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Distribution and abundance of Alvord Chub in Oregon and Nevada.

ABSTRACT--Alvord Chub are small minnows endemic to the Alvord Basin, a endorheic desert basin in southeastern Oregon and northwestern Nevada. Comprehensive distribution surveys were last conducted 30 y ago. Recent, limited surveys raised concern that the range and abundance of Alvord Chub may have contracted. We conducted a comprehensive survey at historically occupied locations in 2013 and obtained mark-recapture population estimates. Despite 2 y of below average precipitation, Alvord Chub were present at the majority of historically occupied drainages, were abundant at many locations, but were restricted in distribution in several drainages. Additionally, we documented current threats, which included water withdrawals, normative fishes, grazing, habitat fragmentation, and desiccation. Based on our observations, we suggest a number of management recommendations.

Key words: Alvord Chub, capture probabilities, desert, desiccation, fragmentation, grazing, mark-recapture, normative fishes, Siphateles alvordensis, water withdrawals

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This study describes the current distribution and abundance of Alvord Chub, Siphateles alvordensis, in the Alvord Basin in Harney County, Oregon and Humboldt County, Nevada. The Alvord Chub is endemic to the Alvord Basin, an endorheic basin located in southeastern Oregon and northwestern Nevada. Aquatic habitats are rare and occur primarily in the Trout Creek drainage in Oregon, the Virgin-Thousand Creek drainage in Nevada, and in several small streams, ponds, and springs. Based on limited historical data, Alvord Chub appear to have been widely distributed within the Alvord Basin across southeastern Oregon and northwestern Nevada (Williams and Bond 1983). Hubbs and Miller (1948) provided a brief description of the uniqueness of the native Alvord Basin fishes and their isolation, which included documentation of Alvord Chub in several unnamed locations in the Alvord Desert region in Oregon and in the Thousand Creek system in Nevada. Only 3 fish species are native to the Alvord Basin, the Alvord Chub, Borax Lake Chub Gila boraxobius (restricted to geothermal Borax Lake), and Alvord Cutthroat Trout Oncorhynchus clarkii alvordensis (presumed to be extinct). Williams and others (1980) and Williams and Bond (1980, 1983) described the distribution and relative abundance of Alvord Chub at locations throughout the Alvord Basin in Oregon and Nevada based on sampling conducted in 1978, 1979, and 1982 (Table 1). Unfortunately, these reports do not list the sample locations where Alvord Chub were not encountered. It is reasonable to assume that Alvord Chub historically inhabited other suitable low-gradient habitats in the basin, from which there is no documentation. Figure 1 illustrates all locations where Alvord Chub were previously collected (through 2012).

Based on recent ad hoc sampling, there was concern that the range of this species may have contracted, thereby warranting a more robust assessment to determine the current species status and whether management action is required. In 1996, the Oregon Department of Fish and Wildlife (ODFW) conducted fish surveys at 5 locations in Oregon that historically supported Alvord Chub (unpubl. data). Alvord Chub were collected from Serrano Pond (n = 224), Serrano Spring (n = 54), Pueblo Slough (n = 430), and Turn Turn Lake (n = 42); no chub were found in Trout Creek. In 1994, the Nevada Department of Wildlife (NDOW) conducted fish surveys at 3 historical locations and reported finding Alvord Chub in Lower Thousand Creek (n = 2) and Big Spring Creek upstream of Dufurrena Ponds (few); none were found in Bog Hot Spring (unpubl. data).

More recently, the Bureau of Land Management (BLM) conducted limited surveys in 2010 and 2012 in Oregon and collected Alvord Chub from Trout Creek in 2010 (n = 7 from 1 location) and 2012 (n = 16, from 1 of 7 locations sampled), but did not capture chub from Turn Turn Lake or Juniper Lake (both desiccate regularly). They also reported that large portions of lower Trout Creek and Pueblo Slough were desiccated. In 2010, BLM discovered a previously undocumented and abundant chub population in Jana's Pond, which is located 0.5 km northeast of Borax Lake. ODFW estimated 1760 (95% CI: 1093 to 2794) chub at Jana's Pond in 2010 (Scheerer and Jacobs 2010). In 2011 and 2012, ODFW collected Alvord Chub (n = 2 and n = 20, respectively) from Serrano Spring. Serrano Pond was desiccated and the water control structure that feeds water to the pond was non-functional during our visits. In Nevada, the Nevada Division of Wildlife (NDOW) with assistance from Dr. Douglas Markle, Oregon State University, collected Alvord Chub in 2011 from Thousand Springs (abundant) and Virgin Creek (Dufurrena Pond 13; abundant). No Alvord Chub were collected from Virgin Creek mainstem, Dufurrena Ponds 19 and 20 (normative fish were abundant in both ponds), or Big Springs Creek. They also noted that Virgin Creek through Virgin Valley desiccated in 2011, except for Dufurrena Pond 13 where chub were abundant. This recent data suggested that Alvord Chub distribution may have contracted and chub abundance may have declined, compared to historic data (Table 1). During recent surveys, the numbers of chub collected at several locations were substantially lower than those collected during earlier surveys. Additionally, no surveys had been conducted in 30 y in many of the historically occupied habitats, thus the status of Alvord Chub was unknown at these locations.

Our objectives were to: 1) describe the current distribution of Alvord Chub in the Alvord Basin; 2) estimate their abundance at occupied sites; and 3) describe current habitat conditions and threats. Note, these surveys were conducted following 2 y of below average precipitation in the Alvord Basin (Western Regional Climate Center 2013).

