Wednesday, November 14, 2012
It may come as a surprise to residents and tourists who eagerly swim or paddle out to play with spinner dolphins, but those animals are often in Hawaiian bays for needed rest, not human recreation.
(Image: Tourists interacting with spinner dolphins. Credit: David Johnston, Duke University.)
And those dolphin-loving humans may actually be driving the animals out of safe coastal habitat into danger and fatigue, according to a new study. Here’s a Duke University press release on the study.
The study identifies coastal resting habitats, and suggests that maps developed from environmental models could be use to protect the charismatic species. It also clearly implies that this does NOT mean all dolphins ought to be off-limits; rather that there are specific resting locales that could be protected.
The spinner dolphin work was prepared by a large team of accomplished research scientists from Hawai`i, across the nation and Australia. It is entitled “Predictive Modeling of Spinner Dolphin (Stenella longirostris) Resting Habitat in the Main Hawaiian Islands.” You can go to the actual study on the peer-reviewed journal PLoS One, here, for details.
There may be bays where dolphins come in ready for play, but in many cases, they are there to rest and sleep—and that’s critical to their alertness and thus their survival, said Johnston.
“Sleep is essential for most animals. When deprived of their necessary ‘zzzz’s,’ they gradually show a decreased ability to process information and remain attentive to environmental stimuli. In technical lingo, we call this a ‘vigilance decrement’,” he said.
The paper says: “Spinner dolphins in Hawai'i exhibit predictable daily movements, using inshore bays as resting habitat during daylight hours and foraging in offshore waters at night. There are growing concerns regarding the effects of human activities on spinner dolphins resting in coastal areas.”
With this insight, the image of dozens of excited humans paddling around in dolphin pods may be of concern.
The authors say that they are working on modeling techniques to identify which bays in the Islands are critical resting spots for the animals. They describe typical patterns of spinners, when humans aren’t interfering:
“Spinner dolphins typically enter protected bays of the main Hawaiian Islands just after dawn, and slowly descend into a resting state over a period of up to two hours. The resting state is defined by slow movements, a cessation of aerial behavior, synchronous dives by tight groups of dolphins that are touching or almost touching, and visual, rather than acoustic, vigilance.”
Thereafter, the dolphins spend a large part of the rest of the day in slow, group swimming that may be part of the resting cycle: “Groups of resting dolphins typically move slowly within bays for four to five hours, after which dolphins undergo a period of “zig-zag swimming” and increase surface activity before moving into deeper waters near sunset to begin night-time foraging.”
The study suggests that spinner dolphins are looking for a predictable blend of water depth, bottom configuration and nearness to deep water for feeding. Using those features, they feel it is possible to identify bays where resting dolphins ought to be protected.
That doesn’t means all spinner dolphins should be off limits for humans seeking interaction, they write: “Limited observations suggest that socially active spinner dolphins might be relatively tolerant of human presence, while resting spinner dolphins may leave an area if forced to interact with humans.”
The authors include Lesley H. Thorne, David W. Johnston, Dean L. Urban5 Julian Tyne4 Lars Bejder, Robin W. Baird, Suzanne Yin, Susan H. Rickards, Mark H. Deakos, Joseph R. Mobley Jr., Adam A. Pack, and Marie Chapla Hill. Their affiliations include Stony Brook University, Duke University Marine Laboratory, Pacific Islands Photo-Identification Network in Honolulu, Cetacean Research Unit atMurdoch University in Western Australia, Nicholas School of the Environment at Duke University, Cascadia Research Collective of Washington State, Hawai'i Marine Mammal Consortium of Kamuela, Hawai'i Association for Marine Education and Research of Lahaina, The Dolphin Institute of Honolulu, Marine Mammal Research Consultants of Honolulu, Psychology and Biology Departments of the University of Hawai'i at Hilo, and Joint Institute for Marine and Atmospheric Research of the University of Hawai'i at Mānoa.
© Jan TenBruggencate 2012