The upper Clark Fork River basin of western Montana supports a poorly understood sculpin (Uranidea spp.) fauna that has perplexed ichthyologists and fish ecologists since the late 1800s. During our study, the basin contained three sculpin taxa whose taxonomy was under revision. All three taxa were formerly referred to the genus Cottus but are now treated as Uranidea. Our goal was to improve understanding of the distribution and ecology of two of the taxa. From 2006 to 2009, we sampled 144 reaches in 31 streams and rivers to determine distributions of each taxa across the study area and within streams. We collected habitat data in 2007 and stream temperature data from 2006–2009 to identify correlates of sculpin distributions. In streams where both taxa occurred, Rocky Mountain Sculpin Uranidea sp. cf. bairdii were downstream and Columbia Slimy Sculpin U. sp. cf. cognata were upstream with a syntopic zone in between. Summer stream temperatures strongly influenced sculpin distributions, with mean August 2007 water temperatures increasing in order of reaches characterized as: Columbia Slimy Sculpin-dominated, syntopic, Rocky Mountain Sculpin-dominated, and no sculpin. Columbia Slimy Sculpin occurred in cold tributaries of the Blackfoot, Clark Fork, and Bitterroot rivers and in two coldwater refugia in the mainstem Bitterroot River. In contrast, Rocky Mountain Sculpin occupied warmer downstream segments of many Blackfoot and Clark Fork river tributaries as well as some mainstem reaches of both rivers but were absent from the Bitterroot River drainage. Persistence of the taxa will likely depend, both directly and indirectly, on future water temperatures, and thus, sculpins are appropriate targets for researching and monitoring biological changes resulting from climate change.
Table 1 Adams_et_al_2015
Table 1. Site locations, sampling dates and effort, numbers of sculpin captured, and habitat data for spring and summer samples from 2006 - 2009. For the Clark Fork River, we arbitrarily set "distance to mouth" = 0.00 for reach 1. Latitude and longitude are given in decimal degrees in the NAD83 datum.
Table 2 Adams_et_al_2015
Table 2.—Complete list of sample reaches, locations, and sculpin captured at each reach during summers 2007-9. Reaches sampled only in summer 2006 are included although not shown on maps. “Distance to mouth” is the stream distance (km) from a reach to the mouth of the stream or river on which the reach is located. For Clark Fork River reaches, distances are from the downstream-most reach. Reaches are numbered from downstream to upstream in each stream. Reaches where we recorded stream temperatures in either 2007 or 2008 are indicated in the thermograph column. Latitude and longitude are given in decimal degrees in the NAD83 datum. The total number of seconds shocked (Total seconds) and the number (N) of samples in which time was recorded are given. “Fish sample N” is the number of summer samples made during 2007-9 (maximum = 3). Where values for “Fish sample N” exceed those for “Seconds N”, electrofishing time was not recorded for all samples at the reach. Reaches with N = 0 for fish samples were sampled either in summer 2006 or spring 2007, but not in any summer from 2007-9. The numbers of Rocky Mountain Sculpin (RMS), Columbia Slimy Sculpin (CSS) and sculpin-present (not identified to taxon because of their small size or uncertainty due to the presence of Cedar sculpin [U. schitsuumsh]) are given. Percent (%) RMS and CSS are the percentages of each taxon, disregarding any unidentified sculpin. Sculpin status indicates the sculpin category to which the reach was assigned for temperature and habitat analyses. Reaches with both RMS and CSS are indicated as syntopic (Syn) and those with only unidentified sculpins as present (Pres). Other abbreviations are as follows: fishing access site (FAS); highway (Hwy.); Montana Fish, Wildlife, and Parks (FWP); US Forest Service (FS).
Table 3 Adams_et_al_2015
Table 3. Minimum, average, and maximum daily water temperature values for each reach during summer 2007. Stream names and reach codes are as in Tables 1 and 2. Sites are organized by sculpin group: no sculpin (none); Rocky Mountain sculpin (RMS) or Columbia slimy sculpin (CSS) only; or both species (syntopic). Daily summary statistics (mean, sample size [N], SD, and SE) by group are given for each temperature metric. Numbers in blue were estimated based on linear regressions (see text).