Papers by Sean M Hartzell
Freshwater Biology, 2017
1. Freshwater species are declining rapidly but more complete data are needed for determining the... more 1. Freshwater species are declining rapidly but more complete data are needed for determining the extent and cause(s) of population declines and extirpations. Integrating newer survey techniques, freely available data, and traditional field work may allow for more effective assessment of population decline. 2. We used detailed historical species records and environmental DNA (eDNA) survey methods to identify changes in population distribution of a long-lived, imperiled stream salamander, the eastern hellbender (Cryptobranchus alleganiensis alleganiensis: Cryptobranchidae). We used logistic regression with Bayesian inference to test whether selected environmental variables may be good predictors of hellbender population persistence and extirpation. 3. Hellbenders persisted in only 42% of the 24 historical record sites. The best fit model indicated electrical conductivity (EC) was the strongest predictor of hellbender population persistence (EC < 278 lS/cm) and extirpation. Conductivity was strongly negatively correlated with canopy cover within the total watershed (r = -0.83, n = 21, p < 0.001) and riparian buffer of the watershed (r = -0.77, n = 21, p < 0.001). 4. Electrical conductivity tends to increase following deforestation, and may inhibit sperm motility and thus limit recruitment of hellbenders and other aquatic vertebrate species with external fertilisation. 5. By integrating historical data, eDNA, field data, and freely available high resolution remote sensing data, our study design allowed for rapid assessment of predictors of and changes in hellbender distribution over a relatively broad geographic area. This cost- and time-effective approach may be used for evaluating other rare aquatic species.
Academia Letters, 2021
Trapping is a commonly used methodology to sample surface water dwelling crayfish for scientific ... more Trapping is a commonly used methodology to sample surface water dwelling crayfish for scientific research, during biological surveys, or by individuals who wish to collect them for food or to use as fish bait (Larson and Olden, 2016). Numerous studies have evaluated the effectiveness of various trap designs and techniques for recruiting crayfish (e.g., Somers and Stetchy, 1986; Rach and Bills, 1987; Stuecheli, 1991; Mangan et al., 2009). Typically, crayfish traps are baited with one or more food items to attract crayfish. Types of bait used to attract crayfish can vary considerably among studies, with various fish species, commercial crayfish bait, pet food, and the liver of livestock being commonly used as bait (Hartzell, 2020a). Some studies have evaluated the effectiveness of different bait types on certain crayfish species (e.g., Somers and Stetchy, 1986; Rach and Bills, 1987) suggesting that different species of crayfish may prefer certain types of bait. However, a large-scale analysis of the bait preferences of crayfish is not available (Larson and Olden, 2016) and data on bait preferences are lacking for many species of crayfish. Allegheny Crayfish (Faxonius obscurus) are medium-sized surface water dwelling crayfish that occur in rocky streams and rivers within parts of eastern North America, from southeastern Ontario to West Virginia (Hobbs 1989). No study appears to have focused on trapping success regarding bait preference of this species. In preparation for/in conjunction with larger ecological and natural history studies of an invasive population of Allegheny Crayfish in eastern Pennsylvania, USA (i.e., Hartzell, 2020b; Wadena et al., unpublished data), I conducted a small study to evaluate the effectiveness of two different types of bait on recruiting Allegheny Crayfish to traps. I evaluated the effectiveness of canned sardines in oil and canned wet chicken-based cat food, two baits which have been used to trap crayfish in other studies (reviewed in Hartzell,
Journal of the Pennsylvania Academy of Science , 2020
With current declines in amphibian and reptile populations, herpetological surveys of protected n... more With current declines in amphibian and reptile populations, herpetological surveys of protected natural areas are crucial to management of these organisms, especially as natural areas become more insular due to surrounding land use. Jakey Hollow Natural Area (JHNA) is a locally significant biological site in Columbia County, PA, consisting of wooded slopes bisected by a small-order stream. This report presents the results of a salamander survey at JHNA during the spring of 2020. Cover object surveys revealed a total of 190 salamanders belonging to seven species. The most common salamanders observed at JHNA were Plethodon cinereus and Desmognathus ochrophaeus, which typify other surveys of similar habitats in Pennsylvania. Other species found in lower abundance were D. fuscus, Eurycea bislineata, Gyrinophilus porphyriticus, P. glutinosus, and Pseudotriton ruber. Future surveys utilizing other techniques may reveal the presence of additional salamander species at this site.