METHODS

We sampled locations known to have supported Alvord Chub historically, including sites on private land (access dependent), using a combination of sampling gears. Historical locations included those with verified specimens in the Oregon State University Ichthyology Collection. We also opportunistically sampled several suitable locations in the vicinity of historical locations where chub had not previously been documented. We used minnow traps (0.16-mm mesh), baited with 'A slice of wheat bread, to obtain mark-recapture population estimates of Alvord Chub. We used seines (3 m wide x 1.2 m tall with 0.64-cm mesh) and hoop nets (0.62 m diameter by 3.1 m long with 0.64-cm mesh) to capture large-bodied, nonnative fishes. When obtaining abundance estimates, we sampled on 3 consecutive days at 8 locations and on 2 consecutive days at 3 locations. We distributed minnow traps haphazardly throughout the wetted area of each site and we based the number of traps we used on the wetted surface area of the site. We set between 24 and 120 traps per site and spaced them approximately 5 m apart. We set the traps in the afternoon and checked them the following morning (approximate 16-h set). On day 1, we marked all fish that we captured with a partial upper caudal fin clip and recorded the number of fish in each of 3 size categories (small <50 mm TL, medium 50 to 74 mm TL, and large [greater than or equal to] 75 mm TL). After fish were marked, we returned them to the water near the location of capture. That afternoon, we reset the traps overnight. The following morning (day 2), we recovered the traps, recorded the number of marked and unmarked fish in each size category, marked all fish with a partial lower caudal fin clip, and released them near the location of capture. That afternoon, we reset the traps overnight. On day 3, we pulled the traps, and recorded the total number of unmarked and marked fish (upper caudal, lower caudal, and both) in each size category.

We estimated the abundance of Alvord Chub at each location using a Huggins closed-capture model (Huggins 1991), implemented in program MARK (White and Burnham 1999), using only catch data from minnow traps in this model. The Huggins model requires a minimum of 3 capture occasions to model the variability in capture probabilities among trapping occasions. We included covariates in the Huggins model, such as fish body size and habitat characteristics, to account for variability in capture probabilities. This variability, if unaccounted for, can result in population estimates that are biased low (Peterson and Paukert 2009). Prior to model fitting, we combined the capture-recapture data from all sites into a single data set, treating each site as a group. We sampled 8 of the 11 locations where we estimated chub abundance on 3 occasions and sampled the other 3 sites on 2 occasions. To account for the missing third sample at the 3 sites, we fixed the capture and recapture probabilities at 0 for the third capture occasion at these 3 locations.

We described the current habitat conditions (model covariates) at each location including site dimensions, site depth (maximum, average, and range), substrate composition, aquatic vegetation (type and percent cover), and water temperature. We measured site dimensions using a laser rangefinder or a graduated depth staff after the last sampling occasion. We measured site depths with a graduated depth staff at a minimum of 5 locations per site. We characterized substrate as the proportion of the wetted area composed of fines (<0.5 mm), sand (0.5 to 2 mm), gravel (3 to 64 mm), cobble (65 to 256 mm), boulder (> 256 mm), and bedrock (native consolidated rock). We described current conditions which affect water quality (grazing), water availability (withdrawals), and/or may be causing fragmentation of habitats (barriers). We recorded Universal Transverse Mercator (UTM) coordinates of each site using a hand-held Global Positioning System (GPS) and took photographs at each site. We measured water temperature using a pocket thermometer when the traps or fyke nets were pulled or when the site was seined. We also collected fin clips and voucher specimens for future genetic and morphometric analyses (up to 10 fish per population and not exceeding 10% of the estimated population abundance, whichever was less).

We began modeling capture probability by fitting a global model with all covariates including: body size (small: <50 mm; medium: [baseline size group] 50 to 74 mm; and large fish: [greater than or equal to] 75 mm); average water temperature (average of all sampling occasions); percent of the site's surface area covered with aquatic vegetation; average and maximum site depth; number of traps used; area and volume of the site; area per trap, which was area divided by the number of traps used; volume per trap, which was site volume divided by the number of traps used; and a parameter representing recapture of marked fish (recapture effect). After fitting the global model, we found overdispersion (c) was 2.51, indicating lack of model fit due to over-dispersion (i.e., variance was in excess of that assumed by the model). A potential source of overdispersion is dependence among samples collected at individual sites (spatial autocorrelation). To account for the extra variability, we modeled capture and recapture probabilities using a hierarchical model (Huggins 1991). We included random effects associated with the intercept (fish capture probability) and recapture effect that varied among sites in the model. The random effects represented unique effects associated with each site on the capture probabilities and recapture probabilities, respectively, which were unexplained by the site-specific covariates. We fit all models using Markov Chain Monte Carlo (MCMC) methods in program MARK with 360,000 iterations and 10,000 burn-in samples (Raftery and Lewis 1996).

We were primarily interested in obtaining the best predicting model of population size and capture probability. Therefore, we fit all subsets of the global model and determined the best approximating model using Deviance Information Criteria (DIC; Spiegelhalter and others 2002). We report the parameter estimates and random effects, expressed as variance components, for the best approximating model and express precision of the estimates using 95% credible intervals, which are equivalent to 95% confidence intervals.

The Huggins model does not directly estimate abundance, but rather abundance (N) is derived using the following formula, N = [M.sub.t]/ (1 - [(1-[p.sub.1])(1-[p.sub.2])(1-[p.sub.3])])/ where [M.sub.t] is the total number of marks in the populations, [p.sub.t] is the probability of capture for occasions (t) 1 to 3. We estimated the capture probabilities using the best approximating model and estimated population size for each site and body size-group, which we summed to estimate total population abundance for each location. We calculated 95% confidence intervals for each population estimate according to Chao (1987).

