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Daily Rules, Proposed Rules, and Notices of the Federal Government

DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R6-ES-2012-0040; 4500030113]

Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the Platte River Caddisfly as Endangered or Threatened

AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of 12-month petition finding.
SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce a 12-month finding on a petition to list the Platte River caddisfly (Ironoquia plattensis) as an endangered or threatened species and to designate critical habitat under the Endangered Species Act of 1973, as amended. After review of all available scientific and commercial information, we find that listing the Platte River caddisfly as an endangered or threatened species is not warranted at this time. However, we ask the public to submit to us any new information that becomes available concerning the threats to the Platte River caddisfly or its habitat at any time.
DATES: The finding announced in this document was made on August 30, 2012.
ADDRESSES: This finding is available on the Internet athttp://www.regulations.govat Docket Number FWS-R6-ES-2012-0040. Supporting documentation we used in preparing this finding is available for public inspection, by appointment, during normal business hours at the U.S. Fish and Wildlife Service, Nebraska FieldOffice, Federal Building, 2nd Floor, 203 West 2nd Street, Grand Island, NE 68801. Please submit any new information, materials, comments, or questions concerning this finding to the above street address.
FOR FURTHER INFORMATION CONTACT: Michael D. George, Field Supervisor, Nebraska Field Office (seeADDRESSES); by telephone (308-382-6468, extension 12); or by facsimile (308-384-8835).mail to:Persons who use a telecommunications device for the deaf (TDD) may call the Federal Information Relay Service (FIRS) at 800-877-8339.
SUPPLEMENTARY INFORMATION: Background

Section 4(b)(3)(B) of the Endangered Species Act of 1973, as amended (Act) (16 U.S.C. 1531et seq.), requires that, for any petition to revise the Federal Lists of Endangered and Threatened Wildlife and Plants that contains substantial scientific or commercial information that listing a species may be warranted, we make a finding within 12 months of the date of receipt of the petition. In this finding, we will determine that the petitioned action is: (1) Not warranted, (2) warranted, or (3) warranted, but the immediate proposal of a regulation implementing the petitioned action is precluded by other pending proposals to determine whether species are either an endangered or threatened species, 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 Act 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 12-month findings in theFederal Register.

Previous Federal Actions

On July 30, 2007, we received a petition dated July 24, 2007, from Forest Guardians (now WildEarth Guardians), requesting that 206 species in the Mountain-Prairie Region, including the Platte River caddisfly, be listed as an endangered or threatened species under the Act, and critical habitat be designated. Included in the petition were analyses, references, and documentation provided by NatureServe in its online database athttp://www.natureserve.org/. We acknowledged receipt of the petition in a letter to the petitioners, dated August 24, 2007, and stated that, based on preliminary review, we found no compelling evidence to support an emergency listing for any of the species covered by the petition. In that letter we also stated that we would begin to assess the information provided in the petition in October 2007.

We published a partial 90-day finding for 38 of the petition's 206 species in theFederal Register(74 FR 41649) on August 18, 2009; the Platte River caddisfly was one of 29 species for which we found there was substantial information indicating that listing may be warranted under the Act. In that document, we announced that we were initiating a status review. On January 12, 2010, WildEarth Guardians filed a complaint indicating that the Service failed to comply with the statutory deadline to complete a 12-month finding for the Platte River caddisfly. This complaint was consolidated with several others, and a multi-district settlement agreement with WildEarth Guardians was approved on September 9, 2011, which included an agreement that the Service would complete the 12-month finding for the Platte River caddisfly by the end of Fiscal Year 2012. Funding for completing the 12-month finding became available in Fiscal Year 2011, and we began work at that time. This notice constitutes the 12-month finding on the July 24, 2007, petition to list the Platte River caddisfly as an endangered or threatened species.

Species Information Species Description

The Platte River caddisfly (Ironoquia plattensis)adult is a small, brown, moth-like insect with a body length of 5.5-6.5 millimeters (mm) (0.21-0.26 inches (in)) and forewing length of 6.5-8.0 mm (0.26-0.31 in) (Alexander and Whiles 2000, p. 2). Wing membranes and veins are light or iridescent brown with white spotting (Alexander and Whiles 2000, p. 2). The Platte River caddisfly has a short proboscis (tubular mouthpart used for feeding) and long antennae, similar to other species of caddisflies (Holzenthalet al.2007, p. 648). Platte River caddisfly adults can be distinguished from those of other species in theIronoquiagenus by their much smaller size (forewing length of 6.5-8.0 mm (0.26-0.31 in) in Platte River caddisflies contrasting with >14 mm (0.55 in) in most otherIronoquiaspecies) (Alexander and Whiles 2000, p. 2).

Like several caddisfly species, Platte River caddisfly larvae construct a case around the abdomen (Mackay and Wiggins 1979, p. 186). All caddisflies produce silk from modified salivary glands, and case-making caddisfly larvae use this silk to fuse together organic or mineral material from the surrounding environment (Mackay and Wiggins 1979, pp. 185-186; Holzenthalet al.2007, p. 644). Cases are generally thought to protect larvae by providing camouflage against predation or resistance to crushing (Mackay and Wiggins 1979, p. 200; Otto and Svensson 1980, p. 855). The Platte River caddisfly case is composed of sand grains and can be up to 16.0 mm (0.63 in) long, while larvae can attain sizes up to 14.0 mm (0.55 in) in length (Vivian 2010, pers. obs.).

Platte River caddisfly larvae have a light brown head and thorax and a yellowish to whitish abdomen (Vivian 2010, pers. obs.), much like the larvae ofIronoquia parvula(no common name) (Flint 1958, p. 59). Larvae in theIronoquiagenus can be distinguished from larvae in other caddisfly genera by four morphological characteristics that are distinguishable under a microscope (Flint 1958, p. 59; Wiggins 1977, p. 248). Differences in larval size (Alexander and Whiles 2000, p. 1) and case material among species have also been noted (Wiggins 1977, p. 248).

Taxonomy

The Platte River caddisfly was formally described as a new species in the order Trichoptera (caddisflies) in 2000 by Alexander and Whiles (2000, p. 2). The Platte River caddisfly is in the family Limnephilidae, or the northern caddisflies, subfamily Dicosmoceniae, and genusIronoquia(Wiggins 1977, p. 181; Alexander and Whiles 2000, p. 1).

The caddisfly family Limnephilidae is considered to be the most ecologically diverse family of Trichoptera (Holzenthalet al.2007, p. 674) and is the largest caddisfly family in North America, with over 900 species in more than 100 genera (Holzenthalet al.2007, p. 674). The Limnephilidae family is dominant at higher latitudes and elevations, has the widest distribution of any caddisfly family, and comprises one-third of all Nearctic (ecozone comprising Arctic and temperate areas of North America and Greenland) caddisfly species (Wiggins 1977, p. 179). Caddisflies in this family may be collected from springs, pools, seeps, marshes, bogs, fens, streams, rivers, and lakes (Wiggins 1977, p. 179). Limnephilids largely feed on larger bits of plant material, such as fallen leaves, or organic materials that form atop rock surfaces (Wiggins 1977, p. 179).

