Daily Rules, Proposed Rules, and Notices of the Federal Government
To assist the reader, the following is a partial list of acronyms that are used in this document.
Section 4(b)(3)(B) of the Act (16 U.S.C. 1531
On March 17, 2008, we received a petition dated March 13, 2008, from five conservation organizations: The Center for Biological Diversity (CBD), Conservation Northwest, the Environmental Protection Information Center, the Klamath-Siskiyou Wildlands Center, and Oregon Wild. The petition asked us to list 32 species and subspecies of snails and slugs (mollusks) in the Pacific Northwest as threatened or endangered under the Act. Additionally, the petition requested that we designate critical habitat concurrent with listing. The petition clearly identified itself as a petition and included identification information regarding the petitioners, as required by title 50 of the Code of Federal Regulations (CFR) in 424.14(a). The petition included the 14 aquatic mollusk species addressed in this finding, and provided supporting information regarding the species' taxonomy and ecology, range, present status, and actual and potential causes of decline.
In a June 27, 2008, letter to the petitioners, we responded that we had reviewed the information presented in the petition and determined that issuing an emergency regulation temporarily
On April 13, 2009, we received a signed email from CBD providing updated taxonomic information regarding some of the 32 petitioned mollusk species (Curry 2009, pp. 1-2). The email indicated that two of the species had been formally described, two others had been combined into a single species that had been formally described, and three additional petitioned species had been combined into a single species that had been formally described. The email provided a citation to the article making the taxonomic changes, and asked us to consider the revised species for listing as endangered or threatened under the Act. We treated this email message as an amendment to the original petition. Therefore, the amended petition asked us to list 29 species and subspecies of mollusks, including the 14 aquatic species addressed here.
We addressed the petition as funding permitted beginning in late 2009, and published a 90-day finding on October 5, 2011 (76 FR 61826). We found that substantial scientific and commercial information had been presented in the petition and existed in our files to indicate listing may be warranted for 26 of the 29 petitioned mollusks. Fourteen of those 26 mollusks are aquatic and 12 are terrestrial. We have initiated a status review of the 14 aquatic mollusks, and present the results here. We intend to review the status of the remaining 12 terrestrial mollusks in fiscal year 2013. This notice constitutes our 12-month finding on the June 27, 2008, petition (as amended on April 13, 2009) to list 14 aquatic mollusks as endangered or threatened.
The mollusks petitioned for listing included the “diminutive pebblesnail (
They note that the Klamath Rim and Fredenburg pebblesnails are protected under the Survey and Manage Program (SMP) of the Northwest Forest Plan (NWFP) (see
In the case of these two mollusks, the “scientific names” were provisional and subject to change in different documents (Frest and Johannes 1993, pp. 46, 49; Frest and Johannes 2000, pp. 264, 273) (see Listable Entity Evaluation, below). However, we have subsequently obtained the survey protocol for aquatic mollusk species under the SMP, and that document identifies
Section 3(16) of the Act defines the term “species” to include “any subspecies of fish or wildlife or plants, and any distinct population segment (DPS) of any species of vertebrate fish or wildlife which interbreeds when mature.” Taxonomic groups or entities that meet the Act's definition of a “species” can be considered for listing under the Act and are, therefore, referred to as “listable entities.” Listable entities can then be listed if they are determined to meet the definition of either an endangered or threatened species.
Of the 14 aquatic mollusks considered in this review, 8 have not been formally described as species or subspecies in a peer-reviewed journal, or in any other source commonly accepted by the scientific community. This is why they have provisional scientific names, including “new species” (or “n. sp.”) and a number, rather than accepted species names. Formal peer-reviewed description, with its opportunities for further review and comment, is the process by which proposed new species and subspecies become generally recognized or rejected by the taxonomic community. We must therefore evaluate whether the best available scientific and commercial information indicates that these eight mollusks constitute valid species, despite their lack of formal descriptions, for the purpose of determining whether the mollusks in question constitute listable entities (16 U.S.C. 1533(b)(3)(A) and (B)). It is rare for us to list entities that have not been formally described, but we have occasionally done so in the past. Examples include two fish: The Hutton tui chub (
The eight aquatic mollusks reviewed here that have not been formally described are: Basalt juga, cinnamon juga, Columbia duskysnail, Fredenburg pebblesnail, Klamath Rim pebblesnail, knobby rams-horn, masked duskysnail, and tall pebblesnail. Table 1 below summarizes basic taxonomic and biological information for these purported species.