RESULTS

We surveyed for Alvord Chub at 46 unique locations in Oregon (n = 25) and Nevada (n = 21), including 38 historically occupied locations. Ten of the sites we visited (22%) were desiccated. We found Alvord Chub at 15 locations (33% of sites visited; 42% of wetted sites); all of these locations were historically occupied. We found Alvord Chub at 6 locations in Nevada (38% of wetted sites) and 9 locations in Oregon (45% of wetted sites). We estimated Alvord Chub abundance at 11 locations. We present the parameter estimates and random effects, expressed as variance components, from the best approximating model of population size in Table 2.

Thousand Creek Drainage

In the Thousand Creek drainage in Nevada, we estimated there were 2850 (95% CI: 2139 to 3835) Alvord Chub in the beaver ponds located downstream of Thousand Creek Gorge (Table 3; Fig. 2). We also encountered normative Redear Sunfish Lepomis microlophus at this site. The habitat in these ponds was in good condition (deep, cool, and densely vegetated, with intact riparian vegetation on shoreline). We did not detect Alvord Chub in 6 sites we sampled upstream of the Thousand Creek Gorge. No chub were encountered in Thousand Creek spring or Thousand Creek ditch, which supply water into Dufurrena Ponds 19 to 22. Normative Guppies Poecilia reticulata were very abundant at these locations. No fish were detected in the unnamed spring near Thousand Creek, or from 2 former stream channels that historically flowed through Dufurrena Ponds 19 to 22. We found Redear Sunfish and White Crappie Pomoxis annularis in Dufurrena Pond 19, but no chub. This pond is managed for warmwater fishing. We did not sample Dufurrena Pond 22, a site historically occupied by chub, which reportedly desiccated earlier in 2013. The pond had a small amount of water (<0.1 m deep) that originated from heavy rains that occurred the week prior to our sampling. This shallow puddle also had a dense algal bloom. We sampled Big Spring, which, during high flows, drains into Big Spring Creek and eventually into Thousand Creek. This site had high-quality habitat (deep, cool, and densely vegetated with intact riparian vegetation on shoreline) but no fish were collected. The water temperature was very cold (4[degrees]C), which likely precludes successful chub colonization and recruitment. We were unable to locate Italian Camp Springs, a historically occupied chub location last sampled by Hubbs in 1934 (Oregon State University Ichthyology Collection record; unpubl. data). Nevada Natural Heritage Program records suggest that Italian Camp Springs and Thousand Creek Spring may be one and the same (E Miskow, Nevada Natural Heritage Program, pers. comm.). The Thousand Creek subbasin was fragmented by the construction of the Dufurrena Ponds in the 1960s, which restrict upstream fish movement. The stream channel downstream of the ponds currently desiccates on an annual basis. It is uncertain whether this desiccation occurred regularly, prior to the construction of the ponds.

Virgin Creek Drainage

In the Virgin Creek drainage in Nevada, Alvord Chub were abundant in the beaver ponds located immediately downstream of the Virgin Creek Gorge (estimate: 13,948; 95% CI: 10,003 to 19,690) (Table 2; Fig. 3). The habitat in these ponds was in good condition (deep, cool, and densely vegetated with intact riparian vegetation on shoreline). Chub were also abundant in Dufurrena Pond 13. We obtained abundance estimates in 2 seasonally isolated pools at this site. We estimated the larger pool contained 1722 Alvord Chub (95% CI: 1583 to 1905) and the smaller pool had 4825 chub (95% CI: 3898 to 6329). The habitat quality in Dufurrena Pond 13 was marginal. The pools were shallow, warm, and turbid, with no aquatic vegetation. We suspect that the dissolved oxygen content was also low in these pools, as we noted fish gulping air at the surface, and we had some trap mortalities, where the fish died with their mouths open and gills flared. The combined Virgin Creek estimate of over 20,000 chub is likely a minimum estimate for the subbasin, because we were unable to secure private landowner access to sample other suitable habitats in the subbasin, like Warm Spring. The Virgin Creek drainage is seasonally fragmented by desiccation; the impoundments (Dufurrena Pond 13 and others on private land) restrict upstream movement during most flow levels.

Bog Hot Creek Drainage

In the Bog Hot drainage in Nevada, Alvord Chub were very abundant in Bog Hot Reservoir (estimate: 151,594; 95% CI: 126,667 to 181,817) and common in middle Bog Hot Creek (aka Rincon Creek) immediately downstream of the reservoir (estimate: 565; 95% CI: 483 to 759). The reservoir habitat was in good condition, except that the spillway was highly eroded with exposed tires and metal T-posts and the water level dropped substantially between site visits when water was diverted for irrigation (approximate 0.5 m decline). The habitat in middle Bog Hot Creek was heavily affected by cattle grazing. Immediately downstream from where we sampled, Bog Hot Creek was diverted into a pasture (sheet flow). No fish were encountered in lower Bog Hot Creek. This section of the creek desiccated earlier during the summer of 2013 (cracked clay substrate and submerged terrestrial vegetation were noted) and the cloudy brown water we observed was likely a result of the heavy rains that occurred the week prior to our sampling. Continental Lake, which receives water from both Bog Hot Creek and Virgin-Thousand Creeks, was dry. The Bog Hot Creek drainage is fragmented. The dike and 2 water control structures on Bog Hot Reservoir prevent upstream fish passage. The irrigation diversion that irrigates the pasture seasonally desiccates the downstream stream channel.