The American Biology Teacher, 2021
Ecological field techniques such as transect surveys are long-used, integral means of immersing s... more Ecological field techniques such as transect surveys are long-used, integral means of immersing students in field exercises to illustrate ecological measures. Many species of crayfish create conspicuous burrows within or near aquatic habitats. Such burrows can easily be identified and measured by students during an ecological field exercise. In this article, we describe a field activity we developed as part of a college-level course in which students utilized transects and calipers to collect counts and measurements of crayfish burrows in order to evaluate their distribution and size among different substratum types along a small stream. This field exercise could be incorporated, with or without modification, into an applicable high school or introductory/intermediate college biology course as a means of illustrating ecological concepts, sampling technique, and/or behavioral biology.
Northeastern Naturalist, 2020
Crayfish are key components of North American aquatic ecosystems, but information about their lif... more Crayfish are key components of North American aquatic ecosystems, but information about their life history is typically lacking or incomplete. No such data are available for invasive populations of Faxonius obscurus (Allegheny Crayfish) in eastern Pennsylvania. I studied the life history of an invasive population in a small tributary in the Susquehanna River drainage of eastern Pennsylvania. Life-history characteristics (i.e., size at sexual maturity, sex ratios, seasonal shifts between reproductive and non-reproductive form in males, glair development, timing of ovigerous females, molting frequency, and size classes) were similar to those reported for many members of the genus Faxonius and largely similar to those reported for populations of Allegheny Crayfish across their native range. However, realized fecundity was greater than reported in West Virginia populations. Female body length was a predictor of realized fecundity, differing from southern populations of this species.
Journal of Negative Results in Ecology and Evolutionary Biology, 2020
Sexual dichromatism consists of inter-sexual differences in coloration within a species and is wi... more Sexual dichromatism consists of inter-sexual differences in coloration within a species and is widespread among animal taxa. The presence of sexual dichromatism in crayfish has not been well-studied. However, spot patterns in a population of rusty crayfish (Faxonius [Orconectes] rusticus) have recently been demonstrated to be sexually dichromatic, which suggests sexual dichromatism might exist in other species of the genus Faxonius. Intraspecific carapace color variation varies considerably within some populations of Allegheny crayfish (Faxonius [Orconectes] obscurus) although the contributing factor to this variation has not been demonstrated conclusively. Here, I utilize digital image analysis to quantify carapace coloration of a sample of Allegheny crayfish from eastern Pennsylvania, USA to determine if carapace color variation in this population can be attributed to sexual dichromatism. No significant difference was found in carapace coloration between sampled male and female Allegheny crayfish, which suggests another factor may be responsible for the carapace color variation observed in this population.
Bios, 2019
The Turkey Hill Oxbow, a small, locally significant forested/wetland area in central Columbia Cou... more The Turkey Hill Oxbow, a small, locally significant forested/wetland area in central Columbia County, Pennsylvania, was surveyed for salamanders during 2015. A comparison of recent records was made to historic collections from this location within the herpetology collection
housed at Bloomsburg University of Pennsylvania (BU). Nine salamander species, encompassing a total of 132 individuals, were found, revealing a slightly greater diversity represented by historic vouchers within the BU herpetology collection (eight species). The most common species were
eastern red-backed salamanders (Plethodon cinereus) and Allegheny mountain dusky salamanders (Desmognathus ochrophaeus); the most uncommon were northern two-lined salamanders (Eurycea bislineata) and red salamanders (Pseudotriton ruber). Two species found in the recent survey (D. ochrophaeus and P. ruber) were not represented by historic vouchers in the BU collection. However, no spotted salamanders (Ambystoma maculatum) were found during this study, despite
historic voucher records for this species from this locality.
Herpetological Review, 2019
Catesbeiana, 2019
The Chincoteague Bay Field Station is located on an approximately 15-hectare plot of land on Virg... more The Chincoteague Bay Field Station is located on an approximately 15-hectare plot of land on Virginia’s Eastern Shore. This area was surveyed opportunistically for herpetofauna primarily via nocturnal visual encounter surveys from early July through mid-August 2017. A total of 141 amphibians and reptiles were encountered during surveys, consisting of seven species of anuran, one snake, one turtle, and unidentified lizards in the genus Pleistiodon. No salamanders were found during surveys, despite historic vouchers of Plethodon cinereus at this locality. The majority of observations consisted of the species Anayrus fowleri and Hyla chrysoscelis. The composition of species observed at this site may likely have been influenced by survey methods used and seasonality. Future survey work may reveal the presence of other species at this locality.
