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CFR Citation: 50 CFR Part 17

RIN ID: RIN 1018-AJ09

NOTICE: PROPOSED RULES

ACTION: Endangered and threatened species:

DOCUMENT ACTION: Proposed rule.

SUBJECT CATEGORY: Endangered and Threatened Wildlife and Plants; Proposed Designation of Critical Habitat for Astragalus lentiginosus var. piscinensis (Fish Slough Milk-vetch)

DATES: We will accept comments until August 3, 2004. Public hearing requests must be received by July 19, 2004.

DOCUMENT SUMMARY: We, the U.S. Fish and Wildlife Service (Service), propose to designate critical habitat pursuant to the Endangered Species Act of 1973, as amended (Act), for the federally threatened Astragalus lentiginosus var. piscinensis (Fish Slough milkvetch). We propose to designate approximately 8,490 acres (ac) (3,435 hectares (ha)) of land in Mono and Inyo Counties, California.

We hereby solicit data and comments from the public on all aspects of this proposal, including data on economic and other effects of the designation. We may revise this proposal prior to final designation to incorporate or address new information received during public comment periods.

SUMMARY: Critical habitat designations—; Fish slough milk-vetch,

SUPPLEMENTAL INFORMATION

It is our intent that any final action resulting from this proposal will be as accurate as possible. Therefore, we solicit comments or suggestions from the public, other concerned governmental agencies, the scientific community, industry, or any other interested party concerning this proposed rule. On the basis of public comment, during the development of the final rule we may find that areas proposed are not essential, are appropriate for exclusion under section 4(b)(2), or not appropriate for exclusion, and in all of these cases, this information would be incorporated into the final designation. We particularly seek comments concerning:
(1) The reasons why any areas should or should not be determined to be critical habitat as provided by section 4 of the Act, including whether the benefits of designation will outweigh any threats to the taxon resulting from the designation;
(2) Specific information on the amount and distribution of Astragalus lentiginosus var. piscinensis and its habitat, and which habitat or habitat components are essential to its conservation and why;
(3) Land use designations and current or planned activities in or adjacent to the area proposed and their relationship to the proposed critical habitat;
(4) Current or planned water withdrawals or diversions in or adjacent to the area proposed and their relationship to the proposed critical habitat;
(5) Any foreseeable economic or other potential impacts resulting from the proposed designation of critical habitat, in particular, any impacts on small entities and to the water user community;
(6) Methodologies that we might use, pursuant to section 4(b)(2) of the Act, to determine if the benefits of excluding an area from critical habitat outweigh the benefits of designating the area as critical habitat;
(7) Whether our approach to critical habitat designation could be improved or modified in any way to provide for greater public participation and understanding, or to assist us in accommodating public concerns and comments;
(8) Additional information that can be used to characterize or more completely understand the regional aquifer that supports aquatic or riparian habitat in Fish Slough, or how local ground water pumping activities affect the hydrology of Fish Slough; and
(9) Information or comment on the merits of the proposed 1,000 meter wide upland area surrounding the alkaline soils, including the need or value of including all or part of this area to ensure an adequate supply of pollinators, manage for control of invasive species, and include sites that could be restored to alkaline soils and reoccupied by Astragalus lentiginosus var. piscinensis.

If you wish to comment, you may submit your comments and materials concerning this proposal by any one of several methods (see ADDRESSES section). Please submit electronic comments in ASCII file format and avoid the use of special characters and any form of encryption. Please also include Attn: ``RIN 1018AJ09'' and your name and return address in the body of your message. If you do not receive a confirmation from the system that we have received your internet message, contact us directly by calling our Ventura Fish and Wildlife Office at phone number (805) 6441766. Please note that the email address ``
fw1fsmv_pch@r1.fws.gov'' will be closed out at the termination of the public comment period.

Our practice is to make comments, including names and home addresses of respondents, available for public review during normal business hours. Individual respondents may request that we withhold their home address from the rulemaking record and we will honor such requests to the extent allowable by law. There also may be circumstances in which we would withhold from the rulemaking record a respondent's identity, as allowable by law. If you wish us to withhold your name and/or address, you must state this prominently at the beginning of your comment. We will not, however, consider anonymous comments. We will make all submissions from organizations or businesses, and from individuals identifying themselves as representatives or officials of organizations or businesses, available for public inspection in their entirety. Comments and materials received will be available for public inspection, by appointment, during normal business hours at the above address.
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Preamble
Designation of Critical Habitat Provides Little Additional Protection to Species

In 30 years of implementing the Act, we have found that the designation of statutory critical habitat provides little additional protection to most listed species while consuming significant amounts of available conservation resources. Our present system for designating critical habitat has evolved since its original statutory prescription into a process that provides little real conservation benefit, is driven by litigation and the courts rather than biology, limits our ability to fully evaluate the science involved, consumes enormous agency resources, and imposes huge social and economic costs. We believe that additional agency discretion would allow our focus to return to those actions that provide the greatest benefit to the species most in need of protection.
Role of Critical Habitat in Actual Practice of Administering and Implementing the Act

While attention to and protection of habitat is paramount to successful conservation actions, we have consistently found that, in most circumstances, the designation of critical habitat is of little additional value for most listed species yet consumes large amounts of conservation resources. Sidle (1987) stated ``Because the ESA can protect species with and without critical habitat designation, critical habitat designation may be redundant to the other consultation requirements of section 7.'' Currently, only 445 species or 36 percent of the 1,244 listed species in the United States under the jurisdiction of the Service have designated critical habitat. We address the habitat needs of all 1,244 listed species through conservation mechanisms such as listing, section 7 consultations, the Section 4 recovery planning process, the Section 9 protective prohibitions of unauthorized take, the Section 6 funding to the states, and the Section 10 incidental take permit process. We believe that it is these measures that may make the difference between extinction and survival for many species. Procedural and Resource Difficulties in Designating Critical Habitat

We have been inundated with lawsuits for our failure to designate critical habitat, and we face a growing number of lawsuits challenging critical habitat determinations once they are made. These lawsuits have subjected us to an everincreasing series of court orders and court approved settlement agreements, compliance with which now consumes nearly the entire listing program budget. This leaves us with little ability to prioritize our activities to direct scarce listing resources to the listing program actions with the most biologically urgent species conservation needs.

The consequence of the critical habitat litigation activity is that limited listing funds are used to defend active lawsuits, to respond to Notices of Intent (NOIs) to sue relative to critical habitat, and to comply with the growing number of adverse court orders. As a result, listing petition responses, our own proposals to list critically imperiled species, and final listing determinations on existing proposals are all significantly delayed.

