Northern Riffleshell ESA

ELEMENT STEWARDSHIP ABSTRACT

for

Epioblasma torulosa rangiana - northern riffleshell

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Element Stewardship Abstract

For EPIOBLASMA TORULOSA RANGIANA

1. IDENTIFIERS

Common Name: NORTHERN RIFFLESHELL

General Description:

Global Rank: G2T2

SHELL: Subquadrate or triangular in outline, very inequilateral, inflated and solid. The anterior end is rounded. The posterior end of the male is somewhat bluntly pointed above, sloping and truncated below; in the female it is inflated in the "brood pouch" region. The ventral margin of males is broadly curved, sinuate in the posterior fourth; it is almost straight in the females except for the expanded region of the brood pouch. The posterior ridge of the male is doubled, rather low and faint. The posterior ridge in female specimens is also doubled, but somewhat obscured by a sharp sulcus before the brood pouch swelling. Beaks are elevated, prominent, located in the anterior fourth. Beak sculpture consists of a few faint corrugations, sometimes broken or occasionally double-looped; the beaks often show signs of abrasion against each other. The surface is interrupted with numerous strong growth rest lines. The epidermis is smooth and shiny, yellowish-green, yellow, brownish, or rarely salmon, usually with numerous fine, faint, wavy green rays. The shell often has a satin-like epidermis when young, but with age it becomes brownish and the rays become obscured. The left valve has two subtriangular, ragged, elevated pseudocardinal teeth, a narrow interdenturn and two short, straight lateral teeth. The right valve has one, sometimes three pseudocardinal teeth, and one larger triangular tooth with a smaller tooth before and behind it. There is one short lateral tooth, often with a vestigial tooth below it. Beak cavities are rather shallow and open. The muscle scars and pallial line are impressed. The nacre is white, rarely salmon.

It is seldom buried to the posterior margin of the shell. The white mantle linings of the female are easily seen.

ANIMAL (from Ortmann, 1912, p 354): "Inner laminae of inner gills entirely connected with abdominal sac. In the female, the inner edge of the mantle in front of the branchial is not parallel to the outer edge, but is more or less remote from it, often quite distant, and it has finer or coarser papillae. Toward the middle of the lower margin, the two edges again approach each other, and are normal farther forward. The mantle between the two edges is peculiarly spongy. Thus, an inner compartment is formed in front of the branchial opening. In the male, the two edges of the mantle do not have this structure, or it is only merely indicated. Brood pouch swollen, kidney-shaped, formed by many ovisacs, occupying the posterior section of the outer gill. Edge of brood pouch blunt, beaded, but not pigmented." EPIOBLASMA RANGIANA has been illustrated by Johnson (1978) and Clarke (1981).

Element Occurrence (EO) Specifications:

An area of suitable natural habitat where evidence indicates an extant or historical population. EO Quality us based upon the density and reproduction potential as well as habitat suitability and size. EO Condition relates to water and substrate quality (e.g., siltation, dredging) and to overall riverine community health, especially host fish populations.

EO Rank Specifications:

"A" Rank:

10- 15+ contiguous miles of small to medium size and free-flowing river with regularly occurring areas of riffles and runs supporting dense population centers for element. Water quality should be at least moderate and without recent chronic deterioration due to increasing threats, and water quality should be consistent along this length. River should be at least somewhat defensible and land use in watershed should include largely manageable threats. In general, populations of other mussel species and fishes are high, indicating quality of habitat and environment. Glass-bottom bucket, snorkel and noodling surveys in the best habitat should produce 6-8+ live individuals/survey hour by experienced person. (Will be higher in easily surveyed substrates and water depths.) Where muskrat predation on mussels in general is high (large middens of dozens to hundreds of shells), element's proportion of muskrat shell middens is regularly 5+%, or 20-30+ fresh to slightly weathered shells can be found per 50 meters of habitat (can be 2-4 times this number). At least occasional juveniles/ sub-adults are regularly discovered, especiallt in muskrat middens.

"B" Rank:

Shorter sections of river (6-9 miles) supporting some relatively high population centers, or long river segments with lower densities. EO quality and condition are lower due to lower quantity of quality habitat or degradation of potential habitat. However, portions of habitat that are degraded show potential for recovery. Surveys reveal 3-5 live individuals/experienced person hour and/or 14% of middens, or 10-19 fresh to slightly weathered shells/50m of habitat.

