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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