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2011 SOUTHEASTERN NATURALIST 10(1):121–132
Life-History Notes on Cambarus hubbsi Creaser (Hubbs
Crayfish) from the South Fork Spring River, Arkansas
Eric R. Larson1,* and Daniel D. Magoulick2
Abstract - Many crayfish species native to the southeastern United States are imperiled
due to small range sizes and anthropogenic impacts such as habitat loss and introduction
of non-native species. Furthermore, effective management of crayfish is limited by the
scarcity of life-history and ecological data for many of these species. We report results
of the first life-history study of the crayfish Cambarus hubbsi (Hubbs Crayfish). We collected
466 Hubbs Crayfish from the South Fork Spring River, AR throughout 2006 and
recorded carapace lengths, wet weights, indicators of reproductive activity, and number
of eggs on ovigerous females. Using length-frequency distributions, we identified four
Hubbs Crayfish age classes and evaluated growth rates by plotting size by season (winter,
spring, summer, autumn). Male Hubbs Crayfish were more common than females in
all seasons except autumn, and males weighed more at equivalent lengths than females.
Reproductive activity in Hubbs Crayfish peaked in late winter and spring, and ovigerous
females were collected in March, April, and June. Ovigerous females were age II or III
and carried few eggs relative to co-occurring crayfish of the genus Orconectes. Compared
to these Orconectes species, Hubbs Crayfish is comparatively slow growing, long lived,
with low reproductive potential, and as a result may be categorized as a K life-history
strategist. Based on this species’ life-history strategy and previously documented habitat
specificity and taxonomic distinctiveness, Hubbs Crayfish may require monitoring and
management attention normally reserved for species with smaller ranges.
North America is home to at least 382 species of crayfish, representing 60%
of world crayfish diversity (Crandall and Buhay 2008). A recent conservation
assessment found 48% of these crayfish are possibly extinct, endangered, threatened,
or vulnerable (Taylor et al. 2007), and crayfish are anticipated to experience
high extinction rates in the future due to this degree of imperilment (Ricciardi
and Rasmussen 1999). Crayfish are predominantly threatened by small natural
range sizes and related vulnerability to localized habitat loss or degradation, as
well as impacts of and displacement by introduced crayfish (Lodge et al. 2000,
Taylor et al. 2007). In addition, the management and conservation of crayfish is
made difficult by the absence of basic ecological and life-history information for
many of these species (Taylor et al. 2007).
Here we report a life-history study on Cambarus hubbsi Creaser (Hubbs Crayfish). Hubbs Crayfish is endemic to, but widely distributed throughout, the Ozark
1School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98105.
2US Geological Survey, Arkansas Cooperative Fish and Wildlife Research Unit, Department
of Biological Sciences, University of Arkansas, Fayetteville, AR 72701. *Corresponding
author - email@example.com.
122 Southeastern Naturalist Vol. 10, No. 1
Plateau of northern Arkansas and southern Missouri (Pflieger 1996). Hubbs
Crayfish is a stream- and river-dwelling crayfish that selects coarse substrates
and fast-flowing riffles and runs, often occurring in lower densities than cooccurring
species of the genus Orconectes (Flinders and Magoulick 2005, 2007).
Although recognized by Taylor et al. (2007) as currently stable and not requiring
conservation attention, Crandall (1998) recommended increasing conservation
prioritization for Hubbs Crayfish due to the species’ restricted habitat specificity
and contribution to regional taxonomic diversity.
In addition, Hubbs Crayfish has disappeared from headwaters of the South Fork
Spring River in Arkansas and Missouri, where the species was previously found
(Pflieger 1996). The recently introduced Orconectes neglectus chaenodactylus
Williams (Gap Ringed Crayfish) is suspected of displacing both Hubbs Crayfish
and the rare endemic Orconectes eupunctus Williams (Coldwater Crayfish) from
these streams through biotic mechanisms (Flinders and Magoulick 2005, Magoulick
and DiStefano 2007). As part of ongoing studies evaluating the potential
threat of the introduced Gap Ringed Crayfish to the South Fork Spring River native
crayfish community (Larson and Magoulick 2008, Rabalais and Magoulick 2006),
we collected life-history information on Hubbs Crayfish from a site in the lower
South Fork Spring River, where the species remains common. Our objectives were
to provide life-history values for this little-studied species that may be applied to
its conservation and management, and contribute to the developing literature on
life histories of crayfish native to the southeastern United States.
