Coastal Services Center

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Marine Mammals Management

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The Marine Mammal Protection Act (MMPA) was enacted in 1972 to protect and manage marine mammals and their products. Its primary purpose is to ensure that marine mammals are maintained at, or in some cases restored to, healthy population levels. Biologists responsible for the management of Pacific walrus have been evaluating the potential of QuickBird high-resolution satellite imagery to be used as an effective tool for population monitoring.

The Project: Monitoring the Pacific Walrus Population in the Bering and Chukchi Seas Ecosystem

The U.S. Fish and Wildlife Service, Marine Mammals Management (MMM) Office in Anchorage, Alaska, is responsible for management of the Pacific walrus in U.S. waters. The primary objective of the walrus program is to ensure that the Pacific walrus in Alaska remain within an optimum sustainable population range and that they continue to be a healthy, functioning component of the Bering and Chukchi seas ecosystems. This objective requires both partnerships with Alaska Native groups and international cooperation with Russia to address conservation issues.

The Pacific walrus inhabits the Bering and Chukchi Seas located between the United States and Russia. Male walrus can weigh up to 2,000 lbs while the female is generally about a third smaller. Both the male and female have ivory tusks, which are elongated upper canine teeth, and their skins are leathery with a reddish color. These marine carnivores are typically found in shallower waters, where they feed at the sea floor foraging on clams and other invertebrates.

The resting sites of the Pacific walrus are called haulouts, named because of the manner in which the walrus must haul their massive bodies out of water to rest upon land or chunks of floating ice. Round Island in Bristol Bay, Alaska, is one of the largest Pacific walrus haulouts in North America. Biologists acquired high-resolution satellite imagery of Round Island from the QuickBird sensor and are investigating its ability to assist them in reliably estimating walrus counts. Satellite imagery is a valuable resource for monitoring the Pacific walrus because population information can be collected in remote areas that are difficult to access.

Deriving Population Estimates from High-Resolution Imagery

Top: A 2.8-m true color QuickBird image of a Pacific walrus haulout site at Round Island, located in Bristol Bay, Alaska.

Bottom: A photograph of the rightmost walrus group visible in the QuickBird image with an inset showing a closer view of the walruses.

The size and color of the Pacific walrus are particularly suitable for detection by high-resolution satellite imagery. They are very large, typically ranging between 1.5 and 3.5 meters in length, and appear as red patches when viewed in a true-color QuickBird image. This reddish color results from increased blood flow at the surface of the skin when walrus are warming out of water, making them easily identifiable against the contrasting colors of the rock or sand beaches.

Large numbers of the male Pacific walrus congregate at haulouts in Bristol Bay from May through October, providing a welcome opportunity for monitoring. Three types of imagery, 70-cm panchromatic, 2.8-m multispectral ,and 70-cm pan-sharpened, are being acquired for the entire island during summer 2002 and 2003.

To obtain walrus counts, each image is classified and the total area occupied by walrus groups is then calculated. Prior analysis of aerial photography has shown that an adult male walrus covers approximately 2.2 square meters when viewed from above. Based on this average value, biologists can estimate the number of walrus present in the satellite imagery. To test the accuracy of the image walrus counts, biologists on the ground conduct manual counts and take photographs within minutes of image collection by the satellite. Synchronizing the manual counts with image collection helps minimize the variation in counts caused by walrus coming and going.

The Result

Testing of the QuickBird imagery for estimating walrus population is currently in the image acquisition phase. Final evaluations will compare the use of unsupervised classification versus supervised classification for the 2.8-m multispectral and 70-cm pan-sharpened products to determine the best technique for estimating walrus abundance. An earlier test was conducted in 2001 for the same study area with a 4-m multispectral IKONOS image pan-sharpened to 1-m. The number of walrus estimated from the IKONOS supervised classification was 1,533. The number of walrus counted by biologists in the field for the same day was 1,524, which is less than one percent difference.

For More Information

• U.S. Fish and Wildlife Service – Alaska Region
• U.S. Fish and Wildlife Service – Alaska Marine Mammals Management Office

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