Craine Creek Drainage

We sampled (visited) 7 locations in the Craine Creek drainage in Nevada and found Alvord Chub in West Creek (estimate: 458; 95% CI: 394 to 608), but not in West Spring. West Creek was a narrow, shallow spring brook that flowed approximately 400 m before terminating in a small marsh. The spring was shallow (approximate 0.1 m deep) with gravel substrate, and was trampled by cattle. We visited Gridley Springs and Gridley Lake. Historical records noted 17 springs at Gridley Springs; we only found remnants of 2 springs, which amounted to damp soil with emergent vegetation and no open water. Gridley Lake had a small amount of water, which originated from a thermal spring (41[degrees]C) and was supplemented by recent rains. The Gridley Spring habitats were negatively affected by heavy cattle grazing. The local landowner reportedly drilled additional irrigation well(s) in recent years, which may have lowered the water table and affected the springs. We did not encounter chub in Craine Creek, despite the presence of suitable habitat (adequate flow, depth, and aquatic vegetation with an intact riparian zone) and likely occasional connectivity to West Creek. Alvord Chub were not historically reported from Craine Creek.

Pueblo Slough

In the Pueblo Slough drainage in Oregon, we collected Alvord Chub from 4 pools in a previously modified wetland associated with Well 6. Compared to photographs from 1996 surveys, open water habitat in this wetland has declined substantially, as emergent plants, primarily Cattails Typha latifolia, have expanded their distribution and density. Despite this loss of suitable open water habitat, chub were abundant, ranging from 234 to 1353 individuals per pool (Table 3; Fig. 3). In addition to the pools associated with the Well 6 wetland, we sampled 6 small pools associated with Wells 1, 3, 8, 1920-1, 1920-2, and 1920-3. These sites were small, shallow puddles (0.10 to 0.20 m deep) and were fishless. Impacts from cattle grazing were widespread in the slough, despite the presence of fences that could have excluded the livestock if the gates had been closed. When the wetlands were modified in the 1970s, dikes were constructed to create impoundments. These dikes fragment the slough habitat and seasonally restrict fish movement. During most years, Turn Turn Lake and a small pond, which is located approximately 5 km south of the lake, desiccate, as they did in 2013. We did not receive landowner permission to sample Red Point School Springs.

Trout Creek Drainage

In Trout Creek in Oregon, we found only a handful of chub (n = 7 total) at 3 sites in the lower end of the canyon. We also collected normative Redband Trout (Oncorhynchus mykiss gairdnerii) from these sites. We visited 4 sites in the lower, valley portion of the drainage; all were desiccated. We were unable to obtain landowner permission to sample on private land encompassing most of the low-gradient sites in the drainage. All of the Trout Creek sites, with the exception of the beaver ponds on BLM property (Trout Creek site 2), were negatively affected by cattle grazing. The beaver ponds at Trout Creek site 2 had good-quality stream habitat (deep, cool, and densely vegetated with intact riparian vegetation), but chub were uncommon.

Ponds near Alvord Lake

We sampled 7 spring fed ponds near Alvord Lake in Oregon 0ana's Pond, Tule Springs 1-3, Salt Spring, and Serrano Spring). Alvord Chub were abundant in Jana's Pond (estimate: 5205; 95% CI- 4459 to 6221). This spring-fed pond is located northeast of Borax Lake and receives seepage runoff from the lake. The habitat is high-quality (deep, cool, and vegetated) and is not affected by grazing. We encountered only 2 chub in the Serrano Spring pool and upper spring brook. Serrano Spring and springbrook are on private land and were affected by cattle grazing. Serrano Pond, an impoundment east of the spring, was dry. Recent work to replace the water control structure on the Serrano Spring pool was completed in 2013; however the gate supplying water to Serrano Pond was closed. No chub were detected in Tule Springs or Salt Spring. Salt Spring is fed by geothermal groundwater and is likely too hot (39.5[degrees]C) to support Alvord Chub. Tule Springs are excavated ponds that contain suitable chub habitat, but no fish were detected. We could not locate Fields Reservoir, which was last sampled in 1934.

Squaw Creek Drainage

We visited 2 locations in the Squaw Creek drainage in Oregon. Juniper Lake was desiccated. Squaw Creek was puddled and contained only normative Lahontan Cutthroat Trout Oncorhynchus clarkii henshawi. An irrigation impoundment on lower Squaw Creek fragments this drainage and seasonally restricts fish movement.

Length-Frequency Distributions

The length-frequency distributions for Alvord Chub populations sampled in 2013 were broad and varied considerably among sites (Fig. 4). We noted 2 apparent size (age) classes at Dufurrena Pond 13, West Creek, and Thousand Creek. Pueblo Slough and Bog Hot Reservoir were dominated by small fish ([less than or equal to] 70 mm FL). Presumptive young-of-the-year chub (approximate 40-50 mm FL) were captured at many sites, most notably in West Creek and Jana's Pond. These small fish, and the presence of a broad size distribution at many locations, suggest that Alvord Chub have successfully recruited at most sites in recent years.

DISCUSSION

In 2013, we completed the first comprehensive survey for Alvord Chub in 30 y. Despite 2 y of below average precipitation, we found chub were abundant at many locations and present, albeit with restricted distribution, in 7 of the 8 historically occupied drainages. We noted numerous threats to the species, including the presence of normative fishes, habitat degradation from cattle grazing, habitat fragmentation resulting from the creation of impoundments, water withdrawals for irrigation, and seasonal desiccation. Due to the limitations of the historical data, where abundance was either categorized or was a count of the number of fish handled, we were unable to assess trends in abundance over time.