None of these eight aquatic mollusks are included in databases of recognized mollusk species, such as the Integrated Taxonomic Information System (ITIS) (2010), or Turgeon
The unpublished descriptions of these eight mollusks are all primarily based on shell characteristics, with occasional mention of certain characters of the animals themselves (such as color). Snail shell characteristics in general can vary due to environmental influences including elevation, calcium content of the surrounding water, and population density (Minton and Lydeard 2003, p. 76; Chak 2007, p. 3). The informal descriptions lack genetic data, data regarding microscopic anatomical features such as the radula (tongue), and photographs or drawings of anatomical features other than the shell. Such data are often highly distinctive, and are of key importance in formal descriptions (for example, Hershler
At the time the petition to list these aquatic mollusks was first submitted, only one of the petitioned mollusks (the nugget pebblesnail) had been formally described (CBD
The primary reason for combining multiple informally described mollusks in the formal descriptions of the Hat Creek and Shasta pebblesnails was that new genetic comparisons had shown those informally described mollusks were not genetically divergent or phylogenetically independent (Hershler
Accordingly, we conclude that the eight mollusks that have not been formally described (as listed in Table 1, above) cannot be considered to be listable entities under the Act at this time, and, therefore, we will not further evaluate the status of these entities. These include the Basalt juga, cinnamon juga, Columbia duskysnail, Fredenburg pebblesnail, Klamath Rim pebblesnail, knobby rams-horn, masked duskysnail, and tall pebblesnail. We, therefore, restrict the remainder of our listing status review to the six mollusks constituting listable entities under the Act. These are the canary duskysnail, the Goose Valley pebblesnail, the Hat Creek pebblesnail, the nugget pebblesnail, the Potem Creek pebblesnail, and the Shasta pebblesnail.
The Northwest Forest Plan (NWFP) is a set of amendments to the resource management plans for USFS and BLM lands within the range of the northern spotted owl (
The ACS was established to protect and restore aquatic ecosystems on NWFP lands (USDA and USDI 1994b, p. B-11; Reeves
Riparian reserves incorporate buffers of 100 to 300 feet (ft) (30.5 to 91.4 meters (m)) around these aquatic features (except for wetlands of less than 1 acre (ac) (0.4 hectares (ha)), which have buffers that extend to the limit of the associated riparian vegetation). The six listable aquatic mollusks considered in this review all occupy springs (including those forming lakes or ponds) and perennial streams, sometimes fish-bearing and sometimes not (a stream is considered fish bearing if it supports any species of fish for any duration of time) (USDA and USDI 1994b, p. B-14). When any of these six mollusks are on NWFP lands in lakes, ponds, or fish-bearing streams, they are protected by buffers extending outward 300 ft (91.4 m) from the streambanks, to the limit of riparian vegetation or to a distance equal to the height of two site-potential trees, whichever is greater (USDA and USDI 1994a, p. 9). “Site-potential tree height” refers to the expected height attainable by a mature conifer growing in the area (Kier Associates 2011a, p. 2). Average site-potential tree height for much of the Pacific Northwest is about 170 ft (51.8 m). When present in non-fish-bearing streams on NWFP lands, the six mollusks are protected by buffers of 150 ft (45.7 m) or equal to the height of one site-potential tree, whichever is greater. These boundaries may be modified based on subsequent watershed analysis (USDA and USDI 1994a, p. 10; USDA and USDI 1994b, p. B-13)).
The second component of the ACS, key watersheds, establishes specific watersheds to be given the highest priority in watershed restoration efforts (USDA and USDI 1994b, p. B-19). None of the key watersheds identified under the ACS are in the known current range of, or upstream from, any of the six aquatic mollusks that qualify as listable entities (REO 2006, p. 5). Accordingly, the key watersheds provision of the ACS does not affect the conservation of those
The third component of the ACS, watershed analysis, is a systematic procedure to collect information on and characterize watersheds on NWFP lands (USDA and USDI 1994b, pp. B-20—B-31). Watershed analysis must be conducted in key watersheds and roadless areas prior to management activities, in riparian reserves prior to changing reserve widths, and in any watershed prior to restoration efforts. Watershed analysis is recommended for all watersheds, and has been conducted on an ongoing basis since its inclusion in the NWFP (USDA 2009, p. 1). Analyses have been conducted for portions of the upper Sacramento River and lower McCloud River watersheds, which support occupied sites of the Shasta pebblesnail and nugget pebblesnail, respectively.
