Hope on the Horizon for the Endangered Scaleshell Mussel
by Andy Roberts
Tracy Divis of the Kansas City Zoo holds endangered mussels propagated at Missouri State University.
Photo Credit: Andy Robers, USFWS
Preventing extinction of threatened and endangered species is always challenging, but consider the obstacles when the species is extremely difficult to find in its native habitat, and it has a particularly complex life history. These are the challenges facing U.S. Fish and Wildlife Service biologists and conservation partners working to recover the federally endangered scaleshell mussel (Leptodea leptodon) face. Fortunately, persistence and ingenuity are paying off.
The scaleshell was historically found in over 50 rivers across 13 states, but now can only be found in just three rivers in Missouri. Even in Missouri, the species is extremely rare. Listed as endangered in 2001, the scaleshell faces threats from habitat destruction and pollution. The plan to recover the scaleshell calls for artificial propagation as a critical tool to boost existing populations and reintroduce the species into portions of its former range.
To complicate matters, many freshwater mussels, the scaleshell included, require a specific host fish as part of their life cycle. Mussel eggs develop into microscopic larvae, called glochidia, within the gills of the female mussel. The female discharges its glochidia into the river where they must attach to gills or fins of a fish to continue developing. Each mussel species has specific fish species needed by the glochidia to develop. Glochidia continue growing on the fish and transform into juveniles. After a few weeks they drop off and land on the river bottom where they grow into adults.
The Service’s Columbia Missouri Field Office has been working with the Missouri Department of Conservation and Missouri State University for over 12 years to develop artificial propagation and rearing methods for the scaleshell. This has been a slow and arduous process because scaleshell, particularly females, are extremely rare and difficult to find. While extensive searches for gravid (pregnant) females that might be used to produce mussels for reintroduction have been ongoing annually since 1999, only a handful of females have been found.
Female scaleshell mussel.
Photo Credit: Dr. M.C. Barnhart
Despite the small number of individuals found, the fish host was identified – freshwater drum. In 2010, the scaleshell was successfully reared for the first time at a new mussel rearing facility at the Kansas City Zoo in Missouri. Over 50 rapidly growing scaleshell, along with thousands of other juvenile mussels of other species of concern, are now being cared for and studied at the Zoo by their staff, Missouri State University, and the Service. In addition, thousands of juvenile scaleshell are growing at Missouri State University facilities and will soon be transferred to the Zoo to grow large enough for release into the wild.
The goal of reintroducing the scaleshell mussel into its former range is now in sight. We have the ability to propagate larvae, rapidly grow large numbers of juveniles, and hold brood stock adults for long periods. Several female scaleshell mussels were collected in 2011 and are being held for broodstock. In 2012, we will have the genetic knowledge needed to help guide our propagation efforts. The Duck, Green and Osage rivers in Tennessee, Kentucky and Missouri, respectively, are examples of rivers being considered for future reintroductions. These rivers have recently been restored and we hope they may once again support populations of the elusive scaleshell mussel.
Andy Roberts, a biologist in the Service’s Missouri Ecological Services Field Office, can be reached at andy_roberts@fws.gov or 573-876-1911.
