U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2020–1137

Prepared in cooperation with the National Park Service

Assessing Native Fish Restoration Potential in Catoctin 

Mountain Park
Caption: Experimental fish enclosure placement in Catoctin Mountain Park, Maryland. Experimental Stream Laboratory at the 

U.S. Geological Survey at the Leetown Science Center in Kearneysville, West Virginia (bottom circle). Blue Ridge sculpin (Cottus 

caeruleomentum) (top circle). Photographs by N.P. Hitt, U.S. Geological Survey.
Assessing Native Fish Restoration 

Potential in Catoctin Mountain Park

By Nathaniel P. Hitt, Karmann G. Kessler, Zachary A. Kelly, Karli M. Rogers, 

Hannah E. Macmillan, and Heather L. Walsh

Prepared in cooperation with the National Park Service

Open-File Report 2020–1137

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

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Suggested citation:

Hitt, N.P., Kessler, K.G., Kelly, Z.A., Rogers, K.M., Macmillan, H.E., and Walsh, H.L., 2020, Assessing native fish 

restoration potential in Catoctin Mountain Park: U.S. Geological Survey Open-File Report 2020–1137, 17 p., 

https://doi.org/ 10.3133/ ofr20201137. 

Associated data for this publication:

Hitt, N.P., Kessler, K., Rogers, K., Macmillan, H., and Walsh, H., 2020, Stream temperature and sculpin growth data 

collected from Catoctin Mountain Park in 2019: U.S. Geological Survey data release, 

https://doi.org/10.5066/P950A13P.

ISSN 2331-1258 (online)
iii

Acknowledgments

We thank Steve Faulkner, Tom O’Connell, Andrea Ostroff, Craig Snyder, Evan Rodway, Joe 

Dehnert, Vicki Blazer, Christine Densmore (U.S. Geological Survey), Lindsey Donaldson, Becky 

Loncosky, Rick Slade, Diane Pavek (National Park Service), John Mullican, Josh Henesy, Michael 

Kashiwagi, and Barbara Johnston (Maryland Department of Natural Resources) for assistance 

with this research. Research protocols were approved by the U.S. Geological Survey Leetown 

Science Center Institutional Animal Care and Use Committee (AEL-2019-001). Funding was 

provided by the FY19 Natural Resources Preservation Program.

v

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Methods...........................................................................................................................................................2

Stream Temperature Assessment ......................................................................................................2

Fish Enclosure Experiment ..................................................................................................................2

Fish Sampling................................................................................................................................2

Histopathology and Fish Health Screening .............................................................................4

Experimental Design ...................................................................................................................4

Statistical Analysis ......................................................................................................................5

Results .............................................................................................................................................................6

Stream Temperature Assessment ......................................................................................................6

Fish Enclosure Experiment ..................................................................................................................6

Discussion.......................................................................................................................................................8

References Cited..........................................................................................................................................11

Appendix 1 Hourly Stream Temperature Plots ....................................................................................14

Figures

1. Study site locations within Catoctin Mountain Park. ............................................................3

2. Example of experimental fish enclosure placement in Owens Creek .................................5

3. Hourly stream temperatures for the warmest site and coolest site during 

summer 2019 ..................................................................................................................................7

4. Daily mean stream temperatures averaged across sites within Owens Creek, 

upper Big Hunting Creek, Blue Blazes Creek, and lower Big Hunting Creek .....................9

Tables

1. Sample site information. .............................................................................................................4

2. Summary of hourly stream temperatures during the 100-day sample period ....................6

3. Comparison of daily mean temperatures within Owens Creek, upper Big 

Hunting Creek, Blue Blazes Creek, and lower Big Hunting Creek ........................................8

4. Relative abundance of fish in three spatially consecutive 100-m sampling areas 

within Owens Creek ...................................................................................................................10

5. Site-level summaries for fish growth and exposure temperatures for the 

caged-fish experiment ...............................................................................................................10

6. Summary of fitted linear mixed models for specific growth rate from the caged 

fish experiment ............................................................................................................................10
vi

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

yard (yd) 0.9144 meter (m)

Area

acre 0.4047 hectare (ha)

Mass

ounce, avoirdupois (oz) 28.35 gram (g)

International System of Units to U.S. customary units

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

meter (m) 1.094 yard (yd)

Area

hectare (ha) 2.471 acre

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F 

= (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C 

= (°F – 32) / 1.8.

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.
vii

Abbreviations

AIC Akaike information criterion

ANOVA analysis of variance

CATO Catoctin Mountain Park

CI confidence intervals

DD20 Degree-days above 20 °C

MD-DNR Maryland Department of Natural Resources

MDT mean daily temperature

MWAT maximum weekly average temperature

NOAA National Oceanic and Atmospheric Administration

SGR specific growth rate

USGS U.S. Geological Survey

Assessing Native Fish Restoration Potential in Catoctin 

Mountain Park

By Nathaniel P. Hitt, Karmann G. Kessler, Zachary A. Kelly, Karli M. Rogers, Hannah E. Macmillan, and 

Heather L. Walsh

Abstract

Biological conservation is a fundamental purpose of 

the National Park system, and Catoctin Mountain Park 

(CATO) supports high-quality habitat for native fishes in 

the headwaters of the Chesapeake Bay watershed in eastern 

North America. However, native Blue Ridge sculpin (Cottus 

caeruleomentum) have been extirpated in Big Hunting Creek 

above Cunningham Falls in CATO. Prior research indicates 

that infection by the fungal-like protist Dermocystidium is a 

likely cause for the extirpation, but elevated stream temperatures also have been observed in the study area, and it remains 

unknown whether thermal stress may exacerbate infections or 

otherwise limit habitat suitability for fishes in CATO.

