Federal Register: September 8, 2010 (Volume 75, Number 173)

DOCID: fr08se10-31 FR Doc 2010-22038

Veterans Affairs Department

CFR Citation: 50 CFR Part 17

Docket ID: [Docket No. FWS-R6-ES-2009-0065]

MO ID: [MO 92210-0-0008-B2]

NOTICE: Part II

DOCID: fr08se10-31

DOCUMENT ACTION: Notice of revised 12-month finding.

SUBJECT CATEGORY:

Endangered and Threatened Wildlife and Plants; Revised 12-Month Finding to List the Upper Missouri River Distinct Population Segment of Arctic Grayling as Endangered or Threatened

DATES: The finding announced in this document was made on September 8, 2010.

DOCUMENT SUMMARY:

We, the U.S. Fish and Wildlife Service (Service/USFWS), announce a revised 12month finding on a petition to list the upper Missouri River Distinct Population Segment (Missouri River DPS) of Arctic grayling (Thymallus arcticus) as endangered or threatened under the Endangered Species Act of 1973, as amended. After review of all available scientific and commercial information, we find that listing the upper Missouri River DPS of Arctic grayling as endangered or threatened is warranted. However, listing the upper Missouri River DPS of Arctic grayling is currently precluded by higher priority actions to amend the Lists of Endangered and Threatened Wildlife and Plants. Upon publication of this 12month finding, we will add the upper Missouri River DPS of Arctic grayling to our candidate species list. We will develop a proposed rule to list this DPS as our priorities allow. We will make any determination on critical habitat during development of the proposed listing rule. In the interim, we will address the status of this DPS through our annual Candidate Notice of Review (CNOR).

SUMMARY:

Interior Department, Fish and Wildlife Service

SUPPLEMENTAL INFORMATION

Background

Section 4(b)(3)(B) of the Endangered Species Act of 1973, as amended (ESA) (16 U.S.C. 1531 et seq.), requires that, for any petition containing substantial scientific or commercial information indicating that listing the species may be warranted, we make a finding within 12 months of the date of receipt of the petition. In this finding, we determine that the petitioned action is: (a) Not warranted, (b) warranted, or (c) warranted, but immediate proposal of a regulation implementing the petitioned action is precluded by other pending proposals to determine whether species are endangered or threatened, and expeditious progress is being made to add or remove qualified species from the Federal Lists of Endangered and Threatened Wildlife and Plants. Section 4(b)(3)(C) of the ESA requires that we treat a petition for which the requested action is found to be warranted but precluded as though resubmitted on the date of such finding, that is, requiring a subsequent finding to be made within 12 months. We must publish these 12month findings in the Federal Register.

Previous Federal Actions

We have published a number of documents on Arctic grayling and have been involved in litigation over previous findings. We describe our actions relevant to this notice below.

We initiated a status review for the Montana Arctic grayling (Thymallus arcticus montanus) in a Federal Register notice on December 30, 1982 (47 FR 58454). In that notice, we designated the purported subspecies, Montana Arctic grayling, as a Category 2 species. At that time, we designated a species as Category 2 if a listing as endangered or threatened was possibly appropriate, but we did not have sufficient data to support a proposed rule to list the species.

On October 9, 1991, the Biodiversity Legal Foundation and George Wuerthner petitioned us to list the fluvial (riverine populations) of Arctic grayling in the upper Missouri River basin as an endangered species throughout its historical range in the coterminous United States. We published a notice of a 90day finding in the January 19, 1993, Federal Register (58 FR 4975), concluding the petitioners presented substantial information indicating that listing the fluvial Arctic grayling of the upper Missouri River in Montana and northwestern Wyoming may be warranted. This finding noted that taxonomic recognition of the Montana Arctic grayling (Thymallus arcticus montanus) as a subspecies (previously designated as a category 2 species) was not widely accepted, and that the scientific community generally considered this population a geographically isolated member of the wider species (T. arcticus).

On July 25, 1994, we published a notice of a 12month finding in the Federal Register (59 FR 37738), concluding that listing the DPS of fluvial Arctic grayling in the upper Missouri River was warranted but precluded by other higher priority listing actions. This DPS determination predated our DPS policy (61 FR 4722, February 7, 1996), so the entity did not undergo a DPS analysis as described in the policy. The 1994 finding placed fluvial Arctic grayling of the upper Missouri River on the candidate list and assigned it a listing priority of 9. On May 4, 2004, we elevated the listing priority number of the fluvial Arctic grayling to 3 (69 FR 24881).

On May 31, 2003, the Center for Biological Diversity and Western Watersheds Project (Plaintiffs) filed a complaint in U.S. District Court in Washington, D.C., challenging our ``warranted but precluded'' determination for Montana fluvial Arctic grayling. On July 22, 2004, the Plaintiffs amended their complaint to challenge our failure to emergency list this population. We settled with the Plaintiffs in August 2005, and we agreed to submit a final determination on whether this population warranted listing as endangered or threatened to the Federal Register on or before April 16, 2007.

On April 24, 2007, we published a revised 12month finding on the petition to list the upper Missouri River DPS of fluvial Arctic grayling (72 FR 20305) (``2007 finding''). In this finding, we determined that fluvial Arctic grayling of the upper Missouri River did not constitute a species, subspecies, or DPS under the ESA. Therefore, we found that the upper Missouri River population of fluvial Arctic grayling was not a listable entity under the ESA, and as a result, listing was not warranted. With that notice, we withdrew the fluvial Arctic grayling from the candidate list.

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On November 15, 2007, the Center for Biological Diversity, Federation of Fly Fishers, Western Watersheds Project, George Wuerthner, and Pat Munday filed a complaint (CV07152, in the District Court of Montana) to challenge our 2007 finding. We settled this litigation on October 5, 2009. In the stipulated settlement, we agreed to: (a) Publish, on or before December 31, 2009, a notice in the Federal Register soliciting information on the status of the upper Missouri River Arctic grayling; and (b) submit, on or before August 30, 2010, a new 12month finding for the upper Missouri River Arctic grayling to the Federal Register.

On October 28, 2009, we published a notice of intent to conduct a status review of Arctic grayling (Thymallus arcticus) in the upper Missouri River system (74 FR 55524). To ensure the status review was based on the best available scientific and commercial data, we requested information on the taxonomy, biology, ecology, genetics, and population status of the Arctic grayling of the upper Missouri River system; information relevant to consideration of the potential DPS status of Arctic grayling of the upper Missouri River system; threats to the species; and conservation actions being implemented to reduce those threats in the upper Missouri River system. The notice further specified that the status review may consider various DPS designations that include different life histories of Arctic grayling in the upper Missouri River system. Specifically, we may consider DPS configurations that include: Fluvial, adfluvial (lake populations), or all life histories of Arctic grayling in the upper Missouri River system.

This notice constitutes the revised 12month finding (``2010 finding'') on whether to list the upper Missouri River DPS of Arctic grayling (Thymallus arcticus) as endangered or threatened.

