In 2003, the National Park Service initiated a survey of Cambarus (Punticambarus)

crayfish in Valley Creek in Valley Forge National Historical Park (VAFO), southeastern

Pennsylvania. The Valley Forge Cambarus is one of the few populations of the species

known to exist in the region. In June 2008, the invasive rusty crayfish, Orconectes

rusticus, was found in Valley Creek for the first time and assumed to possess a serious

threat to the native crayfish. To address this threat, NPS began a removal program to

maintain the relative abundance of O. rusticus below 20% of the total crayfish

population. O. rusticus were removed by dip-netting from Valley Creek between 2009

and 2013. Changes in O. rusticus abundances were evaluated by assessing the changes in

Catch Per Unit Effort (CPUE), size frequency distribution, relative abundance, and

removal of reproductive potential. CPUE for native crayfish declined but remained

constant above the dam for O. rusticus. Average adult and juvenile sizes increased as the

crayfish density was reduced. After 6,000+ hours of removal effort, the relative

abundance of O. rusticus was still approximately 20% of total crayfish abundances.

However, the reproductive potential of O. rusticus was reduced by 535,000 eggs below

the dam and by over 350,000 eggs above the dam. The NPS management goal may have

been met, but the absence of information on the native species population has obscured

benefits of the removal program, and an abundant O. rusticus populations remains.

©Copyright by Brenda R. Wasler January 8, 2015

All Rights Reserved

Invasion of O. rusticus in Valley Forge National Historical Park, Pennsylvania

by Brenda R. Wasler

A CAPSTONE PROJECT

submitted to

Oregon State University

in partial fulfillment of the requirements for the

degree of

Master of Natural Resource Management

Presented January 8, 2015 Commencement June 2015

ACKNOWLEDGEMENTS

The author expresses sincere appreciation to the following people for their

invaluable assistance, guidance, and support in the process of completing my graduate

degree:

To Kristina Heister of the National Park Service, for the opportunity to work at

Valley Forge, which inspired me to take my career in a different direction, and gave me

the impetus to pursue my graduate work;

To the Hawks Women’s Ice Hockey team, for harassing, threatening, and supporting

me through the process, providing fruity girly beverages when I was ready to stop, and

finally critiquing the final draft;

To Colleen Rourke and Steve Long of USACE, for their guidance in using GIS;

To the NPS Crayfish Corps for their hours of dedication, and for supplying the data

we collected;

To Joan Hagar, for her willingness to step in on short notice, and for getting me the

elusive range data;

To Sam Chan, for his willingness to take me on during his travels across many time

zones and at the last minute;

To John Chapman, for his encouragement, guidance, and tireless efforts over many

afternoons working through the project with me;

To Anita Morzillo, for being my support in times of panic, my encouragement

through the tough times, and my sounding board when I didn’t know which way was up;

To my family, for encouraging me to keep going;

To my husband, John, for his technical support as I destroyed laptop after laptop,

keeping me on track, and not letting me quit.

TABLE OF CONTENTS

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

Methods............................................................................................................................... 5

Site Description ............................................................................................................... 5

Study Area ....................................................................................................................... 6

Control Methods .............................................................................................................. 6

Data Collection ................................................................................................................ 7

Results ............................................................................................................................... 10

Discussion ......................................................................................................................... 12

Further Study ................................................................................................................. 18

Literature Cited ................................................................................................................. 37

INTRODUCTION Keystone species maintain structure in ecosystems by their greater impact relative to

their abundances or biomasses (Paine, 1995). Crayfish play a keystone role in rivers by

providing a link in the nutrient transfer between macrophytes, invertebrates, and

vertebrates in the food chain. Thus, declines in native crayfish populations may have far-

reaching consequences for both aquatic and terrestrial ecological communities.

Landscape changes, habitat alterations, and the introduction of invasive species have

impacted aquatic communities (Hill & Lodge, 1999; Rabalais & Magoulick, 2006; Hein

et al. 2007), resulting in almost half of the known 362 species of crayfish in North

America becoming extinct, endangered, threatened, or of special concern (Taylor &

Redmer, 1996; Etchison et al. 2012).

For many crayfish species, geographic range and population status data are not

available due to a lack of comprehensive studies. In Pennsylvania, several local surveys

have been conducted (Kuhlmann & Hazelton, 2007; Lieb et al. 2007; Lieb et al. 2011),

but the last comprehensive state-wide inventory of crayfish fauna was completed in 1906

(Ortmann 1906). Ortmann identified two widely distributed dominant species of crayfish

in southeastern PA: Orconectes limosus and Cambarus bartonii (Lieb et al. 2011).

Ortmann’s survey, which included 52 of the 67 Pennsylvania counties, has not been

reproduced, leaving the current conservation status of O. limosus and C. bartonii within

southeastern Pennsylvania unknown.

Twelve native and two invasive crayfish species were known until recently in

Pennsylvania (Lieb et al. 2011). The thirteenth native species, identified preliminarily as

Cambarus (Punticambarus) sp., was documented in 2003 by Lieb et al. (2007) in a

survey for the National Park Service (NPS) in Valley Forge National Historical Park

(VAFO) in southeastern Pennsylvania. Subsequently, Lieb et al. (2011) examined the

distribution and relative abundance of southeastern Pennsylvania’s crayfish and identified

C. (P) sp. as limited to eight streams in the Delaware River watershed, and Pickering and

Valley Creeks in the Schuylkill River watershed.