TheIronoquiagenus belongs to the subfamily Dicosmoceniae, which mostly occurs in cool, lotic (running water) environments, except forIronoquia,which occurs in temporary pools (Flint1958, p. 59; Wiggins 1977, p. 248). The genusIronoquiais comprised of six species: the Platte River caddisfly (I. plattensis),I. punctatissima(no common name) (Walker 1852),I. parvula(no common name) (Flint 1958),I. dubia(no common name) (Stephens 1837),I. lyrata(no common name) (Ross 1938), andI. kaskaskia(no common name) (Ross 1944), with the Platte River caddisfly being the most recently described (Encyclopedia of Life 2011, entire). All of these species exceptI. dubia(Europe) occur only in North America (Williams and Williams 1975, p. 829; Ćuk and Vučković 2010, pp. 232, 234).

Ironoquiais the only genus within the Dicosmoceniae subfamily that occurs in temporary waters (Wiggins 1977, p. 248). In North America,Ironoquiais mostly found throughout the central and eastern portions of the United States (Wiggins 1977, p. 248) and is most often collected from temporary pools or wetlands but can also occur in perennial waters (Flint 1958, p. 61; Ćuk and Vučković 2010, p. 234). The Platte River caddisfly has been found to co-occur withI. punctatissima,which is a common species on the Great Plains, butI. punctatissimais morphologically distinct and much larger than the Platte River caddisfly (Alexander and Whiles 2000, p. 1; Gelusoet al.2011, p. 1024).

The Platte River caddisfly is thought to be most closely related toI. parvula(Alexander and Whiles 2000, p. 1), which occurs in Ohio and the northeastern United States (Flint 1958, p. 59; Wiggins 1977, p. 248; Swegmanet al.1981, p. 141; Garono and MacLean 1988, p. 148). Platte River caddisfly adults are smaller and have lighter color and more pronounced spotting on the wings thanI. parvula(Alexander and Whiles 2000, p. 2). We find that Alexander and Whiles (2000, entire) provide the best available information on the taxonomy of the Platte River caddisfly, and no other challenges to the taxonomy have been raised since the Platte River caddisfly was described. Therefore, we consider the Platte River caddisfly a valid species for listing under the Act.

Habitat Description

The Platte River caddisfly was discovered in 1997, in a warm-water slough (backwater area or marsh that is groundwater fed) in south-central Nebraska along the Platte River on Mormon Island (hereafter type locality), which is land owned by the Platte River Whooping Crane Maintenance Trust (hereafter Crane Trust (a conservation organization)) southwest of Grand Island, Nebraska (Whileset al.1999, p. 534; Goldowitz 2012, pers. comm.). This slough had an intermittent hydroperiod (duration of inundation) and held water 75-90 percent of the time or about 275-330 days out of the year (Whileset al.1999, p. 534; Goldowitz 2004, pp. 2-3). The area lacked trees (Whileset al.1999, p. 534) and was located within the largest remaining tract of native prairie in the Central Platte Valley (Goldowitz 2004, p. 2).

Intermittent wetlands, such as the type locality, have been described as any water body that holds water for about 8 to 10 months during the year (Wigginset al.1980, p. 100); some intermittent sites may or may not completely dry in a year (Tarr and Babbitt 2007, p. 6). These wetlands differ from ephemeral wetlands (that hold water for a relatively short period of time (e.g., 4 months)) and permanent wetlands (rarely dry) (Tarr and Babbit 2007, p. 6). Intermittent wetlands dry when the groundwater table drops below the ground surface.

Since the Platte River caddisfly was discovered, surveys have mostly found the caddisfly in sloughs with intermittent hydroperiods; however, the caddisfly has also been found in sloughs with permanent hydroperiods (Goldowitz 2004, p. 5; Meyer and Whiles 2008, p. 632; Vivian 2010, p. 54; Gelusoet al.2011, p. 1024). In sloughs with permanent hydroperiods, the caddisfly has been observed in lower numbers, which is true of otherIronoquiaspecies, likely because of the presence of more predators in permanent waters(Wigginset al.1980, p. 148; Vivian 2010, p. 54). The caddisfly has not been observed in ephemeral wetlands (Vivian 2009, pers. obs.).

In general, the intermittent wetlands where the caddisfly occurs are found along the floodplains of the Platte, Loup, and Elkhorn Rivers in central Nebraska (LaGrange 2004, p. 15) and are shallow, linear depressions that are historical channel remnants of these river systems (Friesenet al.2000, p. 4-8). The presence of water in these sloughs is influenced by groundwater levels and trapped surface run-in (Friesenet al.2000, p. 4-8). Groundwater levels are controlled by river stage (flows), precipitation, and evapotranspiration (Wescheet al.1994, p, iii). Platte River flows are principally tied to snowmelt from the Rocky Mountains and local precipitation events (Simons and Associates 2000, pp. 2-5), while Loup River and Elkhorn River flows are tied to the Ogallala Aquifer (Petersonet al.2008, p. 5). Sloughs that support the caddisfly vary in their distance to the main river channel. Most sloughs are adjacent to the main channel, while some occur in areas more than 0.4 kilometers (km) (0.25 miles (mi)) away.

Sloughs with the Platte River caddisfly are typically described as lentic (with little to no flow) (Whileset al.1999, p. 533; Alexander and Whiles 2000, p. 2). However, two sites do contain some flow, and the caddisfly appears to occur in higher densities in areas with flowing water than in stagnant areas (Harner 2012, pers. comm.). Because of their groundwater connection, sloughs with the caddisfly may maintain thick ice cover on surface waters through the winter without completely freezing to the bottom (Whileset al.1999, p. 534; Goldowitz 2004, p. 2). Slough substrata often consist of a thick layer of detritus and silt overlying sand (Whileset al.1999, p. 534; Alexander and Whiles 2000, p. 6). Soils in the sloughs consist of a mixture of loam, sand, and gravelly sand and tend to be frequently flooded and poorly drained (Natural Resources Conservation Service (NRCS) Web Soil Survey 2009, entire).

Because it is an inhabitant of intermittent waters, the Platte River caddisfly is tolerant of large fluctuations in water chemistry (Williams 1996, p. 634; Whileset al.1999, p. 534). Large variations in water quality (e.g., pH, conductivity, total dissolved solids, dissolved oxygen, turbidity, and temperature) have been observed among five forested sites where the caddisfly occurs (Vivian 2010, pp. 81, 96). Furthermore, average conductivity and pH in sloughs with the caddisfly reported by Vivian (2010, pp. 81, 96) differed from the average values reported by Whileset al.(1999, p. 534) and Gelusoet al.(2011, p. 1022). The gradient of water chemistry observed between forested sloughs and the type locality is likely a result of the differences in habitat types, and demonstrates that the Platte River caddisfly can withstand a broad range of water quality.