The Thousand Creek drainage in Nevada was the only drainage where we collected nonnative, non-salmonid fishes. Guppies were very abundant in Thousand Creek Spring and in the ditch that diverts the creek into Dufurrena Ponds 19 to 22. Guppies were first noted in the spring, and sporadically in the diversion ditch, in the 1980s (Williams and Bond 1983). Immediately downstream in the drainage, the Dufurrena Ponds 19 to 22 are managed for warmwater sport fishing and contained predatory Redear Sunfish, White Crappies, and reportedly Yellow Perch Perea flavescens and Largemouth Bass Micropterus salmoides. No Alvord Chub were collected from these habitats. Downstream of the ponds and upstream of the gorge, Thousand Creek was desiccated. Downstream of the Thousand Creek Gorge, beaver ponds provided high-quality chub habitat (deep, cool, and densely vegetated with intact riparian vegetation). This was the only location where we documented the coexistence of Alvord Chub and normative, non-salmonid fishes. We are concerned that if Guppies expand their range downstream or if the Redear Sunfish abundance increases, or both, chub in this drainage may become extirpated. We recommend regular monitoring of chub and nonnative fish abundance (every 2 to 3 y) at this location, to evaluate whether management action becomes necessary to save them from extirpation in this drainage. Management action may include removal of the Guppies from Thousand Creek spring and ditch and the reintroduction of Alvord Chub from the Thousand Creek Beaver Ponds into the spring and historical channels. This might be achieved by pumping the spring dry and/or applying rotenone to remove Guppies; then routing the spring discharge back into the historical channels, which do not contain normative fishes, and desiccating the ditch.

In addition, we found normative Redband Trout in Trout Creek, nonnative Lahontan Cutthroat Trout in Squaw Creek, and Lohr et al. (2012) found normative Redband Trout in Virgin Creek. These trout are ecologically similar to the basin's extinct native trout, the Alvord Cutthroat Trout, and it is unclear whether they pose a substantial threat to the Alvord Chub.

We noted widespread impacts from cattle grazing in Alvord Chub habitats. In Alvord Chub habitats where there was no cattle grazing, the riparian vegetation was lush and intact, the pond banks were stable, the water clarity was high, and the water temperature was cool. In habitats where recent cattle grazing occurred, riparian vegetation was sparse or absent, the pond banks were typically eroded and muddy, the water was turbid, and algal blooms were common. We recommend protecting the stream channels and ponds from cattle and feral burro access at Bog Hot Creek, West Spring, Pueblo Slough, Trout Creek, Dufurrena Pond 13, and Gridley Springs.

Successional conversion of open-water wetland habitat to emergent wetland habitat, which is unsuitable for fish, is likely limiting Alvord Chub at several locations, including Gridley Springs, Serrano Pond, and Pueblo Slough. In addition to protecting these habitats to reduce/exclude grazing impacts, we recommend habitat restoration to increase the amount of openwater habitat. At Gridley Springs, pools could be excavated at one or two spring locations and chub could be reintroduced, perhaps from nearby West Creek. At Serrano Spring, water could be diverted from the spring pool through the new water control structure to restore habitat in the currently dry, diked Serrano Pond. Alvord Chub will probably recolonize Serrano Pond from the spring pool after the flow and habitat is restored. At Pueblo Slough, we also recommend habitat restoration to expand open water habitat. In the 1970s, the BLM drilled 9 artesian wells (in addition to 8 wells privately drilled in the 1920s), constructed 3 dikes, and excavated 4 ponds at Pueblo Slough to enhance habitat for fish and wildlife, primarily migratory birds. Since then, decreasing water tables, sediment deposition, and dense aquatic vegetation growth have reduced the perennial wetted surface area 87% from 86 acres to 2.3 acres (D Bingham, BLM, pers. comm.). In 2013, the BLM developed a proposal and submitted NEPA documents to restore open-water habitat at Pueblo Slough. This long-term, multi-phase project proposes to restore open-water habitat at the site by reducing pond surface areas and increasing pond depths to provide cooler, more reliable perennial habitats. During restoration at Pueblo Slough and Gridley Spring, we urge caution and recommend excavating pools adjacent to, but not at the spring sources, to prevent possible disruption of spring flows and negative impacts on native invertebrate populations.

We recommend assessing the genetic structuring and diversity of all Alvord Chub populations. These analyses can reveal patterns of historical connectivity, inform managers regarding which populations are suitable donor stocks for future introductions, and identify populations that have undergone bottlenecks and require genetic augmentation. For example, after restoration is completed at Gridley Springs (assuming it is initiated), the next step would be to reintroduce Alvord Chub. While West Creek is a likely donor site, due to its close proximity to Gridley Spring, if this donor population is found to have undergone a recent genetic bottleneck and associated loss of diversity, then another choice of donor stock may be advisable. In addition, genetic analyses at Serrano Spring could determine whether this small population has undergone a genetic bottleneck and could assist managers in choosing a suitable donor population, if they choose to supplement this population in the future.

Finally, we recommend repeating this comprehensive survey every 5 y. Much has changed since the last comprehensive surveys were conducted 30 y ago. Williams and Bond reported that "more than 100 fish can be easily collected from Serrano Pond in a single seine haul" whereas we set 48 traps overnight on successive days and captured only 2 chub. They also reported that Alvord Chub occurred in Dufurrena Pond 19, Dufurrena Pond 22, and West Spring, where we found none. Had comprehensive surveys been conducted more frequently in the past 3 decades, perhaps these changes in fish numbers could have been noted and management actions could have been taken to prevent these substantial declines. We also recommend surveying additional spring habitats in the Alvord Basin to potentially discover additional, previously undocumented Alvord Chub populations. The largest Alvord Chub population in Oregon, which is located at Jana's Pond, was discovered in this way.