2

The conservation status of the presumed native species C. (P) sp. became a particular

concern in 2008, when Orconectes rusticus (rusty crayfish)) were discovered below the

dam in Valley Creek within VAFO. O. rusticus is native to the Ohio River and its

tributaries (Taylor & Redmer, 1996), but has spread to the Great Lakes, Mid-Atlantic,

and New England regions since the 1970’s (Fig. 2). O. rusticus were first recorded in the

south-central region of Pennsylvania, in the lower Susquehanna River, in 1976

(Pennsylvania Sea Grant, n.d.), but a survey in 2005 did not observe O. rusticus in Valley

Creek (Lieb et al. 2007b).

O. rusticus is a particularly aggressive species, known to collapse fisheries and

extirpate native crayfish populations (Capelli, 1982; Taylor & Redmer, 1996; Lodge et al.

2000, Hein et al. 2007, Lieb et al. 2007). O. rusticus is a major threat to crayfish species

diversity, especially in the case of C. (P) sp. in VAFO, which are especially vulnerable to

introduced competitors due to their limited abundance and range (Lodge et al. 2000).

Factors that may contribute to expansion of O. rusticus may include its voracious

and opportunistic feeding on all macrophytes, invertebrates, and fish eggs in their habitats

(Pennsylvania Sea Grant, n.d.). O. rusticus consume up to twice as much food as similar-

sized crayfish species, due to their higher metabolic rates (Momot, 1992), and grow faster

and to larger sizes than native species (up to body lengths of 12 cm) (Lieb et al. 2011).

O. rusticus have proportionately larger claws and a thicker exoskeleton than the native

crayfish, which provides defense against fish predators. These anatomical advantages

allow O. rusticus to avoid predation more often than natives, (Gunderson, 2009), remain

in open feeding sites for longer periods (Stein, 1977), and reach higher population

densities higher densities (up to 13 adults per square meter) than those of similar species

(Lodge & Lorman, 1987).

O. rusticus negatively impact fish populations by the consumption of their eggs,

reduction of available invertebrate prey, and destruction of aquatic habitat (Lodge &

Lorman, 1987) (McCarthy et al. 2006). Although O. rusticus are eaten by fish, they

provide less nutritional benefit than the other invertebrates due to the higher ratio of

exoskeleton to soft tissue (Gunderson, 2009). Lower food quality means slower growth

3

for fish populations, reducing their survival. Juvenile fish species also endure more

competition for benthic invertebrates from O. rusticus than native crayfish (Stein, 1977).

O. rusticus reduce aquatic plant abundance, thereby reducing species diversity (Lodge &

Lorman, 1987; Olden et al, 2006). After O. rusticus invasions, Wilson et al (2004) found

that fish species that compete for prey with rusty crayfish decline over time, while

McCarthy et al. (2006) observed that larval midges, mayflies, and stoneflies decline as

the invasive crayfish population increases.

The reproductive capability of O. rusticus also provides an additional survival

advantage over the native VAFO species. The mating season of O. rusticus extends from

late summer into winter, with the female storing the sperm capsule in her seminal

receptacle until the eggs are ready to fertilize in the spring when water temperatures

increase (Gunderson, 2009). Females lay 300-700 eggs, which are attached to their

abdominal swimmerets. The eggs hatch in three to six weeks, depending on water

temperature (Lieb et al. 2007). Young crayfish cling to the female's swimmerets for three

to four molts, and may remain with the female for several more weeks for protection

during this vulnerable life stage. Juveniles molt eight to ten times before reaching

maturity at carapace lengths of approximately 16 mm. Although some O. rusticus reach

sexual maturity by the first autumn, most mature after one year (Hein et al. 2007).

Growth slows after maturity with mature males molting twice per year, and mature

females molting once per year after the release of their young. Males are usually larger

than females of the same age (Gunderson, 2009). The average O. rusticus life span is 3-4

years (Hein et al. 2007).

In response to the invasion, NPS began a removal program to maintain the relative

abundance of O. rusticus at 20% of the total crayfish population, with this baseline

defined as 2008 condition in Valley Creek. In order to promote the co-existence of the

native crayfish C. (P) sp. with O. rusticus, invasive crayfish were removed from Valley

Creek within VAFO by volunteers in the “Crayfish Corps” from April- September in

2009-2013. The objective of this study is to evaluate the effectiveness of the removal

4

program by determining the changes in the invasive crayfish population based on Catch

Per Unit Effort, Size Frequency Distribution, and reduction of reproductive potential.

