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Sanctuary Rocky
Intertidal Open
Ocean & Endangered
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Northern Elephant Seals ã Autonomous Pinniped Environmental Samplers
Northern elephant seals are part-time residents on rookery beaches in the Monterey Bay National Marine Sanctuary, where they spend up to four months per year. The remaining time is spent on foraging trips in the open North Pacific Ocean or near the coast of Alaska (see Figure 1). Research at UC Santa Cruz to understand the behavior and movements of northern elephant seals has utilized small electronic tags that archive and store temperature and depth data for later retrieval after the animal is recaptured. When combined with position data from Advanced Research and Global Observation Satellite (ARGOS) tags, the temperature and depth data provide valuable information on the seals, including habitat preferences, physiological data, environmental data, and movement patterns. The results have unraveled much of the mystery surrounding where the northern elephant seals go in the North Pacific and how they use the oceanic environment in foraging. Data collected to learn about the seals can also tell us something about the ocean. Oceanographers go to great lengths to collect oceanographic data and compile it into databases used to characterize the ocean. These archived data are used for a variety of purposes, including input to ocean models, weather prediction, and analysis of climate change. While more and more surface data are taken by satellites and buoys, data from below the surface often require sensors deployed from ships. Expendable bathythermographs, or XBTs, for example, can be dropped from oceanographic vessels or from "ships of opportunity" like freighters or tankers. XBTs measure the temperature as they fall through the water and transmit the data back to recording devices. The resulting temperature profiles are sparsely distributed in time and space, providing poor coverage for most of the ocean; moreover, the data are expensive to collect from ships. During their long foraging trips, northern elephant seals dive continuously, with little time spent at the surface. Dives typically last twenty minutes and go routinely to depths of 600 meters (1,920 feet). The potential volume of oceanographic data that a single elephant seal could collect on a single foraging trip is immense.
We reasoned that if properly instrumented, calibrated, and archived, the elephant seal tags could provide oceanographic data for parts of the ocean where these are sparse or lacking. Thus, our objectives were to evaluate existing temperature profiles taken from northern elephant seals and, if the data met quality standards adequately, to add these records to the National Oceanic and Atmospheric Administration (NOAA) World Ocean Database.
Taking this step with data collected by animal tags has been hindered in the past by the accuracy of the sensors and geographic position where the measurements were taken. The newer generation tags have greatly improved measurement accuracy, and we determined that the quality of seal-collected temperature data are on par with that from XBTs. The position data from ARGOS, while not up to the standards of oceanographic buoys, meet that of several other platforms used. Thus, the seal data met the requisite criteria. We carefully evaluated data from foraging trips of six female and three male elephant seals tagged in central California between March 1998 and March 1999. Temperature and depth data, measured and stored every thirty seconds, were retrieved after the animals returned to the rookery months later. Portions of the track where both ARGOS and temperature-depth data were available from these nine animals (Figure 1) show differences between males and females. A comparison of temperature profiles from seal temperatures at the surface showed excellent correspondence with other sources of surface temperature data and similarity with other sources of subsurface data. These data were put into NOAA's World Ocean Database under a new category -- "APBT," for auto-nomous pinniped bathythermograph. A total of 75,665 APBTs over 41,702 kilometers of seal trackline came from these nine seals alone. This work shows that biological autonomous sampling systems used
in behavioral studies have potential to contribute oceanographic
data in a cost-effective manner. The northern elephant seal represents
but one species covering portions of the northeast Pacific Ocean.
Research programs presently exist on a variety of species, including
southern elephant seals and other pinnipeds, tunas and billfishes,
sharks, seabirds, marine turtles, and whales. With improving technology,
such tags will be applied to even more marine animals and the
approach described here can be applied to other species to improve
ocean data availability. George Boehlert1, Dan Costa2, and Dan Crocker3 |
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For comments or question please refer to the Webmaster Last modified on: Jan 15, 2000 |
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