Distribution
Newcomb's snail is endemic and restricted to the island of Kauaʻi. A number of very large watersheds traverse the southeast quadrant of the Kauaʻi island, including Olokele Stream, Hanapēpē Stream and Waimea River, all of which have numerous tributaries. No recent surveys for Newcomb's snails have been undertaken in the Hanapēpē watershed, or in any of the large neighboring stream systems, because they are located on privately owned lands and are difficult to reach because of the rough terrain. It is possible that Newcomb's snail populations remain in that region of Kauaʻi.
Until about 1925, snails were collected from small sites located in Kalalau Stream, Hanakoa Stream, Hanakāpī`ai Stream, Wainiha River, and Keālia Stream. Three of these populations (Hanakoa Stream, Hanakāpī`ai Stream, Wainiha River) are now thought to be extirpated. Since about 1993, Federal and State agencies, academic researchers, and other interested parties have conducted opportunistic surveys at approximately 50 sites along numerous streams and their associated tributaries and springs on Kaua'i, and have located four previously unknown populations of Newcomb's snail. These recently discovered populations are located in Lumaha`i River, the Hanalei River, Makaleha Stream (a tributary to Kapa`a Stream), and the North Fork Wailua River. With the exception of the snails at Makaleha Springs, most of these populations have only been observed once or twice. Recently, two individual snails were reported from a single site in Limahuli Stream in the Hanalei District of Kauaʻi's north shore. However, if a viable population of Newcomb's snail exists in the Limahuli watershed, its location remains unknown, therefore Limahuli Stream is not considered to have a "population" of Newcomb's snails.
Recent survey work conducted from 1994 to 2003, limits the known range of Newcomb's snail to small sites located in a total of six watersheds in north- and east-facing drainages on Kauaʻi. They are: Kalalau Stream, Lumaha`i River, Hanalei River (four subpopulations), Keālia Stream, Makaleha Stream (two subpopulations), and the North Fork Wailua River. The term "subpopulation" refers to a discreet group of individuals, separated from other discrete groups within a single watershed. Because of low mobility, no interaction between subpopulations exists. No historical information is available on the population sizes of Newcomb's snail. However, anecdotal reports indicate the Kalalau Stream and Lumaha`i River populations of Newcomb's snails are larger in comparison to the other four.
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