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Scaleshell Mussel

Summary of Status Assessment

 

BIOLOGICAL INFORMATION:

Leptodea leptodon has been virtually extirpated from its historical range. Of the 53 river drainages that once supported the species, only 13 and possibly one other support populations today. Despite the inherent problems in assessing population trend for rare species, information obtained from surveys and a review of threats allow inferences regarding population trend to be made. Although many of the L. leptodon populations were extirpated before 1970, available information suggests that population declines are continuing. For example, survey results from the Kiamichi River show a decline in population numbers. Leptodea leptodon occurrence is documented from 1925, 1971, 1982, and 1984. By 1987, only old shells were encountered, and over the last several years, survey efforts have been unsuccessful in finding even a shell. Similarly, specimens from the St. Francis Rivers were collected in 1985 and subsequent searches in 1987 and 1996 failed to collect a shell. The decline of these populations, even without statistically derived data, is apparent.

 

Moreover, many of the extant occurrences are documented by only single specimens despite subsequent surveys. Based on comparisons of past and current population numbers and potential threats, it is believed that 10 of the 14 potentially extant populations are declining.

 

THREAT SUMMARY:

Existing and potential threats pose imminent danger for L. leptodon's continued survival. Anthropogenic induced habitat degradation is the most pervasive threat to existing populations, with contamination and sedimentation impacting four populations, damming and impoundment two potentially three, and in-stream mining two. These populations, as a result of these threats, are relegated to small patches of habitat with no potential for expansion. As populations are further isolated, the opportunity for dispersal among local populations is eliminated as well. For example, within St. Francis, Spring, and Kiamichi rivers, mussel habitat is extremely limited, and consequently, L. leptodon expansion or dispersal among populations is impossible.

 

Additionally, other factors that typically are unimportant in terms of population viability are now significant. Commercial use and natural predators, for example, were probably insignificant historically in terms of L. leptodon's long-term survival; however, the loss of populations and recolonization potential have made L. leptodon vulnerable to any and all mortality.

 

Without intervention the threats will continue unabated. Existing regulations have had beneficial impacts but have not and cannot prevent the continuing decline of the species. Federal listing, however, would confer additional protection by invoking penalties for direct or indirect take (e.g., habitat destruction), by providing section 6 funding for research and management, by qualifying for Land and Water Conservation funds, and by providing a forum for developing a coordinated, rangewide recovery strategy.

 

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Last updated: July 16, 2014