Life history and population biology of the endangered tan riffleshell (Epioblasma florentina walkeri) (Bivalvia : Unionidae)

The tan riffleshell (Epioblasma florentina walkeri) is listed by the US Fis h and Wildlife Service as endangered, and is restricted to only I reproduci ng population in Indian Creek of the upper Clinch River, Virginia. We inves tigated its fish hosts, efficacy of infestation methods, suitability of hos t populations, and population demographics. Fish were collected and infeste d with tan riffleshell glochidia to examine potential hosts. juveniles tran sformed on at least 5 of the tested species: fantail darter (Etheostoma fla bellare), greenside darter (E. blennioides), redline darter (E. rufilineatu m), snubnose darter (E. simoterum), and 1 or 2 cottids: banded sculpin (Cot tus bairdi) or mottled sculpin (C. carolinae). Fantail darters from 4 drain ages were collected and infested with glochidia to compare the suitability of various populations of the most successful host. The number of juvenile mussels obtained from fantail darters collected from Indian Creek ((x) over bar +/- 1 SD = 59.22 +/- 10.01) was significantly higher than those transf ormed on fantail darters from the Roanoke River ((x) over bar = 9.45 +/- 10 .64), where the tan riffleshell. does not occur. Variation in transformatio n success supports the hypothesis that host fish suitability is mediated by varying immune responses, and that coadaptation of sympatric host fish and mussel populations seemingly enhances compatibility. No significant differ ence (ANOVA, p = 0.39) existed between the numbers of juvenile tan rifflesh ells produced by fish using 2 different infestation techniques. The populat ion of tan riffleshells in Indian Creek was similar to 2000 adults using Sc humacher's modification of Schnabel's maximum likelihood estimator. Sex rat io was near 1: 1, and size-frequency distributions of males and females wer e not significantly different. Maximum age of the population, determined by thin-sectioning of valves, was 11 y; similar to 70% of the population was <6 y.