Vegetation in sloughs occupied by the caddisfly is typical wetland flora, such asTyphaspp. (cattails),Schoenoplectus fluviatilis(river bulrush),Eleocharisspp. andCyperusspp. (sedges), andLemnaspp. (duckweed); some sloughs support nonnative, invasive vegetation, includingPhalaris arundinacea(reed canarygrass),Phragmites(common reed), andLythrum salicaria(purple loosestrife). Plant species along slough banks and margins include woody species, such asFraxinus pennsylvanica(green ash) andPopulus deltoides(cottonwood), and grass species, such asSpartina pectinata(prairie cordgrass)and smooth brome (Bromus inermis,invasive). Various forbs are also present throughout the slough. Most areas where the Platte River caddisfly has been observed since it was described have an abundance of woody vegetation, which contrasts with the treeless, wet meadow environment encountered at the type locality and one other population at the Crane Trust (Whileset al.1999, p. 534; Vivian 2010, p. 56; Vivian 2011, pp. 33-35). Overall, the Platte River caddisfly is tolerant of a range of conditions, including variations in hydroperiod, water quality, and vegetation, but thrives in intermittent sloughs.

Life History and Ecology

The Platte River caddisfly lifecycle was characterized by Whileset al.(1999, entire). The caddisfly is univoltine (one generation per year). The adult flight period for the Platte River caddisfly is between late September and mid-October. Adults first emerge around late-September and live for about 7 to 10 days, with the entire emergence period lasting 3 to 4 weeks. While active, adults oviposit (lay eggs) on the surface film of the water, the eggs sink to the bottom of the slough, and larvae hatch as first instars (life stage between molts) sometime in November. Aquatic larvae overwinter in the slough as first instars. In late winter, larvae construct their case (Vivian 2010, pers. obs.) and begin feeding and growing rapidly and proceed through four more instars. Between late April and early June, fifth (final) instars climb upslope from the water and aestivate (pass stressful time periods in a dormant condition) during the summer months when it is typically dry along the adjacent slough banks (Whileset al.1999, pp. 535-536; Gelusoet al.2011, p. 1023). Platte River caddisfly larvae eventually pupate (metamorphose between larva and adult) along slough margins in the larval case. Pupation lasts about 4 weeks until adult emergence in late September.

While in its aquatic stage, the Platte River caddisfly is considered a shredder and largely feeds upon senescent (aged) plant tissue (Whileset al.1999, pp. 542-543). As one of the few shredders present in sloughs, the Platte River caddisfly plays an important role in the decomposition of organic matter in these systems (Whileset al.1999, pp. 539, 543). In its terrestrial stage, the Platte River caddisfly does not feed (Whileset al.1999, p. 537), and as an adult, the species has the ability to ingest liquids (Holzenthalet al.2007, p. 648).

The Platte River caddisfly likely has a lifecycle adapted to the intermittent wetlands found along the Platte, Loup, and Elkhorn River systems (Whileset al.1999, p. 537; Vivian 2010, pers. obs.). For example, larval emigration to adjacent mesic grassland habitat and adult emergence were found to coincide with early summer drying and fall inundation of the wetlands, respectively (Whileset al.1999, pp. 537, 542). The Platte River caddisfly is dependent upon water for the egg and larval stages of its lifecycle, (e.g., for at least 7 to 8 months out of the year) (Whileset al.1999, pp. 537-539).

While most caddisflies have an entirely aquatic larval phase, allIronoquiaspecies are known to aestivate in leaf litter near the receding water line during the summer months prior to pupating (Flint 1958, p. 61; Williams and Williams 1975, p. 830; Wiggins 1977, p. 248; Johansson and Nilsson 1994, p. 21; Whileset al.1999, p. 534). However, some aestivating Platte River caddisfly larvae have been found to burrow beneath the ground surface (Gelusoet al.2011, p. 1024). This behavior may be a way to withstand summer drying of sloughs or to avoid desiccation, as reported for other caddisflies (Mackay and Wiggins 1979, p. 187; Wigginset al.1980, p. 179; Johannson and Nilsson 1994, p. 21; Gelusoet al.2011, p. 1024), as soil temperatures in unshaded areas can reach 54 degrees Celsius (°C) (129 degrees Fahrenheit (°F)) in the summer (Vivian 2010, pers. obs.). This behavior could protect aestivating larvae against late spring (May-June) flows, which are characteristic of the Platte River system and could scour (wash) larvae downstream (Simon and Associates 2000, p. 8) and other disturbances characteristic of the Great Plains ecosystem, such as livestock grazing (Gelusoet al.2011, p. 1024).

Historical Range and Distribution

Data collection on the range of the Platte River caddisfly began in 1999, shortly after it was discovered, and continued in 2004 (Goldowitz 2004, p. 3). Surveys were conducted at 48 locations along the Platte and Loup Rivers, and the Platte River caddisfly was found at 9 of these sites (Goldowitz 2004, p. 5). These populations occupied an approximately 100-km (60-mi) stretch of the central Platte River that extends from south of Gibbon, Nebraska (Kearney County), to Central City, Nebraska (Merrick County). Surveys for the caddisfly on the Loup River were negative (Goldowitz 2004, p. 9). Monitoring efforts in 2004 did not find the caddisfly at the type locality, despite a consistent adult emergence pattern in the preceding 7 years and the species' prior abundance at that site (Goldowitz 2004, p. 8). Because of its apparent rarity, the caddisfly was designated a Tier 1 species in Nebraska as per the State's natural legacy plan (Schneideret al.2005, p. 93). Tier 1 species are those that are at risk of extinction on a global scale or at risk of becoming extirpated from Nebraska (Schneideret al.2005, p. 17).

Current Range and Distribution

Through 2004, the Platte River caddisfly was only known from the Platte River (Goldowitz 2004, p. 9). However, surveys for new Platte River caddisfly populations resulted in the discovery of the species on the Loup and Elkhorn Rivers in Nebraska in 2009 and 2010 (Vivian 2010, p. 50). Close visual examination of adults and larvae at sites on the Loup and Elkhorn Rivers demonstrated that the species was notI. parvulaand confirmed the presence of the Platte River caddisfly on these systems. However, because of the distance between some caddisfly populations on the Platte, Loup, and Elkhorn Rivers, we determined there was a need to identify potential genetic differences for the species among sites. Genetic analyses indicated that there is a low amount of gene flow among all three rivers, and that a population tested on the Elkhorn River was genetically divergent, but not different, from the populations on the Platte and Loup Rivers (Cavallaroet al.2011, p. 7). This genetic divergence appears to be a product of geographic isolation as opposed to habitat fragmentation.