The purpose of this study was to quantify spatial variation in summer stream temperatures and to evaluate the effects 

of temperature on sculpin growth rates and susceptibility 

to Dermocystidium infection. We used observational and 

experimental methods to address these objectives. First, we 

deployed stream temperature gages at 10 sites throughout the 

study area to assess hourly and daily temperatures during the 

summer of 2019. Second, we conducted an in situ fish enclosure experiment at five of the temperature sites to assess fish 

growth and susceptibility to Dermocystidium infection over 

a 45-day exposure period. For this experiment we collected 

sculpin from a stream in CATO that supports a robust population of Blue Ridge sculpin (Owens Creek) and held them in 

quarantine for 50 days in the Experimental Stream Laboratory 

at the U.S. Geological Survey (USGS) Leetown Science 

Center. Pre-exposure histopathology confirmed the absence of 

Dermocystidium infection prior to the introduction of fish into 

experimental enclosures.

We found that stream temperatures were warmer where 

sculpin have been extirpated than elsewhere in CATO where 

sculpin persist. However, the fish enclosure experiment 

revealed a positive effect of temperature on fish growth, suggesting that increased food availability and foraging rates 

compensated for increased metabolic demands in the warmest sites. Moreover, fish held in enclosures did not develop 

Dermocystidium infection. Our results therefore suggest that 

current environmental conditions in upper Big Hunting Creek 

may be suitable for Blue Ridge sculpin reintroduction, and 

this could ultimately lead to sportfishing opportunities by 

increasing the forage base for native brook trout (Salvelinus 

fontinalis).

Introduction

Native species conservation is a fundamental purpose of 

the National Park system within the U.S. Department of the 

Interior as established by the Organic Act of 1916. Catoctin 

Mountain Park (CATO) in central Maryland supports a prized 

trout fishery and a healthy community of native fishes (Hitt 

and others, 2017a) with one exception: native Blue Ridge 

sculpin (Cottus caeruleomentum; Kinzinger and others, 2000) 

appear to have been extirpated from Big Hunting Creek 

above Cunningham Falls. Infection by a fungal-like protist 

Dermocystidium sp. is hypothesized to have facilitated the 

extirpation (Blazer and others, 2016), and such infections have 

been linked to fish population declines elsewhere (Rowley and 

others, 2013). However, elevated stream temperatures in the 

study area (Hitt and others, 2017a) also may be an underlying 

cause, either as a direct physiological effect or by exacerbating 

infection rates (Kocan and others, 2009; Karvonen and others, 

2010). Resource managers at CATO therefore, could benefit 

from understanding why this native species was extirpated and 

whether reintroduction is feasible.

We have high confidence that Blue Ridge sculpin have 

been extirpated from Big Hunting Creek above Cunningham 

Falls. Fish surveys in 2008 confirmed the species was present, 

but subsequent annual surveys by the U.S. Geological Survey 

(USGS) and Maryland Department of Natural Resources 

(MD-DNR) did not detect the target species despite intensive 

sampling effort (Blazer and others, 2016). Moreover, the high 

abundance of this species in nearby Owens Creek (Hitt and 

others, 2017a) and the effect of Cunningham Falls as a fish 

passage barrier also supports our assertion that sculpin have 

been extirpated from Big Hunting Creek above the waterfall.

Sculpin reintroduction may be particularly important for 

brook trout (Salvelinus fontinalis) conservation because sculpin are prey for large stream-dwelling trout (Meredith and others, 2014), and additional management actions are currently 

underway to enhance the population of brook trout in Hunting 
2 Assessing Native Fish Restoration Potential in Catoctin Mountain Park

Creek through the manual removal of brown trout from upper 

Big Hunting Creek (M. Kashiwagi, MD-DNR, oral commun., 

August 17, 2019). Sculpin often have an important role in 

food webs and energy flows in stream ecosystems (Adams and 

Schmetterling, 2007) and they constitute a large component of 

the fish assemblage in nearby Owens Creek (Hitt and others, 

2017a) that suggests their extirpation from upper Big Hunting 

Creek may substantially alter stream ecosystem structure and 

function.

Methods

Stream Temperature Assessment

We collected hourly stream temperature data from 10 

sites between June 1 and September 9, 2019, (100 days) to 

observe maximum summer temperatures in the study area 

(fig. 1). Our stream temperature survey included three sites 

in Owens Creek, three sites in upper Big Hunting Creek (that 

is, above Cunningham Falls), two sites in lower Big Hunting 

Creek, and two sites in Blue Blazes Creek. We used Onset 

ProV2 and Tidbit water temperature gages, and both are rated 

to an accuracy of ±0.02 °C. Gages were secured within perforated polyvinyl chloride (PVC) cases and attached to rebar 

driven into substrates following Snyder and others (2015). 

We checked gage accuracy prior to deployment in water baths 

with controlled temperatures.

We calculated thermal summary statistics for each site 

and compared sites and streams using analysis of variance 

(ANOVA). We also calculated maximum weekly average 

temperature (MWAT) as an index of thermal habitat suitability 

for native brook trout because the species typically is absent 

when this measure exceeds 23.3 °C (Wehrly and others, 2007). 

