Paddlefish (Polyodon spathula) COSEWIC assessment and status report: chapter 8

Limiting Factors and Threats

It is not known what led to the demise of the paddlefish in Canada, or the Great Lakes. Trautman (1981) suggested that its extirpation from Lake Erie could have been the result of blocking of upstream spawning migrations by dams on tributaries and/or destruction of the spawning habitat.

In the U.S., habitat degradation and destruction have been the most obvious changes that could have affected paddlefish distribution and abundance (Dillard et al. 1986). The water use practices and the construction and operation of dams and impoundments have eliminated traditional spawning areas (paddlefish can live in reservoirs, but need streams to spawn in), interrupted migrations, altered flow regimes, dewatered streams, and eliminated backwater nursery and feeding areas (Graham 1997; Pflieger 1997). Sparrowe (1986) suggested that structural changes to, and on, big river systems have adversely affected most of the original habitat.

The Missouri, Mississippi and Ohio rivers are the heartland of the American agriculture industry. Along these rivers and their tributaries agricultural development has resulted in habitat degradation through soil erosion, and fertilizer and pesticide runoff. Industrial pollution and problems with municipal wastes are also a major concern along the Ohio River and tributaries of the Mississippi (Sparrowe 1986; NatureServe 2007).

Paddlefish mature slowly and are easily caught, and like sturgeon, they are susceptible to over-harvest (Mettee et al. 1996). Poaching is a major concern, as the females are sought for their roe, which can be made into caviar and egg prices can be as high as $154 a kg (NatureServe 2007). In 1997, biologists estimated that nearly 1000 females had been illegally harvested in Kentucky alone (Rasmussen and Graham 1998). All captured fish are killed, and since the sexes are not easy to differentiate, four to five males are taken for every female with eggs – translating into 5000-6000 fish sacrificed for caviar.

The genetic integrity of the species is also threatened by release of inbred hatchery stock, and introductions from other parts of the range (NatureServe 2007).

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