The Platte River is formed at the confluence of the North Platte and South Platte Rivers in west-central Nebraska, just east of North Platte, and generally flows east until it meets the Missouri River along the eastern edge of Nebraska (Williams 1978, pp. 1-2). The North Platte River originates in the Rocky Mountains of Colorado, flows north through central Wyoming and then southeast into Nebraska (Williams 1978, p. 1); the South Platte River originates in Colorado and flows northeast until it meets the Platte River at North Platte, Nebraska (Simons and Associates 2000, p. 2). Platte River flows are largely dependent upon snowmelt from the Rocky Mountains and local precipitation events (Simons and Associates 2000, pp. 2-5).

The Loup and Elkhorn Rivers are tributaries of the Platte River system. The Loup River contains several tributaries, including the North Loup, Middle Loup, South Loup, and Cedar Rivers in Nebraska. The Loup River isformed at the confluence of the Middle Loup and North Loup Rivers near St. Paul, Nebraska, and flows east until it meets the Platte River at Columbus, Nebraska, in the eastern third of the State. The Loup River drains groundwater from the Sandhills and the underlying Ogallala Aquifer, and its tributaries flow northwest to southeast, while the Loup flows east or northeast until it meets the Platte River (Petersonet al.2008, pp. 2-5). The Elkhorn River drains wet meadows and plains in north-central Nebraska, and flows east-southeast until it meets the Platte River near Omaha, Nebraska (Petersonet al.2008, pp. 2-5).

In Nebraska, there is a gradient of precipitation from west to east. Just east of the Rocky Mountains in central Nebraska there is a predominant rain shadow effect that results in low amounts of precipitation in western Nebraska. Precipitation generally increases as one travels east towards Nebraska's eastern border (Simon and Associates 2000, p. 2).

Surveys for the Platte River caddisfly between 2009 and 2011 identified 35 caddisfly populations out of 115 sites visited, including 5 of the 9 sites identified by Goldowitz (2004, entire) (Vivian 2010, p. 46; Gelusoet al.2011, entire; Figure 1 below). With these recent survey efforts, the caddisfly is now known from a 390-km (240-mi) stretch of the Platte River that runs from near Sutherland, Nebraska (Lincoln County), to near Schuyler, Nebraska (Platte County), and from the Loup and Elkhorn River systems (Figure 1 below). Within this range, there is approximately a 155-km (93-mi) gap in the distribution of the caddisfly between Hershey, Nebraska, and Elm Creek, Nebraska (Vivian 2010, p. 51). Twenty-four surveys for the caddisfly were conducted in this gap, and the caddisfly was not found (Vivian 2010, p. 50).

EP30AU12.062

From recent survey efforts, one site near Shelton, Nebraska, is presumed extirpated (Riens and Hoback 2008, p. 1; Vivian 2010, p. 48). Also, the Platte River caddisfly was observed at the type locality in 2010 (Gelusoet al.2011, p. 1023), after not having been observed there during surveys in 2004 and 2007-2009 (Goldowitz 2004, p. 8; Riens and Hoback 2008, p. 1; Vivian 2010, p. 53). Survey work in 2009-2011 also identified 13 sites along the Platte, Loup, Elkhorn, and Cedar Rivers that contained discarded larval cases but no live individuals (Vivian 2010, p. 46). Finding a site with a caddisfly case in a slough along the Cedar River indicates that the Platte River caddisfly is likely present in the basin. However, observing live individuals at a site is needed to confirm its presence there, because it is thought that discarded larval cases degrade slowly and could represent generations from previous years (Vivian 2010, pp. 49, 55-56).

Aside from the Cedar River, it appears that more surveys for the Platte River caddisfly could result in the discovery of additional populations on other river drainages in Nebraska, including the Niobrara and Republican Rivers. More survey work on the Platte, Loup, and Elkhorn drainages would likely result in the discovery of new populations on these systems as well. Between 2009and 2011, satellite imagery was used to identify potential caddisfly habitat throughout Nebraska prior to conducting surveys (Vivian 2010, p. 38). There are additional areas of remaining potential Platte River caddisfly habitat along Nebraska's major river systems that have yet to be surveyed (Vivian 2011, pers. obs.). Thus, ongoing surveys are likely to expand the known range of the Platte River caddisfly.

Population Densities

At the type locality, the Platte River caddisfly was considered an abundant component of the slough ecosystem. In 1997-1998, an average of 805 ± 194 larvae per square meter (m2) was observed throughout the aquatic life stage of the caddisfly lifecycle, and 410.67 larvae per m2were present in the aquatic environment in May 1998 (Whileset al.1999, pp. 537, 540). Gelusoet al.(2011, p. 1022) reported a mean density of 553 ± 284 Platte River caddisfly larvae per m2(n = 19) from a site at the Crane Trust on Shoemaker Island (hereafter “Wild Rose Slough”), which is located about 5 km (3.2 mi) upstream of the type locality. With the exception of these two sites, the Platte River caddisfly has been found to occur in lower densities (Whileset al.1999, pp. 539-540).

In May of 2009 and 2010, aquatic larval densities were measured at 18 sites with a Platte River caddisfly population on the Platte River only, and larval densities ranged from zero to 125.7 individuals per m2(Vivian 2010, p. 64). Aestivating (terrestrial life stage) larval densities at 12 of 13 sites sampled ranged from zero to 116 individuals per m2(Vivian 2010, p. 65). Day and nighttime sampling found anywhere between zero and eight adults per hour of observation (Vivian 2010, pp. 65-66).

The aquatic and terrestrial larval densities reported by Vivian (2010, pp. 40-41) are not directly comparable to Whileset al.(1999, p. 535), because different methodologies were used, and a different volume of sediment was sampled during the aquatic sampling period (Meyeret al.2011, p. 110). Meanwhile, Gelusoet al.(2011, p. 1022) used the same aquatic sampling method as Vivian (2010, pp. 40-41) but sampled slightly earlier in 2010. Nonetheless, the methods used during 2009-2010 sampling were internally consistent, and these results demonstrate that the caddisfly occurs in varying densities across its range (Vivian 2010, pp. 40-41; Harner 2012, pers. comm.). Although some densities reported by Vivian (2010) are low compared to what has been reported for other caddisfly species (Mayer and Likens 1987, p. 266; Roeding and Smock 1989, p. 152; Bunn and Hughes 1997, pp. 343-344; Stewart and Downing 2008, p. 145), observations on the numbers and density variations of Platte River caddisfly larvae and adults are consistent with those reported for otherIronoquiaspecies (Flint 1958, p. 60; Swegmanet al.1981, p. 131; MacLean and MacLean 1984, p. 56; Garono and MacLean 1988, p. 147; Gray and Johnson 1988, p. 180; Ćuk and Vučković 2010, pp. 233-234). Therefore, the Platte River caddisfly andIronoquiaspp., in general, are more abundant in some areas than in others.