The final component of the ACS, watershed restoration, focuses primarily on restoring watershed aquatic habitat through the prevention of road-related runoff, restoration of riparian vegetation, and restoration of instream habitat complexity (USDA and USDI 1994b, p. B-31). The Shasta-Trinity and Lassen National Forests are currently planning or implementing several such watershed restoration projects (USDA 2012a, pp. 4, 5; USDA 2012b, pp. 3, 5), although none of the currently active projects involve locations near sites occupied by the mollusks addressed in this status review at the present time.
The SMP, like the ACS, was established under the NWFP and is particularly applicable, in varying degrees, to the six listable aquatic mollusks considered here. The six mollusks were protected under the SMP (when on Federal lands subject to the NWFP), but the SMP program was discontinued in 2007 (USDA and USDI 2007, pp. xii, xiii; CBD
For Category A species, the SMP requires predisturbance, strategic surveys (conducted in areas not currently under consideration for habitat-disturbing projects), management of all known sites to support species persistence, and annual species reviews (Molina
Section 4 of the Act (16 U.S.C. 1533) and implementing regulations (50 CFR part 424) set forth procedures for adding species to, removing species from, or reclassifying species on the Federal Lists of Endangered and Threatened Wildlife and Plants. Under section 4(a)(1) of the Act, a species may be determined to be endangered or threatened based on any of the following five factors:
(A) The present or threatened destruction, modification, or curtailment of its habitat or range;
(B) Overutilization for commercial, recreational, scientific, or educational purposes;
(C) Disease or predation;
(D) The inadequacy of existing regulatory mechanisms; or
(E) Other natural or manmade factors affecting its continued existence.
In making these findings, we discuss information below pertaining to each species in relation to the five factors provided in section 4(a)(1) of the Act. In considering what factors might constitute threats to a species, we must look beyond the simple exposure of the species to a particular factor. Instead we must evaluate whether the species may respond to the factor in a way that causes actual impacts to the species. If there is exposure to a factor and the species responds negatively, the factor may be a threat and, during the status review, we attempt to determine how significant a threat it is. The threat is significant if it drives or contributes to the risk of extinction of the species such that the species warrants listing as endangered or threatened as those terms are defined by the Act. However, the identification of factors that could impact a species negatively may not be sufficient to compel a finding that the species warrants listing. The information must include evidence sufficient to suggest that the potential threat has the capacity (is of sufficient magnitude and extent) to affect the species' status such that it meets the definition of endangered or threatened under the Act.
After considering the five factors, we assess whether each species is endangered or threatened throughout all of its range. Generally, we next consider in our findings whether a DPS or any significant portion of the species' range meets the definition of endangered or is likely to become endangered in the foreseeable future (threatened).
Under the Act and our implementing regulations, a species may warrant listing if it is endangered or threatened throughout all or a significant portion of its range. The Act defines “endangered species” as any species which is “in danger of extinction throughout all or a significant portion of its range,” and “threatened species” as any species which is “likely to become an
Two recent district court decisions have addressed whether the SPR language allows the Service to list or protect less than all members of a defined “species”:
Consistent with that interpretation, and for the purposes of this finding, we interpret the phrase “significant portion of its range” in the Act's definitions of “endangered species” and “threatened species” to provide an independent basis for listing; thus there are two situations (or factual bases) under which a species would qualify for listing: a species may be endangered or threatened throughout all of its range; or a species may be endangered or threatened in only a significant portion of its range. If a species is in danger of extinction throughout a significant portion of its range, the species is an “endangered species.” The same analysis applies to “threatened species.” Based on this interpretation and supported by existing case law, the consequence of finding that a species is endangered or threatened in only a significant portion of its range is that the entire species shall be listed as endangered or threatened, respectively, and the Act's protections shall be applied across the species' entire range.
We conclude, for the purposes of this finding, that interpreting the significant portion of its range phrase as providing an independent basis for listing is the best interpretation of the Act because it is consistent with the purposes and the plain meaning of the key definitions of the Act; it does not conflict with established past agency practice (i.e., prior to the 2007 Solicitor's Opinion), as no consistent, long-term agency practice has been established; and it is consistent with the judicial opinions that have most closely examined this issue. Having concluded that the phrase “significant portion of its range” provides an independent basis for listing and protecting the entire species, we next turn to the meaning of “significant” to determine the threshold for when such an independent basis for listing exists.
