Developing an initial watershed classification for American Samoa

DiDonato, Guy

The American Samoa archipelago is composed of five main islands: Tutuila, Aunu'u, Ta'u, Olosega, and Ofu. Tutuila is the largest island (53 mi2) with the most people (55,414 people as of 2000). Population growth and its attendant pressures on natural habitats and resources has highlighted the need for aquatic resource monitoring in American Samoa Of special concern are coral reef habitats, reef fish assemblages, and surface water ecosystems. A watershed classification is a useful framework upon which to develop agency monitoring programs, especially stream and nearshorc marine monitoring programs, as a classification scheme can provide a priori expectations concerning the condition of adjacent aquatic habitats. US Census data from 2000 were used to calculate population density in Territorial watersheds, and density was used as a surrogate for human disturbance within each watershed. From population density data, four watershed classes were defined: pristine (less than 100 individuals/mi2), minimal (greater than 100 but less than 500 individuals/mi2), intermediate (greater than 500 but less than 1000 individuals/mi2), and extensive (greater than 1000 individuals/mi2). Watershed classification is the first step to establishing an integrated monitoring program for Territorial waters. For instance, ASEPA developed a stream monitoring program based on this classification scheme. Preliminary results from that stream monitoring are consistent with the expected changes in stream condition across watershed class. Whether other aquatic habitats (e.g., beaches) are also consistent with this scheme is unknown at this time.