5

Methods SITE DESCRIPTION

Valley Forge National Historical Park (VAFO) is a rare open space in a region

bisected by transportation corridors and dense residential and commercial development in

southeastern Pennsylvania, approximately 20 km northwest of Philadelphia, in Chester

and Montgomery Counties (Fig. 2). VAFO includes 1,416 hectares (60. 6 km2) of fields

and forest on gently rolling hills bordered by steep slopes. The VAFO includes

approximately 55 km of tributaries and the 3.2 km Valley Creek, which flows into the

Schuylkill River. The creek is 10 meters wide and has a moderate gradient that includes

pools, riffles, and meanders. Limestone seeps and the forested surrounding riparian zone

maintain cool water temperatures in the creek.

Valley Creek is designated under the Pennsylvania Water Quality Standards as an

Exceptional Value watershed. PA Code, Chapter 93.4b identifies the high water quality

of the stream based on chemical characteristics and biological assessment of physical

habitat, benthic macroinvertebrates, and fishes. Additional protection including anti-

degradation requirements, are provided by regulation in PA Code Chapter 93.4a to

maintain and protect the water quality.

The Pennsylvania Fish and Boat Commission lists Valley Creek as a “Class A Wild

Trout Stream,” which supports more than 40 kilograms of brown trout biomass per

hectare (Valley Creek Trustee Council, 2004). These naturally reproductive brown trout

populations allow for “catch and release” fishing. As an additional safeguard to protect

the native ecosystem, live bait are not allowed within VAFO (National Park Service,

2012). The Schuylkill River, downstream of VAFO, is the most likely source of the

original O. rusticus for Valley Creek. Lieb et al. (2011) found O. rusticus in the

Schuylkill River, where they were probably introduced as live bait by anglers. O. rusticus

can move over land (2008, pers. obs.) and thus could have bypassed the three-meter-high

dam on Valley Creek to invade VAFO from the Schuylkill River.

6

STUDY AREA

For the study, Valley Creek within VAFO park boundaries was divided into four

reaches (Fig. 2).

Below Dam

• Section 1 – Confluence with the Schuylkill River upstream 735m to the

VAFO dam.

Above Dam

• Section 2 – VAFO Dam upstream to the Covered Bridge.

• Section 3 – Covered Bridge upstream to the Iron Bridge.

• Section 4 – Iron Bridge upstream to the I-276 Pennsylvania Turnpike Bridge

(VAFO park boundary).

CONTROL METHODS

Following the discovery of O. rusticus in Valley Creek in 2008, NPS compared

requirements, advantages, and limitations of O. rusticus control methods (Table 1).

Initially, it was expected that the VAFO dam may have prevented the upstream spread of

O. rusticus (Lieb et al. 2011). To test this hypothesis, the extent of the invasion above

the first dam on Valley Creek was investigated by a presence-absence survey in several

tributaries to Valley Creek. Although a lower density of O. rusticus was found in these

tributaries than in the main stem within VAFO, O. rusticus was already present

throughout the upper Valley Creek watershed.

NPS’s first effort to control O. rusticus was trap and removal. Twenty minnow traps

(Fig. 3) baited with chicken or fish (Hein, Vander Zanden, & Magnuson, 2007) were

weighted with rocks and set over the reach of Valley Creek within VAFO for six days per

week from July through August 2008. This method was successful for capturing

crayfish, but checking the traps daily (Fig. 4) was labor-intensive and took three to four

people approximately four hours to locate the traps, record the data, and reset them in the

stream. The traps were susceptible to tampering and loss during flooding (Fig. 5).

7

Additionally, non-target species, including wild brown trout (Salmo trutta) and Northern

water snakes (Nerodia sipedon), were harmed by the traps.

A mark-recapture survey was initiated in 2008 by removing one claw of each

captured O. rusticus and then releasing them. However, regeneration of claws made it

difficult to discern whether recaptured specimens had lost their claws naturally or by

marking. Carapace marking was considered, but a marking method could not be

identified that would be easy and ethical to implement, inexpensive, and retained long-

term throughout molts. O. rusticus molt frequently, up to eight to 10 times in their first

two years (Gunderson, 2009), and generally lose topically-applied pigment during each

molt (Brandt & Schreck, 1975). Although NPS sought data on the movement, range, and

density of O. rusticus, eventually it was decided that capture efforts would be most

beneficial if they were removed from the reproducing population after capture, rather

than released after marking. The mark-recapture efforts were therefore cancelled.

The NPS and Stroud Water Research Center then tested the effectiveness of electro-

fishing on crayfish in 2008. Non-target species were affected, while crayfish under rocks

were seldom impacted (Carline, 2001). Additionally, the expensive electro-fishing

equipment required specialized skills and raised safety concerns.

Control efforts were changed to dip-netting in 2009. Dip-netting did not require

daily trap monitoring, reduced incidental harm to non-target species, and allowed more

flexibility in scheduling surveys. This flexibility encouraged the use of volunteer groups,

which provided additional labor and extended the NPS budget for the removal program.

NPS developed the “Crayfish Corps” (Fig. 6) for this effort. More than 3,200 school-age

children and adults from schools, civic groups, and corporations participated in this

activity, which stimulated local interest in ecology while contributing over $45,000 worth

of volunteer labor to the park project over the next five years.

DATA COLLECTION

The Crayfish Corps consisted of 10-15 collectors per event who were managed by

two rangers and assigned to survey each stream section. Each section required three

hours to survey. Volunteers were trained to identify O. rusticus by their large grayish-

8

green to reddish-brown chelae, black bands adjacent to orange claw tips, and their rusty-

orange spots on each side of the carapace (Fig. 1). Experienced surveyors confirmed

identification during the survey.

