Altamaha spinymussel
The Altamaha spinymussel (Elliptio spinosa) is a freshwater mussel that is endemic to the Altamaha River drainage of southeastern Georgia. It was described from the Altamaha near its mouth at Darien in 1836. The spinymussel is associated with stable, coarse to fine sandy sediments of sandbars and sloughs and appears to be restricted to swiftly flowing water buried approximately 2 to 4 inches below the substrate surface. As the name implies, the shells of these animals are adorned with one to five prominent spines. These spines may by straight or crooked, reach lengths from 0.4 to 1 inch; and are arranged in a single row somewhat parallel to the posterior ridge.
Photo by Jimmy Rickard, FWS
The Altamaha River Basin is well known for its unique and highly endemic mussel fauna. Unfortunately, a number of these endemics are in decline (Wisniewski et al. 2005), including the Altamaha spinymussel, which in 2002 was elevated to candidate status for Federal listing by the U.S. Fish & Wildlife Service. Populations of other endemic mussels in the Altamaha River such as the Altamaha arcmussel (Alasmidonta arcula) and Inflated floater (Pyganodon gibbosa) are also declining in contrast to most other Altamaha River Basin unionids, which are widespread and abundant (Wisniewski et al. 2005).
The historical range of the Altamaha spinymussel is restricted to the Coastal Plain portion of the Altamaha River, and the lower portions of its three major tributaries, the Oconee, Ocmulgee, and Ohoopee Rivers. The Altamaha is formed by the confluence of the Ocmulgee and Oconee Rivers and lies entirely within Georgia’s State boundary. Since its description, the unique spinymussel has been sought by many collectors and is found in numerous collections, both public and private. Large-scale, targeted surveys for the mussel have been conducted only since the 1970's. Recent surveys have revealed a dramatic decline in the number of populations and number of individuals throughout the species’ historical range. (Click on map for a larger image)
Over 550 person-hours have been spent searching for the Altamaha spinymussel from 1997 through 2006. However, only 34 E. spinosa were collected live from the 233 sites surveyed. Additionally, researchers with the Georgia Cooperative Wildlife and Fishery Research Unit at UGA and Georgia Department of Natural Resources sampled 103 sites within the Altamaha Basin during 2006-2007 finding 7 live E. spinosa (5 sites). The results of these surveys suggest that E. spinosa populations are extremely small in comparison to populations of other Altamaha River Basin unionids, which are widespread and abundant. Populations of several species within the Altamaha Basin appear to be comprised of multiple year classes ranging from juveniles with byssal threads used for attachment to substrates to adults approaching their maximum lengths. However, there appears to be no evidence of recent reproduction of E. spinosa and the lengths of these individuals are relatively similar, suggesting that successful reproduction has not occurred for some time.
Researchers are unsure of the reason for the small population size and lack of recent recruitment of these individuals, and speculate that unsuitable habitat, the presence of toxins, or declining host fish populations may be responsible. Directing research to focus on these factors is difficult due to the lack of basic life history information for these species such as determining the appropriate host fish. The Georgia Wildlife Action Plan mollusk technical committee identified that host fish determination was the highest priority research need for E. spinosa, which was designated as a high priority species by the Georgia Department of Natural Resources (2005). Determining the primary host fishes for this species will provide the foundation upon which future research should be built. This will allow resource managers to examine if appropriate host fishes are present in sufficient numbers to sustain populations of Altamaha spinymussel. Furthermore, fish habitat use models may be generated and used to make inferences as to habitat used by this species. Lastly, this species may be propagated to complete toxicity studies for all life stages and possibly provide stock to enhance existing populations within the Altamaha River Basin.