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Page 42 PART 3: CONSERVATION APPROACH Management Units For the purposes of three species management, Utah state waters will be grouped into management units based upon U.S. Geological Survey (USGS) four-digit Hydrologic Cataloging Unit numbers as opposed to the Division's Regional dividing system that is based on political divisions and not watershed divisions (see Figure 3-1), as management units organized by hydrologic units are more appropriate for describing populations and metapopulations of the three species. The USGS's Hydrologic Unit Code (HUe) system identifies river basins with a series of hierarchical numbers. Smaller watersheds receive longer codes. For example, the entire upper Colorado River Basin is HUC 14. The San Rafael River is in the four-digit HUC code 1406 and its tributaries of Ferron, Huntington, and Cottonwood creeks are located within the eight-digit HUC code 14060009 (see Figure 3-1). Using the USGS's method, roundtail chub is found within portions of HUC codes 1403 (the Colorado River above the confluence with the Green River), 1404 (the upper Green River), 1406 (the middle Green River and its tributaries such as the Price, San Rafael, and Duchesne rivers), 1407.(the lower Colorado River at Lake Powell and its tributaries of the Escalante and Dirty Devil rivers), and 1408 (the San Juan River and its tributaries). Flannelmouth sucker are found in each of these HUCs in addition to 1501 (the Virgin River system), part of the lower Colorado River Basin. The bluehead sucker is also found within the aforementioned 14 codes, but not within 1501. They are, however, found in HUCs 1601 (the Bear River) and 1602 (the Weber River) in the Bonneville Basin. The database maintained by the Utah Natural Heritage Program includes occurrences of bluehead sucker in the Virgin River system, but this is inconsistent with other published authors (e.g., Holden and Minckley 1980; Morvilius and Fridell 2004). The closely related desert sucker (Catostomus clarki) does occur in the Virgin River drainage. For the purposes of this management plan, flannelmouth sucker in the lower Virgin River (HUC 1501) are considered lower basin populations. Bluehead sucker located in the Snake and Bonneville drainages (HUes 1704, 1602, and 1601, respectively) are considered separate from one another and from Colorado Basin bluehead sucker populations, though genetic distinctness has yet to be proven. The remaining management units are located within the upper Colorado River Basin; however, for purposes of managing these populations, San Juan River populations will be considered distinct from populations outside of the 1408 HUC; populations within HUC 1407 will be considered distinct from those found in 1406 and others further north, and so on. White River populations are currently considered distinct (HUC 1405); however, they may be added to another population segment at a later date. In fact, each of the populations in these geographically divided management units may be found to be closely related to or. even identical toa population in another management unit through genetic analyses. Potentially, however, the inverse may also occur: each stream segment analyzed through genetic work may be a localized and distinct population. If or when this occurs, the Team will discuss whether to continue with the current management units or to create new ones based on the updated information. Goal development Development of goals for three species conservation poses several unique challenges arising from