Surveys were conducted during average water flows and low turbidity in water depths

of up to one meter. Riffles and pools with cobble substrates (rock sizes 64 mm to 256

mm) were the focus of the effort, while silt substrates were scanned for transient crayfish.

Air and water temperature, date, hours, and participant information were noted at the

beginning of each survey. Surveyors formed a line from bank to bank and moved slowly

upstream, overturning rocks and sweeping crayfish into fourteen-inch-diameter fine-

meshed nets (Fig. 7). All rocks were turned over in each area before proceeding. Native

crayfish were released downstream of the surveyors, while O. rusticus were stored in a

bucket and frozen for data collection.

O rusticus carapace length (CL) was measured to the nearest 0.01 mm from the

anterior tip of rostrum to posterior dorsal edge of carapace using digital calipers

(Mundahl & Benton, 1990). Sex was identified by the presence (or absence) of modified

fifth pair walking legs (gonopods) or annulus ventralis on males and the absence of these

appendages on females.

Person-hours were estimated from the number of volunteers multiplied by the hours

per survey. All native and invasive crayfish were counted, and carapace lengths of all O.

rusticus recorded. Catch Per Unit Effort (CPUE) was estimated from the number of each

species caught per person-hour in each stream section. Thus, CPUE standardizes the

catch to the rate of crayfish caught per hour to compare the catch among years and

sections, while controlling for level of volunteer effort.

Size Frequency Distributions (SFD) were graphed from the numbers of O. rusticus

grouped into 2-mm CL increments. The relative abundances of O. rusticus were

estimated from their frequencies relative to natives. Weight per length was estimated

from twenty-seven O. rusticus, ranging between 14- and 47-mm CL, weighed

individually to the nearest gram, and from the average weights of three crayfish with 13-

mm CL weighed together. Biomass of O. rusticus was estimated from the sum of CL

9

frequencies multiplied by expected weights per length (Hein et al. 2007). Fecundity was

estimated from carapace lengths, calculated as Fecundity = 10(1.0672+CL*0.0357) (Hein et al.

2007). Lost reproductive potential was estimated from the number of the invasive

crayfish collected and the associated egg production removed from the population.

10

RESULTS The surveys included 6,070 person-hours by 3,230 participants in the 304 events

over the five year study (Fig. 8). Survey hours above the dam in 2012 were twice the

hours completed in 2009. Below the dam, survey hours peaked in 2010, and then were

reduced gradually through the course of the study.

Approximately 12,000 O. rusticus were removed while 24,000 native crayfish were

captured and released during the study (Fig. 9). Crayfish captured below the dam peaked

at about 3,200 O. rusticus and 1,400 natives in 2010, and decreased through 2013 to 300

O. rusticus and 100 natives. More natives were captured above the dam than O. rusticus.

Natives captured peaked above the dam at 6,000 in 2011 and decreased to about 2,000 by

2013, while O. rusticus collections ranged between 600 and 1,200 over the course of the

study.

O. rusticus populations above and below the dam contained a juvenile (< 16-mm

CL) and an adult cohort (>19-mm CL) each year (Fig. 10; Fig. 11). O. rusticus above the

dam were larger than below the dam, while more crayfish were captured below the dam.

Size variation was greater among O. rusticus above the dam and the sizes of O. rusticus

increased, as density decreased below the dam. Above the dam, average O. rusticus size

and density increased until 2013 when the average size declined.

The ratio of O. rusticus to native crayfish remained nearly constant among years (Fig.

12), but the highest proportions of native crayfish were in 2013 above the dam and in

2010 below the dam. The O. rusticus population thus appears to be decreasing below the

dam, but less time was spent there by the volunteers as the study progressed and the

change could be a sample artifact. The CPUE for O. rusticus remained stable above the

dam, while below the dam, it declined sharply between 2011 and 2013 (Fig. 13). The

CPUE of native crayfish declined above and below the dam over time.

The biomass of removed male and female O. rusticus below the dam declined (Fig.

14). Above the dam, male and female biomass increased slightly through 2012 and then

11

declined in 2013. Removals reduced reproductive potential of O. rusticus 535,000 eggs

below the dam and by 350,000 eggs above the dam (Fig. 15).

The stream temperatures of Valley Creek varied seasonally between 10°C and 20°C,

with lowest temperatures in April and highest temperatures in July (Fig. 16). The highest

percentages of O. rusticus relative to total crayfish captured occurred when water

temperatures in Valley Creek were between 18° C and 20° C (Fig. 17).

12

DISCUSSION The 20% abundance of O. rusticus relative to the total crayfish population in 2008 in

Valley Creek was used as a baseline that NPS believed would permit coexistence of the

native species with the invasive species. The proportions of crayfish captured among

years remained relatively stable, suggesting that the two species may co-exist in Valley

Creek, if the removal effort continues at the current intensity. Based on the crayfish

captured in this effort, the native species appears to continue to persist and remain the

dominant species, despite the invasion by the notoriously aggressive O. rusticus.