Taxonomy and Species Description

The Arctic grayling (Thymallus arcticus) belongs to the family Salmonidae (salmon, trout, charr, whitefishes), subfamily Thymallinae (graylings), and it is represented by a single genus, Thymallus. Scott and Crossman (1998, p. 301) recognize four species within the genus: T. articus (Arctic grayling), T. thymallus (European grayling), T. brevirostris (Mongolian grayling), and T. nigrescens (Lake Kosgol, Mongolia). Recent research focusing on Eurasian Thymallus (Koskinen et al. 2002, entire; Froufe et al. 2003, entire; Froufe et al. 2005, entire; Weiss et al. 2006, entire) indicates that the systematic diversity of the genus is greater than previously thought, or at least needs better description (Knizhin et al. 2008, pp. 725726, 729; Knizhin and Weiss 2009, pp. 1, 78; Weiss et al. 2007, p. 384).

Arctic grayling have elongate, laterally compressed, troutlike bodies with deeply forked tails, and adults typically average 300380 millimeters (mm) (1215 inches (in.)) in length. Coloration can be striking, and varies from silvery or iridescent blue and lavender, to dark blue (Behnke 2002, pp. 327328). The sides are marked with a varying number of Vshaped or diamondshaped spots (Scott and Crossman 1998, p. 301). During the spawning period, the colors darken and the males become more brilliantly colored than the females. A prominent morphological feature of Arctic grayling is the saillike dorsal fin, which is large and vividly colored with rows of orange to bright green spots, and often has an orange border (Behnke 2002, pp. 327328). Distribution

Arctic grayling are native to Arctic Ocean drainages of Alaska and northwestern Canada, as far east as Hudson's Bay, and westward across northern Eurasia to the Ural Mountains (Scott and Crossman 1998, pp. 301302; Froufe et al. 2005, pp. 106107; Weiss et al. 2006, pp. 511 512; see Figure 1 below). In North America, they are native to northern Pacific Ocean drainages as far south as the Stikine River in British Columbia (Nelson and Paetz 1991, pp. 253256; Behnke 2002, pp. 327 331).
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FIGURE 1. Approximate worldwide distribution of Arctic grayling (Thymallus arcticus) at the end of the most recent glacial cycle. The Missouri River distribution is based on Kaya (1992, pp. 4751). The distribution of the extinct Michigan population is based on Vincent (1962, p. 12) and the University of Michigan (2010). The North American distribution in Canada and Alaska is based on Behnke (2002, p. 330) and Scott and Crossman (1998, pp. 301302). The Eurasian distribution is based on Knizhin (2009, p. 32) and Knizhin (2010, pers. comm.).

Arctic grayling remains widely distributed across its native range, but within North America, the species has experienced range decline or contraction at the southern limits of its distribution. In British Columbia, Canada, populations in the Williston River watershed are designated as a provincial ``red list'' species, meaning the population is a candidate for further evaluation to determine if it should be granted endangered (facing imminent extirpation or extinction) or threatened status (likely to become endangered) (British Columbia Conservation Data Centre 2010). In Alberta, Canada, Arctic grayling are native to the Athabasca, Peace, and Hay River drainages. In Alberta, the species has undergone a range contraction of about 40 percent, and half of the province's subpopulations have declined in abundance by more than 90 percent (Alberta Sustainable Resource Development (ASRD) 2005, p. iv).

Distribution in the Conterminous United States

Two disjunct groups of Arctic grayling were native to the conterminous United States: One in the upper Missouri River basin in Montana and Wyoming (extant in Montana, see Figure 2), and another in Michigan that was extirpated in the late 1930s (Hubbs and Lagler 1949, p. 44). Michigan grayling formerly occurred in the Otter River of the Lake Superior drainage in northern Michigan and in streams of the lower peninsula of Michigan in both the Lake Michigan and Lake Huron drainages including the Au Sable, Cheboygan, Jordan, Pigeon, and Rifle Rivers (Vincent 1962, p. 12).

Introduced Lake Dwelling Arctic Grayling in the Upper Missouri River
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System and western U.S. populations of Arctic grayling have been established in lakes outside their native range in Arizona, Colorado, Idaho, Montana, New Mexico, Utah, Washington, and Wyoming (Vincent 1962, p. 15; Montana Fisheries Information System (MFISH) 2009; NatureServe 2010). Stocking of hatchery grayling in Montana has been particularly extensive, and there are thought to be up to 78 introduced lacustrine (lakedwelling) populations resulting from these introductions (see Table 1 below). Over threequarters of these introductions (79.5 percent) were established outside the native geographic range of upper Missouri River grayling, while only 16 (20.5 percent) were established within the watershed boundary of the upper Missouri River system.
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FIGURE 2. Historical (dark grey lines) and current distribution (stars and circled portion of Big Hole River) of native Arctic grayling in the upper Missouri River basin. White bars denote mainstem river dams that are total barriers to upstream passage by fish.
TABLE 1. Introduced Lakedwelling Populations of Arctic Grayling in Montana. The primary data source for these designations is MFISH (2009). Number of Introduced River Basin (Exotic) Populations\a\ Outside Native Geographic Range In Montana
Columbia River 23 Middle Missouri River 2 Saskatchewan River 1 Yellowstone River 36\b\ Within Watershed Boundary Of Native Geographic Range In Montana Upper Missouri River 16 Total Exotic Populations 78 \a\List of populations does not include lake populations derived from attempts to reestablish fluvial populations in Montana, native adfluvial populations, or genetic reserves of Big Hole River grayling. \b\Many of these populations may not reproduce naturally and are only sustained through repeated stocking (Montana Fish, Wildlife and Parks 2009, entire).

For the purposes of this finding, we are analyzing a petitioned entity that includes, at its maximum extent, populations of Arctic grayling considered native to the upper Missouri River. Introduced populations present in Montana (e.g., Table 1) or elsewhere are not considered as part of the listable entity because we do not consider them to be native populations. Neither the Act nor our implementing regulations expressly address whether introduced populations should be considered part of an entity being evaluated for listing, and no Service policy addresses the issue. Consequently, in our evaluation of whether or not to include introduced populations in the potential listable entity we considered the following: (1) Our interpretation of the intent of the Act with respect to the disposition of native populations, (2) a policy used by the National Marine Fishery Service (NMFS) to evaluate whether hatcheryorigin populations warrant inclusion in the listable entity, and (3) a set of guidelines from another organization (International Union for Conservation of Nature and Natural Resources (IUCN)) with specific criteria for evaluating the conservation contribution of introduced populations.

Intent of the Endangered Species Act

The primary purpose of the Act is to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved. The Service has interpreted the Act to provide a statutory directive to conserve species in their native ecosystems (49 FR 33890, August 27, 1984) and to conserve genetic resources and biodiversity over a representative portion of a taxon's historical occurrence (61 FR 4723, February 7, 1996). This priority on natural populations is evident in the Service's DPS policy within the third significance criteria. In that, a discrete population segment may be significant if it represents the only surviving natural occurrence of the taxon that may be more abundant elsewhere as an introduced population outside of its historical range.