MWAT was used previously by Snyder and others (2015) to 

forecast thermal habitat suitability for native brook trout in 

the Blue Ridge physiographic region where the study area is 

located. We used data from the summer sampling period (100 

days) for all sites to evaluate brook trout habitat suitability and 

spatial trends. We also used a subset of the temperature data 

for fish cage sites during the exposure period to evaluate fish 

growth rates (see below).

To interpret water temperature patterns, we used precipitation records from a remote automatic weather station 

located at CATO (administered and maintained by the Western 

Regional Climate Center). We approximated the timing of 

designated “significant” rainfall events based on daily precipitation levels that exceeded the average daily precipitation 

during 2019 plus one standard deviation (13.4 millimeters per 

day). Using this criterion, the study period included 12 days 

with significant rainfall events and cumulatively composed 

a period of near-average precipitation based on long-term 

climate data (1895–2019) maintained by the National Oceanic 

and Atmospheric Administration (NOAA) (data not shown). 

In contrast, the study area during this time period experienced 

above-average air temperatures based on NOAA long-term 

climate data, and this pattern was observed across much of the 

eastern United States during summer 2019 (data not shown).

Fish Enclosure Experiment

The fish enclosure experiment consisted of four steps: (1) 

we collected Blue Ridge sculpin from a 300-meter (m) section of Owens Creek; (2) we quarantined fish at the Leetown 

Science Center for 50 days, during which time we conducted 

a histology analysis for a subset of individuals to confirm 

absence of Dermocystidium and other pathogens and parasites; 

(3) we moved disease-free fish to a series of wire-mesh cages 

in the study area for a 45-day exposure period; and (4) we 

evaluated individual growth and Dermocystidium infection 

status after the exposure period with respect to site location 

and stream temperatures during the exposure period.

Fish Sampling

We collected sculpin from Owens Creek on May 24, 

2019, and June 7, 2019, using 1-pass backpack electrofishing methods (Reynolds and Kolz, 2012) for a total of three 

sequential 100-m sampling reaches. We enumerated all captured fish at the species level and returned all fish to the stream 

except for a subset of adult sculpin we retained for caged 

fish experiments. We observed many young-of-year (age-0) 

sculpin but did not count them in the fish survey nor include 

them in experimental collections. We transported collected fish 

to the USGS Leetown Science Center (LSC) in stream water 

with ice and bubblers to maintain temperature and dissolved 

oxygen levels.

We quarantined fish collected from Owens Creek at the 

LSC Experimental Stream Laboratory for 50 days (June 7 to 

July 26, 2019) following guidance from Maryland Department 

of Natural Resources (B. Johnston, MD-DNR, oral commun., 

November 29, 2018). Fish were maintained in a series of 

riffle chambers within recirculating channels supplied with 

particulate and ultraviolet (UV) filtration. Laboratory stream 

temperatures were held at approximately 13 °C. Following a 

1-week acclimation period, we injected a 12-millimeter (mm) 

passive integrated transponder tag ventrally in each fish to 

enable individual identification. We fed fish daily with frozen 

bloodworms at a rate of approximately 5 percent of fish biomass per day. As a biosecurity protocol to prevent introduction 

of novel pathogens or parasites into the environment, the LSC 

Experimental Stream Laboratory treats effluent water with a 

hypochlorite solution (>200 milligrams per liter) following 

standard operating procedures and USGS Leetown Science 

Center Institutional Animal Care and Use Committee approval 

(protocol AEL-2019-001).
Methods 3

OWC.1

OWC.2

OWC.3

UBH.2

UBH.3

BBC.1

BBC.2

LBH.1

LBH.2

525

575

450

475

525

500

500

500

475

475

450

450

525

575

450

475

400

425

350

325

400

400

325

350

425

425

350

450

325

475

500

550

300

375

275

275

300

300

225

250

250

375

39°40'

39°39'

39°38'

77°30' 77°29' 77°28' 77°27' 77°26'

0 0.25 0.5 1 KILOMETER

EXPLANATION

Extent of Catoctin Mountain Park (CATO)

Cunningham Falls

CATO headquarters

Temperature gage

Elevation contour—25 meter intervals

ME

VT NH

MA

NY

PA

CT RI

NJ

OH

DC DE WV

MD

KY VA

TN NC

MI

UBH.1

0 0.25 0.5 1 MILE

Base from ESRI, 2020

Hydrology from U.S. Geological Survey, National Hydrography Dataset, 2020

Digital elevation data from U.S. Geological Survey, EROS, 2020

North American Datum of 1983, UTM Zone 18 North

Location of study area

Hunting Creek Lake

525

Owens Creek

Upper Big Hunting Creek

Blue Blazes Creek

Lower Big Hunting Creek

Figure 1. Study site locations within Catoctin Mountain Park (CATO). 
4 Assessing Native Fish Restoration Potential in Catoctin Mountain Park

Histopathology and Fish Health Screening

We periodically inspected fish for external abnormalities 

(that is, Dermocystidium cysts, parasites, lesions) during the 

quarantine period, and we selected 10 individuals at random 

for pre-exposure histopathology analysis. Selected fish were 

euthanized with tricaine methanesulfonate (Tricaine-S, Syndel, 

Ferndale, Washington), slit ventrally, and placed in zincbuffered formalin (Z-Fix, Anatech, Battle Creek, Michigan) 

for >48 hours. Specimens were then decalcified in ethylenediamine tetraacetic tetrasodium salt dihydrate (EDTA; SigmaAldrich) at pH 7.2 for 2–4 days. After decalcification, transverse sections of the body were embedded into paraffin blocks, 

sectioned at 5 micrometers, and stained with hematoxylin and 

eosin (Luna, 1992) for visual inspection with 4–60x magnification following Blazer and others (2016). Pre-exposure 

histology analysis confirmed the absence of Dermocystidium

infection. We used the same methods for histological analysis 

for fish collected from enclosures after the exposure period 

(see below).

