Even highly-sexed, smart mammals can be ‘mean jerks’
THE research vessel Martha Jane glided slowly across the teal waters of Sarasota Bay on Florida’s Gulf Coast under a cloudless sky.
“There’s 2094!” one of the scientists on the boat called out. “She’s still with us!”
The bottlenose dolphin known to researchers as 2094 had been the focus of a dramatic rescue from a fishing line a year ago.
Number 2094 is one of thousands of dolphins registered in the Sarasota Dolphin Research Programme’s database, each individual identified by the nicks and notches on their dorsal – or back – fins.
The world’s longest-running study of a wild dolphin population, the Sarasota effort has sighted and recorded more than 5750 dolphins and made the shallow waters of Sarasota Bay a living laboratory for 53 years.
In 1970, when the Sarasota Dolphin Research Programme launched, the mammals were the subject of numerous romantic myths, including that they were intelligent and kind – animals that could be friends and even movie stars.
However, research has shown that, while they are highly intelligent, they have sensory systems that are different from those of humans and a complex and unique means of communication. Listening stations the programme installed around Sarasota Bay have recorded thousands of hours of dolphin vocalisations, and the team’s work with collaborators has shown that each dolphin has its own whistle, used for life like a name.
When the programme started, no one knew whether dolphins generally ranged widely or stayed local – key information for wildlife managers. Using radio tracking devices and other tools, the researchers found that the roughly 170 dolphins that live in Sarasota Bay are organised in a definable range that is their home for life.
Generation after generation also stay in the same area and raise families. One 67-year-old female has given birth in a particular neighbourhood at least 12 times. Before the study began, scientists had no idea bottlenose dolphins could live into their 60s in the wild.
Nurseries made up of mothers and their youngest calves will swim together for a while, and independent juveniles join up with each other to practice skills needed later in life.
Randy Wells, the director of the programme, which is administered by the Brookfield Zoo Chicago, said that over the years, the team documented pairs of the same males surfacing together, in a sort of buddy system that begins around the age of 10 and can last a lifetime. The pairs – which are unusual among mammals – protect the animals from predators when they’re resting. And during mating, one dolphin often stands guard while the other spends time with a female.
Bottlenose dolphins are very active sexually, Wells says. Both hetero- and homosexual interactions are used to create social bonds, he says, not just for procreation.
The animals in this study are urban dolphins, living among a burgeoning human population and constant exposure to boat traffic. Programme staff were among the first to document the threats of death and serious injury to the dolphins caused by interactions with recreational fishing.
“Interaction with fisheries is the most common cause of death,” said Gretchen Lovewell, programme manager of Mote Marine Laboratory’s Stranding Investigations Programme, based in Sarasota.
Lovewell works closely with Wells’s team to help fill in the dolphins’ life story, studying the animals’ skeletons to determine the cause of death – and how they lived. The bones sometimes reflect a darker side of dolphin behaviour, one that belies the smiling caricature perpetuated by sympathetic images. The animals have powerful tails and beaks and use them against each other during conflicts. With males reaching more than 2.8m in length and weighing as much as 300kg, such conflicts can be lethal.
Some of the bones of calves that Lovewell has examined show signs of being bashed by adult dolphins – deep teeth marks, broken bones and bruising around the babies’ jaws where adults apparently rammed them.
“Dolphins can be big, mean jerks,” Lovewell says.
Sharks are a natural enemy and researchers have documented more healed shark bite marks on paired males than single males, leading scientists to believe wounded paired dolphins survive attacks more often.
Climate change has scientists concerned for the dolphins’ future.
“With climate change, rising water temperatures in areas where they live come close to the dolphins’ body temperature, and there’s a limit to how much blubber they can shed to adapt,” Wells said.
In some ways, dolphins can serve as canaries in a global ocean coal mine.
Data gathered by the programme over the years has contributed to National Oceanic and Atmospheric Administration management plans for the species and has guided officials’ handling of environmental disasters.
Michael Moore, senior scientist at the Woods Hole Oceanographic Institution in Massachusetts, said teams and tools developed by the Sarasota Dolphin Research Programme led to a whole new understanding of how these disasters impact marine mammals. “None of this would have happened without the tools Randy Wells and his team developed,“said Moore. |