Fragmentation and dewatering transform Great Plains stream fish communities

Abstract

Abstract. Biodiversity in stream networks is threatened globally by interactions between habitat fragmentation and altered hydrologic regimes. In the Great Plains of North America, stream networks are fragmented by .19 000 anthropogenic barriers, and flow regimes are altered by surface water retention and groundwater extraction. We documented the distribution of anthropogenic barriers and dry stream segments in five basins covering the central Great Plains to assess effects of broad-scale environmental change on stream fish community structure and distribution of reproductive guilds. We used an informationtheoretic approach to rank competing models in which fragmentation, discharge magnitude, and percentage of time streams had zero flow (a measure of desiccation) were included to predict effects of environmental alterations on the distribution of fishes belonging to different reproductive guilds. Fragmentation caused by anthropogenic barriers was most common in the eastern Great Plains, but stream desiccation became more common to the west, where rivers are underlain by the depleted (i.e., extraction . recharge) High Plains Aquifer. Longitudinal gradients in fragmentation and desiccation contributed to spatial shifts in community structure from taxonomically and functionally diverse communities dominated by pelagic reproductive guilds where fragmentation and desiccation were least, to homogenized communities dominated by benthic guilds where fragmentation and desiccation were common. Modeling results revealed these shifts were primarily associated with decline of pelagic reproductive guilds, notably small-bodied pelagophilic and lithopelagophilic fishes that declined in association with decreased fragment length and increased number of days with zero flow. Graph theory combined with a barrier prioritization approach revealed specific fragments that could be reconnected to allow fishes within these guilds to colonize currently unoccupied fragments with the mitigation or removal of small dams (,10 m height). These findings are useful for natural resource managers charged with halting or reversing the prevailing pattern of declining fish diversity in the Great Plains. Our study represents one of the most comprehensive assessments of fish diversity responses to broad-scale environmental change in the Great Plains and provides a conservation strategy for addressing the simultaneous contributions of fragmentation and flow alteration to the global freshwater biodiversity crisis.

Fish fauna in tributaries of the Suiá-Miçú River (upper Xingu river basin), in the Cerrado-Amazon transition zone, eastern state of Mato Grosso, Brazil

“…Species with opportunistic life-history strategy usually exhibit small adult body sizes, rapid sexual maturity, high reproductive effort, and low juvenile survival (Winemiller 1989, 2005, Winemiller et al 2008, characteristics that favor establishment in altered environments (Cunico et al 2011). Another important life history feature of P. araguaienses is that it is a non-migratory species; the loss of connectivity by the construction of reservoir benefits non-migratory fish species over those with dispersion affinity (Perkin et al 2015).…”

Rethinking refuges: Implications of climate change for dam busting

“…The value of impoundments as artificial refuges must of course be balanced against the impact of dams on existing natural refuges. Dams can impede the access of fish to natural refuges by physically blocking migratory pathways and increasing the number of no-flow days (Perkin et al, 2015). Dams may also reduce the ability of rivers to maintain natural refuges such as oxbows and scour pools, as they can negatively impact fluvial geomorphic processes and disrupt the dynamics of the habitat mosaic (Hauer and Lorang, 2004).…”

“…Crucially, these assessments need to be underpinned by regionally specific data. For example, Perkin et al (2015) provide an example of a comprehensive modelling exercise leading to predictions of which dams if removed are likely to yield optimal environmental gains, in particular the expansion or recovery of populations of small, pelagic-spawning fishes in large and historically perennial streams in the central USA. By contrast, in the current study, we draw on examples from South Africa and south-western Australia that are dry temperate regions, characterised by smaller, non-perennial streams.…”

“…draw down) that facilitate alien fish control . Therefore, although the optimisation approach provided by Perkin et al (2015) represents a very useful template for progress, the focus in temperate dryland streams may shift from main channel specialists that have evolved in perennial streams (e.g. pelagic spawners) to threatened species/guilds that have adapted to regular cycles of drying and flooding.…”

Chemical variability of water and sediment over time and along a mountain river subjected to natural and human impact

“…The effects of barriers on the ecological integrity of various European rivers have been intensively studied (Koster and Crook, 2008;Kemp and O'Hanley, 2010;Mueller et al, 2011;Rolls, 2011;Rolls et al, 2014, Sondermann et al, 2015Perkin et al, 2015), obtaining information which is crucial for the successful restoration of river ecosystems. Recently, more attention has focused on the impact of small dams or weirs on biocoenosis, which is important for successful management and restoration of stream ecosystems.…”