High-tech tags on marine animals yield valuable data for biologists and oceanographers

Researchers are enlisting seals, sea lions, tunas, and sharks to serve as ocean sensors, outfitting these top predators with electronic tags that gather detailed reports on oceanographic conditions and, in many cases, transmit the data via satellite. The data are proving useful to both biologists and oceanographers, yielding new information about the migrations and behavior of the animals and about the environments in which they live.

“We’re using these animals as ocean sensors to tell us about oceanographic conditions, and we’re also learning how they use the ocean–where they go and what they do,” said Daniel Costa, professor of ecology and evolutionary biology at the University of California, Santa Cruz.

Costa, along with Barbara Block of Stanford University, is a principal investigator on a Census of Marine Life project called Tagging Of Pacific Pelagics (TOPP), which is deploying electronic tags on 23 species of apex predators in the North Pacific Ocean. He is also collaborating with researchers at the Sea Mammal Research Unit (SMRU) at the University of St. Andrews in Scotland on a project in the Southern Ocean around Antarctica called Southern Elephant Seals as Oceanographic Samplers (SEaOS).

Costa and SMRU’s Michael Fedak organized several sessions focusing on this area of research at the 2006 Ocean Sciences Meeting, February 20-24, in Honolulu. Costa and other researchers will present the results of tagging studies involving California sea lions, northern elephant seals, tuna, salmon sharks, and albatross in the North Pacific, as well as southern elephant seals, Antarctic fur seals, and crabeater seals in the Southern Ocean.

California sea lions are proving to be an excellent platform for monitoring oceanographic conditions along the California coast, Costa said. State-of-the-art tags developed at SMRU can now capture an animal’s location, swim speed, and the depth and duration of dives, as well as the temperature and salinity of the seawater and how that changes with depth. As the sea lions travel along the coast diving for food, their tags transmit data back to the researchers via satellite.

“They are a great animal for collecting oceanographic data and giving us updates on ocean conditions in the California Current,” Costa said.

The electronic tags are essentially miniaturized computers with various sensors on them. They can be fixed harmlessly onto the fur of a seal or sea lion, and will stay on for several months before falling off when the animal molts. Data recorded during a dive are transmitted to satellites when the animal comes to the surface to breathe.

Costa’s group has been providing water temperature and salinity data gathered by California sea lions to physical oceanographer Yi Chao at the Jet Propulsion Laboratory in Pasadena. Chao and his colleagues are incorporating the data into a computer model designed to simulate and predict ocean circulation patterns in the California coastal region. Preliminary results indicate that plugging in the sea lion data substantially increases the predictive capabilities of the model, Costa said.

“It’s like predicting the weather. To get accurate predictions, the weather models have to be constantly updated with new data from weather stations all over the country,” he said.

The researchers are also gaining new insights into the lives of California sea lions, said Michael Weise, a graduate student working with Costa on the sea lion studies.

“This technology brings a whole new dimension to our understanding of how California sea lions are using their environment,” Weise said.

During 2004 and 2005, for example, the researchers observed unusual movement patterns of sea lions associated with anomalies in sea surface temperatures. Normally, upwelling of cold deep water brings nutrients into the coastal waters off California and supports a highly productive food web. But the 2004-05 season was marked by unusually warm water along the coast, and the sea lions were forced to change their diets and their foraging patterns, Weise said.

“The sea lions disappeared from Monterey Bay, as did the bait fish. We were only able to tag three male sea lions that year, and they went much farther off shore than usual to find food. They’ve always been described as a strictly coastal species, but they went as far out as 300 miles from the coast,” he said.

At the same time, Costa’s group was also tracking the movements of elephant seals and albatrosses. These species, which typically forage across a broad area of the North Pacific Ocean, showed little change in their movement patterns in 2004 and 2005. As platforms for ocean sensors, northern elephant seals and California sea lions can provide complementary information because of their different foraging patterns, Costa said.

“Elephant seals provide incredible coverage of the North Pacific, while the sea lions are good along the coastal upwelling region,” he said.

Similar complementarity is provided by southern elephant seals and crabeater seals in the Southern Ocean. Costa led a study of crabeater seals during the Antarctic winters of 2001 and 2002, tagging 34 seals and tracking their foraging patterns. Crabeater seals are specialized for feeding on Antarctic krill and forage along the continental shelf of Antarctica at the edge of the ice pack.

Southern elephant seals, in contrast, forage widely in the offshore waters. The SEaOS project led by SMRU’s Fedak is deploying electronic tags on elephant seals at three locations in the Southern Ocean. The oceanographic data gathered by the seals on their foraging trips from these different locations provide circumpolar coverage of the Southern Ocean, Costa said.

“We are collecting a tremendous amount of data in this area of the world and working with physical oceanographers to incorporate these data into oceanographic models,” he said.

Researchers can use these Antarctic seal species to obtain oceanographic data for a region of the ocean and times of the year for which there are no good sources of data, Costa said. This is particularly important because of the major role played by the Southern Ocean in the global climate system.

“Much of the world’s weather is determined by what happens in the Antarctic, so understanding the Southern Ocean is a key to understanding global climate,” Costa said.

Costa began using electronic data recorders to study the diving behavior of elephant seals in 1983. Since then, the miniaturization of electronic components and sensors, plus advances in satellite technology, have led to dramatic improvements in the tags. Recent innovations developed at SMRU have greatly improved the ability to pinpoint an animal’s geographic location, and researchers are adding new capabilities to the tags, such as measuring the chlorophyll content of the water (an indicator of algal blooms or “primary productivity”).

“We can now use animals to show us things like the thermal properties and cooling rates of the ocean and the structure of the water column, and they can often get valuable data that would be hard to collect by other means,” Costa said.