Threats

Please refer to the section Listing Requirements under the Endangered Species Actheading for a complete description of the threats to pallid sturgeon.

Here is a brief summary.

The species was essentially extirpated from approximately 28% of the historical range due to impoundment, and the remaining unimpounded range has been modified by channelization and bank stabilization, or is affected by upstream impoundments that alter flow regimes, turbidity, and water temperatures (Hesse et al. 1989; Keenlyne 1989; USFWS 2000a). River channelization, bank stabilization, impoundment, altered flow regimes, and their effects are documented throughout the range of the pallid sturgeon and each can negatively affect pallid sturgeon life-history requirements.

• The most obvious effects to habitat are associated with the six main-stem Missouri River dams. These dams and their operations have: 1) truncated drift distance of larval pallid sturgeon (Kynard et al. 2007; Braaten et al. 2008), 2) created physical barriers that block normal migration patterns, 3) degraded and altered physical habitat characteristics, 4) greatly altered the natural hydrograph (Hesse et al. 1989), and 5) reulted in subtle changes in river function that influence both the size and diversity of aquatic habitats, connectivity (Bowen et al. 2003), and benthos abundance and distribution (Morris et al. 1968). Moreover, these large impoundments have replaced large segments of riverine habitat with lake conditions. Damming of the upper Missouri River has altered river features such as channel morphology, current velocity, seasonal flows, turbidity, temperature, nutrient supply, and paths within the food chain (Russell 1986; Unkenholz 1986; Hesse 1987).

• In addition to the main- stem Missouri River dams, important tributaries like the Yellowstone River, Platte River, and Kansas River have experienced similar affects due to dams and water resource development in their respective watersheds. Other issues that have influenced habitat formation and maintenance are associated with maintaining navigation channels on portions of the Missouri River as well as efforts to control flooding. The Mississippi River has received a substantial amount of anthropogenic modification through time, and some changes resulting from those modifications have likely been detrimental to pallid sturgeon.

• These anthropogenic habitat alterations likely adversely affect pallid sturgeon by altering the natural form and functions of the Mississippi River (Simons et al. 1974; Baker et al. 1991; Theiling 1999; Wlosinski 1999). Anthropogenic alterations to tributaries may have contributed to habitat degradation in the Mississippi River as well. Impoundment of major tributaries reduced sediment delivery to the main channel (Fremling et al. 1989) resulting in channel degradation and reduction in shallow water habitats (Simons et al. 1974; Bowen et al. 2003). Thus dams, bank stabilization, and channelization activities, individually and cumulatively when implemented within the range of pallid sturgeon, should be considered threats to the species.

Overall water quality can have both immediate and long-term effects on the species. New information, post-listing suggests that water quality can affect individuals during many life phases and localized and/or regionally poor or degraded water quality should be viewed as a threat to the species. More information is needed to evaluate the exposure and effects of environmental contaminants to pallid sturgeon. In response to this need, in 2008, a basin-wide contaminants review for pallid sturgeon was initiated. To date, this investigation has identified pesticides, metals, organochlorines, hormonally active agents, and nutrients as contaminants of concern throughout the species’ range. However, additional data are needed to quantify and qualify the magnitude of this threat.

Entrainment has been documented to occur in the few instances it has been studied. Thus it is a greater threat than anticipated in the original version of this plan. The overall effects from entrainment are variable and will be dependent on population demographics, exposure time, quantity of un-screened diversion points, and duration of diversion point usage, (i.e., year-round versus seasonal or sporadic operation). Further evaluation of entrainment associated with dredging operations, water diversion points, and commercial navigation is necessary across the pallid sturgeon’s range to adequately evaluate and quantify this threat.

Current State regulations and protections afforded under the Endangered Species Act, including the similarity of appearance rule, coupled with adequate enforcement, appear sufficient to manage, to the maximum extent practicable, the threat from overutilization for commercial, recreational, scientific, or educational purposes. However, absent protections under the Endangered Species Act, adequate State harvest regulations and enforcement will be necessary to protect the species from overharvest.

At the time of listing, neither disease nor predation was discussed as a threat, primarily due to limited information. New data have highlighted both disease and predation as issues of potential concern and should be considered as likely threats. At this writing, data are inadequate to quantify the magnitude of the threat either may impose.

Energy development and invasive species are two threats that may have substantial deleterious effects on pallid sturgeon populations. Strict adherence to existing environmental laws will be necessary to minimize effects from these threats and more data will be needed to adequately evaluate the extent and magnitude of these effects.