Differences in life history may account for the persistence of the native species in the

presence of an aggressive invader. Although information on the native species is limited,

it is presumed that their habitat preferences include the cold water of spring-fed limestone

streams where temperatures are not as extreme as those streams fed by snowmelt and

precipitation runoff. The water in limestone streams picks up alkaloids, providing less

acidic water than other streams where pollution has lowered the pH (Utah State

Extension, 2015).

Habitat preferences of O. rusticus include clear, well-oxygenated water (Capelli,

1982) in both lotic and lentic environments (Taylor & Redmer, 1996). O. rusticus prefer

water temperatures between 20°C and 25°C (Mundahl & Benton, 1990). The stream

temperature of Valley Creek varied seasonally between 10°C and 20°C, with lowest

temperatures in April and highest temperatures in July. The highest percentages of O.

rusticus relative to total crayfish occurred when water temperatures in Valley Creek were

between 18° C and 20° C. O. rusticus may be seasonally exposed to water temperatures

ranging from near 0° C to 39° C in their native streams (Mundahl & Benton, 1990).

Invasive species in general tend to be more tolerant of lower water quality and warmer

temperatures than native species (Carline et al., 2011).

Greater than 20% of the Valley Creek watershed consists of impervious surfaces and

stormwater runoff has a significant impact on water resources. Storm water management

improvements to mitigate flooding has been the focus of the Chester County Water

13

Resources Authority and its state, local, and Federal partners since 2003 (Chester County

Water Resources Authority, 2010). Disturbances that change the thermal regime of the

water body may allow O. rusticus to invade new waters, displacing native species

(Mundahl & Benton, 1990). A gradual increase in water temperatures in Valley Creek

existed over the course of this study (Fig. 16). Detailed water temperature data from

previous years may be available that would identify whether increased stream

temperatures may have created habitat conditions conducive to an invasion by O.

rusticus.

Although the NPS management goal of maintaining the relative abundance of O.

rusticus at 20% of the total crayfish population appears to have been met as a result of the

Crayfish Corps effort, the dip-netting method did not appear to be practical for

continuous management of O. rusticus. After expending 6000+ hours of effort, the

relative abundance was still approximately 20% in 2013. Nevertheless, capturing and

removing the crayfish served as a rapid management response to the invasion, while other

approaches are investigated.

Other O. rusticus management options for NPS include physical, biological, and

chemical control methods. Physically trapping the crayfish using minnow traps was

ruled out as a management method after the initial season in 2008. The labor involved in

maintaining the traps was not sustainable in the long-term, and the incidental harm to

other species was not acceptable to NPS. Other physical methods may include draining

of streams and diversion of flowing channels, and the construction of physical or

electrical barriers to preclude crayfish movement. These approaches might reduce the

population of invasive species; however, eradication is unlikely unless the population is

restricted in range, size, and sources of replenishment. In Valley Creek within VAFO,

eradication is not a realistic management goal because sources of O. rusticus exist both

upstream and downstream of the study area. Physical methods have environmental costs,

such as damage to the habitat, impacts to riparian zones, and incidental harm to non-

target species, which, when weighed against the environmental benefits of employing

14

them, were found to have an inordinately high negative impact to the native aquatic

ecosystem.

Chemical biocides, including organophosphate, organochlorine, and pyrethroid

insecticides can be used to control crayfish, but these compounds are not crayfish-

specific and would harm non-target species, including native crayfish and other benthic

organisms. Another possible chemical solution may be to use pheromones to enhance

trapping success of the invasive crayfish. Stebbing et al. (2003) examined the

possibilities of pheromones to attract Pacifastacus leniusculus into traps, but crayfish-

specific chemical pheromones have not yet been developed.

Potential biological control methods include the use of fish predators, such as eels,

perch, and pike that are partial to eating crayfish. The amount of cover, type of fish

predator, and preferred habitat of the invasive crayfish are all important variables in

determining the success of the biological control. Diseases and toxin-producing microbes

that affect targeted species are other potential options, but limitng the detrimental effects

to the invasive species is generally not practicable (Holdich et al., 1999).

Although dip-netting was also labor-intensive, the use of the Crayfish Corps

volunteers resulted in many positive benefits. Citizen science, the collaboration between

scientists and volunteers (Rotman et al., 2012), encourage the public to participate in

data-gathering activates related to their personal interests, while collecting large-scale

field data that would otherwise be difficult for resource agencies to obtain (Kim et al.,

2011). Citizen science projects, such as the NPS Crayfish Corps, was an effective public

outreach tool to bring people to the park, and removed many more invasive crayfish from

Valley Creek than NPS could have achieved with only its employees. Since the survey

protocols were simple, the risk of deviating from standardized procedures was

minimized. Training volunteers in O. rusticus appearance and using experienced

surveyors to confirm identifications mitigated the risk of incorrect identification of

invasive species. The Crayfish Corps provided an effective public outreach tool to social

and environmental organizations, as well as corporations and schools. Fulfillment of

community service requirements was a common motivation for volunteerism. In addition

15

to fulfilling this need, volunteers had the opportunity to learn directly about invasive

species by experiencing natural resource management in action.

