August 13, 2013
Last month, alarming numbers of dead bottlenose dolphins started turning up on the beaches of Virginia and other states in the Mid-Atlantic region. In an average July, the Virginia Aquarium & Marine Science Center—which operates a Stranding Response Team to collect and analyze beached animals—encounters seven dolphins washed ashore. In July 2013, the team picked up 44 animals.
Overall, the East Coast has seen at least 124 dolphin deaths since July—a rate that authorities say is seven times higher than normal. All of this led the National Marine Fisheries Service, a branch of the NOAA, to officially designate the deaths as an “unusual mortality event” last week, which means that increased federal funds will be allotted to help researchers investigate what’s going on.
Currently, dozens of marine biologists along the Atlantic are examining stranded dolphin carcasses for clues. Last week, Charles Potter, a marine mammal expert with the Smithsonian Natural History Museum, traveled to Virginia Beach to assist with the Virginia Aquarium & Marine Science Center’s investigation.
“We basically perform necropsies of the carcasses that come in,” Potter says. “We’re assuming nothing, and looking at the entire animal for the cause of death, and any abnormal tissues. We also harvest a whole suite of specimens from each carcass, and these are sent out to labs for analysis.” During his time in Virginia Beach, he conducted five in-depth necropsies—animal autopsies—in total.
The investigation is still in its earliest stages, but researchers have a few potential suspects in mind. In 1987—when the last major die-off of Atlantic dolphins occurred, resulting in the deaths of 740 animals—morbilivirus was found to be the main culprit. At least one dolphin found this year has tested positive for the same virus, which produces lesions in the lungs and central nervous system tissue, and Potter speculates that the time that’s passed since the previous epidemic has allowed for a generation of dolphins never exposed to the pathogen.
But establishing a potential cause of the die-off as a whole is much harder than diagnosing a particular cause of death for any one individual. With humans, if you ask someone in the hospital what a specific patient died from, you may be told that the person had pneumonia, explains Potter, who also participated in the 1987 investigation. “But that’s only because we become so debilitated by other factors that, at some point, we can’t clear our airways, and we develop these pneumonia infections,” he says. In much the same way, it’s possible that a susceptibility to morbilivirus or other pathogens found in the dolphins could be caused by a separate, underlying factor.
That underlying factor might be a particularly disconcerting one: humans. Disproportionate numbers of males and calves are among the dolphins turning up dead, which makes Potter and other suspicious that environmental contaminants—such as heavy metals, pesticides and hydrocarbons—might play a role.
“Males don’t have a mechanism for shedding contaminants,” he says. “The females shed significant amounts of their lipid-soluble contaminants through lactation, so the calf gets a hell of a dose early on in life, and some of the most outrageous levels of contaminants we’ve seen have been in calves.” It’s possible that the overall buildup of contaminants in these animals—along with other stresses attributable to human activity, such as increased noise and competition for space and food with humans—is making them more susceptible to infectious pathogens.
Potter says that he and other investigators will continue testing the dolphins for the virus, contaminants and other factors so they can try to find further clues to solve the mystery. Getting the animals in a fresh condition is crucial to collecting as much useful information as possible. “All too often, the response team will go out and pick up a carcass and will hear that it was first seen the night before, so by 9 o’clock in the morning, it’s been lying out there since sunup, and we’ve lost a tremendous amount of data,” he says. “As soon as someone sees a dolphin, whether dead on the beach or in distress, they need to call it in to the authorities immediately.”
The NOAA operates a Stranding and Entanglement Hotline for all marine life. If you find a dolphin, they recommend staying away from it and calling the hotline at 1-866-755-6622.
August 6, 2013
Last week, we looked at evidence that bottlenose dolphins use distinctive whistles to identify themselves, suggesting that these creatures, among the smartest in the animal kingdom, use the noises in a way that’s roughly analogous to our use of names to identify people.
Now, a separate study confirms dolphins’ ability to recognize these “names”—and indicates that they’re able to remember them over time far longer than we imagined. In tests of 43 dolphins kept in captivity around the United States, Jason Bruck of the University of Chicago found that the animals reacted differently upon hearing whistles that belonged to dolphins they’d shared tanks with up to 20 years previously, as compared with those of dolphins they’d never met.
The findings, published today in the Proceedings of the Royal Society B, could force us to reconsider what we imagine animals are capable of remembering over time. If they hold up, they’d represent the longest-held memories we’ve seen thus far in any non-human animals.
The basics: High-pitched whistles, or “chirps,” are made by bottlenose dolphins in friendly social settings. Acoustic analysis has shown that the whistles differ slightly from individual to individual, and that the whistle a particular dolphin makes is consistent over time.
Previous studies with this dolphin species have found that the animals are more likely to move towards a speaker [PDF] emitting the whistle of of a relative than a random bottlenose and that mothers frequently emit the whistles of their calves when separated from them, suggesting that they’re calling out their names in hopes of finding them.