Although population densities have been reported for over half of all known Platte River caddisfly populations, there is a lack of general information on population trends for this species, with the exception of a few sites, including the type locality, Wild Rose Slough, one site near Shelton, Nebraska, and one site near Chapman, Nebraska, where restoration work conducted by the Service in 2007 resulted in a population decline at that site. Sites with lower population densities may always remain naturally low. Therefore, with the information available and the increase in the number of known populations, it is difficult to discern if the number of Platte River caddisfly individuals and populations is remaining steady, increasing, or decreasing.

Summary of Information Pertaining to the Five Factors

Section 4 of the Act (16 U.S.C. section 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 an endangered or threatened species 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 this finding, information pertaining to the Platte River caddisfly in relation to the five factors provided in section 4(a)(1) of the Act is discussed below. In considering what factors might constitute threats to a species, we must look beyond the exposure of the species to a particular factor to evaluate whether the species may respond to that 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 in 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 these factors are operative threats that act on the species to the point that the species may meet the definition of an endangered or threatened species under the Act.

Factor A. The Present or Threatened Destruction, Modification, or Curtailment of the Species' Habitat or Range Landscape-Level Changes in Hydrology

Reductions in groundwater levels or river flows as a result of water development can adversely impact aquatic habitats and their associated macroinvertebrate communities. Existing and future water development along the Platte, Loup, and Elkhorn Rivers could adversely impact the Platte River caddisfly and its habitat. Adverse impacts could occur through the loss of water during critical life stages or changes in hydrology that result in intermittent wetlands becoming too ephemeral to support the Platte River caddisfly. We examine this topic in detail below.

Hydroperiod can be an important factor in determining the composition of macroinvertebrate communities in wetlands. For instance, Whiles and Goldowitz (2005, p. 466) found that slough hydroperiod influenced macroinvertebrate taxa diversity and abundance, with more taxa present in intermittent sloughs than in sloughs with more ephemeral or permanent hydroperiods. Sloughs with intermittent hydroperiods typically have fewer predators than permanent wetlands and can offer safe refugia for various taxa if they can withstand habitat drying (Williams 1996, p. 634; Wissingeret al.1999, p. 2103; Tarr and Babbitt 2007, p. 3). Sites with more permanent hydroperiods likely offer a more suitable environment for potential predators of the caddisfly, such as fish and amphibians, thereby reducing larval densities (Whiles and Goldowitz 2001,p. 1836; Whiles and Goldowitz 2005, pp. 468, 470). Certain permanent sloughs with the Platte River caddisfly also appear to be more food-limited than others as these areas have less standing vegetation (Vivian 2011, p. 18). The amount of available food can limit the abundance of shredder species (Roeding and Smock 1989, p. 149), such as the Platte River caddisfly (Vivian 2011, p. 18).

The type locality from which the Platte River caddisfly was described had an intermittent hydroperiod (Whileset al.1999, p. 536). The Platte River caddisfly was not found at four other sloughs near the type locality during the time of the life history study; these sloughs had hydroperiods that differed from that of the type locality—they were thought to be either too ephemeral or permanent for the caddisfly (Whileset al.1999, p. 542; Whiles and Goldowitz 2001, p. 1832; Whiles and Goldowitz 2005, p. 466). Also, the Wild Rose Slough site contains ephemeral, intermittent, and permanent reaches, and the Platte River caddisfly has only been observed in the intermittent (Vivian 2010, pers. obs.) and permanent reaches of the slough (Gelusoet al.2011, p. 1022). In other parts of its range, the Platte River caddisfly has been found in sloughs with more permanent hydroperiods, albeit in lower numbers than in sloughs with intermittent hydroperiods (Vivian 2010, p. 54; Gelusoet al.2011, p. 1022).

The caddisfly occurs in higher densities in intermittent sloughs than in sloughs with permanent hydroperiods. For instance, the type locality and Wild Rose Slough have intermittent hydroperiods (Vivian 2010, pers. obs.) and have supported or currently support the largest known larval densities of the Platte River caddisfly (Whileset al.1999, p. 536; Vivian 2010, pers. obs.; Gelusoet al.2011, p. 1022). Relatively low densities of the caddisfly have been found at other sites that have longer hydroperiods and experience less water level fluctuation (Vivian 2010, p. 54). Thus, it is thought that sloughs with intermittent hydroperiods are ideal for the Platte River caddisfly. Although intermittent wetlands represent ideal Platte River caddisfly habitat, permanent wetlands may become important during and following a drought as sites that support source populations for recolonization following extended dry periods. However, ephemeral wetlands do not remain wet long enough to support the species' lifecycle.

Overall, landscape-level changes in hydrology that result from reservoir construction, river channel diversions, and groundwater withdrawal for irrigation could adversely impact the Platte River caddisfly and its habitat through the loss of water during critical life stages or degradation of its habitat. Since European settlement in the 1850s, the Platte, Loup, and Elkhorn Rivers have all experienced some degree of water development for various purposes; the Platte River has experienced the largest amount of modification of these systems. Starting in the mid-1800s, the tributaries of the Platte River were gradually developed to deliver water for irrigation via main and lateral canals, and eventually larger water storage projects along the main channels of the river were constructed (Eschneret al.1981, pp. 3, 5). Water development projects were implemented to make the region more suitable for agriculture, and more than 7,000 canals were constructed along the river between 1851 and 1930 (Simons and Associates 2000, pp. 5-9). Over-appropriation of water in the Platte Basin became an issue as early as 1876, and dams were constructed to create more reliable supplies of water (Eschneret al.1981, p. 10; Simons and Associates 2000, pp. 7-8).

Several hundred storage reservoirs and six principal dams are present in the Platte River Basin, and together they impound more than 7.6 million acre-feet of water for irrigation (Simons and Associates 2000, p. 8). Each reservoir project contains several miles of associated canals (Simons and Associates 2000, p. 13). Because of dams and diversions along the Platte Basin, over 70 percent of the Platte River flow is estimated to be diverted before it reaches Lexington, Nebraska (Currieret al.1985, p. 120; Sidleet al.1989, p. 91), which is about 48 km (30 mi) upstream of where most Platte River caddisfly populations along the Platte River are found. As a result of this development, the river has been described as one of the most heavily managed river systems in the United States (Simons and Associates 2000, p. 14; LaGrange 2004, 274 15).