The accelerated schedules of courtordered designations have left us with almost no ability to provide for adequate public participation or to ensure a defectfree rulemaking process before making decisions on listing and critical habitat proposals due to the risks associated with noncompliance with judiciallyimposed deadlines. This in turn fosters a second round of litigation in which those who fear adverse impacts from critical habitat designations challenge those designations. The cycle of litigation appears endless, is very expensive, and in the final analysis provides relatively little additional protection to listed species.

The costs resulting from the designation include legal costs, the cost of preparation and publication of the designation, the analysis of the economic effects and the cost of requesting and responding to public comment, and in some cases the costs of compliance with the National Environmental Policy Act (NEPA); all are part of the cost of critical habitat designation. None of these costs result in any benefit to the species that is not already afforded by the protections of the Act enumerated earlier, and they directly reduce the funds available for direct and tangible conservation actions.

Background

Astragalus lentiginosus Douglas ex Hook. var. piscinensis Barneby (Fish Slough milkvetch), was described by Barneby (1977). The type specimen was collected from BLM Spring in the central portion of Fish Slough 8 miles (mi) (13 kilometers (km)) north of the town of Bishop, California. Spellenberg (1993) retained this variety in his treatment of Astragalus, which was published in the most recent edition of The Jepson Manual of Higher Plants of California. The genus Astragalus is in the pea family (Fabaceae).

Astragalus lentiginosus var. piscinensis is a prostrate perennial, with fewbranching stems that are up to 39 inches (in) (1 meter (m)) in length and covered with stiff, appressed hairs. Leaflets, flowers, and fruits are described in the final listing rule (63 FR 53596).

The Service listed Astragalus lentiginosus var. piscinensis as threatened under the Act on October 6, 1998 (63 FR 53596). Please refer to our final listing rule for a more detailed discussion of the species' taxonomic history and description. A. l. var. piscinensis is not listed by the State of California as a rare, threatened, or endangered taxon, and is not a state candidate for listing as threatened or endangered.

Status and Distribution

The entire known range of Astragalus lentiginosus var. piscinensis is restricted to a 6 mi (9.7 km) long area of alkaline habitat that parallels Fish Slough, a wetland oasis in Inyo and Mono Counties, California. Fish Slough is located in the northern end of the Owens Valley area, along the eastern edge of the Sierra Nevada Mountains in central California. The Fish Slough area is approximately 4,200 feet (ft) (1,280 m) in elevation. Alkaline habitat at Fish Slough is characterized by soil that has a sandy or silty texture and a white appearance. This alkaline habitat forms a ring around the seasonally and permanently flooded wetland habitat in the slough itself. The alkali flat and alkali scrub habitats in the Fish Slough ecosystem were mapped in 1991 (Ferren 1991a). Approximately 540 ac (219 ha) of alkaline habitat were present in Fish Slough when this mapping effort was completed. For reasons that are not precisely known, A. l. var. piscinensis does not inhabit the entire alkaline habitat present in Fish Slough (Ferren 1991a; Odion et al. 1991).

A comparison of the distribution of alkaline habitat that exists in Fish Slough today with aerial photographs taken in 1950 suggests the geographic extent of alkaline habitat in Fish Slough has decreased over time (Anne Halford, Bureau of Land Management, pers. comm. 2004). There has not been an effort to precisely map the boundary of the alkaline areas in the photographs, but some of the areas that previously possessed alkaline soil would now be mapped as xeric uplands that would not be likely to support Astragalus lentiginosus var. piscinensis.

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(LADWP) and Bureau of Land Management (BLM) performed the first comprehensive survey to locate all of the Astragalus lentiginosus var. piscinensis in Fish Slough (Novak 1992). The survey documented approximately 3,200 widelyscattered individuals within a 530ac (214 ha) area. This survey also demonstrated that multiple sites that had been occupied by A. l. var. piscinensis in the 1980s and 1991 were larger in geographic extent than previously suspected. One site where six plants were documented in the 1980s and 1991 had no plants in 1992. Another site experienced a decline in the number of observed plants from 44 in 1983 to 8 in 1992. The areas where A. l. var. piscinensis occurred in 1992 were resurveyed in 2000, and it was determined that the overall number of mature plants declined from the 3,200 individuals in 1992 to 1,543 plants in 2000 (A. Halford, pers. comm. 2004). The 2000 survey did not result in the discovery of any new, additional patches of A. l. var. piscinensis, and the overall distribution of the taxon in 2000 was similar to what was observed in 1992.

Fish Slough can be divided into northern, central, and southern areas. Sixty percent of the known Astragalus lentiginosus var. piscinensis plants occur in the northern portion of the slough on land owned by the LADWP. In 1991, LADWP staff constructed an 80ac (32ha) cattle exclosure in the northern portion of Fish Slough; in 1992, over 95 percent of the A. l. var. piscinensis plants documented in the northern portion of Fish Slough were within this exclosure. Approximately 35 percent of the known A. l. var. piscinensis plants occur in the central portion of the slough on lands owned and managed by the BLM or the LADWP. The remaining 5 percent of the known plants occur as scattered patches in the southern portion of the slough located north of the McNally Canal. This land is owned by the BLM or the LADWP. The area south of McNally Canal contains little habitat suitable for A. l. var. piscinensis (Novak 1992).

Staff from the LADWP and the BLM collect population trend data for Astragalus lentiginosus var. piscinensis in five monitoring plots on land owned by the LADWP. Two monitoring plots are located in the 80ac (32ha) cattle exclosure, where grazing has not occurred since 1991. The other three monitoring plots are subject to grazing. One grazed plot is north of the cattle exclosure, and the other two are in the central portion of Fish Slough near BLM Spring. Monitoring of the five plots occurred annually between 1991 and 2002 (Paula Hubbard, LADWP, pers. comm. 2003; A. Halford, pers. comm. 2003), except for one plot near BLM Spring in 1995, and for the plot north of the cattle exclosure in 1996. When trend data were collected, there was an effort to quantify the number of seedlings, immature plants, and mature plants in each plot.