For this project, Bruck sought to test the animals’ ability to distinguish between whistles of dolphins they’d previously shared tanks with from those of others they’d never met. Relying on records kept by a consortium of six different aquatic facilities that frequently rotate dolphins for breeding purposes (the Brookfield Zoo in Chicago, the Indianapolis Zoo, the Minnesota Zoo, Dolphin Quest: Bermuda, the Texas State Aquarium and The Seas at Walt Disney World), he was able to sort out which of the 43 dolphins included in the study had previously lived together, and which had never met.
To test their memories, he used an underwater speaker to repeatedly play various dolphins’ recorded whistles and then observed their responses, specifically noting whether they largely ignored the noise, turned their head towards the speaker, swam towards it, or even made forceful contact with the gate protecting the acoustic equipment.
When they dolphins heard unfamiliar whistles, they tended to get bored quickly, showing little response. On the other hand, their reactions upon hearing whistles from animals they’d previously lived with were notably different. “When they hear a dolphin they know, they often quickly approach the speaker playing the recording,” Bruck said in a press statement. “At times they will hover around, whistle at it, try to get it to whistle back.” This held regardless of the age or sex of the animal, and was also true for both unrelated pairs of dolphins that had lived together and family members.
The time period for which the dolphins had been separated from others ranged widely, from 4 to 20 years. Interestingly, though, quantitative analysis of the reactions showed that the time apart made no difference: Whether the pairs had been separated for 5 or 15 years, the dolphins demonstrated a similar level of response upon hearing a familiar whistle.
In the most extreme example, Bailey (a female dolphin who now lives in Bermuda) recognized the whistle of Allie (who lives at the Brookfield Zoo). They most recently lived together at Dolphin Connection in the Florida Keys, 20 years and six months ago.
Previously, monkeys have demonstrated the ability to remember the faces of other monkeys after three years apart, while elephants have been shown to recognize others’ vocalizations ten years later. If these new findings are accurate—and the dolphins’ behavior truly reflects memories they’ve held for decades, rather than, say, reactions to some other aspect of the recordings—they’d be the longest-held memories by any animals species by a wide margin. Along with other recent research on the surprising distinctiveness of individual animals’ personalities, the findings reveal how, in many ways, the most intelligent animals differ less from humans than we long imagined.
They also prompt another question, ripe for further research: When the dolphins appear to react to the whistles, what exactly is going on in their minds? It’s easy to speculate that the noises correspond to names, it’s hard to say how far the analogy can be taken. “We don’t know yet if the name makes a dolphin picture another dolphin in its head,” Bruck said. “That’s my goal—to show whether the call evokes a representational mental image of that individual.”
July 22, 2013
If you’ve spent any time around bottlenose dolphins—or even watched Flipper—you’re probably familiar with the sound. The marine mammals make high-pitched, repetitive whistling noises constantly, whenever they’re engaging in friendly social interactions:
Researchers have long noticed that different dolphins each produce their own idiosyncratic whistles; as a result, some have speculated that these sounds might correlate to something like dolphin “names,” with each creature repeating its own name as it mingles with others.
In 2006, Stephanie King and Vincent Janik, a pair of biologists at the University of St. Andrews in Scotland, found that (pdf) dolphins were more likely to move towards an audio speaker emitting the whistle of a relative than a random, unrelated bottlenose, suggesting that the unique acoustic signature of the chirp conveyed some information about the dolphin that produces it.
Then, this past February, they published another study that gave further evidence to this idea, as they found that mothers were likely to copy their offspring’s distinctive whistle when they were temporarily separated during experiments. The paper provided the tantalizing suggestion that the mothers were “calling out” for their calves, much like humans would do if they were similarly separated.
Now, an article published today in the Proceedings of the National Academy of Sciences provides further evidence that these whistles are used to distinguish one dolphin from another, and that the dolphins identify themselves by the sound of their own chirp. In the study, the researchers found that when they recorded the signature whistles of wild bottlenoses and played them back to them, they responded by repeating the call. When the researchers played the chirps of other dolphins, the creatures stayed silent, or made unrelated, non-whistling noises.
King and Janik gathered data over the course of a decade by following wild bottlenose populations off the east coast of Scotland and recording the distinctive whistles. For each experimental trial, they used underwater speakers to play the dolphin groups one of three types of chirps: an exact copy of the one of the dolphins’ own whistles, the whistle of another dolphin in a nearby group that may have been familiar, or the whistle of an unfamiliar dolphin from a distant population. The dolphins’ responses (if any) within the next minute were recorded.