The Loup River has also been impacted by water development projects. The Loup Basin includes the North, Middle, and South Loup Rivers, and within the basin there are four mainstem diversion dams (U.S. Bureau of Reclamation (USBR) 2011, entire). The largest diversion dam, the Loup Diversion Dam, diverts around 69 percent of the Loup River flow away from the main channel for a distance of 35 miles in Nance and Platte Counties in Nebraska (Loup Power District and HDR Engineering 2008, p. 4-39). Each diversion dam has several miles of associated lateral canals to divert water to irrigated farmland (USBR 2011, entire). Also, three impoundments are present along tributaries of the Loup River Basin (Loup Power District and HDR Engineering 2008, pp. 3-5), but the system lacks mainstem dams. The Elkhorn River is generally free of impoundments and diversions (LaGrange 2004, p. 21; Petersonet al.2008, p. 5).

Habitat Loss Resulting From Changes in Hydrology

Dams and diversion projects are known to result in changes in hydrological, geophysical, and ecological characteristics of river systems (Simons and Associates 2000, p. 15; Schrammet al.2008, pp. 237-238). Dams and diversions dampen the natural flow regime and change the hydrology of river systems, contribute to the downcutting and degradation of the river bed, reduce the amount of sediment flowing downstream, and reduce the amount of water reaching floodplain wetlands (Kingsford 2000, p. 109; Bowenet al.2003, p. 809). These changes affect the ability of managed river systems to remain in a state of dynamic equilibrium, which contributes to the creation and maintenance of a diversity of habitats along a river's floodplain (Bowenet al.2003, p. 809). Water development projects may ultimately cause a river to become disconnected from its floodplain (Bowenet al.2003, p. 809) and reduce the ability of rivers to continually inundate and create new backwater habitats via peak flows (Schrammet al.2008, pp. 237-238).

Channel Narrowing

As a result of reduced flow through the Platte River system, the main channel of the Platte River narrowed by about 65 to 80 percent between the mid-19th century and 1969 (Williams 1978, p. 8; Eschneret al.1981, p. 45) and further narrowed by up to 25 percent between 1970 and 1999 (Murphyet al.2004, p. 102). Channel narrowing has resulted in a reduction in wetland habitat along the Platte River through a drying of adjacent sloughs. Between 1938 and 1982, an estimated 45.2 percent of wet meadow habitat along the central Platte River was lost (Sidleet al.1989, pp. 98-99), and this corresponded to a 53.4 percent reduction in active channel width during the same time period (Peakeet al.1985, entire; Sidleet al.1989, pp. 98-99). The drying of linear slough depressions along the river also facilitated the development of row crops along what used to be wet bottomlands (Currieret al.1985, p. 113).Many wetlands were initially converted to cropland through wetland draining via ditches and land leveling (Currieret al.1985, p. 113). Wetland losses and channel shrinkage data for the Loup River are currently unavailable; however, wetland losses have likely occurred concurrent with the narrowing of the river channel downstream of diversion projects.

Historically, channel narrowing on the Platte and Loup River systems resulting from water development likely resulted in direct losses of suitable Platte River caddisfly habitat prior to the species' discovery in the late-1990s. During recent survey efforts, the Platte River caddisfly was not found between Hershey and Elm Creek, Nebraska, despite 24 surveys being conducted in this reach (Vivian 2010, p. 50). We do not know if the caddisfly ever occurred in this stretch of river, but it is present upstream and downstream of Hershey and Elm Creek, Nebraska, respectively (Vivian 2010, p. 50), and this stretch is likely one of the most dewatered and incised (disconnect of a river from its floodplain as a result of a decline in river bed elevation) portions of the Platte River (Murphyet al.2004, p. 56). Since the species was first described in 2000, no known population losses have occurred as a result of channel narrowing and subsequent wetland drying.

Aside from the draining of adjacent wetlands, channel narrowing has resulted in an increase in woody vegetation cover along the Platte River (Johnson 1994, entire). Downstream of Kearney, Nebraska, channel narrowing continues to reduce the amount of active channel area, and the amount of forest cover continues to increase (Murphyet al.2004, p. 95), despite no new impoundments having been constructed in the Platte basin since 1956 (Johnson 1994, pp. 77-78). The establishment and proliferation of woody vegetation along the river acts to stabilize the river and can further contribute to channel narrowing through the trapping of sediments (Friedmanet al.1996, p. 341). Meanwhile, an increase in forest cover is not thought to have an adverse impact on the Platte River caddisfly, because most known caddisfly populations are found in forested wetlands, and some forested sloughs support relatively high larval densities of the Platte River caddisfly (Vivian 2010, p. 64). It is unlikely that any future increases in forest cover will adversely affect the Platte River caddisfly.

Channel Degradation

Aside from channel narrowing, impoundments and diversions can contribute to the downstream degradation of river systems, and these projects can have lasting impacts. Impacts to the Platte River resulting from past water development projects, which may affect the caddisfly, are ongoing. For instance, reduced sediment loads resulting from impoundments that block the passage of sediments and water discharges below diversion returns and dams are known to impact river systems and result in channel bed degradation. The North Platte River historically provided the majority of the sandy sediment to the Platte River system, but the amount of sediment inputs to the river greatly declined with the closing of the mainstem dams on the North Platte River (Murphyet al.2004, p. 101). Near Overton, Nebraska, the Johnson-2 (J-2) diversion return releases sediment-free water into the Platte River and creates localized scour and an additional sediment imbalance.

As a result of impoundments and diversion returns, less sediment flows into the Platte River than flows out, and this contributes to the erosion and a lowering of elevation of the river bed (Murphyet al.2004, p. 101). Erosion may also result from a coarsening of sediments in the river, which is a result of coarser sediment being supplied from the South Platte River as opposed to the fine sands that used to come from the North Platte River (Murphyet al.2004, p. 115). Erosion results from a change in sediment size, because smaller sediment is transported downstream more quickly than coarser sediments (Murphyet al.2004, p. 119). This downcutting (or incision) further narrows the active channel and acts to drain adjacent floodplain wetlands (Murphyet al.2004, p. 129). Channel incision resulting from the sediment imbalance along the Platte River is thought to be largely complete upstream of Kearney, Nebraska, but has only slightly affected the river between Kearney and Grand Island, Nebraska, indicating that the trend of degradation is moving downstream (Murphyet al.2004, pp. 113, 129). Channel incision and degradation resulting from the sediment imbalance in the Platte River and a coarsening of sediments is anticipated to take decades to be fully complete (Murphyet al.2004, pp. 128-130).

The effects of channel degradation and its impacts on the Platte River caddisfly and its habitat can be observed downstream of the J-2 return. Diversion returns, like the J-2 return, that put clear water directly into the main channel of the Platte River, can contribute to the downcutting of the river bed and subsequent draining of adjacent floodplain wetlands. For instance, in 2010, surveys for the Platte River caddisfly were conducted downstream of the J-2 return near Overton, Nebraska, at Dogwood Wildlife Management Area (WMA). Within the WMA, several linear depressions were observed, and these areas were dry but showed signs of past beaver (Castor canadensis) activity, indicating that the area had once supported slough habitat (Vivian 2010, p. 51). Given that the depressions were dry, habitat for the caddisfly was absent (and so was the species) and, therefore, it seems that the downcutting of the Platte River near Overton, Nebraska, has contributed to the loss of potentially suitable caddisfly habitat at Dogwood WMA.