Data collected from LADWP plots provide insight into how the abundance of Astragalus lentiginosus var. piscinensis has varied over time at specific sites. An average of 33 plants was present in ungrazed plot 1 between 1991 and 1996, but this declined by 61 percent to an average of 13 plants between 1997 and 2002. Similarly, in ungrazed plot 2, an average of 104 plants was present between 1991 and 1996; this declined by 52 percent to an average of 50 plants between 1997 and 2002. In the grazed plot north of the cattle exclosure (plot 3), an average of 41 plants was present between 1991 and 1996, while the average present between 1997 and 2002 was 48 (an increase of 17 percent). In grazed plot 4, north of BLM Spring, an average of 15 plants was present between 1991 and 1996; this number declined by 53 percent to an average of 7 plants between 1997 and 2002. In grazed plot 5, north of BLM Spring, an average of 7 plants were present in the plot between 1991 and 1996; this number declined by 86 percent to an average of 1 plant between 1997 and 2002. If data from all plots (i.e., grazed and ungrazed) are considered together, the average number of plants in the plots declined by approximately 41 percent between the two periods. The number of immature plants observed within a plot has exceeded the number of mature plants in that plot for only one plot (grazed plot 3) during the monitoring period, and this only occurred twice. The number of seedlings present in different plots has varied over time, with the greatest number of seedlings occurring in the northern portion of the slough in ungrazed plot 2 and grazed plot 3. The plant census data collected within and outside the cattle exclosure suggest that the decline in A. l. var. piscinensis within the monitoring plots may be caused by one or more factors that may not relate directly to grazing activities, and suggest that low numbers of cattle in an area may not necessarily have an adverse effect on A. l. var. piscinensis.

Staff from the BLM also monitor changes in the abundance of Astragalus lentiginosus var. piscinensis at five plots established in 1997 or 1998 on lands under their jurisdiction. Three of the plots are near the middle of Fish Slough. The number of A. l. var. piscinensis in two of these plots declined from 14 plants in 1997 to 3 plants in 2003, and from 47 plants in 1998 to 5 plants in 2003. At the third plot near the middle of Fish Slough, the number of plants has varied between 19 and 22 individuals during a 7year period. At the two plots near BLM Spring, the number of A. l. var. piscinensis has remained relatively constant between 1997 and 2003, with one plot having between 39 and 46 individuals, and the other plot having between 6 and 8 plants. The only plot where a substantial number of young individuals were seen between 1997 and 2003 was located near BLM spring.

Threats

Previously identified threats to Astragalus lentiginosus var. piscinensis include the presence of roads, effects related to the use of motorized offroad vehicles, effects related to cattle grazing, and herbivory by native vertebrates and insects (USFWS 1998). A potential threat to A. l. var. piscinensis not previously identified in other documents includes competition with, or displacement by, nonnative plant species (P. Hubbard, pers. comm. 2003). The modification of wetland habitats which results from ground water pumping or water diversion activities that alter the surface and underground hydrology of Fish Slough are also a threat to the taxon (USFWS 1998).

The use of motorized offroad vehicles and the presence of roads have affected habitat occupied by Astragalus lentiginosus var. piscinensis. Approximately 19 mi (30.6 km) of roads exist within 3,280 ft (1,000 m) of the alkaline habitats within Fish Slough. South of BLM Spring, on the east side of the slough, a road bisects one cluster of the listed plants, and offroad vehicle use in the central portion of the slough has been documented (Novak 1992). Soil compaction and topographic changes resulting from road presence and offroad vehicle activity can affect soil moisture regimes in Fish Slough, and potentially result in changes in seasonal inundation patterns that may adversely affect A. l. var. piscinensis.

Roads through upland areas in Fish Slough also create increased levels of human visitation that would otherwise be unlikely if roads were absent. Roads have been associated with negative impacts that alter the biotic integrity of both terrestrial and aquatic habitats (Trombulak and Frissell 2000). A growing body of published literature indicates that vehicular traffic along road networks in terrestrial habitats increases the likelihood that nonnative plant seeds will be introduced into areas
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where they were previously absent (Wace 1977; Schmidt 1989; Lonsdale and Lane 1994). Some of the nonnative plant species in Fish Slough (e.g., five hook bassia (Bassia hyssopifolia)) are identified as pest plants of ecological concern (CalEPPC 1999) and have the potential to invade and degrade the quality of alkaline habitats and compete with Astragalus lentiginosus var. piscinensis.

The BLM does not permit grazing on lands they administer in Fish Slough. With the exception of the 80ac (32ha) cattle exclosure in the northern portion of Fish Slough, lands under LADWP management that support Fish Slough milkvetch are grazed (P. Hubbard, pers. comm. 2003). The LADWP has not completed a management plan that provides specific prescriptions to guide grazing activities in Fish Slough. Currently, there are approximately 40 head of cattle and up to 8 horses in Fish Slough between late summer and March annually (P. Hubbard, pers. comm. 2003). The LADWP schedules grazing activities so cows are absent from the slough during the milkvetch growing season.

We believe that moderate to intense levels of cattle grazing in Fish Slough could result in a number of adverse effects. For example, the composition of the local plant community could be altered by reducing or eliminating species that cannot tolerate trampling and increasing the abundance of plant species that are tolerant to trampling. Other taxa that were not previously part of the native plant community may be introduced as a result of grazing activities (e.g., introduction of seeds of nonnative species from supplemental feed that is not weed seed free). The regular presence of cattle in an area could result in the creation of cattle trails that are devoid of vegetation, and therefore reduce the amount of habitat that could be occupied by Astragalus lentiginosus var. piscinensis. Trampling by livestock can also reduce the number of burrows or other nesting sites available for bee pollinators (Sugden 1985), and actions that concentrate the presence of cattle in a particular location (e.g., placement of salt licks) may lead to an increased likelihood that individual A. l. var. piscinensis plants could be trampled.

Native herbivores may exert a substantial effect on the reproductive output of individual Astragalus lentiginosus var. piscinensis plants. Infestations of root systems by phloemsucking insects and high rates of rabbit herbivory have been reported for A. l. var. piscinensis individuals that were present in the central portion of Fish Slough (Mazer and Travers 1992). Ferren (1991a) observed rabbit feces adjacent to individuals that had been stripped of leaves, flowers, and seeds, and assumed these plants had been browsed or otherwise adversely affected by rabbits. Mazer and Travers (1992) found that plants in the central portion of Fish Slough experienced high herbivory levels when compared to plants in the northern portion of the slough. Some plants in the center of the slough had 80 percent of their branches grazed by rabbits or rodents, while in the northern portion of the slough fewer than 20 percent of the branches of some plants had been grazed. Herbivory of A. l. var. piscinensis by rodents and insects has also been noted during the aforementioned surveys of longterm monitoring plots (P. Hubbard, pers. comm. 2003). A large percentage of A. l. var. piscinensis seeds in Fish Slough may be perforated by holes that are created by weevils or wasps. In addition, gopher activity and ant colonies under previously live plants have been noted during monitoring activities. It is not known if herbivory of A. l. var. piscinensis plants is responsible for low recruitment levels of the listed plant taxon.

