Daily Rules, Proposed Rules, and Notices of the Federal Government
Section 4(b)(3)(B) of the Endangered Species Act of 1973, as amended (Act) (16 U.S.C. 1531
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 at
We published a partial 90-day finding for 38 of the petition's 206 species in the
The Platte River caddisfly (
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; Holzenthal
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 of
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 genus
The caddisfly family Limnephilidae is considered to be the most ecologically diverse family of Trichoptera (Holzenthal
The Platte River caddisfly is thought to be most closely related to
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 (Whiles
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 (Wiggins
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; Geluso
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 (Friesen
Sloughs with the Platte River caddisfly are typically described as lentic (with little to no flow) (Whiles
Because it is an inhabitant of intermittent waters, the Platte River caddisfly is tolerant of large fluctuations in water chemistry (Williams 1996, p. 634; Whiles
Vegetation in sloughs occupied by the caddisfly is typical wetland flora, such as
The Platte River caddisfly lifecycle was characterized by Whiles
While in its aquatic stage, the Platte River caddisfly is considered a shredder and largely feeds upon senescent (aged) plant tissue (Whiles
The Platte River caddisfly likely has a lifecycle adapted to the intermittent wetlands found along the Platte, Loup, and Elkhorn River systems (Whiles
While most caddisflies have an entirely aquatic larval phase, all
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 (Schneider
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 not
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 is
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; Geluso
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 (Geluso
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 2009
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 (m
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 m
The aquatic and terrestrial larval densities reported by Vivian (2010, pp. 40-41) are not directly comparable to Whiles
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.
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.
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; Wissinger
The type locality from which the Platte River caddisfly was described had an intermittent hydroperiod (Whiles
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 (Whiles
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 (Eschner
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 (Currier
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; Peterson
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; Schramm
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; Eschner
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 (Murphy
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 (Murphy
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 (Murphy
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 (Murphy
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 (
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 (Murphy
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 and
Currently, the Crane Trust area supports the highest known densities of the Platte River caddisfly (Whiles
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 (Murphy
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 (
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 (Murphy
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.
An altered hydrograph (graph of stream flow through time) can result
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.
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 (Currier
In the United States, there are introduced and native varieties of
Following dam construction in the Platte Basin, irrigation demands were met through the pumping of groundwater (Eschner