The effects of the J-2 return can be observed up to 29 km (18 mi) downstream of the return, although these effects are most pronounced closest to the return (Murphyet al.2004, p. 142). Between 1989 and 2002, the Platte River bed depth eroded 1.8 meters (6 feet) immediately downstream of the J-2 return, and eroded 0.76-meter (2.5 feet) 29 km (18 mi) downstream from the return during the same time period (Murphyet al.2004, p. 106). At Grand Island, Nebraska, the river bed eroded 0.27-meter (0.89-foot) between 1933 and 1995 (Murphyet al.2004, p. 113). It is anticipated that the process of incision as a result of the J-2 return will continue downstream all the way to Grand Island, but it is expected to progress slowly (Murphyet al.2004, pp. 113-114). For instance, the river could incise by 0.60-meter (2 feet) from 1940 bed elevation levels within 100 years, 48 km (30 mi) downstream of the return. However, these same impacts are expected to take 400 years to affect the area 100 km (60 mi) downstream of the return (Murphyet al.2004, p. 114), an area where seven of the 35 known Platte River caddisfly populations occur. This incision could further narrow the central Platte River and contribute to the draining of adjacent wetlands and sloughs occupied by the Platte River caddisfly.

It is likely that channel incision has contributed to a loss in available Platte River caddisfly slough habitat in the past and could adversely affect the remaining sloughs on the central Platte River (Lexington, Nebraska to Chapman, Nebraska, where several populations of the Platte River caddisfly occur) in the future. The impacts of channel degradation on Platte River caddisfly habitat are best demonstrated by the effects observed at Dogwood WMA andat the Crane Trust on Shoemaker and Mormon Islands. Harner and Whited (2011, pp. 17-18; Harner 2012, pers. comm.) demonstrated that although there was two times more river discharge in the Platte River in 1999 than in 1951, less slough habitat was available at the Crane Trust in 1999 than was present in 1951. Between 1951 and 1999, the amount of available slough habitat declined by 0.3-hectare (0.8-acre) at Wild Rose Slough (which is deeper and more entrenched, resulting in less surface area lost) on Shoemaker Island and 3.6 hectares (8.8 acres), or about 28 percent, at the type locality on Mormon Island (Harner and Whited 2011, pp. 17-18). Declines in the amount of slough habitat were attributed to channel incision of the Platte River, or a drop in the groundwater table, or both, as land leveling has not occurred along the stretch of the river owned by the Crane Trust. These results demonstrate that even though river discharge in 1999 was greater than in 1951, more water in the Platte River does not necessarily mean that the floodplain will be inundated enough by elevated groundwater to support sloughs where the Platte River caddisfly occurs (Harner and Whited 2011, p. 23).

Currently, the Crane Trust area supports the highest known densities of the Platte River caddisfly (Whileset al.1999, p. 537; Vivian 2010, p. 47; Gelusoet al.2011, p. 1022) and is one of the largest remaining stretches of intact prairie in the Central Platte Valley. However, although the Crane Trust protects the parcel where the caddisfly occurs, this area is not buffered from the effects of upstream water development and nearby groundwater pumping (Harner and Whited 2011, pp. 23-24; Harner 2011, pers. comm.). The documented decline in the amount of available slough habitat between 1951 and 1999 (Harner and Whited 2011, entire) illustrates that effects of past and current degradation to the river channel are ongoing even though there have been no major water projects implemented on the Platte River since 1956 (Johnson 1994, p. 78). If left unchecked (Murphyet al.2004, p. 114), future channel degradation could eventually result in as much as a total loss of Platte River caddisfly habitat at the Crane Trust and other nearby sloughs. For instance, Harner and Whited (2011, p. 14) demonstrated that groundwater declines greater than 0.5-meter (1.5-2.0 feet) from 1999 levels could result in slough drying at the type locality in years with similar precipitation and river discharge (Harner and Whited 2011, p. 20).

Although Harner and Whited (2011) demonstrated an ongoing trend in channel degradation within the central Platte River near the Crane Trust at Alda, Nebraska, the Platte River caddisfly is still present at the type locality and Wild Rose Slough more than 10 years following 1999 (year of reference used in the study). There are also extant Platte River caddisfly populations upstream of the Crane Trust, where the effects of channel degradation are more pronounced, such as near Elm Creek, Nebraska, where the channel bed incised by 0.76-meter (2.5 feet) between 1989 and 2002 (Murphyet al.2004, p. 106). Meanwhile, the type locality and Wild Rose Slough occur more off channel than the forested sloughs adjacent to the river channel and may be less buffered from the effects of channel incision, because hydroperiod is known to decrease with increasing distance from the river channel (Whileset al.1999, p. 533). Therefore, habitat loss at the Crane Trust likely does not represent the norm throughout the range of the Platte River caddisfly.

If left unchecked, future channel degradation could result in future losses in slough habitat and subsequent extirpation of the Platte River caddisfly from the central Platte River. However, various programs and entities are acting to maintain current habitat conditions on the central Platte River. The central Platte River is actively managed by several organizations to benefit endangered (E) and threatened (T) species (whooping crane (Grus americana) (E), interior least tern (Sterna antillarum athalassos) (E),piping plover (Charadrius melodus) (T), and pallid sturgeon (Scaphirhynchus albus) (E)) that depend on an open and braided river system. One such organization is the Headwaters Corporation, which is the nongovernmental organization responsible for overseeing the Platte River Recovery Implementation Program (PRRIP) (discussed more below and under Factor D).

PRRIP was established in 2006, by an agreement between the Bureau of Reclamation, the Service, and the States of Colorado, Wyoming, and Nebraska to manage Platte River flows and habitat to meet the needs of endangered and threatened species that use the Platte River. For instance, PRRIP plans to clear and lower vegetated islands in the river to create a more open channel to benefit endangered species, and this action would increase the amount of sediment in the river (Murphyet al.2004, p. 143; U.S. Department of the Interior (DOI) 2006, p. 5-60). PRRIP also seeks to offset the sediment imbalance in the river by adding sand to the central Platte River (DOI 2006, p. 5-55) and release pulse flows to maintain present channel conditions (DOI 2006, p. 3-11). Outside PRRIP, some work of removing riparian vegetation has already been executed by organizations such as the Nebraska Public Power District (Kinzelet al.2006, entire). Other entities, such as the Partners for Fish and Wildlife Program (PFW), are actively restoring sloughs along the central Platte River to benefit wildlife, and these areas could eventually provide suitable habitat for the Platte River caddisfly. Ongoing efforts to maintain and improve current conditions along the central Platte River should help stem the ongoing degradation of the river and reduce the amount of potential losses of slough habitat throughout the Platte River portion of the species' range.

