Vol. 3, No. 4 Contents
Headline Back Issues
Fall 1999
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Satellite data shed new light on lobster life in Penobscot BayBy Nick Houtman Orono, Maine - Scientists studying lobsters in the Gulf of Maine are using satellite technology to gain a better understanding of why the commercially valuable crustaceans live where they do. Every day, satellites passing over the Gulf scan the environment below and beam information about water temperatures back to Earth. Since 1986, electronic images have been accumulating like pictures in a family album.
Thomas is a specialist in remote sensing technology and former Executive Director of the Atlantic Centre for Remote Sensing of the Oceans in Bedford, Nova Scotia. He now directs the Satellite Oceanography Data Laboratory at the University of Maine. He uses satellite images to understand how temperature and circulation patterns in the world's oceans change from season to season and year to year, and what the consequences of those changes are for marine ecosystems. His projects range from the North and South Pacific and the South China Sea to the Gulf of Maine.
Focus on Penobscot BayWith support from a four-year NOAA grant to the Island Institute in Rockland, Maine, Thomas, along with Bigelow Lab in Boothbay Harbor and about 120 lobstermen, have been taking aim at Penobscot Bay and other areas of the Maine coast. Penobscot Bay accounts for about half of Maine's total lobster haul. Historically, parts of the Bay are thought to have provided spawning beds for cod, although local cod populations were fished out earlier in this century. Asserting the Bay's importance to the future of the lobster resource, Philip Conkling, President of the Island Institute, said, "This project is the first time an interdisciplinary team of scientists has worked with a large number of fishermen to put together a comprehensive understanding of the ecosystem of the largest bay in the Gulf of Maine." Notes Thomas, "Of real interest to us is whether or not this piece of the coast is oceanographically behaving like the coast east and west of us, and whether our study years are average conditions. You can get a good handle on the big picture in space and time with satellite data." Evan Richert, Director of the Maine State Planning Office, says that the project could become a model for studies elsewhere. "State resource managers have never really had a good handle on predicting trends in our coastal fisheries, but through this project we are developing tools and techniques that can tell us whether lobster abundance is increasing or decreasing in the Bay. It is a model we can use in other bays in the Gulf of Maine." Scenes arrive dailyThomas receives images - called "scenes" in the trade - directly from the satellites each day using a tracking dish and ground station on the roof of Libby Hall at the University of Maine. These data are supplemented by historical data supplied by scientists at the University of Rhode Island. There, the satellite images are adjusted to account for changes in satellite technology and atmospheric conditions. Data are also correlated with information from ships and buoys. "For historical studies, looking for subtle changes over time, this is a very good data set," says Thomas. To date, he has received scenes from 1986 through 1995. Once the data arrive from Rhode Island, Thomas combines the daily scenes into monthly, seasonal, and yearly averages, compares them against each other, and looks for significant anomalies. The results to date haven't contained any big surprises. "The dominant seasonal pattern is that in winter, the coldest water is in-shore and there's a gradient to warmer water off-shore. In summer, this flips around. The coldest water is off-shore and the warmer water is near shore, due to the Eastern Maine Coastal Current. With the satellite data, we're looking at changes in the strength and spatial pattern from year to year." Just as the Gulf Stream brings warm water north along the East Coast, the Eastern Maine Coastal Current brings cold water southwest along the Maine coast from the Bay of Fundy to Mt. Desert Island, where it often veers offshore toward the open Gulf. Lobsters like it warmerThe yearly temperature differences, clearly revealed by the satellite images, are of interest because, according to Bob Steneck, SMS professor studying lobster population trends, different lobster settlement patterns occur in each area. "Laboratory studies have shown that lobster settlement is dependent on the temperature of sea water," says Steneck. "Studies by two Canadians, Huntsman in the 1920s and Boudreau in the 1980s, are consistent with my observations that lobster settlement is lower in regions having colder sea water temperatures. Andy's [Thomas] satellite images show us for the first time that temperature patterns may correspond to the places where lobster settlement is greatest and to the years in which lobster settlement is greater. This is an exciting step forward." The satellite images can also give scientists important clues about the forces at work in determining temperature. If temperature trends are consistently up or down across the entire region, for example, large-scale regional, not local, factors could be the cause. On the other hand, local weather or circulation factors can cause temperature trends to vary from place to place. "What goes on near-shore may not be what happens off-shore," says Thomas, "and the same goes for areas to the east and west along the coast." Over the next two years, scientists will expand the record and study it to determine what temperature patterns are most closely associated with ecological change, such as population shifts in lobster or sea urchins. "It may not be absolute temperature that's the important thing for a particular species or particular behavior. It may be the relative position of a frontal zone or perhaps the timing within the season of a particular event or something like that. It may be where the coastal boundary of the Eastern Maine Coastal Current was that year," Thomas explains. Ultimately, because they indicate circulation and seasonal variability, the temperature patterns measured by satellites are an important scientific tool. By creating numerical models that use temperature to improve their equations and test their results, researchers attempt to mimic natural systems more closely. "Our overall goal is to use satellite data to their fullest potential for ecological management. As we work toward better predictions of abundance of future fisheries and potential harvests, they provide a unique view of the environment. Satellite data won't answer all the questions, but by combining these data with [field] measurements and numerical modeling, better answers to many of our monitoring and management questions can be found," Thomas says. For more information on the University of Maine satellite imaging project, visit: http://wavy.umeoce.maine.edu/sodl.htm. |
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For Andrew Thomas, associate professor in the University of Maine School of Marine Sciences (SMS), this image record has become a valuable research tool. He is part of a team of scientists and lobstermen funded by the National Oceanic and Atmospheric Administration (NOAA) to use satellite-derived temperature data to investigate how lobster populations vary with environmental changes.
Satellite data can fill in "one piece of the puzzle" for biologists who need to understand why lobster populations rise and fall or what causes blooms of harmful algae, says Thomas. While biologists may be prime users of his results, the images of temperature patterns in ocean waters have also intrigued fishermen and other citizens.