We also collected kidney and spleen samples for viral and 

bacterial assessment of the 10 fish used for pre-exposure histological analysis. This analysis was conducted by personnel 

at the Lamar National Fish Hatchery (U.S. Fish and Wildlife 

Service, Lamar, Pennsylvania) following standard methods of 

the American Fisheries Society (American Fisheries SocietyFish Health Section, 2016). Results indicated the absence of 

viral and bacterial targets and are catalogued as Case #19-161 

in the National Wild Fish Health Survey maintained by the 

U.S. Fish and Wildlife Service.

Experimental Design

We constructed 11 cages for use as experimental fish 

enclosures. Cages were constructed from PVC pipes (2.5 centimeter [cm] diameter) and 0.6 cm wire mesh and measured 

approximately 1 m by 1 m by 0.4 m. We deployed cages in 

five sites (table 1) with two cages per site for all sites except 

for Owens Creek (OWC.3) where three cages were deployed. 

All cages were placed in riffle habitats and fixed to the stream 

bottom with rebar. We added natural substrates to the bottom 

of each cage and deployed cages >7 days prior to introducing fish to enable benthic macroinvertebrate colonization as 

a food source. We visited sites multiple times per week to 

remove leaves and woody debris from the exterior of cages. 

Similar cage designs and deployment strategies were used for 

sculpin research by Zimmerman and Vondracek (2006), and an 

example from our study is shown in figure 2.

We randomly assigned 3 fish per cage for a total of 33 

individuals. We introduced fish into cages on July 26, 2019 

and removed them on September 9, 2019 (45 exposure days). 

We measured individual weights in situ on August 1 and 

September 9, yielding 39 days for growth analysis. However, 

for three individuals we measured initial weights on August 5, 

and for one individual we measured initial weight on 

August 9, yielding 35 and 31 days for growth analysis in those 

cases, respectively. We calculated specific growth rate (SGR) 

following Cook and others (2000) as

 SGR = 

_ln( Wf) − ln( Wi) t × 100 (1)

where

Wf is the final weight in grams;

Wi is the initial weight in grams; and

t is time in days.

This calculation expresses SGR as percent body weight 

gain per day. Sample size was reduced from 33 to 31 individuals for analysis owing to one likely mortality (OWC.3) and 

one escape (UBH.3). Fish cages were co-located with temperature sites except for LBH.2, in which cages were located 

~250 m downstream of the temperature gage.

Table 1. Sample site information. Site latitude and longitude are given in Universal Transverse Mercator zone 17N coordinates (NAD83 

datum). Stream temperature was measured hourly in all sites. OWC, Owens Creek; UBH, upper Big Hunting Creek; BBC, Blue Blazes 

Creek; LBH, lower Big Hunting Creek; *, fish cage site. 

Stream Site code Latitude Longitude Elevation 

(meters)

Upstream basin area 

(hectares)

OWC OWC.1 39.662757 -77.480462 387 753.4

OWC.2 39.665322 -77.479902 371 771.3

OWC.3* 39.666235 -77.479124 370 787.2

UBH UBH.1 39.636481 -77.483223 437 641.1

UBH.2* 39.636142 -77.481513 431 663.8

UBH.3* 39.634602 -77.478495 425 787.6

BBC BBC.1* 39.637175 -77.449296 309 146.4

BBC.2 39.635287 -77.450635 296 157.6

LBH LBH.1 39.633224 -77.449957 283 2,104.0

LBH.2* 39.631374 -77.446842 282 2,145.3
Methods 5

Statistical Analysis

We evaluated individual growth rates with model selection techniques in a linear mixed-modeling framework. We 

compared a series of fitted models with all combinations of 

site-level covariates including elevation (a proxy for air temperature), upstream basin area (a proxy for habitat volume), and 

two summaries of water temperature: mean daily temperature 

(MDT) and accumulated degree-days above 20 °C (DD20). 

Site-level covariates were treated as fixed effects in the linear 

models. We also included a random-intercept by cage in all 

models to account for possible effects of cage placement within 

a site or differences in density-dependent competition across 

cages. We scaled numeric covariates to a mean of zero and 

standard deviation of one (that is, z-score transformation) to 

facilitate comparisons. Elevation and upstream basin area were 

not significantly correlated among cage sites (Pearson’s r = 

–0.40; p = 0.25).

We compared candidate models using Akaike information 

criterion (AIC) scores (Burnham and Anderson, 2002) and evaluated the significance of covariates in top-performing models 

based on 95-percent confidence intervals generated from 1,000 

bootstrapped samples. We used functions in R packages lme4 

version 1.1-23 (Bates and others, 2015) and MuMIn version 

1.43.17 (Barton, 2020) to fit and evaluate linear mixed-models. 

We estimated the coefficient of determination for each model 

with and without random effects (that is, conditional and marginal R2, respectively) to evaluate the proportion of variance in 

growth explained by each component of the model (Nakagawa 

and Schielzeth, 2013). All statistical analysis and plotting was 

conducted in R version 3.6.3 (R Core Team, 2020). Stream temperature and fish growth data used in this analysis are available 

from Hitt and others (2020).