Later, when the team blindly interpreted the dolphins’ recorded responses—that is, listened to the speaker’s call and the dolphin’s response, without knowing if the speaker had initially played a familiar or unfamiliar whistle, and simply coded whether the two sounds matched—it turned out that the animals were far more likely to call back to the whistle with the same one if it was their recorded chirp in the first place.
For eight of the 12 trials using a member of the group’s signature whistle, at least one dolphin in the group responded back with it, compared with just two of the 22 trials using either the familiar or unfamiliar controls. Additionally, the bottlenoses were much more likely to swim towards the speaker when it was one of their group’s chirp played, further suggesting they were responding to a well-known stimulus.
Admittedly, there are several hurdles to be cleared before we can confidently say that the dolphins are responding to their own names by calling back. The most significant issue with this particular experiment is that the researchers had no way of knowing which dolphin in the group responded to the speaker in any given instance, so it could have been the dolphin whose whistle was just played, or another one. They attempt to account for this by comparing the data to background rates of whistle copying in dolphins and find that it’s unlikely other dolphins in the group are responsible, but it’s still a limitation.
Nevertheless, combined with their previous work on dolphin whistles, this work suggests that dolphins’ signature chirps have a clear individualized meaning when used in social settings. And though some scientists disagree, it’s tempting to speculate that when they played the whistles, the researchers were effectively calling these dolphins by name—and the dolphins were repeating it back to them, as if to say, “I’m right here.”
If this were true, it’d mean that these dolphins have a significantly different grasp of vocal signals to import meaning than any other non-human animals we know of. Birds, bats and elephants all use specific sounds to label particular items in their environment, but researchers believe these acoustic markers are static—they’re simply taught by a parent to an offspring and then repeated over time. If dolphins are assigning unique, arbitrary names to each individual, it suggests they’re more like us than we’ve ever considered.
July 11, 2013
When most people think about organisms growing on the seafloor around Antarctica (if they think of them at all), a few short words come to mind: cold, slow, and dull. But under the right conditions, seafloor life on Antarctia’s continental shelf can grow very quickly, according to new research published today in Current Biology. The collapse of ice shelves in the Antarctic over the past two decades due to warmer waters bathing their undersides has already changed seawater conditions enough to allow typically slow-growing communities of glass sponges to sprout up under the more transient sea ice that has replaced the shelf.
“These things aren’t as unexciting as we thought; they are actually very dynamic,” says polar ecologist James McClintock of the University of Alabama, who was not involved in the research. “The idea that they [glass sponges] could recruit and grow rapidly when these ice shelves break up is exciting, and suggests that the seafloor is going to change more quickly than we imagined.”
Glass sponges are the architects of the most diverse community on the seafloor under ice shelves. Like corals, glass sponges provide habitat for many other organisms. Their basket-like inner cavities are rare nurseries in the cold water, and small marine isopods, juvenile starfish, brittle stars, and even fish eggs have been found inside. As they die, they leave behind silica mats meters deep on the seafloor, providing prime substrate for crinoids, anemones, and other sponges to settle and grow. Also like corals, glass sponges grow slowly. Most grow only two centimeters each year, which makes the largest ones hundreds of years old.
Food scarcity is the reason for this slow growth. Antarctic waters have a very short growing season just weeks long, when sunlight and warmer water foster blooms of phytoplankton. During this brief period, phytoplankton feeds zooplankton, and waste products from the latter organisms feed bacteria and animals (like glass sponges) that filter particles and bacteria from the water. Even how much of that bounty an animal receives depends on whether it has settled in a current carrying food–or if those manna-bringing currents are blocked by ice. That said, it’s no surprise that, with so little food available, most organisms on the seafloor grow very slowly.
Ice also poses a hazard to life on the Antarctic seafloor. Icebergs and other types of sea ice, if they encounter shallower waters from where they calved, can dig ditches into the seafloor up to 350 meters wide and 15 meters deep, obliterating any living organisms from the area. Ice crystals (known as anchor ice) can grow on non-moving objects such as sponges, rocks and seaweed, eventually causing them to float up from the seafloor and merge with the ice ceiling. Additionally, brinicles, icy fingers of saltwater, shoot down from frozen ice at the surface, killing everything they touch as they spread across the seafloor.
But the past couple decades have seen changes to the ice cover in the Antarctic. Two large ice shelves known as Larsen A and Larsen B collapsed in 1995 and 2002 respectively. This freed more open water for phytoplankton to bloom, left more seafloor area free from regular iceberg scraping, and potentially altered how warm water and food circulate through the area. But given the slow pace of life in Antarctica, scientists weren’t expecting to find much when in 2011 they cut through the transient sea ice to survey the
seafloor once beneath the Larsen A ice shelf . Much to their surprise, they discovered that communities of small glass sponges had sprung up in the four years since their last visit.