ACKNOWLEDGMENTS

We gratefully acknowledge the field assistance by B Bangs, B Bauman, S Hum, K Keefe, E Miskow, and J Mort. We thank the 2 reviewers, S Lohr and S Parmenter, whose comments improved this manuscript. We deeply appreciate cooperation of private landowners in the Alvord Basin who allowed us access to their land. Thanks also to Burns BLM for housing at the Fields bunkhouse, to Sheldon Refuge for the use of the showers and restrooms at the bunkhouse, and to NDOW for use of their travel trailer parked at Sheldon Refuge. This work was funded by the Bureau of Land Management (cooperative agreement L10AC20301). This work was conducted under US Fish and Wildlife National Wildlife Refuge System Research and Monitoring Special Use Permit 14620-13-0018 and Nevada Department of Wildlife Scientific Collection Permit S36891.

PAUL D SCHEERER

Oregon Deportment of Fish and Wildlife, 28655 Highway 34, Corvallis, OR 97333 USA

JAMES T PETERSON

USGS Oregon Cooperative Fish and Wildlife Research Unit, 104 Nash Hall, Oregon State University, Corvallis, OR 97331

USA

SHAUN CLEMENTS

Oregon Department of Fish and Wildlife, 28655 Highway 34, Corvallis, OR 97333 USA

LITERATURE CITED

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* Lohr S, Hudson JM, Koski M, Whitesel TA. 2012. Fish and aquatic habitat surveys at Sheldon-Hart Mountain National Wildlife Refuge Complex. 57 p. Available from US Fish and Wildlife Service Columbia River Fisheries Program Office, 1211 SE Cardinal Court, Suite 100, Vancouver, WA 98683.

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* Scheerer PD, Jacobs SE. 2010. 2010 Borax Lake chub investigations. Oregon Department of Fish and Wildlife Annual Report. Corvallis, OR: US Fish and Wildlife Service contract 13420-08-J814 and BLM contract L07PX02726.12 p. Available from: Oregon Department of Fish and Wildlife, 28655 Highway 34, Corvallis, OR 97333.

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Williams JE, Bond CE. 1983. Status and life history notes on the native fishes of the Alvord Basin, Oregon and Nevada. Great Basin Naturalist 43: 409-420.

* Williams JE, Williams CD, Bond CE. 1980. Survey of fishes, amphibians, and reptiles on the Sheldon National Wildlife Refuge, Nevada. Portland, OR: US Fish and Wildlife Service. Contract 14-16-000178025. 53 p. Available from: US Fish and Wildlife Service, 2600 SE 98th Avenue, Suite 100, Portland, OR 97266.

* Unpublished

Submitted 12 August 2014, accepted 16 December 2014. Corresponding Editor: Robert Hoffman.

TABLE 1. Relative abundance of Alvord Chub during three
sampling periods since 1974. Sites not surveyed are denoted
with "NS". Numbers represent the number of chub collected,
with the exception of Jana's Pond which was a mark-
recapture estimate. Williams and Bond (1983) did not define
the terms "rare", "common", or "abundant" and used the term
"intermittent" for sites where chub were present when the
site was not desiccated. Note, 2 sites were only sampled in
1934 and are documented in the Oregon State University
Ichthyology Collection.

                                  Relative abundance

                       1974-1982         1994-1996   2010-2012
Location               surveys           surveys     surveys

OREGON

Juniper Lake           present           0           0

Serrano Spring         abundant          54          2-20

Serrano Pond           abundant          224         dry

Fields Reservoir       present in 1934   NS          NS

Jana's Pond            NS                NS          1760

Trout Creek            common            0           7-19

Pueblo Slough          abundant          430         3-22

Red Point              abundant          abundant    NS
School Springs

Turn Turn Lake         abundant          42          0

NEVADA

Thousand Creek         rare              NS          NS
Spring

Thousand Creek         common            2           abundant

Unnamed spring near    common            NS          NS
Thousand Creek

Italian Camp Spring    present in 1934   NS          NS

Dufurrena Pond 19      common            NS          0

Dufurrena Pond 22      abundant          NS          NS

Virgin Creek           abundant          NS          18

Dufurrena Pond 13      common            NS          abundant

Bog Hot Reservoir      abundant          NS          NS

Bog Hot Creek          rare              0           NS

Continental Lake       intermittent      NS          NS

Warm Creek             abundant          NS          NS

Gridley Springs        common            NS          NS

West Spring            common            NS          NS

West Creek             common            NS          NS

Location               Source--Reference

OREGON

Juniper Lake           Bond (1974); ODFW unpublished data (1996); BLM
                       unpublished data (2012)

Serrano Spring         Williams and Bond (1983); ODFW unpublished data
                       (1996, 2011, 2012)

Serrano Pond           Williams and Bond (1983); ODFW unpublished data
                       (1996, 2011, 2012)

Fields Reservoir       OSU museum record

Jana's Pond            Scheerer and Jacobs (2010)

Trout Creek            Williams and Bond (1983); ODFW unpublished data
                       (1996); BLM unpublished data (2010, 2012)

Pueblo Slough          Williams and Bond (1983); ODFW unpublished data
                       (1996); BLM unpublished data (2010; 2012)

Red Point              Williams and Bond (1983); ODFW unpublished data
School Springs         (1996)

Turn Turn Lake         Williams and Bond (1983); ODFW unpublished data
                       (1996); BLM unpublished data (2012)
NEVADA

Thousand Creek         Williams and Bond (1983)
Spring

Thousand Creek         Williams and others 1980; Williams and Bond
                       (1983); NDOW unpublished data (1994)

Unnamed spring near    Williams and Bond (1983)
Thousand Creek

Italian Camp Spring    OSU museum record

Dufurrena Pond 19      Williams and others 1980; Williams and Bond
                       (1983); NDOW unpublished data (2011)