Figure 2. Example of experimental fish enclosure placement in Owens Creek (site OWC.1). Photograph by N.P. Hitt, U.S. 

Geological Survey.
6 Assessing Native Fish Restoration Potential in Catoctin Mountain Park

Results

Stream Temperature Assessment

Observed stream temperatures ranged from 11.2 °C in 

Owens Creek (OWC.1) to 26.6 °C in lower Big Hunting Creek 

(LBH.1) (table 2; fig. 3) Temperatures exhibited more temporal variation in Big Hunting Creek than elsewhere: a site 

(UBH.1) in upper Big Hunting Creek showed the largest range 

in observed temperatures (13.6 °C; table 2), and a site (LBH.1) 

in lower Big Hunting Creek showed the largest standard 

deviation in observed hourly temperatures (2.4 °C; table 2). 

Hourly temperatures within streams exhibited close correspondence across sites (appendix 1, figs. 1.1–1.4) and were highly 

correlated (Pearson’s r >0.99 for all pairwise combinations).

Daily mean temperatures were significantly different 

among streams during the study period (F = 10.8, df = 3, 

p<0.0001) with lower temperatures in Owens Creek than in 

upper or lower Big Hunting Creek (table 3). Moreover, daily 

mean temperatures in Owens Creek were consistently cooler 

than other streams during the study period (fig. 4). In contrast, 

lower and upper Big Hunting Creek alternated as the warmest 

sites (fig. 4), likely owing to effects of precipitation on discharge from Hunting Creek Lake, which separates the upper 

and lower Big Hunting Creek sites (fig. 1). Daily mean stream 

temperatures in Blue Blazes Creek generally showed an 

intermediate pattern between Owens Creek and Big Hunting 

Creek (fig. 4), but the maximum observed temperature in Blue 

Blazes Creek was only 1.1 degrees cooler than observed in 

upper Big Hunting Creek (table 2).

Grand-mean temperatures did not exceed the 20 °C 

threshold for physiological stress in brook trout (table 2), 

but all sites exceeded this value for maximum temperatures 

(table 2) and daily mean temperatures (fig. 4). However, the 

accumulated time above 20 °C (DD20) showed important 

differences among streams: DD20 was 10 times greater in 

upper Big Hunting Creek than Owens Creek and was 14 

times greater in lower Big Hunting Creek than Owens Creek 

(table 2). Likewise, MWAT was below the 23.3 °C threshold 

for brook trout occurrence in Owens Creek and Blue Blazes 

Creek but exceeded this threshold in upper and lower Big 

Hunting Creek sites (table 2).

Fish Enclosure Experiment

We observed 361 fish representing 7 taxonomic families 

and 8 species within 300-m of Owens Creek (table 4). The 

most abundant species was Blue Ridge sculpin (65 percent) 

followed by blacknose dace (21 percent). Brook trout composed approximately 4 percent of the total catch and included 

age-0 (young-of-year) fish as well as adult (age 1+) fish 

(table 4). Incidental inspection of brook trout gills showed no 

sign of Dermocystidium infection.

Pre-exposure histological analysis confirmed the absence 

of Dermocystidium infection in all sampled specimens held 

during the quarantine period (see Methods). The in situ exposure period encompassed 45 days (July 26 to September 9, 

2019) during a period of time when sites in Big Hunting 

Creek were warmer than in Owens Creek or Blue Blazes 

Creek (fig. 3). A significant rainfall event during the exposure 

period appeared to increase temperatures in LBH owing to 

surface water runoff from Hunting Creek Lake. Histological 

analysis also detected myxozoan cysts in the muscle, ovary, 

and liver tissues from several specimens, and parasitic worms 

were observed in the lumen of the gut in several specimens. 

Myxozoan cysts and parasitic worms were detected in specimens from all streams, and there was no observable host 

response to these infections.

Post-exposure histological analysis detected no 

Dermocystidium infection in fish held in in situ enclosures. 

Fish growth rates (SGR) ranged from –0.088 in Blue Blazes 

Creek (BBC.1) to 0.559 in lower Big Hunting Creek (LBH.2) 

(table 5). Mean SGR was positive in all sites, but generally 

greater in Big Hunting Creek sites (UBH.2 and LBH.2) than 

Table 2. Summary of hourly stream temperatures during the 100-day sample period (June 1, 2019, to September 9, 2019). The minimum, 

mean, maximum, standard deviation, and maximum weekly average temperature are expressed in degrees Celsius.

Stream code Site code Minimum Mean Maximum Standard 

deviation

Maximum weekly 

average temperature

OWC OWC.1 11.20 17.65 22.39 1.85 20.96

OWC.2 11.22 17.81 22.63 1.89 21.28

OWC.3 11.22 17.87 22.75 1.90 21.38

UBH UBH.1 11.78 19.12 25.38 2.19 23.56

UBH.2 12.07 19.22 25.26 2.10 23.62

UBH.3 12.20 19.15 25.23 2.10 23.24

BBC BBC.1 11.76 18.33 23.59 2.02 22.59

BBC.2 11.64 18.61 24.27 2.11 23.07

LBH LBH.1 13.86 19.38 26.57 2.38 24.58

LBH.2 13.40 19.33 26.23 2.31 24.27
Results 7

elsewhere (table 5). For instance, mean sculpin growth in the 

control site where fish were initially collected (OWC.1) was 

approximately five times lower than observed in Big Hunting 

Creek sites (table 5).

Linear mixed models revealed stronger effects of 

temperature than other predictors on fish growth (table 6). 

