Fish go 'ping' in the deep
Wildlife biologists on land do it. Now marine biologist Charles Greene is spearheading a plan to help marine scientists do it too.
Dr. Greene and more than a dozen colleagues from across the United States are laying the groundwork for a multimillion-dollar observatory here to track whales, dolphins, tuna, marlin, sea turtles, and a vast menagerie of other open-ocean creatures as they ply the waters off the big island of Hawaii. The observatory would turn up to 500 cubic kilometers (119 cubic miles) of ocean into the world's largest aquarium and give scientists their most comprehensive peek yet into marine life.
An ability to track key species 24/7 - until now largely the province of terrestrial biologists - would help answer long-elusive questions surrounding the habits and life of key marine animals. It also could provide information critical to preserving Hawaii's valuable fisheries and saving endangered species.
For example, high-speed ferries are expected to begin sailing through a humpback-whale national marine sanctuary in 2006. Sonar-listening devices pinpointing the whales' location could help ferry captains avoid collisions with the animals.
The large fish at the top of the food-chain that the observatory aims to study represent a $55 million-a-year industry for the state, Greene says, yet "we have no idea how these animals respond to natural changes." That holds doubly true for human influences such as noise and pollution, he adds.
The observatory's centerpiece is an array of "passive" underwater listening devices tailored to capture the sounds marine animals make and pass them to the observatory as the sounds are captured. It would cover a 150-kilometer stretch of the Kona-Kohala coast down to a depth of 1,000 meters. Using special tags that emit pings, the team also envisions tracking key species.
Acoustic data will be combined with data from satellites and sensors that measure the ocean's physical characteristics, revealing a wealth of information about the island's marine ecosystems and the ocean conditions that influence them. For example: cold nutrient-laden waters that rise to the surface near the islands can be affected in little-known ways by large-scale eddies and currents. Scientists want to figure out the impact of these eddies and currents on fish movements.
The project highlights a growing emphasis in marine science to augment sporadic measurements from research ships with long-term, detailed observations at fixed spots along coasts or in the deep ocean. Ocean observatories also are likely to play an increasing role in managing marine resources.
Yet the new Hawaiian Ocean Resources and Ecosystems Observing System appears to be the only large observatory proposed so far dedicated to taking a comprehensive look at marine biology. And because of its location, it is focusing on a broad class of fish whose members often get closer scrutiny in a fish market than in their natural setting.
"We know so little about the abundance and migration paths" of many of these species, says Jules Jaffe, a research scientist at the Scripps Institution of Oceanography in La Jolla, Calif., and a lead collaborator on the project.
The large acoustic observatory also highlights the way civilian sonar technologies have advanced over the past two decades, researchers say. Today's equipment is much more sensitive to very weak sounds than its predecessors. And modern computer software and hardware are allowing scientists to process and interpret the signals they get in more meaningful ways.
"It's almost magic that we can do this," says an enthusiastic Peter Wiebe, a marine biologist at the Woods Hole Oceanographic Institution in Woods Hole, Mass. Dr. Wiebe says that studies over the past two decades have shown how different types of marine animals - from plankton to shrimp and shellfish - reflect sound differently, depending on the animals' shape, their outside covering, the nature of their organs, and the frequency of the sound. This is allowing researchers to develop more accurate estimates of the types of creatures that inhabit marine ecosystems.
In addition, new generations of pinging tags can be placed on large animals like whales to get information on their locations. Once retrieved, the tags also show how deep the whales dive, as well as the conditions of the water. As the tags get smaller, Dr. Wiebe says, they could be used on a broader array of animals.
Scientists are combining these techniques with the use of underwater vehicles that steer themselves through the deep to gain unprecedented - if still rudimentary - insights into a variety of marine-animal behaviors. Wiebe cites an upcoming project in Antarctica that will combine sonar-equipped autonomous underwater vehicles (AUVs) with the latest in sonar tags. The AUV will use its sonar to identify and follow large patches of krill, a small shrimplike crustacean critical to the food chain, from beneath the patch. Meanwhile, scientists will tag whales to watch their behavior as they eat the krill.
In the long run, engineers are working to develop cameras that use sound to record images instead of light. And beyond identifying broad types of marine animals, researchers are working to determine if each species reflects sound in a unique way, adds David Farmer, dean of the Graduate School of Oceanography at the University of Rhode Island at Narragansett.
Yet for the team, which has a five-year grant from the Office of Naval Research to train marine biologists on these technologies, the observatory holds the promise of more than interesting science and sustainable fisheries. The planning team, which includes the National Oceanic and Atmospheric Administration's Pacific Islands Fisheries Science Center, the Naval Undersea Warfare Center, and two local nongovernmental organizations, also is keenly interested in the observatory's potential effect on the local economy.
The presence of a research ship and the observatory as a whole could provide high-tech jobs for the island - and offer young students a window on ways science can improve the management of resources Hawaiians have valued for centuries. It could be a fitting way, Greene says, to help the community benefit from the science he and his colleagues "extract" from the island.