National Marine Fishery Service Hatchery Policy

In 2005, the NMFS published a final policy on the consideration of hatcheryorigin fish in Endangered Species Act listing determinations for Pacific salmon and steelhead (anadromous Oncorhynchus spp.) (NMFS 2005, entire). A central tenet of this policy is the primacy of the conservation of naturally spawning salmon populations and the ecosystems on which they depend, consistent with the intent of the Act (NMFS 2005, pp. 37211, 37214). The policy recognizes that properly managed hatchery programs may provide some conservation benefit to the evolutionary significant unit (ESU, which is analogous to a DPS but applied to Pacific salmon) (NMFS 2005, p. 37211), and that hatchery stocks that contribute to survival and recovery of an ESU are considered during a listing decision (NMFS 2005, p. 37209). The policy states that since hatchery stocks are established and maintained with the intent of furthering the viability of wild populations in the ESU, that those hatchery populations have an explicit conservation value. Genetic divergence is the preferred metric to determine if hatchery fish should be included in the ESU, but NMFS recognizes that these data may be lacking in most cases (NMFS 2005, p. 37209). Thus, proxies for genetic divergence can be used, such as the length of time a stock has been isolated from its source population, the degree to which natural broodstock has been regularly incorporated into the hatchery population, the history of nonESU fish or eggs in the hatchery population, and the attention given to genetic considerations in selecting and mating broodstocks (NMFS 2005, p. 37209).

The NMFS policy applies to artificially propagated (hatchery) populations. In this finding, however, the Service is deciding whether selfsustaining populations introduced outside its natural range should be included in the listable entity. Thus, the NMFS policy is not directly applicable. Nonetheless, if the NFMS policy's criteria are applied to the introduced lakedwelling populations of Arctic grayling in Montana and elsewhere, these populations do not appear to warrant inclusion in the entity being evaluated for listing. First, there does not appear to be any formally recognized conservation value for the [[Page 54713]]
introduced populations of Arctic grayling, and they are not being used in restoration programs. Recent genetic analysis indicates that many of the introduced Arctic grayling populations in Montana are derived, in part, from stocks in the Red Rock Lakes system (Peterson and Ardren 2009, p. 1767). Nonetheless, there have been concerns that introduced, lakedwelling populations could pose genetic risks to the native fluvial population (Arctic Grayling Workgroup (AGW) 1995, p. 15), and in practice, these introduced populations have not been used for any conservation purpose. In fact, efforts are currently underway to establish a genetically pure brood reserve population of Red Rock Lakes grayling to be used for conservation purposes (Jordan 2010, pers. comm.), analogous to the brood reserves maintained for Arctic grayling from the Big Hole River (Rens and Magee 2007, pp. 2224).

Second, introduced populations in lakes have apparently been isolated from their original source stock for decades without any supplementation from the wild. These populations were apparently established without any formal genetic consideration to selecting and mating broodstock, the source populations were not well documented (Peterson and Ardren 2009, p. 1767), and the primary intent of culturing and introducing these grayling appears to have been to provide recreational fishing opportunities in high mountain lakes. Guidelines Used in Other Evaluation Systems

The IUCN uses its Red List system to evaluate the conservation status and relative risk of extinction for species, and to catalogue and highlight plant and animal species that are facing a higher risk of global extinction (http://www.iucnredlist.org). IUCN does not use the term ``listable entity'' as the Service does; however, IUCN does clarify that their conservation ranking criteria apply to any taxonomic group at the species level or below (IUCN 2001, p.4). Further, the IUCN guidelines for species status and scope of the categorization process focus on wild populations inside their natural range (IUCN 2001, p. 4; 2003, p. 10) or socalled ``benign'' or ``conservation introductions,'' which are defined as attempts to establish a species, for the purpose of conservation, outside its recorded distribution, when suitable habitat is lacking within the historical range (IUCN 1998, p. 6; 2003, pp. 6, 10). Guidelines for evaluating conservation status under the IUCN exclude introduced populations located outside the recorded distribution of the species if such populations were established for commercial or sporting purposes (IUCN 1998, p. 5; 2003, p. 24). In effect, the IUCN delineates between introduced and native populations in that nonbenign introductions do not qualify for evaluation under the IUCN Red List system. Naturalized populations of Arctic grayling in lakes thus do not meet the IUCN criterion for a wild population that should be considered when evaluating the species status for two reasons. First, there remains `suitable habitat' for Arctic grayling in its native range, as evidenced by extant native populations in the Big Hole River, Madison River, Miner Lake, Mussigbrod Lake, and Red Rock Lakes. Second, the naturalized populations derived from widespread stocking were apparently aimed at establishing recreational fisheries.

Our interpretation is that the ESA is intended to preserve native populations in their ecosystems. While hatchery or introduced populations of fishes may have some conservation value, this does not appear to be the case with introduced populations of Arctic grayling in the conterminous United States. These populations were apparently established to support recreational fisheries, and without any formal genetic consideration to selecting and mating broodstock, and are not part of any conservation program to benefit the native populations. Consequently, we do not consider the introduced populations of Arctic grayling in Montana and elsewhere in the conterminous United States, including those in lakes and in an irrigation canal (Sun River Slope Canal), to be part of the listable entity.

Native Distribution in the Upper Missouri River System

The first EuroAmerican ``discovery'' of Arctic grayling in North America is attributed to members of the Lewis and Clark Expedition, who encountered the species in the Beaverhead River in August 1805 (Nell and Taylor 1996, p. 133). Vincent (1962, p. 11) and Kaya (1992, pp. 47 51) synthesized accounts of Arctic grayling occurrence and abundance from historical surveys and contemporary monitoring to determine the historical distribution of the species in the upper Missouri River system (Figure 2). We base our conclusions on the historical distribution of Arctic grayling in the upper Missouri River basin on these two reviews. Arctic grayling were widely but irregularly distributed in the upper Missouri River system above the Great Falls in Montana and in northwest Wyoming within the presentday location of Yellowstone National Park (Vincent 1962, p. 11). They were estimated to inhabit up to 2,000 kilometers (km) (1,250 miles (mi)) of stream habitat until the early 20th century (Kaya 1992, pp. 4751). Arctic grayling were reported in the mainstem Missouri River, as well as in the Smith, Sun, Jefferson, Madison, Gallatin, Big Hole, Beaverhead, and Red Rock Rivers (Vincent 1962, p. 11; Kaya 1992, pp. 4751; USFWS 2007; 72 FR 20307, April 24, 2007). ``Oldtimer'' accounts report that the species may have been present in the Ruby River, at least seasonally (Magee 2005, pers. comm.), and were observed as recently as the early 1970s (Holton, undated).

Fluvial Arctic grayling were historically widely distributed in the upper Missouri River basin, but a few adfluvial populations also were native to the basin. For example, Arctic grayling are native to Red Rock Lakes, in the headwaters of the Beaverhead River (Vincent 1962, pp. 112121; Kaya 1992, p. 47). Vincent (1962, p. 120) stated that Red Rock Lakes were the only natural lakes in the upper Missouri River basin accessible to colonization by Arctic grayling, and concluded that grayling there were the only native adfluvial population in the basin. However, it appears that Arctic grayling also were native to Elk Lake (in the Red Rocks drainage; Kaya 1990, p. 44) and a few small lakes in the upper Big Hole River drainage (Peterson and Ardren 2009, p. 1768).