The South Fork Spring River is a major tributary of the Spring River watershed,
which drains 3926 km2 of the Salem Plateau physiographic region in
north-central Arkansas and south-central Missouri. Agricultural pasture and forest
dominate land cover in the Spring River drainage, with no substantial urban
areas. The Spring River drainage contains a diverse stream-dwelling crayfish
community consisting of six native species and the recently introduced Gap
Ringed Crayfish, which remains restricted to the West Fork and upper South Fork
Spring River (Flinders and Magoulick 2005).
Life-history sampling for Hubbs Crayfish was conducted in the lower South
Fork Spring River at a site (36º21'N, 91º37'W) immediately downstream of the
Highway 289 bridge at Saddle, AR. The sample site included a large, fast-flowing
riffle and downstream run, as well as an adjacent side channel with multiple
smaller riffles and runs. High current velocities and large substrates at the site
were consistent with previously documented habitat preferences of Hubbs Crayfish (Flinders and Magoulick 2005, 2007; Pflieger 1996).
Hubbs Crayfish were collected over 14 sampling occasions from January to
December 2006 using a “kick seining” technique in which the substrate was
2011 E.R. Larson and D.D. Magoulick 123
physically disturbed and crayfish were flushed by the current into a downstream
3-mm mesh net. Kick seining was conducted for 3–4 hours per sampling occasion.
For all Hubbs Crayfish collected, we measured wet weight with a portable
field scale (to nearest 0.1 g) and total carapace length (TCL)—the distance from
the anterior tip of the rostrum to the posterior edge of the carapace—with vernier
calipers (to nearest 0.1 mm). We then recorded sex and reproductive activity as
either gonopod form (I or II) for male crayfish or presence of visible glair gland
secretions (hereafter referred to as glair) or eggs for female crayfish. Form I gonopods
indicate maturity or seasonal reproductive activity in male crayfish of the
family Cambaridae, while glair is visible under the abdomen of female crayfish
and used to adhere eggs to pleopods (swimming legs). Egg counts were conducted
non-destructively (without removal of eggs) in the field. All Hubbs Crayfish were
released at the site of collection immediately following the recording of data. The
thermal regime at the site was documented by an Onset Computer Corporation
HOBO® temperature logger recording temperature (ºC) at hourly intervals from
February to December 2006.
Life-history data for Hubbs Crayfish were combined by season for analysis,
with seasons defined as winter (January–March), spring (April–June), summer
(July–September), and autumn (October–December). We evaluated size
structure, age structure, and growth rates for Hubbs Crayfish by creating lengthfrequency
histograms by season, and then fitted normal distributions to these
histograms with maximum likelihood estimation (MacDonald and Green 1988).
Minimum size, maximum size, and means and standard deviations for each age
class were plotted by season and fitted with spline lines to represent growth rates.
Age classes turned over (e.g., Age 0 became Age I, etc.) between the winter
and spring, and the spring age structure (0, I, II, and III) is used throughout the
manuscript when discussing age-class attributes. Potential differences in lengthweight
relationships between male and female crayfish were tested with analysis
of covariance (ANCOVA) on log-transformed lengths and weights combined
across all seasons.
Sex ratios (M:F) were calculated for each season and tested for significance
against the null hypothesis of an equal 1:1 sex ratio with chi-square (χ2) tests.
The percent of Form I males and females with glair or eggs (ovigerous) by season
were calculated, and mean sizes and standard deviations for these reproductive
crayfish are provided. We plotted sex ratios and percent reproductive activity by
sampling occasion for comparison to continuous stream water temperatures. We
calculated water-temperature means and ranges by season, with coefficients of
variation (CV) provided as a measure of seasonal water temperature variability.