While collection of data via citizen science is a valuable endeavor, it is most useful if

it is applied towards management recommendations. Public outreach, not only to solicit

assistance, but later to share results and management implications, is an important

component of a successful volunteer program. Interpretation of such efforts (i.e., “why

does this program matter?”) provides scientific context for the data collection effort.

Early in the Crayfish Corps, NPS presented an overview of the invasive crayfish to

environmental agencies and organizations, including Valley Forge Trout Unlimited

Chapter and Valley Creek Restoration Partnership, and schools within the region.

Continued outreach to these key stakeholders, through presentations and interpretive

displays of Crayfish Corps’ results, fosters a collaborative partnership and encourages

continued participation in the program.

Although the removal effort and outreach program were very successful, the data

collected may be biased for several reasons. NPS decided to spend less time below the

dam and focus on the more closed population above the dam, due to the likely

immigration upstream from the Schuylkill River. The reduced number of crayfish

captured below the dam over time may have resulted from unequal survey hours among

sections. In addition, limited knowledge about crayfish and not marking native crayfish

as they were captured could have allowed overestimates of their abundances by counting

individuals multiple times throughout the term of the study.

Time of day, weather, and stream conditions may also have impacted the accuracy of

the survey. Juvenile crayfish tend to be active during bright sunny days, while the mature

crayfish are more active on cloudy days and at night (Nale, n.d.). Differences in

microhabitats preferred by life stages may have placed some crayfish out of the survey

paths during daylight hours. O. rusticus prefer cobble habitat, which allows them to hide

when necessary (Taylor & Redmer, 1996; Hill & Lodge, 1999). Although O. rusticus are

usually found in less than 1 m water depths they have also been found at depths of up to

14.6 m (Taylor & Redmer, 1996). Adult O. rusticus prefer deeper (>20 cm) pool areas

16

(Mundahl & Benton, 1990), while juveniles normally occupy shallow (<15 cm) riffle

areas bordering stream edges. Adults can force juveniles into shallow (<15 cm) areas

bordering stream edges (Butler & Stein, 1985), causing them to often be found in water

1.5° C to 6.8° C warmer than adults (Mundahl & Benton, 1990).

By focusing predominately on shallow sections of cobble substrates with riffle and

pool complexes, the captures frequency was biased towards the crayfish that prefer those

habitat characteristics. Bank to bank surveys were the goal but the main channel areas of

less than 1 meter were most accessible and more thoroughly surveyed by the methods

used here. Main-channel areas are particularly important for large, reproductively mature

males (Lieb et al. 2007), while the juveniles seek cover under banks and within

vegetation, where they are protected from both predators and the capture efforts.

Interactions between volunteer efforts and species life history also influence the

results of this study. CPUE data suggests immigration of crayfish into the VAFO

population from other sources may have a significant impact on the O. rusticus

population within Valley Creek. The CPUE for natives declined in all stream sections

through 2013, while the CPUE for O. rusticus remained constant above the dam over the

five year study. O. rusticus removal thus, did not exceed recruitment. A density-

dependent population exhibits constant population numbers after removal of a portion of

the population, as competition is reduced and crayfish move upstream to take advantage

of more available resources. This is illustrated in the measure of CPUE, showing

declines in 2010 and 2012 after relatively higher CPUEs in 2009, 2011, and 2013 (Figure

13). A constant influx of a CL size class at which crayfish are large enough evade

predators would be expected in the SFD after years of elevated CPUE.

A high level of effort was not correlated with CPUE. The lowest CPUE, recorded in

2013, corresponded to the lowest level of effort. The year of most survey hours, 2012,

had the second lowest CPUE out of all years. Increasing the survey intensity does not

appear to be the controlling factor in reducing the invasive crayfish population. Despite

varying survey intensity over the study, the rate of capture remained steady for the O.

rusticus population above the dam.

17

Adult and juvenile sizes increased as the crayfish density was reduced. This increase

in size could reduce competition and increase food and habitat suitability per crayfish.

Sibley (2000) found that continuous trapping is preferable to short-term intensive

trapping, which may stimulate younger maturation age and greater egg production.

Trapping is also biased towards larger CL crayfish, so the smaller individuals remain,

taking advantage of the lack of competition to grow rapidly (Sibley, 2000). Larger

crayfish have greater reproductive capacity (Table 2), increasing the proportionate effect

on recruitment and exacerbating the invasion. Estimated lost egg production below the

dam declined due to differing survey intensities above and below the dam. Above the

dam, the removal of reproduction potential was positively correlated with SFD.

Although the fecundity of O. rusticus is being reduced by the removal of females,

mortality needs to be greater than recruitment to prevent replacement within the

population. Since O. rusticus live 3-4 years, recruitment needs to be 25-30% to maintain

equilibrium within the population. However, because of the high reproductive capacity

of O. rusticus, it takes very few females for replacement to occur. Since females store

the sperm until fertilization conditions are optimum (Gunderson, 2009), introduction of a

male is not necessary. Therefore, a particular focus for management should be on

removing the larger females from the population, since they have the greatest impact on

recruitment.

