Recent habitat association and the historical decline of Notropis simus pecosensis

Small-bodied, riverine minnows that historically characterized fish assemblages of Great Plains river, in North America have declined because of river fragmentation, dewatering, river channel degradation, river salinization and normative species introductions. The Pecos bluntnose shiner Notropis simus pecosensis, a member of this guild, persists in one segment of the Pecos River, New Mexico, USA. We characterized habitat associations for the species at two spatial scales. In general, N. s. pecosensis associated with fluvial habitats, but velocity association depended on body size, with larger individuals using swifter habitats. All N. s. pecosensis associated with relatively low depths (3-51 cm), which were most abundant in sites with relatively wide river channels (>25 m), especially when discharge was between 0.5 and 4.0 m(3) s(-1). The Pecos River sub-segment that is occupied by the core population of N. s. pecosensis (V-ii) had a unique combination of being buffered from direct dam effects by intervening segments and sub-segments, high sub-segment length, substantial sediment inputs from numerous uncontrolled tributaries, substantial base flow provided by irrigation return flows and groundwater inflows, high channel width in relation to discharge and low salinity. Although no unoccupied Pecos River segment appears to be suitable for N. s. pecosensis, habitat restoration opportunities exist within all occupied sub-segments (V-i, V-ii and V-iii) via base flow enhancement and river channel restoration. Restoration that offsets chronic effects of dams may be necessary to conserve the species. Restoration would also benefit other rare riverine minnows that coexist with N. s. pecosensis. Copyright (C) 2008 John Wiley & Sons, Ltd.