Statistical analyses were conducted in R (R Development Core Team 2008).
We collected 466 Hubbs Crayfish: 81 individuals in winter, 159 in spring,
113 in summer, and 113 in autumn. Four age classes of Hubbs Crayfish were
124 Southeastern Naturalist Vol. 10, No. 1
identified from length-frequency histograms (Fig. 1). Age 0 crayfish recruited to
the population in the spring, with the first juvenile detected at 5.2 mm TCL on
15 May at a water temperature of 16 ºC, and grew to a mean size of 11.7 (± 1.9
SD) mm TCL by autumn. Age I crayfish grew from a mean size of 13.2 (± 3.0 SD)
mm TCL in winter to 19.5 (± 2.3 SD) mm TCL by autumn, and Age II crayfish
grew from a mean size of 18.9 (± 0.6 SD) mm TCL in winter to 25.5 (± 1.2 SD)
mm TCL by autumn (Table 1, Fig. 2). Age III crayfish were detected at mean
sizes of 26.7 (± 2.1 SD) mm TCL in the winter and 29.2 (± 0.8 SD) mm TCL in
the spring, but were absent or rare by summer (Table 1, Fig. 2). As a result, Age
III may be the maximum age for Hubbs Crayfish in this population. The largest
Hubbs Crayfish found during the study was a 30.7-mm-TCL individual collected
on 11 January. Male Hubbs Crayfish weighed significantly more than female
Hubbs Crayfish at equivalent lengths (F = 7.01, P < 0.01).
Although sex ratios were slightly male-dominated in winter, spring, and summer
and female-dominated in autumn, none were statistically significant from a
1:1 sex ratio (Table 1). The overall male-dominated sex ratio of 227:205 (1.11)
was also not significantly different from a 1:1 sex ratio (χ2 = 1.12, P = 0.29).
Reproductive activity for Hubbs Crayfish peaked in winter and spring and was
lowest in summer (Table 1, Fig. 3). Fifty percent of male crayfish were Form I,
and 29% of female crayfish had glair on 17 March at 13 ºC. During the summer
months of August and September, no Form I male crayfish and no female crayfish with glair were collected. The first Form I male in autumn was found on 14
Figure 1. Length-frequency histograms by season for Hubbs Crayfish from the South
Fork Spring River, AR, 2006.
2011 E.R. Larson and D.D. Magoulick 125
October at 15 ºC, and 23% of males were Form I by 22 November at 8 ºC. The
first female with glair in autumn was found on 22 November, and 33% of females
had glair by 16 December at 10 ºC.
Three female crayfish with eggs were collected over the course of the study. A
27.4-mm-TCL female with 11 eggs was collected on 18 March at 12 ºC, a 24.4-mm-
TCL female with 54 eggs was collected on 16 April at 22 ºC, and a 24.2-mm-TCL
female with 33 eggs was collected on 12 June at 24 ºC. These crayfish were all at
least Age II based on size. Similarly, the smallest Form I male was 18.7 mm TCL
and collected on 31 May at 16 ºC, and the mean size of all Form I males was 24.0 mm
TCL (± 3.6 SD). The smallest female collected with glair was 17.5 mm TCL and collected
on 12 June, and mean size of all females with glair was 23.0 mm TCL (± 2.9
SD). These results indicate that Hubbs crayfish require at least one year, and more
likely two years, to reach reproductive maturity.
Cambarus is the second most diverse genera of crayfish in the world, with
nearly 100 species found in North America (Crandall and Buhay 2008). Lifehistory
information is rare for Cambarus crayfish, with exceptions including
Table 1. Summary statistics by season for river temperature (ºC), Hubbs Crayfish size by age class
(mm TCL), sex ratio (M:F), and proportion of the population reproductively active (%). Seasons
are winter (January, February, March), spring (April, May, June), summer (July, August, September),
and autumn (October, November, December). Coefficients of variation (CV) are reported
for river temperature as a measure of consistency and variability within season. Age classes were
determined and TCL means and standard deviations calculated by fitting normal distributions to
length-frequency histograms (Fig. 1) with a maximum likelihood mixed model (MacDonald and
Green 1988). Age classes turned over between winter and spring (e.g., Age 0 became Age I, etc.).