Investigations into the condition and viability of Astragalus lentiginosus var. piscinensis seeds suggest that a large fraction of its viable seeds will germinate under laboratory conditions, but that a large proportion of seeds may be parasitized. Of the 2,901 seeds collected from 35 plants in Fish Slough on September 10, 2000, 1,039 seeds (36 percent) were found to have been parasitized by one or more insect species (Wall 2001). The identity of the insects has not been determined, but may include a weevil (Joy Fatooh, BLM, in litt. 2003), or a wasp (Wall 2001). Parasitism of a seed is believed to always result in damage to the seed embryo (Joy Fatooh, BLM, in litt. 2002).

The proliferation of nonnative plant species in Fish Slough has the potential to adversely affect Astragalus lentiginosus var. piscinensis. Nonnative salt cedar (Tamarix ramosissima), five hook bassia, Russian thistle (Salsola iberica), and pepperweed (Lepidium latifolium) would compete with A. l. var. piscinensis for available space, nutrients, and water if the different species had overlapping distributions. The presence of pepperweed in Fish Slough is especially problematic since that species is able to colonize and rapidly spread into a variety of habitat types, including alkaline areas where A. l. var. piscinensis is present (P. Hubbard, pers. comm. 2003). Currently, dense concentrations of nonnative plant species are not found with A. l. var. piscinensis. Recognizing that nonnative competition could be a problem, LADWP, BLM, and California Department of Fish and Game (CDFG) staff systematically work to control the spread of nonnative plant species in Fish Slough.

Natural changes in, or humaninduced modifications of, aquatic habitat in Fish Slough may reduce the number of Astragalus lentiginosus var. piscinensis. A longterm threat to the milkvetch may include the expansion of Fish Slough Lake. The increased size of the lake may be due to natural geologic processes (e.g., earthquakes), or humancaused actions (e.g., the construction of Red Willow Dam, a small earthen berm). Expansion of Fish Slough Lake from natural processes or human caused actions has resulted in increased soil inundation, expansion in the distribution of emergent wetland vegetation, and loss of suitable alkaline habitat for Fish Slough milkvetch (Ferren 1991c). Beavers (Castor canadensis) have been observed in Fish Slough Lake and the Northwest Springs area, and their presence sometimes results in changes in local soil moisture conditions as they construct ponds. The construction of a beaver dam near one of the aforementioned longterm monitoring plots on land owned by the LADWP (ungrazed plot 1) appears to coincide with decreases in the number of A. l. var. piscinensis plants that were counted (P. Hubbard, pers. comm. 2004).

The creation of earthen dams, fish barriers, and weirs that facilitate water flow measurements has also likely affected Astragalus lentiginosus var. piscinensis. The dams and fish barriers have been built for a variety of purposes, including habitat enhancement for waterfowl, creation of sport fish habitat, and management activities that were designed to benefit native fish. These activities have also altered the slough hydrology by increasing the size of permanently flooded habitats, modifying surface water drainage patterns, and increasing the length of time that A. l. var. piscinensis habitat is inundated or subject to elevated soil moisture conditions. Each of these effects creates conditions that are less suitable or unsuitable for A. l. var. piscinensis. No new dams have been built in Fish Slough since 1980. Staff from the BLM and CDFG have removed two dams and are analyzing the potential to remove Red Willow Dam, now the single largest water control structure remaining in Fish Slough.

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Water diversion activities associated with mining operations may also affect the hydrology near the southern end of Fish Slough. The Desert Aggregate Mine is situated near the southernmost portion of Fish Slough on lands owned by the LADWP and is 0.75 mi (1.2 km) south of the southernmost known occurrence of Astragalus lentiginosus var. piscinensis. The mine was specifically developed at a site with coarse, permeable gravels and the transmissivity (a measure of the ease at which ground water can move through the aquifer) of the area around the mine is relatively high (Danskin 1998). Ground water pumping activities at pits at the mine in 1986 or 1987 adversely affected riparian vegetation to the extent that large areas of vegetation south and down gradient of the mine and Fish Slough died as water tables declined (P. Hubbard, pers. comm. 2003; Sally Manning, County of Inyo, pers. comm. 2003). The effect of ground water pumping on alkaline habitats around the mine was not documented and so it is unknown if alkaline habitats near the mine were also adversely affected. Mining activities nearest to Fish Slough have been completed.

Three major spring areas are present in Fish Slough. Northeast Spring and Northwest Springs are located in the northern portion of the slough, and BLM Spring is present in the eastcentral portion of the slough. Staff from the LADWP has quantified the amount of water passing through Fish Slough for several decades. The volume of water moving through Fish Slough at one monitoring site declined from 148152 cubic feet per second (cfs) (4,1914,304 liters per second (lps)) in the early 1920s to 8496 cfs (2,3792,718 lps) in the early 1960s. This reduction in water flow is larger than the annual variability in water volume that can be accounted for by seasonal variation in evaporative losses and transpiration by local phreatophytes (Pinter and Keller 1991). The cause for the decrease in water flow through the slough between the 1920s and the 1960s has not been conclusively identified, but may be related to increased ground water pumping in the Chalfant Valley 2 mi (3.2 km) northeast of Fish Slough (Pinter and Keller 1991; MHA 2001).

Analysis of water table levels in a number of wells in Chalfant and Hammil valleys east or northeast of Fish Slough confirms that there is an incremental decrease in the potentiometric surface (i.e., height of the water table) between these valleys and Fish Slough. This decrease suggests that ground water is moving down gradient from Chalfant and Hammil valleys to the Fish Slough area (MHA 2001).

The TriValley Groundwater Management District (District) in Mono County was established in 1989, in part, to review and approve proposals to export water from the District. The District includes Chalfant, Hammil, and Benton valleys. California landowners may extract as much ground water as they can put to beneficial use, and no permit is required to pump ground water (DWR 1996). Between 1999 and 2001, the District considered a proposal by United States Filter Water Resources, Inc. to pump and export 13,700 acrefeet (16.9 billion liters) of ground water per year (MHA 2001). If the project had been approved as initially proposed, captured water would have been conveyed in a closed pipe and diverted to a location south and downgradient of Fish Slough. The project was ultimately abandoned, in part, because of environmental concerns for Fish Slough. The District will continue to consider applications to export water, however, as projects to do so are proposed.

Lack of recruitment is a potential threat to Astragalus lentiginosus var. piscinensis. Staff from the BLM and the LADWP has monitored this taxon from 1992 to 2002, observing that only a few young plants matured and persisted during that time (A. Halford, pers. comm. 2003; P. Hubbard, pers. comm. 2003). Two possible explanations for the lack of recruitment are high rabbit/rodent herbivory of seedlings and changes in soil hydrology or chemistry that make the habitat less suitable for seed germination and plant growth.