Dufurrena Pond 22      Williams and others 1980; Williams and Bond
                       (1983)

Virgin Creek           Williams and others 1980; Williams and Bond
                       (1983); Lohr et al. (2012)

Dufurrena Pond 13      Williams and others 1980; Williams and Bond
                       (1983); NDOW unpublished data (2011)

Bog Hot Reservoir      Williams and others 1980; Williams and Bond
                       (1983)

Bog Hot Creek          Williams and Bond (1983); NDOW unpublished data
                       (1994)

Continental Lake       Williams and Bond (1983)

Warm Creek             Williams and others 1980; Williams and Bond
                       (1983)

Gridley Springs        Williams and others 1980; Williams and Bond
                       (1983)

West Spring            Williams and others 1980; Williams and Bond
                       (1983)

West Creek             Williams and Bond (1983)

TABLE 2. Parameter estimates and random effects, expressed
as variance components, from the best approximating model of
Alvord Chub population size. The models were fit using a
logit link function.

                                                    95% Credible
                                                     intervals

Parameter (1)                  Mean       SD     Lower     Upper

Fixed effects
  Intercept (fish capture    -1.7768   0.3479   -2.5420   -1.1611
    probability)
  Small fish (<50 mm)        -0.2282   0.0332   -0.2939   -0.1636
  Average depth (m)          -0.8411   0.3417   -1.4758   -0.1062
  Number of traps used       0.3996    0.1391   0.0900    0.6543
  Site area                  -0.3971   0.2139   -0.8077   0.0209
  Area-number of traps       -0.1830   0.1039   -0.3806   0.0242
    interaction
  Recapture probability      -0.0073   0.4851   -0.9270   1.0101
Random effects (2)
  Intercept (fish capture    0.8135    0.3967   0.3145    1.8259
    probability)
  Recapture probability      1.4345    0.4350   0.8260    2.4975

(1) Models were fitted using standardized (normalized) data
where a 1 unit change corresponds to a 1 SD change in the
variable.

(2) Random effects are variance components representing
among site variability of the parameter.

TABLE 3. 2013 Alvord Chub abundance estimates, 95%
confidence limits, current threats, and UTM coordinates
(zone 11T) for the 46 locations visited in the Alvord Basin
of Nevada and Oregon. Historically occupied sites are
distinguished by italics. Note: an abundance of zero
indicates non-detection of chub; low numbers of chub could
be present at these locations. Sites not surveyed because
they were desiccated are denoted with "NS".

                                                  Confidence limits

          Site              State    Abundance    Lower      Upper

Big Spring                  Nevada          0
Thousand Creek Spring       Nevada          0
Thousand Creek ditch        Nevada          0
Old Thousand Creek          Nevada          0
  channel #1
Old Thousand Creek          Nevada          0
  channel #2
Thousand Creek              Nevada       2850       2139       3835
  beaver pond
Dufurrena Pond 19           Nevada          0
Dufurrena Pond 22           Nevada         NS
Dufurrena Pond 13--
  small pool                Nevada       4825       3898       6329
Dufurrena Pond 13--
  large pool                Nevada       1722       1583       1905
Virgin Creek beaver pond    Nevada     13,948     10,003     19,690
Bog Hot Reservoir           Nevada    151,594    126,667    181,817
Middle Bog Hot Creek        Nevada        565        483        759
Lower Bog Hot Creek         Nevada          0
Continental Lake            Nevada         NS
West Spring                 Nevada          0
West Creek                  Nevada        458        394        608
Gridley Lake                Nevada         NS
Gridley Spring 1            Nevada         NS
Gridley Spring 2            Nevada         NS
Craine Creek 1              Nevada          0
Craine Creek 2              Nevada          0
Juniper Lake                Oregon         NS
Squaw Creek                 Oregon          0
Serrano Spring              Oregon          2
  and Springbrook
Serrano Pond                Oregon         NS
Trout Creek 1--USGS gage    Oregon          1
Trout Creek 2--             Oregon          1
  Beaver Pond/
  Backwater
Trout Creek 3               Oregon          5
Trout Creek 4-Riggs         Oregon         NS
Trout Creek 5--             Oregon         NS
  Smith/Gilbert
Jana's Pond                 Oregon       5205       4459       6221
Salt Spring                 Oregon          0
Tule Spring 1--eastern      Oregon          0
Tule Spring 2--middle       Oregon          0
Tule Spring 3--western      Oregon          0
Pueblo Slough Pool 6A       Oregon       1353       1007       1993
Pueblo Slough Pool 6C       Oregon        930        794       1097
Pueblo Slough Pool 6B       Oregon        740        568       1018
Pueblo Slough Pool 6D       Oregon        234        197        293
Pueblo Slough Well 1        Oregon          0
Pueblo Slough Well 3        Oregon          0
Pueblo Slough Well 1920-1   Oregon          0
Pueblo Slough Well 1920-2   Oregon          0
Pueblo Slough Well 1920-3   Oregon          0
Pueblo Slough Well 8        Oregon          0
Turn Turn Lake              Oregon         NS

