Part of our weekly "In Focus" series—stepping back, looking closer.

When Louisiana Fisheries and Wildlife personnel discovered a dead bottlenose dolphin near Elmer's Island late last year, they figured it was another victim of the 2010 BPf oil spill.

So they were shocked when an onsite necropsy showed no signs of oil-related injury, or of bacterial infection, biotoxins, or disease—the most common causes of death in dolphins.

Instead, the Louisiana officials found a tiny piercing on the right side of the dolphin's blowhole. That hole would later reveal the cause of death: a small bullet lodged in the animal's lung.

The killing turned out to be another in a growing string of apparent attacks on dolphins and other marine mammals reported along the Gulf Coast in recent months.

According to a December report by the National Oceanic and Atmospheric Administration (NOAA), in 2012 three dolphins with gunshot wounds were found "stranded" (or washed ashore) along the Gulf Coast—the highest number since 2004.

In addition to those with gunshot wounds, several mutilated dolphins—with severed heads, missing tails, full-body slashes across their abdomens, and missing pieces of jawbone—have been discovered in recent months off the shores of Alabama, Florida, and Texas. While the general mortality rate has not increased in dolphins, scientists and animal-rights advocates are finding an unusual amount of evidence suggesting human harm to the animals.

Last June, for instance, a dolphin was spotted swimming in Perdido Bay, near the Florida-Alabama border, with a screwdriver sticking out of its head. A day later the dolphin was found dead in the water just west of Dupont, Alabama.

Such incidents prompted NOAA's Office of Law Enforcement (OLE) to launch a federal investigation last November into crimes against dolphins in the Gulf. Killing a dolphin or any other marine mammal is a federal crime punishable by up to $100,000 in fines and a year in jail.

Because the dolphin attacks have occurred sporadically, along all 1,680 miles of the Gulf Coast, officials do not believe they are the work of "one single madman," as Humane Society field director Sharon Young explains. "It may be comforting to think it's one person doing this," she says, "but it really isn't."

Unusual Cruelty

Getting to the reasons behind these deaths and injuries and piecing together the evidence needed to prosecute those responsible is proving tricky. At present, different theories abound.

Brian Kot, a post-doctoral marine research scientist at Texas A&M University, describes the dolphin shootings as a "thrill kill," in which gunmen use the marine mammals for target practice. As for the maimings, Kot suspects that such incidents almost always occur after the animals are already dead.

"Marine mammals often get close to boats, but they don't come into contact," Kot explained. "The only way a person could stab a marine animal is after it has died."

It's hard to imagine why a person would perform such a cruel act on an innocent animal, even if it were already dead. Yet psychologists see it all the time, most commonly in the form of antisocial personality disorder (frequently termed "sociopathy"), which is characterized by extreme disregard for the safety of others.

Herbert Nieburg, a Connecticut-based clinical psychologist and consultant for the Federal Bureau of Investigation (FBI), said patients with this disorder often pursue "wanton thrill-seeking" and get a pleasurable feeling of power from hurting a more vulnerable creature.

Not all people with the disorder commit violent crimes, he notes. But most of those who commit these kinds of acts—especially children who repeatedly hurt animals—will develop the disorder.

Randall Lockwood, senior vice president of the Forensic Sciences and Anti-Cruelty Projects department at the American Society for the Prevention of Cruelty to Animals (ASPCA), says, "One of the things that seems to underlie most intentional animal cruelty and acts of abuse is a need for power and control. A lot of severe animal cruelty [comes from an] absence of empathy, and also a sense that [the perpetrators] have a right to do these things."

In the case of the recent attacks on dolphins, Lockwood adds, it's hard to assess the killers' intentions.

The Humane Society's Young says that many people collect "souvenirs" from dead dolphins. "They may take a jawbone home because they think it is cool," she says, adding that some "collectors" will cut off the animal's tail.

No Friend of Fishers

Most documented cases of dolphin mutilations and shootings can be traced back to fishermen, though cruelty is not their prime motivator.