Previous Federal Action

On October 6, 1998, the Service published a final rule in the Federal Register (63 FR 53596), which determined endangered status for three plant taxa and threatened status for two plant taxa, including Astragalus lentiginosus var. piscinensis. Please refer to the final rule listing the taxon for information on previous Federal actions prior to October 6, 1998. In the final rule listing A. l. var. piscinensis, the Service determined that endangered status for this taxon was not warranted because a significant portion of the listed plant occurrences in northern Fish Slough were protected by a cattle exclosure, thereby reducing threats from grazing and trampling. In addition, the land where the taxon occurred was receiving specific management consideration at the time the final rule was published due to its inclusion in a special management unit administered by the BLM. The Service determined that, while this taxon may not have been in immediate danger of extinction, it was likely to become endangered in the foreseeable future throughout all or a significant portion of its range, and listing as threatened was warranted.

At the time Astragalus lentiginosus var. pinscinensis was listed, we determined that designation of critical habitat was not prudent because the potential benefits were outweighed by the potential negative effects of designating critical habitat. We believed that designation of critical habitat could result in increased threats of illegal collection and vandalism and the designation would not compel or require a private or other nonFederal landowner to undertake active management for the taxon or to modify proposed project activities in the absence of a Federal nexus.

On November 15, 2001, the Center for Biological Diversity and the California Native Plant Society filed a lawsuit in the U.S. District Court for the Southern District of California challenging our determination not to designate critical habitat for eight desert plants, including Astragalus lentiginosus var. pinscinensis (Center for Biological Diversity et al. v. Norton, No. 01 CV 2101). On July 1, 2002, the Court ordered the Service to reconsider its not prudent determination and propose critical habitat, if prudent, for A. l. var. pinscinensis on or before November 15, 2003. On September 9, 2003, the court issued a subsequent order that required the Service to publish a proposed critical habitat designation for A. l. var. pinscinensis by June 1, 2004.

We have reconsidered our evaluation of the threats posed by vandalism in the not prudent determination, and now determine that the threats to Astragalus lentiginosus var. pinscinensis from specific instances of vandalism are limited, if not speculative. Accordingly, we withdraw our previous determination that the designation of critical habitat is not prudent for A. l. var. pinscinensis and determine that the designation of critical habitat is prudent. At this time, we have sufficient information necessary to identify specific areas as essential to the conservation of this plant taxon and are therefore proposing critical habitat (see ``Methods'' section below for a discussion of information used in our reevaluation).

Critical Habitat

Section 3(5)(A) of the Act defines critical habitat as(i) the specific areas within the geographic area occupied by a species, at the time it is listed in accordance with the Act, on which are
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found those physical or biological features (I) essential to the conservation of the species and (II) that may require special management considerations or protection; and (ii) specific areas outside the geographic area occupied by a species at the time it is listed, upon a determination that such areas are essential for the conservation of the species. ``Conservation'' means the use of all methods and procedures that are necessary to bring an endangered or a threatened species to the point at which listing under the Act is no longer necessary.

The designation of critical habitat does not affect land ownership or establish a refuge, wilderness, reserve, preserve, or other conservation area. It does not allow government or public access to private lands. Under section 7 of the Act, Federal agencies must consult with us on activities they undertake, fund, or permit that may affect critical habitat and lead to its destruction or adverse modification. However, the Act prohibits unauthorized take of listed species and requires consultation for activities that may affect them, including habitat alterations, regardless of whether critical habitat has been designated. We have found that the designation of critical habitat provides little additional protection to most listed species.

To be included in a critical habitat designation, habitat must be either a specific area within the geographic area occupied by the species on which are found those physical or biological features essential to the conservation of the species (primary constituent elements, as defined at 50 CFR 424.12(b)) and which may require special management considerations or protection, or be specific areas outside of the geographic area occupied by the species which are determined to be essential to the conservation of the species. Section 3(5)(C) of the Act states that not all areas that can be occupied by a species should be designated as critical habitat unless the Secretary determines that all such areas are essential to the conservation of the species. Our regulations (50 CFR 424.12(e)) also state that, ``The Secretary shall designate as critical habitat areas outside the geographic area presently occupied by the species only when a designation limited to its present range would be inadequate to ensure the conservation of the species.''

Regulations at 50 CFR 424.02(j) defines special management considerations or protection to mean any methods or procedures useful in protecting the physical and biological features of the environment for the conservation of listed species. When we designate critical habitat, we may not have the information necessary to identify all areas which are essential for the conservation of the species. Nevertheless, we are required to designate those areas we consider to be essential, using the best information available to us. Accordingly, we do not designate critical habitat in areas outside the geographic area occupied by the species unless the best available scientific and commercial data demonstrate that unoccupied areas are essential for the conservation needs of the species.

Section 4(b)(2) of the Act requires that we take into consideration the economic impacts, the effect on national security, and any other relevant impact, of specifying any particular area as critical habitat. We may exclude areas from critical habitat designation when the benefits of exclusion outweigh the benefits of including the areas within critical habitat, provided the exclusion will not result in extinction of the species.

Our Policy on Information Standards Under the Endangered Species Act, published in the Federal Register on July 1, 1994 (59 FR 34271), provides criteria, establishes procedures, and provides guidance to ensure that our decisions represent the best scientific and commercial data available. It requires our biologists, to the extent consistent with the Act and with the use of the best scientific and commercial data available, to use primary and original sources of information as the basis for recommendations to designate critical habitat. When determining which areas are critical habitat, a primary source of information should be the listing package for the species. Additional information may be obtained from a recovery plan, articles in peer reviewed journals, conservation plans developed by States and counties, scientific status surveys and studies, biological assessments, or other unpublished materials and expert opinion or personal knowledge.

Section 4 of the Act requires that we designate critical habitat on the basis of what we know at the time of designation. Habitat is often dynamic, and species may move from one area to another over time. Furthermore, we recognize that designation of critical habitat may not include all of the habitat areas that may eventually be determined to be necessary for the recovery of the species. For these reasons, critical habitat designations do not signal that habitat outside the designation is unimportant or may not be required for recovery.

Areas that support populations, but are outside the critical habitat designation, will continue to be subject to conservation actions implemented under section 7(a)(1) of the Act and to the regulatory protections afforded by the section 7(a)(2) jeopardy standard, as determined on the basis of the best available information at the time of the action. Federally funded or permitted projects affecting listed species outside their designated critical habitat areas may still result in jeopardy findings in some cases. Similarly, critical habitat designations made on the basis of the best available information at the time of designation will not control the direction and substance of future recovery plans, habitat conservation plans, or other species conservation planning efforts if new information available to these planning efforts calls for a different outcome. Methods

As required by the section 4(b)(2) of Act and regulations at 50 CFR 424.12, we used the best scientific information available to determine areas that contain the physical and biological features that are essential for the conservation of Astragalus lentiginosus var. piscinensis, and that may require special management considerations or protection. This includes information from our own documents, including the data from the final rule listing the taxon as threatened (66 FR 27901), recent biological surveys, reports and aerial photos, documentation provided by staff from the BLM and the LADWP, and discussions with botanical and hydrologic experts. We also conducted two site visits to Fish Slough, and met with staff from the BLM, the LADWP, and CDFG to solicit their views on various management aspects involving A. l. var. piscinensis.