Thermal summaries of DD20 and MDT were included in the 

top-performing models (that is, lowest AIC scores) (table 6), 

and bootstrapped 95-percent confidence intervals exceeded 

zero for each scaled parameter (0.03–0.16 and 0.02–0.15, 

respectively) indicating a positive effect of water temperature on fish growth. In contrast, the next best model included 

an effect of upstream basin area (table 6), but this predictor was not significantly different from zero in bootstrapped 

95-percent confidence intervals (–0.03–0.14). Thermal effects 

in the top performing models explained between 24 and 28 

percent of the variation in sculpin growth (R2

marginal), and with 

the inclusion of random effects these models each explained 

approximately 51 percent of the observed variation in sculpin 

growth (R2

conditional; table 6).

June July August September

Month

12

14

16

18

20

22

24

26

Hourly stream temperature, in degrees Celsius

EXPLANATION

LBH.1

OWC.1

Cage exposure period

Figure 3. Hourly stream temperatures for the warmest site (LBH.1) and coolest site (OWC.1) during summer 2019 (100 

days). Tick marks on the x-axis show the first day of each month. Site locations are mapped in figure 1. Grey vertical lines 

indicate significant rainfall events (see text).
8 Assessing Native Fish Restoration Potential in Catoctin Mountain Park

Discussion

Native species conservation is a fundamental objective of the National Park system, and our study provides new 

inferences for stream fish conservation planning in CATO by 

linking observational and experimental research. We monitored stream temperatures and conducted a caged-fish experiment in CATO to assess fish growth and disease susceptibility 

during the summer of 2019 (100 days of temperature monitoring and 45 days of in-situ exposure for 33 fish). Our study 

demonstrated that (1) stream temperatures are significantly 

warmer in Big Hunting Creek (above and below Cunningham 

Falls) than in Owens Creek, (2) sculpin growth increased 

with temperature, and (3) Dermocystidium did not infect fish 

held in experimental enclosures in the study area. For these 

reasons we suggest that environmental conditions in upper Big 

Hunting Creek may be suitable for reintroduction of native 

Blue Ridge sculpin. Here we discuss our results in the context 

of prior research, and we provide recommendations for future 

research and conservation planning in the study area.

Observed stream temperatures in 2019 were largely 

consistent with prior surveys. As observed during summers of 

2015 and 2016 (Hitt and others, 2017a), we found that Owens 

Creek was colder than Big Hunting Creek in 2019 (table 2 and 

table 3). We also found that mean stream temperatures in 2019 

(table 2) were within the range of mean temperatures observed 

at the stream-level in 2015 and 2016 (Hitt and others, 2017a). 

Likewise, Big Hunting Creek sites showed the highest maximum temperatures within the study area in 2015 and 2016 

(Hitt and others, 2017a) as well as 2019 (table 2). However, 

sites in Big Hunting Creek exceeded the thermal threshold 

for brook trout (MWAT >23.3 °C; Wehrly and others, 2007) 

in 2019 (table 2), whereas they did not exceed this threshold 

in 2015 or 2016 (Hitt and others, 2017a). Thermal habitat 

therefore may be a limiting factor for brook trout conservation 

in Big Hunting Creek. Moreover, elevated temperatures may 

exacerbate competition with nonnative brown trout (Salmo 

trutta) (Hitt and others, 2017b), and this is the subject of an 

ongoing investigation by MD-DNR, USGS, and the National 

Park Service to evaluate brook trout responses to manual 

removal of brown trout in upper Big Hunting Creek.

We attribute elevated temperatures in upper Big Hunting 

Creek to pond runoff from outside CATO and elevated 

temperatures in lower Big Hunting Creek to runoff from Big 

Hunting Lake located within Cunningham Falls State Park. To 

the contrary, we cannot attribute elevated stream temperatures 

in upper Big Hunting Creek to the so-called blowdown section 

(that is, riparian disturbance from a storm in 2004) because a 

temperature gage located at the upstream extent of the blowdown section also showed elevated temperatures. Moreover, 

precipitation events had different effects in different streams. 

For instance, a significant rainfall event on July 21–22, 2019, 

increased temperatures in lower Big Hunting Creek but 

decreased temperatures in Owens Creek (fig. 3). Prior research 

also has shown cooling effects of precipitation on stream 

temperature (Merriam and others, 2017) and warming effects 

of runoff from upstream impoundments (Lessard and Hayes, 

2003; Kelly and others, 2016).

The fish assemblage observed in Owens Creek during 2019 was very similar to prior surveys. For instance, the 

density of Blue Ridge sculpin was 83 fish/100 m in 2015 (Hitt 

and others, 2017a) and 78 fish/100 m in 2019 (table 4) even 

though the total amount of habitat sampled in Owens Creek 

was much greater in 2015 than 2019 (4,600 m and 300 m, 

respectively). All eight species observed in 2019 were detected 

in Owens Creek in 2015 (Hitt and others, 2017a). However, 

two species were observed in 2015 but not 2019 (brown trout 

and Potomac sculpin [Cottus girardi]) probably because the 

sampling design in 2015 included areas further downstream 

than in 2019.