The distribution of native Arctic grayling in the upper Missouri River went through a dramatic reduction in the first 50 years of the 20th century, especially in riverine habitats (Vincent 1962, pp. 8690, 97122, 127129; Kaya 1992, pp. 4753). The native populations that formerly resided in the Smith, Sun, Jefferson, Beaverhead, Gallatin, and mainstem Missouri Rivers are considered extirpated, and the only remaining indigenous fluvial population is found in the Big Hole River and some if its tributaries (Kaya 1992, pp. 5153). The fluvial form currently occupies only 4 to 5 percent of its historic range in the Missouri River system (Kaya 1992, p. 51). Other remaining native populations in the upper Missouri River occur in two small, headwater lakes in the upper Big Hole River system (Miner and Mussigbrod Lakes); the Madison River upstream from Ennis Reservoir; and the Red Rock Lakes in the headwaters of the Beaverhead River system (Everett 1986, p. 7; Kaya 1992, p. 53; Peterson and Ardren 2009, pp. 1762, 1768; Figure 1 above, and Table 2 below).
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TABLE 2. Extant Native Arctic Grayling Populations in the Upper Missouri River Basin.
Big Hole River Drainage\a\
1. Big Hole River
2. Miner Lake
3. Mussigbrod Lake
Madison River Drainage
4. Madison RiverEnnis Reservoir
Beaverhead River Drainage
5. Red Rock Lakes
\a\Arctic grayling also occur in Pintler Lake in the Big Hole River drainage, but this population has not been evaluated with genetic markers to determine whether it constitutes a native remnant population.
Origins, Biogeography, and Genetics of Arctic Grayling in North America

North American Arctic grayling are most likely descended from Eurasian Thymallus that crossed the Bering land bridge during or before the Pleistocene glacial period (Stamford and Taylor 2004, pp. 1533, 1546). A Eurasian origin is suggested by the substantial taxonomic diversity found in the genus in that region. There were multiple opportunities for freshwater faunal exchange between North America and Asia during the Pleistocene, but genetic divergence between North American and Eurasian Arctic grayling suggests that the species could have colonized North America as early as the midlate Pliocene (more than 3 million years ago) (Stamford and Taylor 2004, p. 1546).

The North American distribution of Arctic grayling was strongly influenced by patterns of glaciation. Genetic studies of grayling using mitochondrial DNA (mtDNA, maternallyinherited DNA located in cellular organelles called mitochondria) and microsatellite DNA (repeating sequences of nuclear DNA) have shown that North American Arctic grayling consist of at least three major lineages that originated in distinct Pleistocene glacial refugia (Stamford and Taylor 2004, p. 1533). These three groups include a South Beringia lineage found in western Alaska to northern British Columbia, Canada; a North Beringia lineage found on the North Slope of Alaska, the lower Mackenzie River, and to eastern Saskatchewan; and a Nahanni lineage found in the lower Liard River and the upper Mackenzie River drainage (Stamford and Taylor 2004, pp. 1533, 1540). The Nahanni lineage is the most genetically distinct group (Stamford and Taylor 2004, pp. 15411543). Arctic grayling from the upper Missouri River basin were tentatively placed in the North Beringia lineage because a small sample (three individuals) of Montana grayling shared a mtDNA haplotype (form of the mtDNA) with populations in Saskatchewan and the lower Peace River, British Columbia (Stamford and Taylor 2004, p. 1538).

The existing mtDNA data suggest that Missouri River Arctic grayling share a common ancestry with the North Beringia lineage, but other genetic markers and biogeographic history indicate that Missouri River grayling have been physically and reproductively isolated from northern populations for millennia. The most recent ancestors of Missouri River Arctic grayling likely spent the last glacial cycle in an icefree refuge south of the Laurentide and Cordilleran ice sheets. Preglacial colonization of the Missouri River basin by Arctic grayling was possible because the river flowed to the north and drained into the ArcticHudson Bay prior to the last glacial cycle (Cross et al. 1986, pp. 374375; Pielou 1991, pp. 194195). Low mtDNA diversity observed in a small number of Montana grayling samples and a shared ancestry with Arctic grayling from the north Beringia lineage suggest a more recent, postglacial colonization of the upper Missouri River basin. In contrast, microsatellite DNA show substantial divergence between Montana and Saskatchewan (i.e., same putative mtDNA lineage) (Peterson and Ardren 2009, entire). Differences in the frequency and size distribution of microsatellite alleles between Montana populations and two Saskatchewan populations indicate that Montana grayling have been isolated long enough for mutations (i.e., evolution) to be responsible for the observed genetic differences.

Additional comparison of 21 Arctic grayling populations from Alaska, Canada, and the Missouri River basin using 9 of the same microsatellite loci as Peterson and Ardren (2009, entire) further supports the distinction of Missouri River Arctic grayling relative to populations elsewhere in North America (USFWS, unpublished data). Analyses of these data using two different methods clearly separates sample fish from 21 populations into two clusters: one cluster representing populations from the upper Missouri River basin, and another cluster representing populations from Canada and Alaska (USFWS, unpublished data). These new data, although not yet peer reviewed, support the interpretation that the previous analyses of Stamford and Taylor (2004, entire) underestimated the distinctiveness of Missouri River Arctic grayling relative to other sample populations, likely because of the combined effect of small sample sizes and the lack of variation observed in the Missouri River for the markers used in that study (Stamford and Taylor 2004, pp. 15371538). Thus, these recent microsatellite DNA data suggest that Arctic grayling may have colonized the Missouri River before the onset of Wisconsin glaciation (more than 80,000 years ago).

Genetic relationships among native and introduced populations of Arctic grayling in Montana have recently been investigated (Peterson and Ardren 2009, entire). Introduced, lakedwelling populations of Arctic grayling trace much of their original ancestry to Red Rock Lakes (Peterson and Ardren 2009, p. 1767), and stocking of hatchery grayling did not appear to have a large effect on the genetic composition of the extant native populations (Peterson and Ardren 2009, p. 1768). Differences between native populations of the two grayling ecotypes (adfluvial, fluvial) do not appear to be as large as differences resulting from geography (i.e., drainage of origin).
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Habitat

Arctic grayling generally require clear, cold water. Selong et al. (2001, p. 1032) characterized Arctic grayling as belonging to a ``coldwater'' group of salmonids, which also includes bull trout (Salvelinus confluentus) and Arctic char (Salvelinus alpinus). Hubert et al. (1985, p. 24) developed a habitat suitability index study for Arctic grayling and concluded that thermal habitat was optimal between 7 to 17 [deg]C (45 to 63 [deg]F), but became unsuitable above 20[deg]C (68[deg]F). Arctic grayling fry may be more tolerant of high water temperature than adults (LaPerriere and Carlson 1973, p. 30; Feldmeth and Eriksen 1978, p. 2041).

