Oceanographers studying water circulation provide a new tool for biologists trying to protect whales
The death of a right whale last spring has resulted in a new tool for whale researchers. In the course of trying to determine where the whale nicknamed "Staccato" died, a team of oceanographers at Harvard developed a model that may help biologists keep track of floating whale carcasses.
"We get a lot of reports of floaters, and we'd like to take a closer look at many of them, but it often is difficult to relocate a floating whale a few hours after a sighting," says Dana Hartley, coordinator of the federal government's whale Stranding Network in the Northeast.
A lost whale carcass is a lost opportunity for the small community of scientists who are working to save the whale populations in New England waters. When one of the 300 or so highly endangered North Atlantic right whales dies, for instance, scientists want to know which individual is gone and what happened to it. Was it a fertile female? Was it hit by a ship? Did it drown after becoming entangled in fishing gear? Or did it die of natural causes?
The prospects of tracking down floaters improved this year when the Harvard oceanographers put aside their usual work to answer a question about Staccato. Led by Professor Allan Robinson, the Harvard group has been working for years on a model (the Harvard Ocean Prediction System, or HOPS) that simulates and predicts the movement of coastal waters. HOPS takes into account a variety of factors that affect the movement of water, including winds, tides, and water characteristics such as temperature and salinity.
Developed with funding from the Office of Naval Research, HOPS can be adapted to predict water circulation anywhere in the world. The model has already been applied in more than 20 locations in the Atlantic and Pacific oceans and the Mediterranean Sea, and NATO has used HOPS in planning its operations and forecasting in real time for naval maneuvers.
HOPS also has non-military applications. It can predict the movement of plankton and virtually anything else that drifts on or near the surface or at depth. But it had not been used with whales until a National Oceanic and Atmospheric Administration (NOAA) Fisheries agent asked for help figuring out what happened to Staccato.
"It is against the law to kill a whale, even accidentally," explains James Medeiros, a special agent with the NOAA Fisheries law enforcement. "When a whale dies as a result of interaction with humans, we investigate."
An agent investigating a whale's death typically has little to go on -- in Staccato's case, Medeiros knew only that the whale had been seen alive April 15, she was found floating on the 20th off Wellfleet, and she had been hit by a large object -- presumably a vessel.
"I figured that if someone could tell me where she was hit, we could look at shipping records and see what vessels passed through the area around the time she was hit," Medeiros says. "Then we could interview the captains."
Medeiros asked around and heard about a group at Harvard that had a model that simulated water circulation. Could their HOPS model reconstruct the voyage of a whale carcass?
"Certainly," said Professor Robinson of Harvard's Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences. "The model was built to forecast the circulation of water -- it's similar to weather forecasting.
It can be used to predict the movement of any floating object."
Some of the data needed to run the model for Staccato had already been entered when the Harvard team did a study of Massachusetts Bay in 1997. Still, it took several person-days to enter the pertinent data about the waters of Massachusetts and Cape Cod bays, new data sets supplied by Dr. Michael Mickelson of the Massachusetts Water Resources Authority (MWRA) and from a Harvard student cruise. The team also had to enter information about right whales -- the weight and buoyancy of an adult animal, for instance, which results in the carcass being predominantly carried along with the surface flow of water.
When the data were all entered, the Harvard team ran the program, recreating conditions in local waters for the five day period between April 15 and April 20.
"We released a lot of whales to see where they ended up," said Dr. Pierre Lermusiaux, a postdoctoral oceanographer who carried out the simulations together with Dr. Patrick Haley and Wayne Leslie. To be precise, the HOPS model set simulated whales adrift from 800 different sites every twelve hours for five days -- a total of 8,000 virtual drifters in all. In real time, the program took about 8 hours to run.
The important virtual whales are the ones that drifted to the site where the real whale, Staccato, was observed dead the evening of April 20. The locations where the simulated whales began drifting are displayed on color maps the scientists provided. The HOPS map shows that if the Staccato died the evening of April 15, she most likely died in a fairly small patch of water a few miles off Plymouth. Likely death sites are calculated at 12 hour intervals up to the time the whale was discovered on April 20.
"They provided really specific information about where the carcass must have been floating to end up where it was found on April 20," Medeiros said. As it turned out, the spot where the animal died is probably not the spot where she was hit.
"The lab phase of the autopsy surprised us," Medeiros said. "It turns out the whale lived for a week or more after she suffered the broken jaw, so knowing where she died did not help us figure out what hit her."
While the Harvard lab's efforts did not crack the Staccato case, the work they did with their HOPS model may help solve a different problem.
"A lot of times we get calls about floaters but they come in late in the day and we can't get a boat or airplane out to look at them until the next morning," Hartley said. "If we had a sighting this afternoon in Massachusetts Bay, we could ask the Harvard team to run their drift program overnight. In the morning we'd have a map pilots could use to search for the floater."
"The model isn't going to pinpoint the exact coordinates of the floater, but it provides a reasonably small box inside which the pilots can start their search," Medeiros agreed.
"It would be great if we could follow-up more of the sighting reports," Hartley said. "If we can get to more floaters, we can learn more about what we need to do to protect animals like Staccato."
"Predicting the movement of floaters with useful accuracy represents an example of an important new forecast capability for coastal oceans in general," Robinson commented. "Physical dynamical forecasting is now being coupled to biological and chemical dynamical forecasting. This new capability can be expected to improve the efficiency of coastal marine operations and management substantially in the near future."