Primary Constituent Elements

In accordance with section 3(5)(A)(i) of the Act and regulations at 50 CFR 424.12, in determining which areas to propose as critical habitat, we consider those physical and biological features (primary constituent elements) that are essential to the conservation of the species and that may require special management considerations or protection. These include, but are not limited to: Space for individual and population growth, and for normal behavior; food, water, air, light, minerals or other nutritional or physiological requirements; cover or shelter; sites for reproduction, germination, or seed dispersal; and habitats that are protected from disturbance or are representative of the
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known historic, geographic, and ecological distributions of a species.

The proposed critical habitat unit has been delineated to provide sufficient habitat to maintain a selfsustaining population of Astragalus lentiginosus var. piscinensis in Fish Slough and includes those habitat components essential for the conservation of the taxon. These habitat components provide for: (1) Individual and population growth, including sites for germination, pollination, reproduction, pollen and seed dispersal, and seed dormancy; (2) areas that allow gene flow and provide connectivity or linkage between different locations within Fish Slough; and (3) areas that provide basic requirements for growth, such as water, light, and minerals.

The presence of water is essential to the development and maintenance of alkaline soils and habitat upon which Astragalus lentiginosus var. piscinensis depends. The alkaline soils in Fish Slough where alkali flat, alkali scrub, and meadow habitats occur are generally classified as aquic torriorthentsaquent complex with 02 percent slope. These alkaline soils develop as mineralrich, shallow ground water rises under capillary action to the surface by the high evaporation rates which prevail in the Fish Slough area. As this water evaporates at the soil surface, its solute load precipitates, creating a veneer of white salts and minerals. The alkaline habitat that A. l. var. piscinensis occupies is likely to have a water table that fluctuates between 1960 in (0.51.5 m) below the land surface (Odion et al. 1991). In areas where water tables are more 2 m (6.6 ft) deep, capillary action is insufficient to promote and maintain the development of alkaline soils (Odion et al. 1991).

Between May 1999 and October 2001, a variety of in situ and experimental studies were conducted to evaluate the relationship between photosynthetic rates, growth rates, fecundity, and survivorship of Astragalus lentiginosus var. piscinensis as depth to a water table varied (Murray and Sala, 2003). Data from these studies suggest that elevated water tables are likely to adversely affect these variables if local water tables are less than 3540 cm (13.815.7 in) below the land surface. Therefore, water tables that rise too close to the land surface and the root zone of A. l. var. piscinensis may be detrimental to individual plants that are subjected to saturated soils for a prolonged period of time.

Fish Slough is a wetland in an otherwise arid landscape. The average annual rainfall in the town of Bishop is 5.0 in (12.7 centimeters (cm)). The average annual evapotranspiration rates in alkaline meadows or alkaline scrub habitats in the greater Owens Valley area which are most similar to the habitat type occupied by Astragalus lentiginosus var. piscinensis range between 18.540.5 in (47.0102.9 cm) and 15.223.6 in (38.659.9 cm), respectively (Danskin 1998). Because the low annual rainfall and high annual evapotranspiration rates in the Bishop area create an arid environment, it is essential that a substantial and sustained amount of surface and ground water exists to maintain the wetland and riparian habitats that are present in Fish Slough.

The sources of the water that discharge from springs in Fish Slough have not yet been conclusively identified. Available data indicate that Fish Slough water is derived from the Casa Diablo Mountain area (BLM 1984; MHA 2001), the TriValley area, or a combination of the two areas (MHA 2001). The Casa Diablo Mountain area reaches a maximum elevation of 7,913 ft (2,412 m) and is located 9.5 mi (15.3 km) northwest of Fish Slough. The area between Fish Slough and Casa Diablo Mountain is locally referred to as the Volcanic Tableland. The geology of the Volcanic Tableland predominantly consists of the Bishop Tuff, which has a welded ash and tuff surface veneer. Underneath the surface veneer, a thicker, more permeable layer is present in the Volcanic Tableland. The lower unit of the tuff is extensively fractured and faulted, and some areas are more permeable than windblown sand (DWR 1964). These fractures act as conduits that convey ground water from higher elevation areas with greater levels of precipitation to the lower elevation Fish Slough area where low amounts of precipitation predominate. The TriValley area is bounded on the east by the White Mountains, which reach an elevation of up to 14,245 ft (4,342 m), and to the west by a ridge that separates it from Fish Slough. This ridge is less than 280 ft (85 m) higher than the valley floor. The high elevation of the White Mountains promotes the deposition of precipitation. This water then percolates into alluvial fans at the base of the mountains, and ultimately enters the coarse alluvium that is present on the floors of Benton, Hammil, and Chalfant valleys. Because the surface elevation decreases from Benton Valley in the north to Chalfant Valley in the south, and because Fish Slough is lower in elevation than all three of these valleys, ground water tends to move in a southerly or southwesterly direction toward Fish Slough or toward Chalfant Valley east of Fish Slough. A number of fault lines are present in the Fish Slough and Volcanic Tableland area (MHA 2001) and these features likely affect the presence, distribution, and volume of ground water present in the local area (Andy Zdon, MHA Environmental Consulting, Inc., pers. comm. 2004).

The alkaline flats where Astragalus lentiginosus var. piscinensis occurs are typically dominated by a SpartinaSporobolis (cordgrass dropseed) plant association. A. l. var. piscinensis may also occur where a sparse amount of Chrysothamnus albidus (rabbitbrush) exists in the transition zone between SpartinaSporobolis and Chrysothamnus albidusDistichlis (rabbitbrushsaltgrass) plant associations. Sawyer and KeelerWolf (1995) classify the alkaline habitats where A. l. var. piscinensis occurs as a cordgrass series or saltgrass series. Astragalus lentiginosus var. piscinensis is frequently sympatric with Ivesia kingii (alkali ivesia). The higher elevation areas where A. l. var. piscinensis is absent consist of dry shadscale scrub communities that are dominated by various species of Atriplex spp. (saltbush).