Although there are potentially many ways to determine whether a portion of a species' range is “significant,” we conclude, for the purposes of this finding, that the significance of the portion of the range should be determined based on its biological contribution to the conservation of the species. For this reason, we describe the threshold for “significant” in terms of an increase in the risk of extinction for the species. We conclude that a biologically based definition of “significant” best conforms to the purposes of the Act, is consistent with judicial interpretations, and best ensures species' conservation. Thus, for the purposes of this finding, and as explained further below, a portion of the range of a species is “significant” if its contribution to the viability of the species is so important that without that portion, the species would be in danger of extinction.
We evaluate biological significance based on the principles of conservation biology using the concepts of redundancy, resiliency, and representation.
For the purposes of this finding, we determine if a portion's biological contribution is so important that the portion qualifies as “significant” by asking whether
We recognize that this definition of “significant” (a portion of the range of a species is “significant” if its contribution to the viability of the species is so important that, without that portion, the species would be in danger of extinction) establishes a threshold that is relatively high. On the one hand, given that the consequences of finding a species to be endangered or threatened in a significant portion of its range would be listing the species throughout its entire range, it is important to use a threshold for “significant” that is robust. It would not be meaningful or appropriate to establish a very low threshold whereby
The definition of “significant” used in this finding carefully balances these concerns. By setting a relatively high threshold, we minimize the degree to which restrictions will be imposed or resources expended that do not contribute substantially to species conservation. But we have not set the threshold so high that the phrase “in a significant portion of its range” loses independent meaning. Specifically, we have not set the threshold as high as it was under the interpretation presented by the Service in the
The range of a species can theoretically be divided into portions in an infinite number of ways. However, there is no purpose to analyzing portions of the range that have no reasonable potential to be significant or to analyzing portions of the range in which there is no reasonable potential for the species to be endangered or threatened. To identify only those portions that warrant further consideration, we determine whether there is substantial information indicating that: (1) The portions may be “significant,”
For each of the six listable aquatic mollusk species considered, we provide a description of the species and its life history and habitat, an evaluation of listing factors, and our finding as to whether the petitioned action is warranted throughout its range. We then address whether the species may be considered endangered or threatened in any significant portion of its range.
The canary duskysnail was formally named and described in 2003 (Hershler
The canary duskysnail is known from a total of 21 sites in Shasta County, California, including 9 along the lower Pit River (California Natural Diversity Database (CNDDB) 2012, pp. 1-5; Johannes 2012a, pp. 2-7; Pacific Gas and Electric Company (PGE) 2011, pp. 26, 37; Johannes 2012b, p. 11; PGE 2012, p. 27). Of those 21 sites, 7 are on Federal land covered by the NWFP, 1 is on an Indian Public Domain Allotment (PDA), 3 are in State parks, and 10 are on privately owned lands. Repeat site monitoring at eight of those sites (see Factor A, below) shows large shifts in population density and in presence or absence of canary duskysnails at any given site. Site locations fall into three broad areas: The lower Pit River and nearby Burney Creek (11 sites), Hat Creek (2 sites), and the upper Fall and Tule River area (8 sites).
The canary duskysnail typically occurs in shallow water on the undersides of boulders and cobbles in pond springs and wetted areas near streambeds (the hyporheic zone) (Hershler
Nine of the 21 occupied sites are in or along the lower Pit River below Lake Britton (PGE 2011, pp. 26, 37; Johannes 2012b, p. 11; PGE 2012 p. 27). PGE maintains three dams in this area: Pit 3, 4, and 5 (PGE 2010, p. 5). Each dam sends water from its associated reservoir through tunnels to power-generating stations located just above the reservoirs of the next dam downstream. Flows in the natural river channel below each dam (referred to as the Pit 3, 4, and 5 reaches) have in the past consisted primarily of water from springs and minor tributaries emptying below each dam. In 2007, however, the Pit 3, 4, and 5 dams were issued a new operating license that required increased releases of surface water from the reservoirs into their associated reaches (PGE 2010, p. 2). These releases have the potential to negatively impact the canary duskysnail because reservoir surface water tends to be warmer than spring or creek water (Ellis 2012, p. 1). Because the dams initially lacked the infrastructure to release the required amounts of instream water, the required amounts were not achieved until 2011 (PGE 2012, p. 1). In accordance with a facilities modification plan, interim flow releases of approximately half the required amounts were authorized for 2008 through 2010 while the flow release structures of the dams were improved (PGE 2010, pp. 1, 2).