The numbers of young-of-the-year (YOY) are decreasing, suggesting that the removal

effort is having a negative effect on the reproduction of O. rusticus. However, it is also

possible that there is a bias against smaller individuals using the dip-netting method. The

smallest crayfish may be overlooked by surveyors or inadvertently returned to the stream,

providing a local source for population replacement. Because of the difficulty in

capturing the YOY, a large portion of the population may be excluded from capture, and

the actual SFD may be inaccurately reported.

18

FURTHER STUDY

Mark-recapture and greater knowledge of the native crayfish ecology, population

biology and reproductive success would provide more accurate population data that

would help to monitor the effect of the invasive species on the native population and

inform management efforts. Passive Integrated Transponder (PIT) or Radio-frequency

Identification (RFID) tags are options that would allow for easier analysis of population

movement, but funding for the equipment and availability of trained personnel to use it is

a limiting factor. Another method that is inexpensive and does not require specialized

equipment is Guan’s (1997) marking system that uses a pattern of holes punched in the

uropod. Although these methods may be effective, intrusive marking may affect growth

and survival of the animal, which is undesirable when dealing with a species of concern.

This method may also bias the population structure of the invasive crayfish and have

ethical implications that are not in accordance with the NPS mission.

In lieu of potentially harmful markings, carapace marking with Dykem paint markers

is an inexpensive and non-intrusive method used by Ramalho et al. (2010). Dykem

markers are an oil-based paint marker that produces a durable mark that dries in 30

seconds and can be applied directly on wet or dry surfaces in many color and symbol

combinations. Ramalho et al. (2010) found that the marks were retained for about 9

months. Although this is not long enough to do a year-to-year study of natives, it would

prevent multiple counts of individuals during the survey season

Because of the relatively short life cycle of 3-4 years, rapid, high-volume

reproduction is important for the continuation of the species. Focusing removal activities

during two time periods in the reproductive cycle, late summer and early spring, may

have the most effect on the population. Many crayfish become sexually mature and mate

in the October or November after their birth, but fertilization and egg laying usually

occur the following spring (Nale, n.d.). Concentrating the effort on small size classes in

late summer, before the beginning of the reproductive cycle in the fall, will reduce the

reproducing population.

19

Since O. rusticus populations increase earlier in the spring than the native

populations, the capture efforts should be focused before the young-of-the-year hatch and

leave the mother to prevent recruitment. Most of the effort of this study was concentrated

in the late spring through summer, when higher air temperatures were suited to spending

hours in a cold creek, and volunteer availability was higher. Shifting the collection focus

to earlier in the spring will likely net more invasive crayfish than natives and have a

greater effect than summer collections. The summer collections have managed to keep

the invasive population relatively stable over the course of the study. By removing more

juveniles, the population will dwindle as recruitment is reduced, along with the natural

effects of mortality accounting for approximately 25-30% loss of adults per year.

Upstream of VAFO and throughout the Valley Creek watershed, the current status of

the population of O. rusticus is unknown. Although population appeared to have a low

density in 2008 during the presence/absence investigation, there have not been significant

efforts at collection throughout the upper tributaries since that time. If a reproducing

population has become established in the upper watershed, it replenishes the park’s

population of O. rusticus. Efforts should also be concentrated above the dam, as the

constant source of invasive crayfish from the Schuylkill River into Valley Creek below

the dam negates the removal effort in Valley Creek.

20

Table 1: Summary of crayfish surveying methods applied at Valley Forge National

Historical Park (adapted from Peay, 2003).

Method Requirements Advantages Limitations Trapping Moderate to low flows.

Traps baited with chicken and weighted with rocks.

Less labor required to survey entire stretch within VAFO.

Harm to non-target species. Remove before storms. Subject to tampering.

Electro-fishing

Expensive equipment and skilled operators.

Trained labor to capture, record, and release all species. Failed to affect crayfish under rocks.

Mark-recapture

Effective marking method and scheme. Closed population. Use with trapping or dip-netting.

Allows estimation of population size and dynamics.

Time- and labor-intensive. Marking skills and equipment. Ethical issues with marking method. Fails to reduce reproducing population.

Manual search (dip-netting)

Moderate- to low-flow clear water up to 60 cm deep. Safe entry and exit points to stream. Source of labor and equipment (waders and nets). Warm weather (above 210C) preferred.

Can search actual refuges. Avoids harm to non-target species. Flexibility in scheduling. Public outreach event contributes free labor.

Ineffective for stream bank refuges, deep water, and soft substrates. Safety issues in deep water. Affected by turbidity and flooding. Disturbs habitat.

21

Table 2: Weight and fecundity estimates of O. rusticus. Fecundity calculated based on

carapace length (CL) by Fecundity = 10(1.0672+CL*0.0357) (Hein et al. 2007).