The fish enclosure experiment documented that shortterm exposure to site conditions did not cause Dermocystidium

infection in sculpin. Although the pathological mechanisms 

and taxonomy of the Dermocystidium observed previously in 

the study area are not fully resolved (Blazer and others, 2016), 

our study provides experimental evidence that short-term 

exposure to site conditions does not necessarily yield infection 

in sculpin within the study area. Our use of summer conditions 

Table 3. Comparison of daily mean temperatures within Owens Creek (OWC), upper Big Hunting Creek (UBH), Blue Blazes Creek 

(BBC), and lower Big Hunting Creek (LBH). Pairwise differences between streams are shown as Tukey post-hoc comparisons from 

an ANOVA model with significant streamwise differences in daily mean stream temperatures during summer 2019 (F = 13.6, df = 3, 

p<0.0001). Pairwise differences with 95-percent confidence intervals excluding zero are indexed with *.

Stream comparison Mean difference Lower 95-percent confidence 

interval

Upper 95-percent confidence 

interval

LBH-BBC* 0.87 0.16 1.58

OWC-BBC –0.70 –1.41 0.01

UBH-BBC 0.69 –0.02 1.40

OWC-LBH* –1.57 –2.28 –0.86

UBH-LBH –0.18 –0.89 0.53

UBH-OWC* 1.39 0.68 2.10
Discussion 9

for this experiment is useful because thermal stress is often 

associated with compromised immune system function, which 

may exacerbate pathogen and parasite infections (Marcogliese, 

2001). However, we cannot reject the possibility that longterm exposure may yield infection in sculpin in upper Big 

Hunting Creek because Dermocystidium can become dormant as spores in substrate (Pekkarinen and Lotman, 2003; 

Gozlan and others, 2014) and its virulence may increase below 

approximately 16 °C (Allen and others, 1968), a temperature 

which was observed only on a few nights during the exposure 

period (appendix 1, figs. 1.1–1.4). Likewise, Mahboub and 

Shaheen (2020) observed higher rates of Dermocystidium

infection in Nile tilapia (Oreochromis niloticus) during winter 

than summer.

The fish enclosure experiment also demonstrated that fish 

grew faster in warmer sites, including candidate reintroduction 

locations. Fish growth typically follows a curvilinear response 

to water temperature such that growth rates are optimized at 

some intermediate temperature (Lugert and others, 2016). 

Our results indicated that stream temperature was a stronger 

14

16

18

20

22

24

June July August September

Month

Daily mean stream temperature, in degrees Celsius

EXPLANATION

LBH

UBH

BBC

OWC

Cage exposure period

Figure 4. Daily mean stream temperatures averaged across sites within Owens Creek (OWC), upper Big Hunting 

Creek (UBH), Blue Blazes Creek (BBC), and lower Big Hunting Creek (LBH). Sites are mapped in figure 1. Grey vertical 

lines indicate significant rainfall events (see text).
10 Assessing Native Fish Restoration Potential in Catoctin Mountain Park

Table 4. Relative abundance of fish in three spatially consecutive 100-m sampling areas within Owens Creek. Backpack electrofishing 

proceeded in an upstream direction from OWC.3 (see fig. 1) on May 24, 2019, and June 7, 2019 (see text for details).

Family Scientific name Common name Observed 

abundance

Proportional 

abundance

Fish density (number/100 meters)

Catostomidae Catostomus comersonii White sucker 8 0.022 2.7

Cottidae Cottus caeruleomentum Blue Ridge sculpin 234 0.648 78.0

Leuciscidae Rhinichthys atratulus Blacknose dace 77 0.213 25.7

Rhinichthys cataractae Longnose dace 13 0.036 4.3

Clinostomus funduloides Rosyside dace 4 0.011 1.3

Semotilus atromaculatus Creek chub 5 0.014 1.7

Percidae Etheostoma flabellare Fantail darter 5 0.014 1.7

Salmonidae Salvelinus fontinalis Brook trout (young-ofyear)6 0.017 2.0

Brook trout (age 1+) 9 0.025 3.0

Table 5. Site-level summaries for fish growth and exposure temperatures for the caged-fish experiment. Sample size (n) indicates the 

number of fish introduced in cages in each site. DD20 is the cumulative daily mean temperature above 20 °C during the 45-day exposure 

period. Mean daily water temperatures (MDT) are calculated from hourly data during the 45-day fish exposure period and are given in 

degrees Celsius. Sites are mapped in figure 1.

Specific growth rate Temperature

Site code n Minimum Maximum Mean Standard deviation MDT DD20

OWC.3 8 –0.058 0.160 0.054 0.076 18.4 1.9

UBH.2 5 0.195 0.528 0.318 0.133 19.5 17.2

UBH.3 6 0.000 0.289 0.157 0.106 19.5 16.1

BBC.1 6 –0.088 0.207 0.028 0.130 18.9 4.1

LBH.2 6 0.032 0.559 0.240 0.219 20.4 28.1

Table 6. Summary of fitted linear mixed models for specific growth rate from the caged fish experiment. All models included random 

intercepts by cage. Columns provide degrees of freedom (df), Akaike information criterion (AIC) scores, the relative difference in AIC 

score from the best-performing model (ΔAIC), and the proportion of variance explained by fixed effects (R2

marginal) and by fixed and 

random effects (R2

conditional). Table 5 gives covariates for mean daily temperature (MDT) and degree-days (DD20), and table 1 gives 

covariates for elevation (ELE) and upstream basin size (UBA).

