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 (