PGE was also required by the relicensing requirements to conduct mollusk surveys in 2009, in 2011-2015, in 2018, and every 4 years thereafter until the expiration of the license in 2043 (PGE 2012, p. 1). Following monitoring in 2009, PGE decided to monitor for mollusks in 2010 as well (PGE 2010, p. 54; PGE 2011, p. 1). Accordingly, we now have 3 years of survey data (2009-2011) for a total of 12 sites in the Pit River (four sites downstream of each dam) (PGE 2011, pp. 26, 37; PGE 2012, p. 27). The surveys found canary duskysnails at 8 of those 12 sites (as well as nugget pebblesnails at all 12 sites, as discussed below). A ninth site in the Pit River with canary duskysnails (as mentioned above) was not in a monitored location (Hershler
Four of the eight monitored occupied sites are in the Pit 3 reach, which is the farthest upstream (PGE 2011, pp. 26, 37; PGE 2012, p. 27). During 2009, that reach also showed the lowest average water discharge rates, lowest average water temperatures, and produced the highest average densities of canary duskysnails, thus tending to support the idea that canary duskysnails benefit from lower discharge rates from the dams (PGE 2010, p. 35; PGE 2011, pp. 26, 37; PGE 2012, p. 27). However, as average water discharge rates increased in the Pit 3 reach from 150 cubic ft per second (cfs) in 2009 to 350 cfs in 2011, and as average water temperatures increased as well from approximately 60 to about 63 degrees Fahrenheit (°F) (15.4 to 17.2 degrees Celsius (°C)), canary duskysnail densities rose from 20 to 53 snails per square meter (16.7 to 44.3 snails per square yard) at one location (their highest density in the study), and dropped from 50 to 0 snails per square meter (41.8 to 0 snails per square yard) at another location. The populations thus showed strong fluctuations, with widely differing responses to increasing flows. Similarly, in the Pit 5 reach, 37 snails per square meter (30.9 snails per square yard) were found in 2011 (the year of highest flows) at a location that had supported no snails in the 2 previous years. All other occupied locations had comparatively low population densities, and only one of those showed a clear drop in population density over the 3-year monitoring period (from 4 to 0 snails per square meter (3.3 to 0 snails per square yard)). Therefore, we conclude there are no clear trends in observed survey data attributable to changes in flow releases from dams.
The only other occupied site potentially affected by an impoundment is at Baum Lake (CNDDB 2012, p. 4; Johannes 2012a, pp. 4, 5), a PGE-owned reservoir on Hat Creek, just north of the town of Cassel (Service 1998, pp. 20, 43). Abundant canary duskysnails were found at the site in 2001, under cobbles near the outflow of Crystal Lake, a spring-fed water body that abuts and empties into Baum Lake (CNDDB 2012, p. 4; Johannes 2012a, pp. 4, 5). Although the best available information does not indicate the fate of that population, its presence in 2001 and the abundant number of individual snails found at that time suggest the impoundment of Baum Lake does not constitute a threat. Three other occupied sites (identified in the source material as locations 102, 412, and 514) are located on the margins of spring-fed natural lakes in water bodies draining into the Fall River (Johannes 2012a pp. 3, 6), so the species is capable of surviving in slow-moving lake waters fed by nearby springs.
The Pit River is considered a water-quality limited segment for 198 kilometers (km) (123 miles (mi)) upstream of Shasta Lake; including the locations of all nine canary duskysnail sites known from the Pit River (State Water Resources Control Board (SWRCB) 2010a, p. 164). Nutrients from cattle defecation and fertilizers applied in the course of agriculture enter the Pit River, where they promote algal growth that decreases oxygen levels and increases water temperature. However, as discussed above with respect to impoundments, the only population trend data available for the canary duskysnail does not show clearly decreasing populations, despite any temperature increases or oxygen decreases that may be attributable to water quality.