"There have been incidents of dolphins approaching boats and [raising] the ire of fishermen, who shoot at them in revenge," says Young. That "ire" stems from competition for resources, with fishermen fearful of losing their hard-earned haul—and profit—to hungry dolphins.

Moreover, dolphins occasionally get caught in the gears of boats. According to a NOAA analysis, "Fishermen often mutilate the carcasses of small cetaceans to facilitate disentanglement."

Allison Garrett, a NOAA spokesperson, says the cases involving fishers point to a larger issue: Many beachgoers feed the dolphins, which conditions them to associate humans with food. Since dolphins are avid learners and teachers, they pass that association on to their young.

So a fishing boat could look, to a dolphin, like an invitation for food and social interaction. This may lead to what NOAA officials calls a "brazen attempt," in which dolphins approach a boat and prey on the hooked bait, much to a fisherman's chagrin.

Trouble Far and Wide

Since the Deepwater Horizon disaster, officials and scientists who monitor the effects of oil on ocean life have increased their monitoring of the Gulf Coast. Young says that means "there are more eyes" in the area, and thus more reports of harm being done to dolphins in the region—though not necessarily more actual cases. (While the number of dolphin deaths since the spill has nearly quintupled, the increase has been mostly due to oil damage.)

Soon after the Deepwater Horizon oil rig began gushing, for instance, NOAA began to employ surveillance cameras, weekly helicopter flights, and broad aerial surveys to check the area for stranded marine mammals. Before the accident, such work was seldom done—meaning the likelihood of finding a stranded, maimed, or dead dolphin was low by comparison.

Of course, keeping watch doesn't mean that wildlife will be kept safe. Along the California coast, marine mammal cruelty has been reported for years.

Bill Van Bonn, chief veterinarian at the Marine Mammal Center in Sausalito, spends his days treating seals, sea lions, porpoises, and dolphins. In the past four years, he says, dozens of his patients have appeared with gunshot wounds. Only a few of these animals were eventually released back into the wild. The rest died naturally in captivity or were euthanized because of permanent damage from the wounds.

The center's data indicate that between 2001 and 2011, about 3 percent of the 5,000-plus sea lions treated had gunshot wounds. Van Bonn says the animals he sees represent only a small fraction of the marine mammals being targeted with weapons. Most are simply lost at sea.

A Concern Beyond Count

Indeed, the ocean swallows up much of the evidence that would help authorities prosecute crimes against marine mammals. All but two states—landlocked North and South Dakota—have felonious animal-cruelty laws against such acts.

While it's known that the BP oil spill killed many dolphins, it's unclear how the U.S. dolphin population is faring in general. The issue is one of tracking: There is no way to perform a dolphin head count in the open ocean. The only tracking done in the United States is through "stranding networks" that monitor beached dolphins.

In the coastal states, regional stranding networks—overseen by NOAA's National Marine Fisheries Service—are responsible for much of marine mammal protection and serve as the first responders for beached marine mammals. These networks, composed mostly of volunteers, were implemented in 1992 as part of the Marine Mammal Health and Stranding Response Program. The program was created through an amendment to the Marine Mammal Protection Act of 1972.

Witnesses who find a beached dolphin either contact their local stranding network directly or call the police, who then contact the network. Highly trained volunteers are then sent to the scene to investigate. Depending on what they find, the stranded mammal is either helped back into the water or transported to the closest marine mammal hospital. If the animal is dead when they arrive, the volunteers perform necropsies onsite.

But strandings cannot tell us much about overall dolphin numbers, and in other parts of the world stranding networks are rare. Additionally, different laws apply to different shores. While most of the world has condemned dolphin drive hunting—a practice in which hunters use boats and nets to trap, surround, and drive dolphins onto a beach, where they are killed for food or shipped to aquariums—towns such as Taiji in Wakayama, Japan, still practice the activity and see no cruelty in it. In other countries, like the United States, the practice is considered cruel.

Like whales, dolphins that swim in U.S. waters are safeguarded under the Marine Mammal Protection Act, which specifically forbids human harassment of dolphins—or, for that matter, any interaction with the species.

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