Having a broad, nearlycircumpolar distribution, Arctic grayling occupy a variety of habitats including small streams, large rivers, lakes, and even bogs (Northcote 1995, pp. 152153; Scott and Crossman 1998, p. 303). They may even enter brackish water (less than or equal to 4 parts per thousand) when migrating between adjacent river systems (West et al. 1992, pp. 713714). Native populations are found at elevations ranging from near sea level, such as in Bristol Bay, Alaska, to highelevation montane valleys (more than 1,830 meters (m) or 6,000 feet (ft)), such as the Big Hole River and Centennial Valley in southwestern Montana. Despite this broad distribution, Arctic grayling have specific habitat requirements that can constrain their local distributions, especially water temperature and channel gradient. At the local scale, Arctic grayling prefer cold water and are often associated with springfed habitats in regions with warmer climates (Vincent 1962, p. 33). Arctic grayling are generally not found in swift, highgradient streams, and Vincent (1962, p. 3637, 4143) characterized typical Arctic grayling habitat in Montana (and Michigan) as lowtomoderate gradient (less than 4 percent) streams and rivers with lowtomoderate water velocities (less than 60 centimeters/sec). Juvenile and adult Arctic grayling in streams and rivers spend much of their time in pool habitat (Kaya 1990 and references therein, p. 20; Lamothe and Magee 2003, pp. 1314).

Breeding

Arctic grayling typically spawn in the spring or early summer, depending on latitude and elevation (Northcote 1995, p. 149). In Montana, Arctic grayling generally spawn from late April to midMay by depositing adhesive eggs over gravel substrate without excavating a nest (Kaya 1990, p. 13; Northcote 1995, p. 151). In general, the reproductive ecology of Arctic grayling differs from other salmonid species (trout and salmon) in that Arctic grayling eggs tend to be comparatively small; thus, they have higher relative fecundity (females have more eggs per unit body size). Males establish and defend spawning territories rather than defending access to females (Northcote 1995, pp. 146, 150151). The time required for development of eggs from embryo until they emerge from stream gravel and become swimup fry depends on water temperature (Northcote 1995, p. 151). In the upper Missouri River basin, development from embryo to fry averages about 3 weeks (Kaya 1990, pp. 1617). Small, weakly swimming fry (typically 1 1.5 centimeters (cm) (0.40.6 in.) at emergence) prefer lowvelocity stream habitats (Armstrong 1986, p. 6; Kaya 1990, pp. 2324; Northcote 1995, p. 151).

Arctic grayling of all ages feed primarily on aquatic and terrestrial invertebrates captured on or near the water surface, but also will feed opportunistically on fish and fish eggs (Northcote 1995, pp. 153154; Behnke 2002, p. 328). Feeding locations for individual fish are typically established and maintained through sizemediated dominance hierarchies where larger individuals defend favorable feeding positions (Hughes 1992, p. 1996).

Life History Diversity

Migratory behavior is a common lifehistory trait in salmonid fishes such as Arctic grayling (Armstrong 1986, pp. 78; Northcote 1995, pp. 156158; 1997, pp. 1029, 10311032, 1034). In general, migratory behavior in Arctic grayling and other salmonids results in cyclic patterns of movement between refuge, rearingfeeding, and spawning habitats (Northcote 1997, p. 1029).

Arctic grayling may move to refuge habitat as part of a regular seasonal migration (e.g., in winter), or in response to episodic environmental stressors (e.g., high summer water temperatures). In Alaska, Arctic grayling in rivers typically migrate downstream in the fall, moving into larger streams or mainstem rivers that do not completely freeze (Armstrong 1986, p. 7). In Arctic rivers, fish often seek overwintering habitat influenced by groundwater (Armstrong 1986, p. 7). In some drainages, individual fish may migrate considerable distances (greater than 150 km or 90 mi) to overwintering habitats (Armstrong 1986, p. 7). In the Big Hole River, Montana, similar downstream and longdistance movement to overwintering habitat has been observed in Arctic grayling (Shepard and Oswald 1989, pp. 1821, 27). In addition, Arctic grayling in the Big Hole River may move downstream in proximity to colder tributary streams in summer when thermal conditions in the mainstem river become stressful (Lamothe and Magee 2003, p. 17).

In spring, mature Arctic grayling leave overwintering areas and migrate to suitable spawning sites. In river systems, this typically involves an upstream migration to tributary streams or shallow riffles within the mainstem (Armstrong 1986, p. 8). Arctic grayling in lakes typically migrate to either the inlet or outlet to spawn (Armstrong 1986, p. 8; Northcote 1997, p. 148). In either situation, Arctic grayling typically exhibit natal homing, whereby individuals spawn in or near the location where they were born (Northcote 1997, pp. 157 160).

Fry from river populations typically seek feeding and rearing habitats in the vicinity where they were spawned (Armstrong 1986, pp. 67; Northcote 1995, p. 156), while those from lake populations migrate downstream (inlet spawners) or upstream (outlet spawners) to the adjacent lake. Following spawning, adults move to appropriate feeding areas if they are not adjacent to spawning habitat (Armstrong 1986, pp. 78). Juvenile Arctic grayling may undertake seasonal migrations between feeding and overwintering habitats until they reach maturity and add the spawning migration to this cycle (Northcote 1995, pp. 156 157).
Life History Diversity in Arctic Grayling in the Upper Missouri River

Two general lifehistory forms or ecotypes of native Arctic grayling occur in the upper Missouri River Arctic: Fluvial and adfluvial. Fluvial fish use river or stream (lotic) habitat for all of their life cycles and may undergo extensive migrations within river habitat. Adfluvial fish live in lakes and migrate to tributary streams to spawn. These same lifehistory forms also are expressed by Arctic grayling elsewhere in North America (Northcote 1997, p. 1030). Historically, the fluvial lifehistory form predominated in the Missouri River basin above the Great Falls, perhaps because there were only a few lakes accessible to natural colonization of Arctic grayling that would permit expression of the adfluvial ecotype (Kaya 1992, p. 47). The fluvial and adfluvial lifehistory forms of Arctic grayling in the upper Missouri River do not appear to represent distinct evolutionary lineages. Instead, they appear to represent an example of adaptive radiation (Schluter 2000, p. 1), whereby the forms [[Page 54716]]
differentiated from a common ancestor developed traits that allowed them to exploit different habitats. The primary evidence for this conclusion is genetic data that indicate that within the Missouri River basin the two ecotypes are more closely related to each other than they are to the same ecotype elsewhere in North America (Redenbach and Taylor 1999, pp. 2728; Stamford and Taylor 2004, p. 1538; Peterson and Ardren 2009, p. 1766). Historically, there may have been some genetic exchange between the two lifehistory forms as individuals strayed or dispersed into different populations (Peterson and Ardren 2009, p. 1770), but the genetic structure of current populations in the upper Missouri River basin is consistent with reproductive isolation.