In fact, the numbers of glass sponges had doubled, many belonging to smaller species that are not as common on older Antarctic sponge reefs. And the researchers saw a large increase in the number of sponges between 50-100 square centimeters in volume, suggesting that the young sponges had grown very quickly—and certainly more quickly than just two centimeters a year.
The sudden availability of free space and an influx of food likely explain how these sponges were able to grow so quickly. But where did this extra food come from? Paul Dayton of the Scripps Institution of Oceanography, who studied the ecology of Antarctica’s surrounding sea floor for many years but was not involved in this study, hypothesizes that the melting of the ice shelves increased currents, waves and wind in the area, stirring up the seafloor and resuspending particles and bacteria for the sponges to eat.
The study of the growth of one community in one part of the Antarctic may seem small. But it’s an example of how we can’t predict how ecosystems are going to react to climate change. It’s possible that glass sponges will be “winners,” able to grow better in the particle-heavy water mixed up by currents, or it may just be a short-term change. “I personally see this more as a pulse than [a community] being taken over by glass sponges,” says Dayton. “But with the huge changes coming down as a result of warming and loss of sea ice, it very well could result in a massive change in the Antarctic benthic community.”
June 21, 2013
Sharks have it tougher than most when it comes to public relations. Unlike a number of disgraced celebrities, politicians and athletes who’ve somewhat managed to come out on the other side of a scandal, the marine creatures haven’t been able to shake their bad reputation for 38 years. What’s more, they probably didn’t even deserve it in the first place.
Stephen Spielberg’s Jaws, which premiered this week in 1975, was adapted from a 1974 novel of the same name. The book was inspired by real-life events, a series of shark attacks along the Jersey Shore in July 1916 that killed four people. The type of shark behind the attacks was never confirmed, but Spielberg picked the prime suspect to be his villain: the great white shark. However, the movie has allowed viewers to paint all kinds of sharks as massive, bloodthirsty killers with a taste for revenge.
That’s about 440 species of sharks. Talk about one fish (unknowingly) ruining it for the rest of them
Here’s the thing: most of these sharks don’t have a taste for human blood—they don’t express special interest in mammal blood as opposed to fish blood. Diets vary across the many species around the globe, but they usually include other fish, crustaceans and marine mammals such as seals. The biggest species, the whale shark (which can reach up to 60 feet in length) only feeds on plankton.
And those supposed voracious appetites that in movies give them unnatural speed?
Most of the time, sharks are just not hungry. While they can reach up to 30 miles per hour or more in sudden bursts, they tend to cruise at a lackadaisical pace of about five miles per hour. And sharks that swim with their mouths open aren’t always in attack mode—they open wide to ventilate their gills.
Not all sharks are big enough to ram into and capsize unsuspecting boats, either. About 80 percent of all shark species grow to be less than five feet long. Only 32 species have been documented in attacks with humans, the repeat players being the great white, tiger and bull sharks. Your lifetime risk of suffering an attack from one of these predators is pretty small: 1 in about 3,700,000. Compare that to your odds of dying in a car accident (1 in 84), a fall (1 in 218), a lightning strike (1 in 79,746) or fireworks (1 in 340,733). Yet many people have an irrational fear of sharks, born from movies like Jaws.
Today, an emerging public relations campaign is underway to show that sharks aren’t the bad guys anymore—they’re the victims. According to the International Union for Conservation of Nature, 30 percent of open-ocean sharks and stingrays, their fellow sea dwellers, face extinction. True, 12 people are killed by sharks each year worldwide. However, 11,417 sharks are killed every hour by humans, adding up to roughly 100 million a year. Some of these deaths are intentional: sharks are often hunted for their fins to make soup or caught for sport, their toothy jaws kept as trophies. Others fall prey to recreational fishing or nets meant to protect humans. Still others die because their habitats are slowly disappearing due to human activity, which reduces their food supply and pollutes the water pumping through their gills.
The numbers are stark: In some parts of the world, the scalloped hammerhead shark population has shrunk by 99 percent in the last 30 years. In tropical Atlantic waters, the population of silky sharks is now half of what it was in he early 1970s. The Pacific’s whitetip shark population fell by 93 percent between 1995 and 2010.
This spring, an international organization implemented a ban on international trade in the whitetip, the porbeagle and three species of hammerhead sharks. The Shark Conservation Act, signed into law by President Barack Obama in 2011, closed loopholes in existing shark conservation legislation and promoted U.S.-led protection efforts worldwide. Even Discovery Channel’s Shark Week, which for a quarter of a century has hooked viewers with the promise of a fear-filled thrill ride, is partnering with conservationists to help boost sharks’ public image.
But perhaps the biggest shift in the Jaws-dominated shark culture is this: some survivors of shark attacks are actually teaming up to save the creatures that once nearly killed them. As shark attack survivor Debbie Salamone explains on their PEW Charitable Trust website, “If a group like us can see the value in saving sharks, shouldn’t everyone?”