Survey for Endangered and Other Unionid Species in the Upper Gasconade River Basin, Missouri.

摘要

We conducted qualitative timed searches for unionids at 75 sites in the Upper Gasconade River Basin between July 21, 1998 and Sept. 16, 1999. We collected 5,528 live individuals and a fresh-dead shell of the lilliput (Toxolasma parvus) representing 35 unionid species, and one pea clam (family Sphaeridae) and the Asian clam, Corbicula fluminea, in 120.5 person-hours (Table 3).The Asian clam was present to abundant at 67% of sampling sites. The six most abundant unionid species in this upper section of the basin were the mucket, Actinonaias Ligmentina (33.3%), spectaclecase, Cumberlandia monodonta (28.0%), Wabash pigtoe, Fusconaia flava (4.8%), purple wartyback, Cyclonaias tuberculata (4.5%), spike, Elliptio dilatata (4.2%) and pocketbook, Lampsilis cardium (3.7%). Overall unionid catch per unit effort was 45.9 live mussels/person hour. The mucket occurred at 54 of the 75 (72%) sample sites and spectaclecase at 29 of the 75 (39%). Together these two species comprised 61% of the total live catch in the upper Gasconade River. The scaleshell, Leptodea leptodon, a federal candidate species whose status as endangered is pending, was found live (n=15) at 9 sites and fresh-dead at 6 additional sites in the upper Gasconade River. The majority of these sites were in Pulaski and Laclede counties, Missouri. Six state species of conservation concern (Elliptio crassidens, Cumberlandia monodonta, Alasmidonta marginata, Ligumia recta, Plethobasus cyphyus and Ptychobrancous occidentalis) were also present in this upper portion of the basin. The upper Gasconade River Basin contains a rich mussel fauna, but these populations are fragmented due to habitat degradation. Primary causes include channel instability associated with historic land-use practices and nutrient enrichment from increasing populations of cattle and other livestock.