Distribution of many alkalinetolerant plant species is largely determined by a combination of environmental factors, predominantly soil moisture and salinity. These two factors in combination may affect the physiology of adult and immature plants, seed germination, and seedling survival. Mazer and Travers (1992) suggest that seed germination and successful establishment of Astragalus lentiginosus var. piscinensis seedlings are infrequent events, and that sufficient rainfall is necessary to promote seed germination and survivorship of young plants. The suite of environmental factors that determine where Astragalus lentiginosus var. piscinensis occurs is also likely to determine the composition of the broader plant community of which A. l. var. piscinensis is a part. Changes in soil moisture and salinity are likely to influence not only the abundance and presence of A. l. var. piscinensis but also to affect the persistence and character of the SpartinaSporobolis plant association in which A. l. var. piscinensis occurs.

Upland areas adjacent to the alkaline habitat where Astragalus lentiginosus var. piscinensis currently exists are also important because some of these areas historically possessed alkaline habitat that no longer exists. The longterm success of the conservation of Astragalus lentiginosus var. piscinensis may depend upon efforts to restore the extent and character of the alkaline
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habitat that historically existed. Inclusion of currently unoccupied upland habitat within the proposed critical habitat unit will therefore include the areas that are necessary to promote the conservation of the listed plant taxon. This need is identified in the recovery plan for the taxon (Owens Basin Wetland and Aquatic Species Recovery Plan Inyo and Mono Counties, California (USFWS 1998)).

Mazer and Travers (1992) examined various aspects that relate to the pollination ecology of Astragalus lentiginosus var. piscinensis. They found that A. l. var. piscinensis is dependant on insects for flower pollination and fertilization and the taxon is not capable of producing fruits in the absence of pollinators. Bumblebees (Bombus spp.) in the family Apidae were observed to pollinate A. l. var. piscinensis flowers on three occasions. Bees in the family Megachilidae are believed to be important pollinator insects for Astragalus brauntonii (Fotheringham and Keeley 1998), and various bee taxa in this family may occur in and adjacent to Fish Slough. With other milkvetch species such as A. cibarius and A. utahensis, large bees in the families Anthophoridae and Apidae carry large pollen loads from plant to plant, while a variety of smaller beetle and fly species carry smaller pollen loads. These smaller insects are, therefore, likely to have a smaller potential for pollinating Astragalus plants (Green and Bohart 1975). Unless a specific endemic bee species is responsible for flower pollination, it is possible that multiple bee species pollinate the flowers of A. l. var. piscinensis (Terry Griswold, Utah State University, pers. comm. 2003).

Studies to quantify the distance that bees will fly to pollinate their host plants are limited in number, but the few that exist show that some bees will routinely fly 100 to 500 m (328 to 984 ft) to pollinate plants. Studies by SteffanDewenter and Tscharntke (2000) have demonstrated that it is possible for bees to fly at least 1,000 m (3,280 ft) to pollinate flowers, and at least one study suggests that bumblebees may forage many kilometers from a colony (Sudgen 1985). Studies by SteffanDewenter and Tscharntke (2000) also indicate that if pollinator habitat within 1,000 m of some host plants is eliminated, seed set of some plant species may be decreased by as much as 50 percent. Additional studies suggest that the degradation of pollinator habitat is likely to adversely affect the abundance of pollinator species (Jennersten 1988; Rathcke and Jules 1993).

Bumblebees usually nest in abandoned rodent burrows or bird nests (Thorpe et al. 1980), and bees in the family Megachilidae also nest in underground rodent burrows or in dry woody material. The alkaline nature of the habitat occupied by Astragalus lentiginosus var. piscinensis makes it unlikely that burrowing rodents are present in such areas. We believe insect pollinators are more likely to nest in upland habitats adjacent to alkaline areas because nesting and cover sites for various species of mice, kangaroo rats, and pocket mice are more likely to be common there (T. Griswold, pers. comm. 2003).

The upland areas adjacent to occurrences of Astragalus lentiginosus var. piscinensis are likely to include cover and nest sites for a variety of insects necessary for the pollination of this taxon. Surveys have not been conducted to specifically identify which species are responsible for the fertilization of A. l. var. piscinensis flowers but, at a minimum, they likely include a variety of groundnesting bee taxa. Studies have demonstrated that it is possible for bees to fly 1,000 m (3,280 ft) or more to pollinate flowers. The bees that have been observed on A. l. var. piscinensis include taxa that routinely nest in underground burrows. We believe that rodent burrows are less likely to be common in alkaline habitats and so we have concluded that the bee pollinators that visit A. l. var. piscinensis are more likely to use rodent burrows in upland shrub scrub plant communities within 1001,000 m (3283,280 ft) of the alkaline habitat occupied by the listed plant taxon.

The maintenance of natural conditions in upland areas adjacent to the alkaline habitat where Astragalus lentiginosus var. piscinensis occurs is important because the presence of roads and use of motorized vehicles have a substantial potential to introduce nonnative plant species. These upland areas may act as reservoirs for invasive plant species and facilitate their invasion into the more mesic habitat occupied by Fish Slough milkvetch. Some species such as Lepidium latifolium and Salsola iberica can survive in soils that vary in texture and moisture. Proactive management of upland habitats at Fish Slough is necessary to preclude the establishment of invasive non native plant species that could displace A. l. var. piscinensis and that such control should not be limited to the areas immediately adjacent to alkaline habitats.

The area we are proposing to designate as critical habitat provides some or all of the habitat components and the physical and hydrologic attributes that are essential for the conservation of Astragalus lentiginosus var. piscinensis. Based on the best available information at this time, the primary constituent elements of critical habitat for A. l. var. piscinensis include, but are not limited to:
(1) Alkaline soils that occur in areas with little or no slope, and which overlay a ground water table that is 1960 in (0.51.5 m) below the land surface;
(2) Plant associations dominated by SpartinaSporobolis, or where a sparse amount of Chrysothamnus albidus occurs in the transition zone between SpartinaSporobolis and Chrysothamnus albidusDistichlis plant associations;
(3) Upland areas within 1,000 m (3,280 ft) of the alkaline soils described in (1), that support sites where the listed plant's pollinator populations are likely to nest or obtain cover, that require minimal disturbance and active management to limit the establishment of nonnative plant taxa, and portions of which may be suitable for restoration and recolonization by Astragalus lentiginosus var. piscinensis; and
(4) Hydrologic conditions that provide suitable periods of soil moisture and chemistry for Astragalus lentiginosus var. piscinensis germination, growth, reproduction, and dispersal.

All of the primary constituent elements outlined above do not have to occur simultaneously within the unit to constitute critical habitat for Astragalus lentiginosus var. piscinensis. We determined the primary constituent elements of critical habitat for A. l. var. piscinensis based on the best available scientific and commercial information, including professional studies and reports that pertain to its habitat and ecology and the hydrological conditions that are relevant to the quality of habitat in Fish Slough. These documents include, but are not limited to, BLM (1984); Odion et al. (1991); Ferren (1991a); Mazer and Travers (1992); Danskin (1998); and MHA (2001).