As mentioned previously, water development on the Loup and Elkhorn Rivers has not been as extensive as it has along the Platte River. While there are diversions in place along the Loup River, these diversions have not resulted in extensive channel incision and degradation as has been observed along the Platte River. This can be demonstrated by the lack of vegetation encroachment onto the active river bed. Channel narrowing downstream of diversion projects on the Loup River Basin has likely resulted in a loss of slough habitat in the past. However, the Platte River caddisfly is present immediately upstream of Kent Diversion Dam, and the species is present immediately downstream of the Loup Diversion Dam. The populations in the vicinity of these projects appear secure, because there appears to be ample slough habitat to support the caddisfly at these sites (Vivian 2010, pers. obs.). Potentially suitable habitat that has not been surveyed is also present downstream of all four main diversion projects in the Loup River Basin (Vivian 2012, pers. obs.). Meanwhile, no large-scale projects on the Loup or Elkhorn Rivers are planned. Because of ongoing efforts to maintain present channel conditions in the central Platte River, which is the most degraded portion of the range of the Platte River caddisfly, and because of a general lack of channel degradation on the Loup and Elkhorn Rivers, we conclude that channel degradation does not pose a threat to the Platte River caddisfly.

Altered Hydrograph

An altered hydrograph (graph of stream flow through time) can resultfrom dams and diversion projects. For instance, dams impound water and reduce the amount of water flowing through a river system. Diversion projects can result in a changed hydrograph by altering the timing of flows through a river system and can reduce the amount of water flowing downstream. Historically, the Platte River received a late-spring rise as a result of runoff from Rocky Mountain snowmelt, and water levels then receded through the summer months, with the river nearly drying completely in some years (Eschneret al.1981, pp. 19-20; Simons and Associates 2000, p. 8). Because of water development projects, primarily dams, the historical hydrologic regime of the Platte River has been altered. For instance, at North Platte, Nebraska, peak flows declined from 20,000 cubic feet per second (cfs) in the late 1800s to less than 5,000 cfs after 1940 (Simons and Associates 2000, p. 16). Dams are also known to augment base flows in a river system, meaning that some floodplain wetlands never go dry (Kingsford 2000, p. 111). Following water development on the Platte River, periods of no or little flow have decreased (Simons and Associates 2000, p. 44). A reduction in natural periods of low flow could impact the intermittency of sloughs where the Platte River caddisfly occurs by increasing the permanency of water in certain areas. Despite the potential for sloughs along the Platte and Loup Rivers to be more permanent, the Platte River caddisfly has presumably existed with the presence of dams on the landscape for over 100 years. The species also occurs in permanent sloughs, and these areas could become important source populations for other intermittent wetlands following extended dry periods or drought. Wetlands that were historically intermittent may have become ephemeral wetlands unsuitable for the caddisfly concurrent with water development. However, we have no information to indicate that this has occurred since the species was described in 2000.

At this time, there is no available information to indicate that an altered hydrograph is adversely affecting any populations of the Platte River caddisfly or has resulted in population losses throughout its range. Therefore, we do not consider a changed hydrograph to pose a threat to the Platte River caddisfly.

Invasive Species

Along the Platte River, changes in hydrology have contributed significantly to the encroachment of woody and exotic vegetation onto what used to be the active river bed (Currieret al.1985, p. 119; Johnson 1994, p. 47). In 2002, several areas of the Platte River went completely dry for 2 months because of drought, and in 2003, low to zero flows were recorded for extended periods of time within the Big Bend reach of the Platte (80-mile stretch of the Platte River between Overton and Chapman, Nebraska) (Service 2006, p. 113). During this time, dense invasive vegetation grew within the Platte River channel as a result of lower flows.Phragmites australis(common reed orPhragmites) andPhalaris arundinacea(reed canarygrass), two non-native, invasive species, have proliferated on previously barren sandbars and in wetlands along the Platte River in the last decade. Historically, encroaching vegetation would have been washed away by ice scour, or high spring flows (now dampened by water development), or both (Service 2006 p. 163), but active removal is now required to keep invasive species in check. Invasive species have not proliferated on the Loup and Elkhorn Rivers as much as on the Platte. OnlyP. arundinaceahas been observed in sloughs along the Loup River and in lower abundances than in sloughs along the Platte River.

In the United States, there are introduced and native varieties ofPhragmites australis,and the introduced and hybridized forms have become highly invasive in several States, including Nebraska (NRCS 2002, entire; Blossey 2003, entire).P. australiscan be up to 15 feet tall and quickly crowds out native wetland species once established (Michigan Department of Environmental Quality 2011, entire). There are also native and introduced ecotypes ofPhalaris arundinacea,and the species can be aggressive and invade wetlands.P. arundinaceahas been observed to form dense, monotypic stands and impenetrable mats of stems and leaves and crowd out native plant species (Wisconsin Department of Natural Resources 2007, entire).P. arundinaceawas introduced from Europe for agricultural use (Maureret al.2003, p. 16) and may be the most pervasive emergent plant in wetlands in the Midwest (Spyreaset al.2010, p. 1254). BothP. australisandP. arundinaceahave likely spread along the Platte River as a result of deliberate introductions and changes in hydrology (Andersenet al.2004, p. 787; Strayeret al.2006, p. 649).

BothPhragmites australisandPhalaris arundinaceahave been observed in sloughs where the Platte River caddisfly occurs; however,P. arundinaceais more abundant and more often encountered in these wetlands (Vivian 2010, pers. obs.). These invasive plant species have been observed at 24 out of 35 sites with the caddisfly (Vivian 2011, pers. obs.) and appear to have degraded habitat at five sites with the caddisfly along the Platte River. At three sites,P. arundinaceaappears to have grown thick enough to completely dry out slough margins and to have reduced the amount of available Platte River caddisfly habitat at these sites (Vivian 2009, pers. obs.).P. australisis or was the dominant vegetation present at two sloughs where the caddisfly occurs when these areas were surveyed (Vivian 2009, pers. obs.); this plant has potentially reduced the habitat quality at these sites, as these sites support the lowest known densities of the Platte River caddisfly (Vivian 2010, p. 64.). Nonetheless, no extirpations have been observed as a result of displacement by invasive species, and work is underway along the central Platte River to control and reduce the spread ofP. australis(The Nature Conservancy 2011, entire). In other sloughs that support exotic vegetation, there is no evidence to suggest thatP. australisorP. arundinaceaare encroaching to the point where habitat quality is being reduced or will be reduced in the near future. Because invasive species appear to be impacting the Platte River caddisfly at only a small number of sites throughout its range, we do not consider invasive plant species to pose a threat to the Platte River caddisfly.

Groundwater Development

Following dam construction in the Platte Basin, irrigation demands were met through the pumping of groundwater (Eschneret al.1981, p. 10), particularly along the central Platte River (Currieret al.