Managing the Ocean By Tracking Its Wild Life
BOSTON — Ron O'Dor specializes in seeing under the sea.
Every spring, many thousands of squid congregate off South Africa's coastline. Females cover the bottom of the ocean with fertilized eggs and turn the area into a multimillion dollar fishery. But until South African fishermen invited Dr. O'Dor from Dalhousie University in Halifax, Nova Scotia, and his colleagues to visit the spawning area, no one understood the squid mating ritual.
To learn about the South African squid's mating behavior, O'Dor attached a small transmitter inside the squid's mantle. The transmitter sent sound waves out to floating buoys, which in turn sent signals to a computer that calculated the animal's locations.
By tracking several males and females, the researchers discovered a peculiar mating pattern. Large bull males compete over the females. Once a bull deposits a sac of sperm into the female, smaller males, called sneakers, surreptitiously move in and mate.
It sounds superfluous, even extravagant, studying the mating behavior of squid. But it's important for the fishery, O'Dor says.
"Fishermen prefer the big bulls, but if they only fish them, the fishery will get smaller and smaller and won't have any value," he adds. Knowing the bull male's role assists the fishery in making enlightened management decisions.
Protecting ocean species requires learning about their lifestyles. "This work is critical to management and conservation," says Molly Lutcavage of the New England Aquarium in Boston. However, scientists know relatively little about the basic biology of many of the ocean's inhabitants.
The sea's vast size and inaccessibility make designing instruments for tracking ocean animals a challenge.
To track the North Atlantic right whale, scientists implant small satellite tags into the blubber using a bow, much like bows used in the days of hunting whales. The tags don't hurt the whales and sometimes allow scientists to follow them for months. Researchers say protecting the North Atlantic right whale, a species struggling to recover from centuries of commercial whaling, will require understanding the whales' travels.
"We need to identify the threats facing the whales in their habitats before we can effectively reduce human impact," says Chris Slay of the New England Aquarium. Colliding with fishing vessels and getting caught in nets have caused many premature deaths and delayed the population's recovery.
Right whales migrate annually from their summer feeding grounds in the Bay of Fundy off the coast of Maine and New Brunswick, Canada. But because they travel long distances quickly, where most go during the winter remains a mystery, Mr. Slay says.
With the satellite tag, when the animals break the surface, a saltwater switch prompts the tag to send a radio signal. A satellite receives and reports the whales' positions to a station that transmits the data over the Internet.
The tagging has provided some information about whale movements in the Bay of Fundy. Bruce Mate of Oregon State University in Eugene, says scientists once thought the animals spent the entire summer in the bay. But they discovered some whales continue moving restlessly, sometimes traveling thousands of miles before returning to the bay.
Using a similar satellite tag, Russel Andrews at the University of British Columbia in Vancouver studies Steller sea lions in the Gulf of Alaska. Mr. Andrews wants to know why, in the past 20 years, the western population has dropped by more than 70 percent.
Feeding on the same fish as the area's main fishery, the sea lions might be starving, researchers conjectured. To test this idea, Andrews tracked female sea lions using satellite tags. In addition, pressure gauges recorded the sea lions' dives, and temperature sensors in their stomachs indicated recently swallowed fish. The data, Andrews says, show that nursing mothers were not starving themselves or their pups. He says the problem instead may occur when pups have to forage for food on their own. They may not know the tricks their mothers use and end up going hungry. "We want to start studying the animals while they're being weaned," Andrews says.
Researchers have also used a modified satellite tag on the greatly depleted blue fin tuna. Currently, the highly sought tuna is managed as two stocks, eastern and western, and researchers want to know whether this is practical. At a designated time, the tags pop off the fish, float to the surface, and communicate with satellites. Preliminary data show the tuna do not respect designated international boundaries, Dr. Lutcavage says wryly. This suggests regulations may need modification.
Other studies, using transmitters, track tuna more closely. Determining normal behavior, such as how deep and fast the fish swim, will help indicate how to regulate rod-and-reel fishing, where fishermen catch the fish and then let them go. Researchers want to determine if the fight before the tuna is released affects its survival rate.
Although tracking animals is getting easier, a few hitches remain: Tags come out of whale blubber; some pop-up tags for fish give only the starting and ending locations; and retrieving temperature and dive-depth instruments often requires recapturing the animals.
Nonetheless, information gathered by these remote sensors is invaluable in managing and preserving the sea, scientists say.