Chi-square statistics (χ2) and P-values are provided to report if sex ratios deviate significantly from
a null value of 1:1.
Variable Winter Spring Summer Autumn
Mean 11.7 21.0 20.8 12.1
Range 6.5–17.9 15.5–27.1 16.4–25.9 3.7–22.1
CV 18.5 13.8 7.8 31.8
Size TCL (SD)
Age 0 13.2 (3.0) 5.8 (1.0) 10.1 (2.1) 11.7 (1.9)
Age I 18.9 (0.6) 14.0 (2.0) 19.0 (2.1) 19.5 (2.3)
Age II 26.7 (2.1) 20.2 (3.5) 24.8 (1.7) 25.5 (1.2)
Age III - 29.2 (0.8) - -
Total M:F 38:34 73:62 61:51 55:58
Ratio 1.12 1.18 1.20 0.95
χ2 (P-value) 0.11 (0.74) 0.45 (0.50) 0.45 (0.50) 0.04 (0.84)
M Form I 26.3 13.7 1.6 12.7
F Glair 14.7 14.5 2.0 12.1
F Ovigerous 2.9 3.2 0.0 0.0
126 Southeastern Naturalist Vol. 10, No. 1
widespread and well-studied species such as Cambarus bartonii Fabricius (Appalachian
Brook Crayfish), Cambarus diogenes Girard (Devil Crayfish), and
Cambarus robustus Girard (Big Water Crayfish) (Guiasu 2002). Furthermore, the
vast majority of Cambarus crayfish are distributed east of the Mississippi River,
with the handful of Cambarus species found west of the Mississippi River either
cave-dwelling or terrestrial burrowers (Guiasu 2002). Consequently, Hubbs
Crayfish has a relatively unique combination of taxonomy, distribution, and habitat
preference, comparable only to the closely related stream-dwelling Cambarus
maculatus Hobbs and Pflieger (Freckled Crayfish) found in eastern Missouri’s
Meramec River drainage (Crandall 1998, Pflieger 1996). This distinctiveness
makes Hubbs Crayfish an interesting subject for ecological and life-history inquiries,
and our findings may also have important implications for management
and conservation of this species.
Our results indicate Hubbs Crayfish is a K-life-history strategist due to its
slow growth rates, late age to maturity, and low reproductive potential (Momot
1984), particularly in contrast to co-occurring Orconectes species found in the
Figure 2. Seasonal size distributions for Hubbs Crayfish from the South Fork Spring
River, AR, 2006. Means bounded by standard deviations are provided for each age class,
with minimum (down triangles) and maximum (up triangles) sizes also reported. Age
classes were determined, and means and standard deviations calculated by fitting normal
distributions to length-frequency histograms (Fig. 1) with a maximum likelihood mixed
model (MacDonald and Green 1988). Spline curves are plotted through age class means
to represent the sigmoidal nature of crayfish growth rates by season. Age classes turned
over (e.g., Age 0 became Age I, etc.) between the winter and spring.
2011 E.R. Larson and D.D. Magoulick 127
Spring River drainage (Flinders and Magoulick 2005, Larson and Magoulick
2008). This conclusion is supported by the limited life-history data available for
Hubbs Crayfish in Pflieger (1996) and Flinders and Magoulick (2005). During
state-wide surveys of Missouri crayfish, Pflieger (1996) only collected a single
ovigerous Hubbs Crayfish female in the wild (6 May 1986), although two females
produced eggs in the laboratory. These crayfish carried 57, 76, and 111 eggs at
Figure 3. River
active (Form I
for males, Glair
for females) by
month and season.
from the South
128 Southeastern Naturalist Vol. 10, No. 1
58.4, 61.0, and 66.0 mm total length (TL), respectively. Pflieger (1996) estimated
Hubbs Crayfish at age 0 were 12.7 to 27.9 mm TL and age I individuals were 33.0
to 53.3 mm TL in November of each year. Assuming Pflieger’s (1996) values may
be halved to approximate carapace lengths, they generally support our findings
of slow growth rates and small size structure for age 0 and I Hubbs Crayfish, as
well as late age to maturity in this species.