"C" Rank:

Limited stretch of river (1 -5 mi) supporting low to moderate density population (or longer habitat distance with only low numbers), where good quality habitat does not exist or is limited, or additional potential habitat has been destroyed. Surrounding land use has damaged water and habitat quality and includes threats that are difficult to manage. Surveys reveal 1-2 live individuals/2-3 surveys hours by experienced person; occasionally fresh shells regularly found in muskrat middens or along stream (<I%), including at least some indication of reproduction and recruitment.

"D" Rank:

Short (<I mi) stretch of suitable and/or occupied habitat with a low population; or, a longer river segment but supporting very low numbers. Habitat is scarce, or has been degraded by active threats. Surveys reveal only I or 2 per day of survey work, or a number of surveys produce at least some evidence of extant occurence; shells are rarely ever found in muskrat middens. EO appears to be reproducing little or not at all, i.e., essentially all individuals are old adults. 11. STEWARDSHIP SUMMARY

Refer to the General Freshwater Mussel ESA.

111. NATURAL HISTORY

Range:

This entity replaces E. TORULOSA in the headwaters of the Ohio River drainage; its counterpart in the headwaters of the Tennessee River System is E. TORULOSA GUBERNACULUM. As with most naiads, its present range is a remnant of its former distribution. Historically, this entity was recorded from the mainstern of the Ohio River (Stansbery and Cooney, 1985) but has apparently been extirpated from there. The Ohio State University Museum of Zoology has records for the White and Wabash Rivers in Indiana but it has not been collected there in recent times (Clark, 1976; Abrell, pers. comm.). Taylor and Hughart (198 1) presumed that it was no longer present in the Elk River of West Virginia. Despite such range reductions, there still exist sporadic, presumably healthy populations.

Preferred habitat in Big Darby Creek, Ohio is still inhabited (Walters, pers. obs.).

Habitat:

Ortmann (1919, p 334) reported that this species was "always found ... on riffles, on a bottom of firmly packed and rather fine gravel, in swiftly flowing, shallow water or coarse gravel" and Clarke (1981, p 362) gave its habitat as "highly oxygenated riffle. Preferred habitat appears to require swiftly moving water. The high oxygen concentrations in swift streams may be necessary for survival. It is a species of riffle areas of smaller streams, and as such has fared better than larger river species, which have been heavily impacted by dredging and impoundment. Of the eleven or so species of naiads thought to be extinct in 1971 by Stansbery, most were from this latter type of habitat and all were species of EPIOBLASMA.

Reproduction:

Ortmann (1912, p 3 5 8) reported RANGIANA to be gravid in September and Clarke (198 1, p 352) said it was a "longterm breeder, gravid from late summer to following spring". The female uses the posterior portion of the outer gill as marsupia. It is widely believed that the "brood pouch" swellings of the female shell are caused by the expanded gravid gills, but Stansbery (pers. comm.) and Hoggarth (pers. comm.) do not believe this to be the case.

The host fish is unknown. However, Hill (1986) identified the following fish as possible hosts for the closely related E. CAPSAEFORMIS: spotted darter, redline darter, dusky darter, and the banded sculpin.

Based upon counts of annular growth lines, this species may reach 15+ years of age. It is not known at what ages reproductive maturity begins and ends. Because of the rarity of live material (and their enforced protection), it is not known if existing populations are reproductively active. Because of their small size, it is not known if juveniles are present in any of the populations. It must be emphasized that existing populations may be large, healthy, and reproductively active and still be in imminent danger of extinction if the host fish is not present in the range.

IV. CONDITION

Threats:

EPIOBLASMA seems to be particularly sensitive to impoundment; most species are riffle/run inhabitants and cannot tolerate other habitats. Impoundment by the Norris Reservoir of the Clinch River in Tennessee has resulted in the extirpation of the majority of species below the dam (Ahlstedt, 1984). The construction of the Wilson Dam on the Tennessee River has eliminated 20 of the original 22 Cumberlandian naiad species (Stansbery, 1971).

The existing populations are predominately in agricultural areas impacted by the runoff of pesticides and fertilizers. EPIOBLASMA RANGIANA is banned from export (1977).