs or bounties work?

Pathogens – viruses, bacteria or fungi – could theoretically be used if they were specific enough to target the invasive snakes, but Rodda says that the knowledge of snake diseases “is all about snakes in captivity. Nothing is known about transmission of disease in the wild.”

Considerable time and money would be needed to research pathogen control against the giant constrictors, according to the USGS.

The vertebrate immune system can adapt to many new pathogens, and viruses sometimes evolve to become less lethal. When Australian authorities tried to eliminate a massive outbreak of introduced rabbits with a virus, the virus worked at first, and then the rabbits returned to running rampant.

Bounties were used to eradicate wolves from most of the lower 48 states, but bounties can boomerang if hunters breed the target animals in captivity or distribute them to new habitat. On the Caribbean island of St. Lucia, for example, bounty hunters began breeding the fer-de-lance, a deadly invasive snake from Africa, that was targeted for elimination. “Once you start assigning a value to invasive animals, there is an impetus to some people to keep them out there,” says Robert Reed, a USGS invasive species scientist and herpetologist, “And there is no funding that would allow us to hire people to catch snakes.”

The trapping option

Several projects have tested whether Burmese pythons in Florida can be trapped without harming native snakes and wildlife. Traps can either attract snakes with bait, or be located along a fence that intercepts the snakes and ushers them into a trap.

Reed says both types of traps have caught Burmese pythons in South Florida, but trapping experiments are at an early stage, and the ideal trap probably depends on the context. For example, some former farmland on Florida’s mainland has so many rats that “attractants may not work well because the snakes don’t have to hunt around for food.”

Although it’s too early to know how much trapping will cost, they are not a magic bullet. “Traps alone will not be sufficient to eradicate the Burmese python from the Everglades,” Reed says. “It might be a great option if we are trying to locally control snakes around an area with high ecological value, such as a wood stork rookery,” where reducing the snakes without eliminating them might allow the birds to survive.

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CAPT This trap for Burmese pythons, in use at Key Largo, is about 2 meters long and has entrance funnels at each end; the live rat that serves as bait is protected by a smaller cage from the snake.
ATTRIB Photo by R. Rozar, USGS
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A changing ecosystem?

As Burmese pythons spread through South Florida, it’s too early to say for sure how they are changing the Everglades, an ecosystem that has already sustained massive invasions from other animals and plants, not to mention numerous disturbances to natural water flow.

Some rare species have already been found inside snakes, but biologists are also noticing that some common species are becoming scarce. “In the 1970s, ’80s and ’90s, when I used drive the main [Everglades National] park road, I would see marsh rabbits maybe every 50 meters,” says Mazzotti. “Now I don’t see them anymore, zero; and we are finding fewer in the stomachs of pythons. We find lots of marsh rabbits in areas without pythons. That’s a correlation that does not imply cause and effect, but these are the kind of impacts you would expect.”

As the spotlight turns to the nine giant constrictors, Reed says invasive reptiles are always tough to control. A recent scientific review, he notes, “saw no evidence that an introduced reptile population had every been intentionally eradicated. These are cryptic animals and by the time you notice them, the odds are pretty decent that they are already established.”

Into constrictor control? Meet the strict constrictionists in our bibliography.