Shinyrayed Pocketbook

Lampsilis subangulata

Description

The Lampsilis subangulata (shinyrayed pocketbook) is a medium-sized mussel that reaches approximately 3.3 in (8.5 cm) in length. The shell is subelliptical, with broad, somewhat inflated umbos and a rounded posterior ridge. The shell is fairly thin but solid. The surface is smooth and shiny, light yellowish brown with fairly wide, bright emerald green rays over the entire length of the shell. Older individuals may appear much darker brown with obscure raying. Female specimens are more inflated postbasally, whereas males appear to be more pointed posteri-orly. Internally, the pseudocardinal teeth are double and fairly large and erect in the left valve, and one large tooth and one spatulate tooth are in the right valve. The nacre is white, with some individuals exhibiting a salmon tint in the vicinity of the umbonal cavity. Current taxonomy recognizes the nineteenth-century names Unio subangulatus Lea and Unio kirk-landianus as synonyms of Lampsilis subangulata.

Behavior

The shinyrayed pocketbook siphons water for oxygen and food. It feeds on phytoplankton, tiny zooplankton, and organic detritus. Reproduction involves the female siphoning male sperm from the water, after which the eggs are fertilized and incubated in her gill chamber. The planktonic larvae are parasitic on fish, and later settle to the sedentary adult lifestyle. The shinyrayed pocketbook utilizes largemouth bass (Micropterus salmoides ) and spotted bass (M. punctulatus ) as primary host fishes. The latter species appears to have been introduced into the Apalachicola-Chattahoochee-Flint (ACF) River system.

Habitat

Shinyrayed pocketbook inhabits stable sandy and gravelly substrates in medium-sized streams to large rivers, often in areas swept free of silt by the current. This mussel is endemic to eastern Gulf Slope streams draining the Apalachicolan region of southeast Alabama, southwest Georgia, and north Florida. The center of distribution is the ACF River basin of southeast Alabama, southwest Georgia, and northwest Florida, and the Ochlockonee River system of southwest Georgia and northwest Florida.

Distribution

The shinyrayed pocketbook was described from the Chattahoochee River in Columbus, Georgia. This species historically occurred in mainstems and tributaries throughout the ACF, Chipola, and Ochlockonee River systems. A 1940 study found this species to be generally rare but locally abundant, documenting 94 specimens at eight Chipola River system sites (average of 11.8 per site). It now occurs at only 21% of the historical sites sampled, and is extirpated from the mainstems of the ACF rivers. Populations have declined significantly in the Chipola River. The species occurs at 29 sites in tributaries of the ACF Rivers and the Chipola and Ochlockonee Rivers. Only two sites show evidence of recruitment; however, the largest known population shows no signs of recruitment. During the status survey, 380 sites within the historical range of the shinyrayed pocketbook were sampled, including 28 of 54 (52%) known historical sites. Live individuals were located at six (21%) of the historical sites. This species has apparently been eliminated from all but one site in the Chattahoochee River system in Alabama, and from much of the Chipola River system.

Live individuals were found at 23 of the sample sites during the status survey, including one site in a Chattahoochee River tributary in Alabama, 13 sites (12 on tributaries) in the Flint River system, one locality in the Chipola River, and eight sites (seven mainstem) in the upper half of the Ochlockonee River system. An average of 2.9 live individuals were found per site. During unrelated studies subsequent to the completion of the status survey, ten additional sites for the shinyrayed pocketbook were located in the ACF River system. Eight of these new occurrences were from five Flint River tributaries; one each occurred in tributaries of the Chattahoochee and Chipola Rivers. The latter two records represent streams where the species had not been previously collected. The Flint River system records include one stream where the species had never been collected (a small tributary of a stream where live specimens were found during the status survey), and another stream where it was found during the status survey as a single dead shell; the remaining sites are in tributaries where it was found live during the status survey. The smallest shinyrayed pocketbook specimen recorded during the status survey in the Ochlockonee River system, possibly an older juvenile, measured 1.6 in (4.1 cm) in length. In the ACF River system, the three smallest specimens, measuring 2.17-2.24 in (5.5-5.7 cm) in length, were gravid females. In 1995, four live, apparently juvenile, specimens from 1.2 to 1.6 in (3.0-4.0 cm) in length were located in a Flint River tributary.

A 1996 study sampled the largest known bed of this species for juveniles. A 59 ft (18 m) by 26 ft (8 m) area had 37 adult shinyrayed pocketbooks (average of 1.7 per sq yd [2.1 per sq m]). Whole sub-stratum removal of 54, 2.7 ft (0.25 m) square quadrats within this bed yielded no juveniles of this species. The density of shinyrayed pocketbooks at the four other sites, where quantitative work conducted subsequent to the status survey yielded specimens, never exceeded 0.01 specimens per sq yd (0.08 specimens per sq m).

Threats

Impoundments have permanently altered significant portions of the ACF system. The lower portions of many tributaries were permanently flooded because of these reservoirs, including a known site for the shinyrayed pocketbook in Walter F. George Reservoir. Impoundments have altered about 29% of mainstem riverine habitat on the Flint River. Pre-impoundment records from Seminole and Blackshear Reservoirs exist for three sites for the shiny-rayed pocketbook. Talquin Reservoir flooded about 12% of the riverine habitat in the middle portion of the Ochlokonee River and the lower end of its largest tributary (the Little River). Pre-impoundment records exist for the shinyrayed pocketbook at sites at the upstream end of Talquin Reservoir, now also absent downstream of the dam. This indicates that potential host fish movements may have been blocked. Populations of the shinyrayed pocketbook have been isolated due to major impoundments on the Apalachicola, Flint, and Ochlockonee Rivers. Future impoundments to satisfy expanding urban and surburban demand, particularly in the metropolitan Atlanta area, could damage stream habitats where small populations of the shinyrayed pocketbook exist.

Although muskrats are not common within the range of these species, Piedmont populations of the shinyrayed pocketbook in the upper Flint River system may be subject to some degree of muskrat predation.

Conservation and Recovery

The shinyrayed pocketbook mussel survives in at least 33 sites, almost all of which are in streams running through privately owned land. Its conservation requires the protection of the stream reaches where it persists in small, isolated populations. These habitats must be protected from potential impoundment, other disturbances, and from pollution associated with poor land-use practices that cause erosion and inputs of nutrients and other chemicals. The populations of the shinyrayed pocketbook mussel must be monitored, and research undertaken into its basic biology and ecological requirements. It is particularly important to understand its requirements for breeding, as most populations are not reproducing.

Contacts

U. S. Fish and Wildlife Service
Jacksonville Ecological Services Field Office
6620 Southpoint Drive South, Suite 310
Jacksonville, Florida 32216
Telephone: (904) 232-2580

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

Reference

U.S. Fish and Wildlife Service. 16 March 1998. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for Five Freshwater Mussels and Threatened Status for Two Freshwater Mussels From the Eastern Gulf Slope Drainages of Alabama, Florida, and Georgia." Federal Register 63(50):12664-12687.