Far from Safety

DTAGs are revolutionising the understanding of humpback whales

Written by New York Times | Published: August 26, 2012 2:02:56 am

When the whale known as Touche is hungry for a school of fatty fish,he circles below them,fashioning a net of air by streaming bubbles from his blowhole. Then he corkscrews toward the surface of the Gulf of Maine,herding the fish into an ever tighter packet with the bubbles and his 30-ton body. Finally he opens his jaw wide,takes a monstrous gulp,breathing deeply at the water’s surface.

Then he dives again. Over and over.

Touche’s feeding strategy,captured in June by an electronic tag attached to his back,is of keen interest to scientists tracking North Atlantic humpback whales off Cape Cod.

“Every time we go out and put another tag on,we learn something else,” said Dave Wiley,research director of the Stellwagen Bank National Marine Sanctuary in Massachusetts,who returned to shore recently after plying its waters for two weeks with researchers from several institutions.

For Wiley,the most striking insight is that each humpback has its own set of behaviours,often confounding efforts to generalise about the species.

The Stellwagen sanctuary is prime habitat for a pencil-size schooling fish called the sandlance that draws a host of predators,from the humpbacks to fin whales,minke whales,and bluefin tuna.

Yet the sanctuary’s proximity to land—25 miles from Boston and three miles from the tip of Cape Cod—also means it is heavily used by humans.

On a bright summer day,its waters may be packed with half a dozen whale-watching boats and thousands of recreational and commercial fishing vessels,sailboats and yachts—and that’s just at the surface. The depths abound with ropes connecting strings of lobster pots and webs of fixed fishing gear that stretch across like tennis nets.

Most human-caused deaths of humpbacks occur when whales are struck by passing ships or become entangled in fishing gear,Wiley said. For decades,humpback behaviour was poorly understood because of the difficulty of shadowing the whales in the North Atlantic. The breakthrough was the DTAG,engineered in 1999 at the Woods Hole Oceanographic Institution in Massachusetts.

Unlike satellite tags,which transmit location,typically over a long period of time,DTAGs stay attached for 36 hours at most and record information like speed,depth and audio. They also carry a three-axis accelerometer that measures the front-to-back,side-to-side orientation of the whale.

Heading out for two weeks each summer since 2002,Wiley and a handful of colleagues have successfully tagged humpbacks 90 times,in some cases the same individuals over multiple years. The tag data is overlaid with acoustical studies of prey biomass.

Last month,the taste of success was in the salty air as Wiley’s team unloaded its gear from the 187-foot research vessel. In two weeks,they had tagged 21 humpback whales and identified about 160 individuals,adding a wealth of information to a decade’s worth of observations.

“The DTAG is sort of a revelation and a revolution,” said Ari Friedlaender,a marine ecologist at Duke University who has taken part in the Stellwagen project since 2006.

Scientists have been focusing on New England’s humpback whales since the late 1970s,when they realised that each one had a unique pattern of pigmentation on the underside of its tail,said Peter Stevick,an ecologist at the College of the Atlantic in Bar Harbor,Maine,which maintains the official North Atlantic Humpback Whale Catalog.

The catalog is a compilation of photographs of whales’ tails taken all over the North Atlantic by scientists,whale enthusiasts and tourists. Today it contains photographs of about 7,000 individuals. (Stevick estimates the global humpback population at around 20,000.)

Slowly but steadily,there have been payoffs from this research.

In 2007 the shipping lanes between Boston and New York,which cross the Stellwagen sanctuary,were shifted to avoid whale-packed areas,partly because Wiley’s DTAG data showed that humpbacks spent 60 percent of their time within 50 feet of the surface,in striking distance of boats’ hulls.

Each national marine sanctuary develops its own regulations. In the Stellwagen sanctuary,people are banned from releasing hazardous materials and from any activity that would alter the seafloor. Wiley suggests that strict limits on the speed and approach distance of whale-watching boats would keep the whales safer.

Given the extent of human intrusions,people ask him why he doesn’t head to calmer waters to study humpbacks. To him,the answer is obvious.

“You can go anywhere and study animals and figure out what they do,” Wiley said. “But if you want to return something to them,you need to be working in places where they’re at risk,and they’re at risk right here.”

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