                                         Threats

                                       [H.sub.2]O
          Site              Grazing    withdrawals   Desiccates

Big Spring
Thousand Creek Spring
Thousand Creek ditch
Old Thousand Creek                         yes
  channel #1
Old Thousand Creek                         yes
  channel #2
Thousand Creek
  beaver pond
Dufurrena Pond 19
Dufurrena Pond 22                                       yes
Dufurrena Pond 13--
  small pool
Dufurrena Pond 13--
  large pool
Virgin Creek beaver pond
Bog Hot Reservoir
Middle Bog Hot Creek          yes          yes          yes
Lower Bog Hot Creek                                     yes
Continental Lake                                        yes
West Spring                   yes
West Creek                    yes
Gridley Lake                  yes                       yes
Gridley Spring 1              yes         yes?          yes
Gridley Spring 2              yes         yes?          yes
Craine Creek 1                yes
Craine Creek 2                yes
Juniper Lake                                            yes
Squaw Creek                                yes
Serrano Spring                yes
  and Springbrook
Serrano Pond                  yes                       yes
Trout Creek 1--USGS gage
Trout Creek 2--
  Beaver Pond/
  Backwater
Trout Creek 3
Trout Creek 4-Riggs           yes                       yes
Trout Creek 5--               yes                       yes
  Smith/Gilbert
Jana's Pond
Salt Spring
Tule Spring 1--eastern
Tule Spring 2--middle
Tule Spring 3--western
Pueblo Slough Pool 6A         yes
Pueblo Slough Pool 6C         yes
Pueblo Slough Pool 6B         yes
Pueblo Slough Pool 6D         yes
Pueblo Slough Well 1          yes
Pueblo Slough Well 3          yes
Pueblo Slough Well 1920-1     yes
Pueblo Slough Well 1920-2     yes
Pueblo Slough Well 1920-3     yes
Pueblo Slough Well 8          yes
Turn Turn Lake                                          yes

                                         Threats

          Site              Fragmentation   Nonnatives

Big Spring
Thousand Creek Spring            yes           yes
Thousand Creek ditch                           yes
Old Thousand Creek               yes
  channel #1
Old Thousand Creek               yes
  channel #2
Thousand Creek                                 yes
  beaver pond
Dufurrena Pond 19                yes           yes
Dufurrena Pond 22                yes
Dufurrena Pond 13--
  small pool                     yes
Dufurrena Pond 13--
  large pool                     yes
Virgin Creek beaver pond
Bog Hot Reservoir                yes
Middle Bog Hot Creek
Lower Bog Hot Creek
Continental Lake
West Spring
West Creek
Gridley Lake
Gridley Spring 1
Gridley Spring 2
Craine Creek 1
Craine Creek 2
Juniper Lake                     yes
Squaw Creek                                    yes
Serrano Spring
  and Springbrook
Serrano Pond
Trout Creek 1--USGS gage                       yes
Trout Creek 2--                                yes
  Beaver Pond/
  Backwater
Trout Creek 3                                  yes
Trout Creek 4-Riggs
Trout Creek 5--
  Smith/Gilbert
Jana's Pond
Salt Spring
Tule Spring 1--eastern
Tule Spring 2--middle
Tule Spring 3--western
Pueblo Slough Pool 6A
Pueblo Slough Pool 6C
Pueblo Slough Pool 6B
Pueblo Slough Pool 6D
Pueblo Slough Well 1
Pueblo Slough Well 3
Pueblo Slough Well 1920-1
Pueblo Slough Well 1920-2
Pueblo Slough Well 1920-3
Pueblo Slough Well 8
Turn Turn Lake

                              UTM coordinates

          Site              Easting   Northing

Big Spring                  320963    4643280

Thousand Creek Spring       330020    4638112
Thousand Creek ditch        330105    4637915
Old Thousand Creek          330431    4637838
  channel #1
Old Thousand Creek          330208    4637645
  channel #2
Thousand Creek              338219    4639958
  beaver pond
Dufurrena Pond 19           331988    4637546
Dufurrena Pond 22           333050    4636511
Dufurrena Pond 13--
  small pool                328680    4631461
Dufurrena Pond 13--
  large pool                328680    4631461
Virgin Creek beaver pond    323755    4626280
Bog Hot Reservoir           351768    4641837
Middle Bog Hot Creek        351715    4641745
Lower Bog Hot Creek         354786    4637280
Continental Lake            357511    4640789
West Spring                 340305    4621227
West Creek                  340506    4621244
Gridley Lake                346107    4623610
Gridley Spring 1            344222    4620850
Gridley Spring 2            344379    4620795
Craine Creek 1              344337    4609305
Craine Creek 2              345128    4606665
Juniper Lake                390563    4752257
Squaw Creek                 391484    4756788
Serrano Spring              371101    4700271
  and Springbrook
Serrano Pond                371079    4700261
Trout Creek 1--USGS gage    379902    4667858
Trout Creek 2--             381716    4669572
  Beaver Pond/
  Backwater
Trout Creek 3               382025    4670478
Trout Creek 4-Riggs         369637    4672796
Trout Creek 5--             368254    4681036
  Smith/Gilbert
Jana's Pond                 368430    4687446
Salt Spring                 367017    4685344
Tule Spring 1--eastern      377016    4693192
Tule Spring 2--middle       376952    4693229
Tule Spring 3--western      376899    4693284
Pueblo Slough Pool 6A       369799    4656299
Pueblo Slough Pool 6C       369783    4656329
Pueblo Slough Pool 6B       369670    4656188
Pueblo Slough Pool 6D       369633    4656154
Pueblo Slough Well 1        369253    4654786
Pueblo Slough Well 3        369047    4654623
Pueblo Slough Well 1920-1   369152    4655063
Pueblo Slough Well 1920-2   369161    4655122
Pueblo Slough Well 1920-3   369206    4655193
Pueblo Slough Well 8        369170    4654878
Turn Turn Lake              368874    4666201
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Author:Scheerer, Paul D.; Peterson, James T.; Clements, Shaun
Publication:Northwestern Naturalist: A Journal of Vertebrate Biology
Article Type:Report
Date:Sep 22, 2015
Words:7282
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