The fluvial and adfluvial forms of Arctic grayling appear to differ in their genetic characteristics, but there appears to be some plasticity in behavior where individuals from a population can exhibit a range of behaviors. Arctic grayling fry in Montana can exhibit heritable, geneticallybased differences in swimming behavior between fluvial and adfluvial ecotypes (Kaya 1991, pp. 53, 5658; Kaya and Jeanes 1995, pp. 454, 456). Progeny of Arctic grayling from the fluvial ecotype exhibited a greater tendency to hold their position in flowing water relative to progeny from adfluvial ecotypes (Kaya 1991, pp. 53, 5658; Kaya and Jeanes 1995, pp. 454, 456). Similarly, young grayling from inlet and outlet spawning adfluvial ecotypes exhibited an innate tendency to move downstream and upstream, respectively (Kaya 1989, pp. 478480). All three studies (Kaya 1989, entire; 1991, entire; Kaya and Jeanes 1995, entire) demonstrate that the response of fry to flowing water depended strongly on the lifehistory form (ecotype) of the source population, and that this behavior has a genetic basis. However, behavioral responses also were mediated by environmental conditions (lightKaya 1991, pp. 5657; light and water temperatureKaya 1989, pp. 477479), and some progeny of each ecotype exhibited behavior characteristic of the other; for example some individuals from the fluvial ecotype moved downstream rather than holding position, and some individuals from an inletspawning adfluvial ecotype held position or moved upstream (Kaya 1991, p. 58). These observations indicate that some plasticity for behavior exists, at least for very young Arctic grayling.

However, the ability of one ecotype of Arctic grayling to give rise to a functional population of the other ecotype within a few decades is much less certain, and may parallel the differences in plasticity that have evolved between river and laketype European grayling (Salonen 2005, entire). Circumstantial support for reduced plasticity in adfluvial Arctic grayling comes from observations that adfluvial fish stocked in river habitats almost never establish populations (Kaya 1990, pp. 3134). In contrast, a population of Arctic grayling in the Madison River that would have presumably expressed a fluvial ecotype under historical conditions has apparently adapted to an adfluvial lifehistory after construction of an impassible dam, which impounded Ennis Reservoir (Kaya 1992, p. 53; Jeanes 1996, pp. 54). We note that adfluvial Arctic grayling retain some lifehistory flexibilityat least in lake environmentsas naturalized populations derived from inletspawning stocks have established outletspawning demes (a deme is a local populations that shares a distinct gene pool) in Montana and in Yellowstone National Park (Kruse 1959, p. 318; Kaya 1989, p. 480). While in some cases Arctic grayling may be able to adapt or adjust rapidly to a new environment, the frequent failure of introductions of Arctic grayling suggest a cautionary approach to the loss of particular lifehistory forms is warranted. Healey and Prince (1995, entire) reviewed patterns of genotypic and phenotypic variation in Pacific salmon and warn that recovery of lost lifehistory forms may not follow directly from conservation of the genotype (p. 181), and reason that the critical conservation unit is the population within its habitat (p. 181).

Age and Growth

Age at maturity and longevity in Arctic grayling varies regionally and is probably related to growth rate, with populations in colder, northern latitudes maturing at later ages and having a greater lifespan (Kruse 1959, pp. 340341; Northcote 1995 and references therein, pp. 155157). Arctic grayling in the upper Missouri River typically mature at age 2 (males) or age 3 (females), and individuals greater than age 6 are rare (Kaya 1990, p. 18; Magee and Lamothe 2003, pp. 1617). Similarly, Nelson (1954, pp. 333334) observed that the majority of the Arctic grayling spawning in two tributaries in the Red Rock Lakes system, Montana, were age 3, and the oldest individuals aged from a larger sample were age 6. Mogen (1996, pp. 3234) found that Arctic grayling spawning in Red Rock Creek were mostly ages 2 to 5, but he did encounter some individuals age 7.

Generally, growth rates of Arctic grayling are greatest during the first years of life then slow dramatically after maturity. Within that general pattern, there is substantial variation among populations from different regions. Arctic grayling populations in Montana (Big Hole River and Red Rock Lakes) appear to have very high growth rates relative to those from British Columbia, Asia, and the interior and North Slope of Alaska (Carl et al. 1992, p. 240; Northcote 1995, pp. 155157; Neyme 2005, p. 28). Growth rates of Arctic grayling from different management areas in Alberta are nearly as high as those observed in Montana grayling (ASRD 2005, p. 4).

Distinct Population Segment

In its stipulated settlement with Plaintiffs, the Service agreed to consider the appropriateness of DPS designations for Arctic grayling populations in the upper Missouri River basin that included: (a) All life ecotypes or histories, (b) the fluvial ecotype, and (c) the adfluvial ecotype. The fluvial ecotype has been the primary focus of past Service action and litigation, but the Service also has alluded to the possibility of alternative DPS designations in previous candidate species assessments (USFWS 2005, p. 11). Since the 2007 finding (72 FR 20305), additional research has been conducted and new information on the genetics of Arctic grayling is available. This finding contains a more comprehensive and robust distinct population segment analysis than the 2007 finding.
Distinct Population Segment Analysis for Native Arctic Graying in the Upper Missouri River

Discreteness

The discreteness standard under the Service's and National Oceanic and Atmospheric Administration's (NOAA) joint Policy Regarding the Recognition of Distinct Vertebrate Population Segments Under the Endangered Species Act (61 FR 4722) requires an entity to be adequately defined and described in some way that distinguishes it from other representatives of its species. A segment is discrete if it is: (1) Markedly separated from other populations of the same taxon as consequence of physical, physiological, ecological, or behavioral factors (quantitative measures of genetic or morphological discontinuity may provide evidence of this separation); or (2) delimited by international
[[Page 54717]]
governmental boundaries within which differences in control of exploitation, management of habitat, conservation status, or regulatory mechanisms exist that are significant in light of section 4(a)(1)(D) of the ESA.

Arctic grayling native to the upper Missouri River are isolated from populations of the species inhabiting the Arctic Ocean, Hudson Bay, and north Pacific Ocean drainages in Asia and North America (see Figure 1). Arctic grayling native to the upper Missouri River occur as a disjunct group of populations approximately 800 km (500 mi) to the south of the nextnearest Arctic grayling population in central Alberta, Canada. Missouri River Arctic grayling have been isolated from other populations for at least 10,000 years based on historical reconstruction of river flows at or near the end of the Pleistocene (Cross et al. 1986, p. 375; Pileou 1991, pp. 1011;). Genetic data confirm Arctic grayling in the Missouri River basin have been reproductively isolated from populations to the north for millennia (Everett 1986, pp. 7980; Redenbach and Taylor 1999, p. 23; Stamford and Taylor 2004, p. 1538; Peterson and Ardren 2009, pp. 17641766; USFWS, unpublished data). Consequently, we conclude that Arctic grayling native to the upper Missouri River are markedly separated from other native populations of the taxon as a result of physical factors (isolation), and therefore meet the first criterion of discreteness under the DPS policy. As a result, Arctic grayling native to the upper Missouri River are considered a discrete population according to the DPS policy. Because the entity meets the first criterion (markedly separated), an evaluation with respect to the second criterion (international boundaries) is not needed.