CL (mm) Weight (grams) Fecundity per female 2 0.2521 14 4 0.3101 16 6 0.3815 19 8 0.4693 23 10 0.5774 27 12 0.7103 31 14 0.8739 37 16 1.075 43 18 1.3226 51 20 1.627 60 22 2.0016 71 24 2.4625 84 26 3.0294 99 28 3.7269 117 30 4.5849 137 32 5.6405 162 34 6.9391 191 36 8.5366 225 38 10.502 265 40 12.92 313 42 15.894 369 44 19.554 435 46 24.056 512 48 29.594 604 50 36.407 712 52 44.789 839 54 55.101 989 56 67.787 1,165

22

Fig. 1: Orconectes rusticus (rusty crayfish) identification (Photos by Wasler, 2008;

diagram by United States Geological Survey, 2014).

23

Fig. 2: Left: Range of O. rusticus in 2014 (United States Geological Survey, 2014) with insert of location of Valley Forge National Historical Park (VAFO) study site and O. rusticus records in Pennsylvania.

Right: Sections of Valley Creek within VAFO sampled during NPS crayfish survey effort (2008-2013).

Dam

24

Fig. 3: Crayfish traps baited with chicken or fish were weighted with rocks and placed

along the 3.2 km of Valley Creek within Valley Forge National Historical Park in 2008

(Wasler, 2008).

Fig. 4: Two NPS volunteers dip-net and check traps within Valley Creek in 2008, while

the foreground sign provides information to the public about the effort (Wasler, 2008).

25

Fig. 5: NPS posted informational signs about the trapping program in an effort to promote awareness of invasive species and

the effort to control them.

26

Fig. 6: The NPS Crayfish Corps logo was developed for use on patches and t-shirts,

which were awarded to volunteers after completing one and three survey sessions,

respectively (NPS).

Fig. 7: Fourteen-inch-diameter dip-net used by Crayfish Corps volunteers to capture

crayfish while overturning rocks across the width of Valley Creek.

27

Fig. 8: Person-hours spent surveying by the Crayfish Corps in Valley Creek below the dam (Section 1) and above the dam

(Sections 2, 3, and 4) in Valley Forge National Historical Park.

0

200

400

600

800

1000

1200

1400

1600

2009 2010 2011 2012 2013

Hou

rs sp

ent s

urve

ying

Below dam

Above dam

28

Fig. 9: Numbers of invasive (O. rusticus) and native crayfish captured above and below the dam decreased overall throughout

the study.

0

1000

2000

3000

4000

5000

6000

7000

2009 2010 2011 2012 2013

Cra

yfis

h C

aptu

red

Invasives - Invasives -

Natives - Natives -

29

Fig. 10: Size Frequency Distribution of O. rusticus removed below the dam on Valley Creek showed two CL cohorts that

increased in size as captured crayfish numbers decreased.

0

50

100

150

200

250

300

350

400

450 N

umbe

r of C

rayf

ish

Cap

ture

d

Carapace Length (mm)

2009 2010 2011 2012 2013

30

Fig. 11: Size Frequency Distribution of O. rusticus removed above the dam on Valley Creek showed two CL cohorts that

were more closely related in size between survey years than those CL cohorts below the dam.

0

20

40

60

80

100

120

140

160 C

rayf

ish

Cap

ture

d

Carapace Length (mm)

2009 2010 2011 2012 2013

31

Fig. 12: Relative abundance of invasive (O. rusticus) and native crayfish captured remained relatively stable between years,

with a maximum variation of 15%.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2009 2010 2011 2012 2013

Perc

ent o

f Cat

ch

Natives Returned - Above dam

Natives Returned - Below dam

Invasives removed - Above dam

Invasives removed - Below dam

32

Fig. 13: Catch Per Unit Effort (CPUE) of native species decreased both above and below the dam in Valley Creek. CPUE of

O. rusticus decreased below the dam and remained stable above the dam.

0

1

2

3

4

5

6

7

8

2009 2010 2011 2012 2013

CPU

E Below dam O. rusticus

Below dam native

Above dam O. rusticus

Above dam native

33

Fig. 14: O. rusticus biomass removed from Valley Creek. Biomass of males and females below the dam and males above the

dam converged in 2012.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

2009 2010 2011 2012 2013

Kilo

gram

s of C

rafy

ish

Females below dam

Females above dam

Males below dam

Males above dam

34

Fig. 15: Estimation of O. rusticus reproductive potential removed from Valley Creek. Fecundity calculated based on carapace

length (CL) using the equation: Fecundity = 10(1.0672+CL*0.0357) (Hein et al. 2007).

0

50,000

100,000

150,000

200,000

250,000

2009 2010 2011 2012 2013

Egg

s Rem

oved

Below dam

Above dam

35

Figure 16: Stream temperature of Valley Creek varied seasonally between 10°C and 20°C, with lowest temperatures in April

and highest temperatures in July.

y = 0.0604x + 16.215

10

12

14

16

18

20

22

Jul

Aug

Se

p A

pr

May

Ju

n Ju

l A

ug

Sep

Apr

M

ay

Jun

Jul

Aug

Se

p A

pr

May

Ju

n Ju

l A

ug

Sep

2009 2010 2011 2012

Deg

rees

Cel

sius

Total

36

Figure 17: The highest percentages of invasive crayfish captured relative to total crayfish were captured when water

temperatures were between 18° C and 20° C.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 5 10 15 20 25

Perc

ent o

f O. r

ustic

us c

aptu

red

degrees Celsius

Survey Events

37

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