Includes literature cited (p. 34-36)

Project goals of the Freshwater Ecoregional Measures for the Northern Great Plains Steppe (NGPS) are to: 1) identify and reevaluate the number, diversity and viability of aquatic target occurrences within the Montana portion of the NGPS Ecoregional Plan based on a suite of indicator-based measures set within the aquatic ecological system framework, and 2) determine biodiversity viability measures (for the aquatic ecological system types, or for target species), threat status, and protection of these targets within the portfolio sites of the Ecoregional Plan. Using a combination of field data and GIS data layers, we analyzed the intersection of portfolio sites, 5th code watersheds, target occurrences, and indicator measures (viability, threats, and protection) to form an effective conservation map of selected MT portfolio sites in the NGPS. Overall, 34 of Montanas 43 native fish species reside within the NGPS ecoregion. Nine of these are MT Species of Special Concern (SOC), one of which is listed Endangered by the USFWS and four are potential species of concern (PSOC). All of these fish species, except one have at least one viable occurrence within MTs portfolio sites. The 15 types of prairie aquatic ecological systems (8 biological) are well represented within the portfolio, including associated aquatic macroinvertebrate communities with their SOC species. Threats in the portfolio with the broadest scope and severity are agriculture and surface diversions in the watersheds, while the most pervasive moderate level threats are riparian grazing and presence of northern pike, an introduced piscivorous fish. Effective conservation of aquatic systems in the NGPS portfolio sites in MT is quite low. Six of the 68 (8.9%) evaluated 5th code HUCs representing only two of eight aquatic ecological systems, and only 529 river miles are effectively conserved; if compared to the total river miles in the portfolio sites; this represents only 1.8% of those available. If we consider the criteria of Permanently Secured-Low Threat Viable Watersheds without effective management then the number of 5th code HUCs increases to 24 of the 68 (35%) or 30.6% of the portfolio area. A large percentage of the aquatic ecological systems within the portfolio sites (50 of 68 fifth-code HUCs) have good to excellent viability with moderate to low synergistic threats. Lack of effective land management is the main reason for the paucity of effectively conserved watersheds, because a large proportion of these portfolio sites are still in "unmanaged public" (48%) or privately held lands (approximately 43%). Additionally, our analysis revealed that watersheds with high percentages of "effectively managed" lands (GAP 1 and 2) did not necessarily correlate with higher biointegrity (viable) aquatic systems. We found watersheds with higher percentages of private lands and more agriculture had a significantly greater chance of being viable and higher in biointegrity. This is quite contradictory to previous studies. We did not find clear relationships between the broad-scale conditions and fine-scale assessments. Many of the landscape level threats seemed unrelated to the condition of the aquatic communities in the watershed. Localized impacts and reach-scale community attributes typically took precedence over watershed-level condition. Presence of introduced species and especially the piscivorous, northern pike lowered the integrity of watershed sites (based on the IBI and O/E model), so an abundance of these species will adversely affect the viability rank of the aquatic system regardless of the landscape condition. We identified critical aquatic sites in the portfolio that should be targeted for "effective conservation," as these will accomplish conservation of all lotic aquatic biodiversity present in the Northern Great Plains Steppe of Montana

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