Significance

If we determine that a population meets the DPS discreteness element, we then consider whether it also meets the DPS significance element. The DPS policy states that, if a population segment is considered discrete under one or more of the discreteness criteria, its biological and ecological significance will be considered in light of congressional guidance that the authority to list DPSs be used ``sparingly'' while encouraging the conservation of genetic diversity (see U.S. Congress 1979, Senate Report 151, 96\th\ Congress, 1st Session). In making this determination, we consider available scientific evidence of the discrete population's importance to the taxon to which it belongs. Since precise circumstances are likely to vary considerably from case to case, the DPS policy does not describe all the classes of information that might be used in determining the biological and ecological importance of a discrete population. However, the DPS policy does provide four possible reasons why a discrete population may be significant. As specified in the DPS policy, this consideration of significance may include, but is not limited to, the following: (1) Persistence of the discrete population segment in a unique or unusual ecological setting; (2) evidence that loss of the discrete segment would result in a significant gap in the range of the taxon; (3) evidence that the discrete population segment represents the only surviving natural occurrence of the taxon that may be more abundant elsewhere as an introduced population outside of its historic range; or (4) evidence that the discrete population segment differs markedly from other populations of the species in its genetic characteristics.

Unique Ecological Setting

Water temperature is a key factor influencing the ecology and physiology of ectothermic (body temperature regulated by ambient environmental conditions) salmonid fishes, and can dictate reproductive timing, growth and development, and lifehistory strategies. Groundwater temperatures can be related to air temperatures (Meisner 1990, p. 282), and thus reflect the regional climatic conditions. Warmer groundwater influences ecological factors such as food availability, the efficiency with which food is converted into energy for growth and reproduction, and ultimately growth rates of aquatic organisms (Allan 1995, pp. 7379). Aquifer structure and groundwater temperature is important to salmonid fishes because groundwater can strongly influence stream temperature, and consequently egg incubation and fry growth rates, which are strongly temperaturedependent (Coutant 1999, pp. 3252; Quinn 2005, pp. 143150).

Missouri River Arctic grayling occur within the 4 to 7 [deg]C (39 to 45 [deg]F) ground water isotherm (see Heath 1983, p. 71; an isotherm is a line connecting bands of similar temperatures on the earth's surface), whereas most other North American grayling are found in isotherms less than 4 [deg]C, and much of the species' range is found in areas with discontinuous or continuous permafrost (Meisner et al. 1988, p. 5). Much of the historical range of Arctic grayling in the upper Missouri River is encompassed by mean annual air temperature isotherms of 5 to 10 [deg]C (41 to 50 [deg]F) (USGS 2009), with the colder areas being in the headwaters of the Madison River in Yellowstone National Park. In contrast, Arctic grayling in Canada, Alaska, and Asia are located in regions encompassed by air temperature isotherms 5 [deg]C and colder (41 [deg]F and colder), with much of the species distributed within the 0 to 10 [deg]C isolines (32 to 14 [deg]F). This difference is significant because Arctic grayling in the Missouri River basin have evolved in isolation for millennia in a generally warmer climate than other populations. The potential for thermal adaptations makes Missouri River Arctic grayling a significant biological resource for the species under expected climate change scenarios.

TABLE 3. Differences Between the Ecological Setting of the Upper Missouri River and Elsewhere in the Species' Range of Arctic Grayling. Ecological Setting Variable Missouri River Rest of Taxon Ocean watershed Gulf of Mexico Hudson Bay, Arctic Atlantic Ocean Ocean, or north Pacific Bailey's Ecoregion Dry Domain: Polar Domain: Temperate Steppe Tundra & Subarctic Humid Temperate: Marine, Prairie, Warm Continental Mountains Air temperature (isotherm) 5 to 10 [deg]C 15 to 5 [deg]C (41 to 50 [deg]F). (5 to 41 [deg]F) [[Page 54718]]
Groundwater temperature 4 to 7[deg]C Less than 4 [deg]C (isotherm) (39 to 45 [deg]F). (less than 39 [deg]F) Native occurrence of large None, in most of Bull trout, lake bodied fish predators on the range\a\ trout, northern salmonids pike, taimen \a\Lake trout are native to two small lakes in the upper Missouri River basin (Twin Lakes and Elk Lake), where their distributions presumably overlapped with the native range of Arctic grayling, so they would not have interacted with most Arctic grayling populations in the basin that were found in rivers.

Arctic grayling in the upper Missouri River basin occur in a temperate ecoregion distinct from all other Arctic grayling populations worldwide, which occur in Arctic or subArctic ecoregions dominated by Arctic flora and fauna. An ecoregion is a continuous geographic area within which there are associations of interacting biotic and abiotic features (Bailey 2005, pp. S14, S23). These ecoregions delimit large areas within which local ecosystems recur more or less in a predictable fashion on similar sites (Bailey 2005, p. S14). Ecoregional classification is hierarchical, and based on the study of spatial coincidences, patterning, and relationships of climate, vegetation, soil, and landform (Bailey 2005, p. S23). The largest ecoregion categories are domains, which represent subcontinental areas of similar climate (e.g., polar, humid temperate, dry, and humid tropical) (Bailey 1994; 2005, p. S17). Domains are divided into divisions that contain areas of similar vegetation and regional climates. Arctic grayling in the upper Missouri River basin are the only example of the species naturally occurring in a dry domain (temperate steppe division; see Table 3 above). The vast majority of the species' range is found in the polar domain (all of Asia, most of North America), with small portions of the range occurring in the humid temperate domain (northern British Columbia and southeast Alaska). Occupancy of Missouri River Arctic grayling in a temperate ecoregion is significant for two primary reasons. First, an ecoregion represents a suite of factors (climate, vegetation, landform) influencing, or potentially influencing, the evolution of species within that ecoregion. Since Missouri River Arctic grayling have existed for thousands of years in an ecoregion quite different from the majority of the taxon, they have likely developed adaptations during these evolutionary timescales that distinguish them from the rest of the taxon, even if we have yet to conduct the proper studies to measure these adaptations. Second, the occurrence of Missouri River Arctic grayling in a unique ecoregion helps reduce the risk of specieslevel extinction, as the different regions may respond differently to environmental change.

Arctic grayling in the upper Missouri River basin have existed for at least 10,000 years in an ecological setting quite different from that experienced by Arctic grayling elsewhere in the species' range. The most salient aspects of this different setting relate to temperature and climate, which can strongly and directly influence the biology of ectothermic species (like Arctic grayling). Arctic grayling in the upper Missouri River have experienced warmer temperatures than most other populations. Physiological and lifehistory adaptation to local temperature regimes are regularly documented in salmonid fishes (Taylor 1991, pp. 191193), but experimental evidence for adaptations to temperature, such as unusually high temperature tolerance or lower tolerance to colder temperatures, is lacking for Missouri River Arctic grayling because the appropriate studies have not been conducted. Lohr et al. (1996, p. 934) studied the upper thermal tolerances of Arctic grayling from the Big Hole River, but their research design did not include other populations from different thermal regimes, so it was not possible to make betweenpopulation contrasts under a common set of conditions. Arctic grayling from the upper Missouri River demonstrate very high growth rates relative to other populations (Northcote 1995, p. 157). Experimental evidence obtained by growing fish from populations under similar conditions would be needed to measure the relative influence of genetics (local adaptation) versus environment.

