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D. M. Wilson

Publications and source records attributed to D. M. Wilson.

5 recordsLinked to original sources
USGS1995

Declining populations of the fingernail clam Musculium transversum in the upper Mississippi River

We examined recent temporal trends in the abundance of fingernial clams Musculium transversum (formerly Sphaerium transversum ) in the upper Mississippi River. Historical data on densities of fingernail clams were obtained from regional scientists and published literature. We also sampled benthos in six navigation pools in summer 1991, finding very few fingernail clams. The combined data set, including historical data and sampling results, extended from 1973 to 1992 and was sufficient to statistically evaluate trends in densities of fingernail clams in eight pools. Populations of fingernail clams declined significantly in five of the eight pools examined (Pools 2, 5, 7, 9, and 19), which spanned a 700-km reach of river from St. Paul, Minnesota, to Keokuk, Iowa. Densities in Pool 19, which had the longest historical record on fingernail clam abundance, averaged 30 000 m −2 in 1985 and progressively declined to zero in 1990. Combined data from all eight pools showed a significant decline in abundance of fingernail clams. An evaluation of potential causal factors led us to hypothesize that the population declines in Pools 2 to 9 were linked to point-source pollution rather than to dredging activity or commercial navigation traffic. In Pool 19, the declines of fingernail clams may have resulted from low-flow conditions during drought periods, but the causal mechanisms by which low flow influences fingernail clam abundance are unclear. The decrease in fingernail clam populations may adversely affect certain fish and wildlife, such as migrating lesser scaup Aythya affinis , which feed heavily on the small mollusk. Moreover, the decreases in populations of this pollution-sensitive mollusk may signal a large-scale deterioration in the health of this riverine ecosystem.

Hydrobiologia↗
USGS1993

Spawning activity of paddlefish (Polyodon spathula) in the lower Black River, Wisconsin

We present indirect evidence of successful paddlefish ( Polyodon spathula reproduction in 1989 and 1991 in the lower Black River, Wisconsin, about 5 km upstream of the confluence with the upper Mississippi River. This is the first indication of successful reproduction by paddlefish at the northern end of its range in the central United States. Attempts to document paddlefish Polyodon spathula reproduction by sampling eggs and larvae began in the early 1900s (e.g., Stockard 1907), but the exact timing and location of fish spawning were unknown until the early 1960s. Actual spawning by paddlefish was first observed over gravel bars in the Osage River, Missouri, by Purkett (1961), who then collected eggs and larvae. Paddlefish eggs and larvae have since been collected below dams on the Missouri (Ruelle and Hudson 1977, Unkenholz 1982), Cumberland, and Tennessee Rivers (Pasch et al. 1980, Wall us 1986). However, the spawning areas for most paddlefish populations remain unknown. Because larval paddlefish are rarely sampled, the presence of post-larval and juvenile paddlefish is often interpreted as indirect evidence of successful reproduction. Such evidence has been used in Illinois (Adams 1942), Oklahoma (Houser and Bross 1959), the Missouri River along the Nebraska-South Dakota border (Ruelle and Hudson 1977), Pool 13 of the upper Mississippi River (Gengerke 1978), and Louisiana (Reed et al. 1992) to document successful paddlefish reproduction. We gathered similar evidence from the lower Black River, near La Crosse, Wisconsin. This information is important because Wisconsin represents the northern limit for paddlefish in the central United States (Gengerke 1986) and because attempts to document reproduction by the few remaining localized populations in the state have been unsuccessful (Lyons, In press). Additionally, paddlefish are of special concern in Wisconsin because of low numbers and limited distribution (Johnson 1987). During November 1990, we observed a small paddlefish (about 700 mm total length, TL) in the catch of commercial seine fishermen working in the lower Black River (about 5 km upstream from its confluence with the Mississippi River). On April 15, 1992, commercial fishermen working the same section of the Black River found five small paddlefish (<350 mm TL) in their catch. Additionally, three small paddlefish (about 800 mm TL) were taken on December 28, 1992, during commercial seining operations in the lower Black River. In Pool 13 of the upper Mississippi River, age-1 paddlefish averaged 498 mm fork length (Gengerke 1978), and the growth of paddlefish is faster in backwaters than in the main channel (Rosen 1976, Russell 1986). Therefore, we think that the three 800-mm paddlefish taken on December 28, 1992 were age-1 fish that hatched during spring 1991 near the Lake Onalaska spillway on the lower Black River. We also think that the 700-mm paddlefish observed in November 1990 was an age-1 fish that had hatched in the same area during spring 1989.

Journal of Freshwater Ecology↗