PGE will continue to monitor mollusk populations annually as discussed above (PGE 2012, p. 1), so if impacts from Pit water quality or from the releases themselves do develop, they should be detected. The operating license for the dams includes an adaptive management plan for responding to negative impacts detected by the monitoring program (PGE 2008, pp. 3-6). The Service serves on the Technical Review Group which recommends specific adaptive management responses (PGE 2008, p. 2), and so will remain informed of the effectiveness of those responses. Seven of the nine occupied locations on the Pit River are on Federal land (either Shasta-Trinity National Forest or Lassen National Forest) within the area covered by the NWFP. Activities on those lands with the potential to affect water quality (or to affect the populations directly) would have to meet the requirements of the SMP and the ACS, as discussed
There are no locations occupied by canary duskysnails on the Pit River upstream of the Pit 3 dam at Lake Britton. However, there are two locations each on Burney Creek and Hat Creek, which both flow into Lake Britton. The remaining eight canary duskysnail locations are in the Fall River drainage, generally at the headwater springs (Service 2012a, p. 1). Neither Burney Creek nor Hat Creek is considered water-quality limited (SWRCB 2010a, entire; SWRCB 2010b, entire; SWRCB 2010c, entire). However, the Fall River is affected by sedimentation extending far enough upstream to reach the southernmost of the eight sites in the drainage occupied by canary duskysnails (SWRCB 2010a, p. 148; SWRCB 2011, p. 2). The sedimentation was caused by historical land management activities, and is not likely to constitute a threat to the other sites (Fall River Resource Conservation District (FRRCD) 2005, pp. 1-3; SWRCB 2010a, p. 148).
A final area with impaired water quality is Eastman Lake, at the headwaters of the Little Tule River, a tributary of the Fall River (SWRCB 2010a, p. 148; SWRCB 2011, p. 1). One canary duskysnail site (514) is located at the lake, while two others (102, 263) are just upstream of the inlet (Johannes 2012a, pp. 3, 4, 6). At an average pH of 8.64, the lake water is slightly more alkaline than the established water quality objective range of 6.5 to 8.5 (SWRCB 2010d, pp. 6, 7). The reason for the increased alkalinity is unknown, as is the optimal pH range for the canary duskysnail. However, acidic waters (pH 5 and below) can interfere with shell production, so freshwater snails are generally found in waters that are at least somewhat alkaline (Wyoming Game and Fish Department (WGFD) 2005, p. 548).
Grazing, spring diversions, road construction, and railroad construction have all been mentioned as possible threats to the canary duskysnail (Furnish and Monthey 1999, Sect. 4, p. 14; Service 2011, p. 61831). However, since the time of Furnish and Monthey's conclusions in 1999, the number of known locations has increased from 2 to 21, 10 of which are on protected State or Federal lands (Furnish and Monthey 1999, Sect. 4, pp. 10, 11; Johannes 2012a, pp. 2-7; Johannes 2012b, p. 11; PGE 2011, pp. 26, 37; PGE 2012 p. 27). The SMP (discussed above) has also been reinstated on Federal lands subject to the NWFP. Various habitat improvement measures have been carried out in the upper Fall River drainage, where the majority of occupied sites on private land are located (FRRCD 2005, pp. 1-3). Habitat improvements include exclusion fencing to keep cattle from streambanks, bank stabilization projects, and the replacement and upgrade of a railroad crossing that had collapsed twice in the past (producing extensive siltation on those occasions) (FRRCD 2005, p. 2; Ellis and Haley 2012, p. 1). Landowners also took steps to reduce the potential for serious wildfires and to prevent erosion of sediment from a nearby meadow (FRRCD 2005, p. 3). In Hat Creek, grazing has been eliminated in the general vicinity of the PGE dams since 2001 (Stewardship Council 2007, Vol. 2, p. PM-31). Grazing has also been eliminated from lands surrounding the two privately owned sites occupied by canary duskysnails in the lower Pit River. Forestry has been eliminated in areas near those sites conducted in accordance with a conservation plan developed and implemented by a nonprofit land-management corporation (see
The Shasta crayfish is a federally endangered species that shares essentially the same native range and habitat requirements as the canary duskysnail (Service 2009, pp. 4-6). The two species often co-occur at the same locations (Hershler
In summary, no clear population trends in response to habitat modifications are evident at any of the sites occupied by canary duskysnails, including the eight sites monitored by PGE. The release of additional Pit River waters from the dams under PGE's new licensing agreements does not appear to have resulted in adverse effects on downstream canary duskysnail populations. We also know of no occupied sites that have been permanently lost due to habitat modifications, although population fluctuations at some of the monitored sites included densities of zero during some years. No cause of the fluctuations at the monitored sites was evident. We therefore conclude, based on the best available scientific and commercial data, that the present or threatened destruction, modification or curtailment of its habitat or range does not constitute a significant threat to the species now or in the future.