An apex fish predator that preys successfully on salmonids has been largely absent from most of the upper Missouri River basin over evolutionary time scales (tens of thousands of years). This suggests that Arctic grayling in the upper Missouri River basin have faced a different selective pressure than Arctic grayling in many other areas of the species' range, at least with respect to predation by fishes. Predators can exert a strong selective pressure on populations. One noteworthy aspect of the aquatic biota experienced by Arctic grayling in the upper Missouri River is the apparent absence of a largebodied fish that would be an effective predator on juvenile and adult salmonids. In contrast, one or more species of large predatory fishes like northern pike (Esox lucius), bull trout, taimen (Hucho taimen), and lake trout (Salvelinus namaycush) are broadly distributed across much of the range of Arctic grayling in Canada and Asia (Northern pikeScott and Crossman 1998, pp. 302, 358; taimenVanderZanden et al. 2007, pp. 22812282; Esteve et al. 2009, p. 185; bull troutBehnke 2002, pp. 296, 330; lake trout Behnke 2002, pp. 296, 330). The only exceptions to this general pattern are where Arctic grayling formerly coexisted with lake trout native to Twin Lakes and Elk Lake (Beaverhead County) (Vincent 1963, pp. 188189), but both of these Arctic grayling populations are thought to be extirpated (Oswald 2000, pp. 10, 16; Oswald 2006, pers. comm.). The burbot (Lota lota) is a freshwater fish belonging to the cod family and is native to the Missouri, Big Hole, Beaverhead, Ruby, and Madison Rivers in Montana (MFISH 2010); thus its distribution significantly overlapped the historical and current ranges of Arctic grayling in the upper Missouri River system. Burbot are voracious predators, but tend to be benthic (bottomoriented) and apparently prefer the deeper portions of larger rivers and lakes. A few studies have investigated the diet of burbot where they overlap with native Arctic grayling in Montana, but did not detect any predation on Arctic grayling (Streu 1990, pp. 1620; Katzman 1998, pp. 98100). Burbot apparently do not consume salmonids in significant amounts, even when they are very abundant (Katzman 1998 and references therein, p. 106). The response of Arctic grayling in the Missouri River basin to introduced,
[[Page 54719]]
nonnative trout suggests they were not generally preadapted to cope with the presence of a largebodied salmonid predator. Missouri River Arctic grayling lack a coevolutionary history with brown trout, and there are repeated observations that the two species tend not to coexist and that brown trout displace Arctic grayling (Kaya 1992, p. 56; 2000, pp. 1415). We caution that competition with and predation by brown trout has not been directly studied with Arctic grayling, but at least some circumstantial evidence indicates that Missouri River Arctic grayling may not coexist well with brown trout.

We conclude that the occurrence of Arctic grayling in the upper Missouri River is biogeographically important to the species, that grayling there have occupied a distinctly different ecological setting relative to the rest of the species (see Table 3 above), and that they have been on a different evolutionary trajectory for at least 10,000 years. Consequently, we believe that Arctic grayling in the upper Missouri River occupy a unique ecological setting. The role that this unique setting plays in influencing adaptations or determining unique traits is unclear, and therefore a determination of the significance of this ecological setting to the taxon is unknown.

Gap in the Range

Arctic grayling in the upper Missouri River basin occur in an ocean drainage basin that is distinct from all other Arctic grayling populations worldwide. All other Arctic grayling occur in drainages of Hudson Bay, the Arctic Ocean, or the north Pacific Ocean; the Missouri River is part of the Gulf of MexicoAtlantic Ocean drainage. The significance of occupancy of this drainage basin is that the upper Missouri River basin represents an important part of the species' range from a biogeographic perspective. The only other population of Arctic grayling to live in a nonArctic environment was the MichiganGreat Lakes population that was extirpated in the 1930s.

Arctic grayling in Montana (southern extent is approximately 44[deg]36[min]23[sec] N latitude) represent the southernmost extant population of the species' distribution since the Pleistocene glaciation (Figure 1). The nextclosest native Arctic grayling population outside the Missouri River basin is found in the Pembina River (approximately 52[deg]55[min]6.77[sec] N latitude) in central Alberta, Canada, west of Edmonton (Blackburn and Johnson 2004, pp. ii, 17; ASRD 2005, p. 6). Loss of the native Arctic grayling of the upper Missouri River would shift the southern distribution of Arctic grayling by more than 8[deg] latitude. Such a dramatic range constriction would constitute a significant geographic gap in the species' range, and eliminate a genetically distinct group of Arctic grayling, which may limit the species' ability to cope with future environmental change.

Marginal populations, defined as those on the periphery of the species' range, are believed to have high conservation significance (see reviews by Scudder 1989, entire; Lesica and Allendorf 1995, entire; Fraser 2000, entire). Peripheral populations may occur in suboptimal habitats and thus be subjected to very strong selective pressures (Fraser 2000, p. 50). Consequently, individuals from these populations may contain adaptations that may be important to the taxon in the future. Lomolino and Channell (1998, p. 482) hypothesize that because peripheral populations should be adapted to a greater variety of environmental conditions, then they may be better suited to deal with anthropogenic (humancaused) disturbances than populations in the central part of a species' range. Arctic grayling in the upper Missouri River have, for millennia, existed in a climate warmer than that experienced by the rest of the taxon. If this selective pressure has resulted in adaptations to cope with increased water temperatures, then the population segment may contain genetic resources important to the taxon. For example, if northern populations of Arctic grayling are less suited to cope with increased water temperatures expected under climate warming, then Missouri River Arctic grayling might represent an important population for reintroduction in those northern regions. We believe that Arctic grayling from the upper Missouri River's occurrence at the southernmost extreme of the range contributes to its significance that may increased adaptability and contribute to the resilience of the overall taxon.
Only Surviving Natural Occurrence of the Taxon that May be More Abundant Elsewhere as an Introduced Population Outside of its Historical Range

This criterion does not directly apply to the Arctic grayling in the upper Missouri River because it is not the only surviving natural occurrence of the taxon; there are native Arctic grayling populations in Canada, Alaska, and Asia. That said, there are introduced Lake Dwelling Arctic Grayling within the native range in the Upper Missouri River System and Arctic grayling have been established in lakes outside their native range in Arizona, Colorado, Idaho, Montana, New Mexico, Utah, Washington, and Wyoming (Vincent 1962, p. 15; Montana Fisheries Information System (MFISH) 2009; NatureServe 2010).

Differs Markedly in Its Genetic Characteristics

Differences in genetic characteristics can be measured at the molecular genetic or phenotypic level. Three diff

FOR FURTHER INFORMATION CONTACT

Mark Wilson, Field Supervisor, Montana Field Office (see ADDRESSES); by telephone at 4064495225; or by facsimile at 4064495339. Persons who use a telecommunications device for the deaf (TDD) may call the Federal Information Relay Service (FIRS) at 8008778339.

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