Fixed effects df AIC ΔAIC R2

marginal R2conditional

DD20 4 –17.29 0.00 0.275 0.510

MDT 4 –16.38 0.91 0.236 0.514

UBA 4 –13.55 3.73 0.091 0.530

ELE 4 –12.66 4.62 0.035 0.544

DD20 + ELE 5 –12.13 5.15 0.327 0.532

DD20 + UBA 5 –12.01 5.27 0.284 0.534

MDT + ELE 5 –11.74 5.54 0.310 0.534

MDT + UBA 5 –10.52 6.76 0.226 0.544

ELE + UBA 5 –9.49 7.80 0.206 0.554

DD20 + ELE + UBA 6 –6.53 10.76 0.311 0.558

MDT + ELE + UBA 6 –5.93 11.36 0.298 0.561
References Cited 11

predictor of growth than other predictors (table 5 and table 6), 

which suggests that increased prey availability and foraging 

success accounted for the increased metabolic demands with 

elevated water temperatures in Big Hunting Creek. Moreover, 

although Big Hunting Creek was warmer than Owens Creek 

(table 3), none of the observed water temperatures reached the 

thermal threshold reported for a closely related species (24.3 

°C, mottled sculpin, Cottus bairdii) (Eaton and Scheller, 1996) 

at the daily or hourly time-step (fig. 3 and fig. 4). Our results 

therefore indicate that conditions in the study area are suitable 

for sculpin growth and survival.

Interpreting our growth experiment results requires 

consideration of the effects of enclosures on food availability. 

Using a similar design, Zimmerman and Vondracek (2006)

showed that water flow rate decreases within such enclosures, 

and this can reduce the rate of incoming food for fish held 

in the enclosure. However, they found that sculpin growth 

increased with the size of macroinvertebrates in the drift and 

prey size was not different between enclosures and adjacent 

riffle habitats (Zimmerman and Vondracek, 2006). Although 

we did not quantify macroinvertebrate abundance or biomass 

in this study, our results indicate that the biomass of incoming 

prey was enough to account for increased metabolic demands 

associated with elevated temperatures in Big Hunting Creek. 

Our use of enclosures also restricted the potential for fish 

movement. Although sculpin can move relatively long distances (for example, >1.7 kilometers in 75 days for Potomac 

sculpin, Cottus girardi; Hudy and Shiflet, 2009), mottled 

sculpin generally show highly restricted movement patterns 

(for example, 1.3 m median movement distance over 45 days; 

Petty and Grossman, 2004) consistent with the size of our 

experimental enclosures.

Collectively, our results may suggest that environmental 

conditions in upper Big Hunting Creek are suitable for restoration of native Blue Ridge sculpin. To this end, a reintroduction 

and monitoring plan could be developed to include analysis 

of minimum viable population size for reintroduction, the 

capacity for Owens Creek to serve as a donor population, histopathological analysis of fish before and after reintroduction, 

and fish growth rates and recruitment in upper Big Hunting 

Creek. Results from this further analysis could lead to expanding sportfishing opportunities by increasing the forage base 

for brook trout. We believe this could be a unique opportunity 

for native species restoration in a National Park that combines native species conservation with enhanced sportfishing 

opportunities.

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14 Assessing Native Fish Restoration Potential in Catoctin Mountain Park

Appendix 1 Hourly Stream Temperature Plots

12

14

16

18

20

22

24

26

Hourly stream temperature, in degrees Celsius

June July August September

Month

EXPLANATION

OWC.1

OWC.2

OWC.3

Figure 1.1. Hourly temperature plots during summer 2019 (100 days) in Owens Creek. Tick marks on the x-axis show 

the first day of each month. Site locations are mapped in figure 1 and site codes are given in table 1. Grey vertical lines 

indicate significant rainfall events (see text for methods).
Appendix 1 Hourly Stream Temperature Plots 15

12

14

16

18

20

22

24

26

Hourly stream temperature, in degrees Celsius

June July August September

Month

EXPLANATION

UBH.1

UBH.2

UBH.3

Figure 1.2. Hourly temperature plots during summer 2019 (100 days) in upper Big Hunting Creek. Tick marks on the x-axis 

show the first day of each month. Site locations are mapped in figure 1 and site codes are given in table 1. Grey vertical 

lines indicate significant rainfall events (see text for methods).
16 Assessing Native Fish Restoration Potential in Catoctin Mountain Park

June July August September

Month

12

14

16

18

20

22

24

26

Hourly stream temperature, in degrees Celsius

EXPLANATION

BBC.1

BBC.2

Figure 1.3. Hourly temperature plots during summer 2019 (100 days) in Blue Blazes Creek. Tick marks on the x-axis show 

the first day of each month. Site locations are mapped in figure 1 and site codes are given in table 1. Grey vertical lines 

indicate significant rainfall events (see text for methods).
Appendix 1 Hourly Stream Temperature Plots 17

June July August September

Month

12

14

16

18

20

22

24

26

Hourly stream temperature, in degrees Celsius

EXPLANATION

LBH.1

LBH.2

Figure 1.4. Hourly temperature plots during summer 2019 (100 days) in lower Big Hunting Creek. Tick marks on the x-axis 

show the first day of each month. Site locations are mapped in figure 1 and site codes are given in table 1. Grey vertical 

lines indicate significant rainfall events (see text for methods).

For additional information, contact: 

Director, Leetown Science Center 

U.S. Geological Survey 

11649 Leetown Road 

Kearneysville, WV 25430 

Or visit our website at https://usgs.gov/centers/lsc

Publishing support provided by the West Trenton Publishing 

Service Center
Hitt and others—Assessing Native Fish Restoration Potential in Catoctin Mountain Park—OFR 2020–1137

ISSN 2331-1258 (online)

https://doi.org/10.3133/ofr20201137