Sampling small streams throughout the Spring River drainage from 16 March
to 25 April 1999, Flinders and Magoulick (2005) reported only 12.5% of male
Hubbs Crayfish were Form I and 0% of Hubbs Crayfish females were ovigerous.
These were lower values than those found for four co-occurring Orconectes
species. Additionally, Flinders and Magoulick (2005) found that reproductively
active Hubbs Crayfish were large individuals (>22 mm TCL), also consistent
with our results. Finally, both Pflieger (1996) and Flinders and Magoulick (2005)
reported evidence that Hubbs Crayfish produces eggs later in the spring than
co-occurring Orconectes species, a pattern that could contribute to smaller size
structure and slower growth rates in juveniles of this species (Rabeni 1985).
Larson and Magoulick (2008) documented life histories of both the native
Coldwater Crayfish and introduced Gap Ringed Crayfish in the South Fork
Spring River during 2006. Both of these species exhibited faster growth rates,
earlier ages to maturity, higher fecundities, and greater reproductively active
proportions of their populations than Hubbs Crayfish. Age 0 Coldwater and Gap
Ringed Crayfish were 17–18 mm TCL by autumn, and most of these crayfish
were reproductively active within their first year of life. The smallest reproductively
active Coldwater and Gap Ringed Crayfish were 13–14 mm TCL. At 24
mm TCL, Coldwater and Gap Ringed Crayfish could be expected on average to
carry between 80 and 120 eggs, in contrast to the generally lower values found
for Hubbs Crayfish. Furthermore, at the peak of reproductive activity, virtually
all Coldwater Crayfish males were Form I and 90% of Coldwater Crayfish females
were ovigerous, while 60% of Gap Ringed Crayfish males were Form I and
30% of Gap Ringed Crayfish females were ovigerous.
Momot (1984) interpreted r and K life-history strategies in crayfish as responses
to latitudinal variation in seasonal food availability, arguing that r-selected
crayfish occur at southern latitudes where food supply is constant and K-selected
crayfish occur at northern latitudes where food supply is pulsed with summer.
This interpretation cannot explain r and K life-history strategies among crayfish
occurring at equivalent latitudes in the same streams and rivers. Ecologists have
also historically characterized r-strategists as colonist or disturbance-adapted
species and K-strategists as stable or competition-adapted species (MacArthur
and Wilson 1967). Once again, this characterization does not adequately explain
life-history differences between Hubbs Crayfish and Orconectes species such
as the Coldwater Crayfish because these species occupy the same streams and
consequently experience and are adapted to the same hydrological disturbance
regimes (Lytle and Poff 2004).
However, might these species vary in vulnerability to disturbance due to differences
in habitat selection? Creaser (1931), Pflieger (1996), and Flinders and
2011 E.R. Larson and D.D. Magoulick 129
Magoulick (2005) observed that Hubbs Crayfish burrows under large cobble and
boulders and is infrequently encountered in open habitats. Perhaps burrowing under
large substrates provides Hubbs Crayfish with refuge from disturbances such
as floods that Orconectes crayfish with more general habitat requirements may be
vulnerable to (Clark et al. 2008)? Hubbs Crayfish may also avoid intense predation
pressure from fish by remaining under large substrates, restricting access to
food such as surface-growing periphyton but simultaneously lowering mortality
rates. This hypothesis is supported by Dukat and Magoulick’s (1999) finding that
mortality via predation increased significantly on Hubbs Crayfish relocated from
riffles with high substrate diversity to pools with low substrate diversity. Life history
has been found to strongly influence crayfish habitat selection, competitive
ability, and predation vulnerability (Quinn and Janssen 1989, Rabeni 1985), and
consequently the K-life-history strategy and high habitat specialization of Hubbs
Crayfish are likely linked.