Criteria Used To Identify Critical Habitat

The criteria that have been used to identify the proposed critical habitat unit for Astragalus lentiginosus var. piscinensis include the known range of the taxon, the alkaline habitat where the taxon and its associated flora occurs, the upland areas within 1,000 m (3,280 ft) of the alkaline soils that are occupied by the taxon, and the hydrologic features that are essential to promote the survival and persistence of the taxon.

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A number of botanical surveys have been completed in most of the alkaline habitats in the greater Owens Valley area and Astragalus lentiginosus var. piscinensis has not been found outside of Fish Slough (P. Hubbard, pers. comm. 2003). Mary DeDecker, the botanist who collected the type specimen of A. l. var. piscinensis, traveled extensively throughout the greater Owens Valley area and Inyo and Mono Counties collecting botanical specimens for her herbarium collection. Because her collection does not contain specimens of A. l. var. piscinensis collected outside of Fish Slough (Michael Denslow, Rancho Santa Ana Botanic Garden, pers. comm. 2004), it is unlikely that Fish Slough milkvetch occurs outside of that area surrounding the Fish Slough oasis. Considering this, we conclude that the geographic range of A. l. var. piscinensis is limited to those disjunct occurrences within a 6 mi (9.7 km) stretch of alkaline habitat that borders aquatic habitat in Fish Slough in Inyo and Mono Counties, California. Because the taxon occurs within a relatively limited area and the alkaline habitat within the taxon's range forms a relatively continuous feature in the landscape, we are proposing a single critical habitat unit which is not separated into smaller, separate units. The critical habitat unit being proposed for A. l. var. piscinensis includes virtually all of the known locations of the taxon.

According to a recovery plan that includes Astragalus lentiginosus var. piscinensis (USFWS 1998), all remaining habitat of the taxon needs to be conserved. Virtually the entire geographic area which currently is and potentially can be occupied by the taxon is being proposed as critical habitat. This is being done because these areas are all considered essential to the conservation of the species, in accordance with Section 3(5)(C) of the Act. We have determined, however, that one privatelyowned, 49acre (20ha) parcel within the historic range of A. l. var. piscinensis is not essential for its conservation. That parcel is in Township 6 South, Range 33 East, section 18 of U.S. Geological Survey quadrangle map titled Fish Slough. It is highly unlikely that this area is currently occupied by the taxon and it has little alkaline soil habitat. In addition, there is no chance that the taxon will be reintroduced on this property. Therefore, the parcel is not essential to conservation of the taxon, and is not included in the proposed critical habitat.

The critical habitat units are designed to encompass a large enough area to support existing ecological processes that may be essential to the conservation of Astragalus lentiginosus var. piscinensis. Some upland areas adjacent to the alkaline habitat where A. l. var. piscinensis occurs could potentially be restored to allow the taxon to reoccupy historicallyoccupied areas. Upland areas within 1,000 meters of the alkaline habitat also provide nest sites and cover for pollinators, and are important to help minimize the potential to introduce new nonnative plant species that may adversely affect A. l. var. piscinensis and to control nonnative plant species already present. Because these areas are essential for conservation of the taxon, we have included them in the proposed critical habitat unit in accordance with section 3(5)(A)(ii) of the Act.

Determining the geographic boundary of the critical habitat unit for Astragalus lentiginosus var. piscinensis would be relatively straightforward if the unit boundary was based only on the presence of alkaline soils, the SpartinaSporobolis plant association where Fish Slough milkvetch is found, and an upland zone inhabited by the plant's pollinators. We believe, however, that the longterm maintenance and recovery of A. l. var. piscinensis is ultimately dependent on the maintenance of the hydrologic system that promotes the development and persistence of the alkaline soils and plant communities that A. l. var. piscinensis is associated with. We believe that adverse changes in the hydrology of Fish Slough would reduce or eliminate those physical features essential for the conservation of the taxon.

Delineating a critical habitat unit for Astragalus lentiginosus var. piscinensis that includes the hydrologic system that supports this taxon poses significant challenges because the source(s) of the water that issues from the springs in Fish Slough is not precisely known and the location of the ground water flow paths between these sources and the spring orifices in Fish Slough have not yet been determined. Our current understanding of how pumping activities in Chalfant and Hammil valleys affects spring discharge rates or the local aquifer in Fish Slough is not sufficient to clearly illustrate these cause and effect relationships.

Because we believe the protection of the hydrologic conditions that supports the formation and maintenance of alkaline soils is essential to conserve occupied and suitable unoccupied habitat for Astragalus lentiginosus var. piscinensis, we have identified these hydrologic conditions as a primary constituent element in the ``Primary Constituent Element'' section of this proposed rule even though they may depend upon sources outside the proposed critical habitat unit boundary.

Delineating Critical Habitat

To delineate the critical habitat unit for Fish Slough milkvetch, we used a computerized Geographic Information System to overlay various themes that included the known occurrences of Astragalus lentiginosus var. piscinensis and the primary constituent elements (see Primary Constituent Element section above). To map the distribution of A. l. var. piscinensis, we used information in the California Department of Fish and Game's Natural Diversity Database (CNDDB 2004) and plant distribution data from Novak (1992). These two information sources provide a comparable assessment of the locations of A. l. var. piscinensis.

The upland boundaries of alkaline soils in Fish Slough as depicted in Ferren (1991a) were then digitized. We digitized the boundaries of aquatic habitats and meadows mapped in this Ferren (1991a) and included these within the boundary of the proposed critical habitat unit. These two habitats do not provide suitable habitat for Astragalus lentiginosus var. piscinensis; however, they are included within the proposed unit because the precise boundaries of alkaline habitat in Fish Slough vary on an annual basis, and smallscale conversions of wetland habitat to alkaline flat habitat are likely to occur from time to time. In addition, as this ecosystem is dynamic, we believe that areas of alkaline soils may convert to wetland habitat. The mapped boundary based on alkaline soils also corresponds closely with the distribution of the SpartinaSporobolis and Chrysothamnus albidus Distichlis plant associations which are associated with A. l. var. piscinensis. The alkaline habitat occupied by A. l. var. piscinensis is a visually obvious feature of Fish Slough. It is present at elevations above the lowlying flooded aquatic habitat in Fish Slough and below the elevated and drier areas dominated by coarse alluvial soils lacking a white alkaline appearance. The alkaline habitat occupied by the taxon is dominated by a Spartin

FOR FURTHER INFORMATION CONTACT Diane Noda, Field Supervisor, Ventura Fish and Wildlife Office, U.S. Fish and Wildlife Service, 2493 Portola Road, Suite B, Ventura, CA 93003 (telephone 805/6441766; facsimile 805/6443958).