Habitat selection by Hubbs Crayfish may also interact with sampling methodology
to influence the life-history patterns we observed. Burrowing under
large substrates may make Hubbs Crayfish difficult to collect in contrast to cooccurring
Orconectes species with more general habitat preferences. This could
be particularly problematic in detecting ovigerous crayfish, which become less
active and select isolated habitats while bearing eggs (Mason 1970). Studies of
sampling methodology for stream crayfish have primarily evaluated the influence
of gear and habitat on estimates of abundance, density, or length-frequency (Price
and Welch 2009, Rabeni et al. 1997), but have not evaluated the ability to detect
rare individuals such as ovigerous females. Emerging statistical methods that account
for imperfect detection of target organisms may be useful in future studies
evaluating the presence or abundance of ovigerous crayfish or rare crayfish in
general (MacKenzie et al. 2006).
The introduced Gap Ringed Crayfish is suspected of displacing Hubbs Crayfish from a portion of its former range in the upper South Fork Spring River
(Magoulick and DiStefano 2007, Pflieger 1996), and life-history traits such as
higher fecundity or rapid juvenile growth rates have been implicated as mechanisms
favoring introduced over native crayfish (Butler and Stein 1985, Quinn
and Janssen 1989). However, the coexistence of Hubbs Crayfish across its native
range with at least 11 Orconectes species with life histories similar to the
Gap Ringed Crayfish makes this an unlikely mechanism for displacement. Other
biotic (e.g., susceptibility to fish predation; Dukat and Magoulick 1999, Rabeni
1985) or abiotic (e.g., habitat or hydrological regime alteration; Larson et al.
2009) mechanisms may be responsible for Hubbs Crayfish range contraction in
the South Fork Spring River. Isolating the causal mechanism or mechanisms will
require additional studies on Hubbs Crayfish population dynamics, biotic interactions,
and status and trends of habitat conditions in this and other drainages.
Understanding the life history of Hubbs Crayfish has important implications
for this species’ conservation. Crandall (1998) advocated increased conservation
attention for Hubbs Crayfish due to the species’ unique taxonomy and narrow
habitat specialization. This habitat specialization may make Hubbs Crayfish
130 Southeastern Naturalist Vol. 10, No. 1
vulnerable to both anthropogenic impacts and natural disturbances. Gravel mining
of streams is a common practice throughout the range of Hubbs Crayfish,
and has been found to disproportionately affect populations of riffle- and rundwelling
species relative to co-occurring habitat generalists (Brown et al. 1998).
In addition, the preferred habitats of Hubbs Crayfish can dry extensively due to
seasonal and supraseasonal drought (Brown and Brussock 1991), and crayfish
differ substantially in their tolerance to desiccation and stream drying (Larson
et al. 2009). Although Hubbs Crayfish is known to occupy intermittent streams,
it is not as common in these systems as some Orconectes species (Flinders and
Magoulick 2003), and the resistance and resilience of Hubbs Crayfish to drought
and stream drying is unknown.
Our study complements past work on Hubbs Crayfish habitat specialization
by demonstrating that this species may recover slowly from natural and anthropogenic
disturbances due to its life-history strategy. Some common, widely
distributed crayfish species have recently been found to be suffering dramatic
population declines (Edwards et al. 2009), and consequently, assumptions of
species’ security deserve scrutiny. Monitoring populations of invertebrates with
life histories and habitat preferences that potentially make them vulnerable to
population declines may be advisable, even in instances where the known distributions
of these species are relatively large.
This research was supported by a grant from the Arkansas Game and Fish Commission.
The Arkansas Cooperative Fish and Wildlife Research Unit is supported by the Arkansas
Game and Fish Commission, University of Arkansas, US Geological Survey, and the
Wildlife Management Institute. We are grateful to the South Fork Resort, Saddle, AR for
providing site access. This manuscript was improved through comments and suggestions
from John Aho, Shawna Herleth-King, Jacob Westhoff, and two anonymous reviewers.
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