Freshwater Crayfish, 2019
Sexual dichromatism is a common phenomenon among animal taxa and consists of differing coloration... more Sexual dichromatism is a common phenomenon among animal taxa and consists of differing coloration between sexes in a species. Specimens of the crayfish Faxonius rusticus (Girard) typically have a distinct “rusty” red spot on each side of the cephalothorax. These spots can display variation in both redness and size among specimens; however, little work appears to have been done examining variation in this trait. As a means of investigating possible sexual differences in the color and relative spot size (RSS) of the “rusty” spot in F. rusticus, this work utilized digital image analysis techniques to quantify the color and size of spots in a population of this species. Analyses revealed no difference in RSS between sexes; however, spots of females were significantly redder than those of males. Sexual dichromatism in the spot color of F. rusticus in this population could be relevant to mate discrimination during mating; however, this or other possible functions of this sexual color difference will need to be examined by behavioral studies.
Freshwater Crayfish, 2017
In crayfish, intraspecific coloration can vary due to a variety of factors such as diet, genetic ... more In crayfish, intraspecific coloration can vary due to a variety of factors such as diet, genetic variation, environment, and ontogeny. Ortmann (1906) hypothesized that the crayfish Cambarus bartonii bartonii
and Faxonius obscurus exhibit an ontogenetic shift in color change, with greener coloration in younger individuals of both species diminishing with age in larger specimens. However, this hypothesis has
never been quantitatively tested. This work incorporated digital image analysis to quantify colorationof samples of C. b. bartonii and F. obscurus collected from two locations, respectively, in an eastern
Pennsylvania stream. Examination for relationships between coloration (percent “green dominance”, i.e., the proportion of green in comparison to blue and red in photographs) and body size did not reveal
any significant relationship between these variables in either crayfish species. Therefore, this study does not support the presence of ontogenetic color change in C. b. bartonii and F. obscurus, and
Journal of the Pennsylvania Academy of Science, 2017
Introduction of nonindigenous crayfish species impacts freshwater ecosystems and can result in di... more Introduction of nonindigenous crayfish species impacts freshwater ecosystems and can result in displacement of native crayfish. The crayfish Orconectes limosus and Cambarus bartonii are native to the Susquehanna River drainage in Pennsylvania. However, several nonindigenous crayfish have become established in this drainage. No comprehensive survey exists on crayfish species within the Fishing Creek watershed. Historic records report O. limosus and C. bartonii in
this watershed; however, recent point surveys have documented the presence of the nonindigenous crayfish O. obscurus. We sampled crayfish in 15 sites from the lower reaches of Fishing Creek through its headwaters and major tributaries. We collected a total of 484 crayfish, representing the species O. obscurus and C. bartonii. We found O. obscurus within much of Fishing Creek and some tributaries, but absent from the upper reaches of the watershed, possibly due to a series of
dams. C. bartonii were primarily found in the upper portions of the Fishing Creek watershed, but also found at low abundance with O. obscurus in the central portions of the watershed and in a
small, first order tributary. We collected no O. limosus specimens in our samples, suggesting local extirpation via displacement by O. obscurus, as has been reported elsewhere.
Journal of the Pennsylvania Academy of Science, 2016
Species inventories and distributional analyses at fine resolutions, such as at the county level,... more Species inventories and distributional analyses at fine resolutions, such as at the county level, can provide a wealth of data to inform biological research and management as well as provide important baseline data for long-term biological monitoring. This work represents the first herpetological species and distributional inventory for Columbia County in northeastern Pennsylvania. A review of literature, museum records, and vouchered submissions on the Pennsylvania Amphibian and Reptile Survey (PARS) database confirmed the occurrence of 39 species of amphibians and reptiles within the county. The Eastern Musk Turtle (Sternotherus odoratus) is reported herein as a new county record. Eleven species confirmed within Columbia County are of conservation concern. Known township occurrence data, compiled from museum records, published literature, and field observations are presented for 28 non-imperiled species and (with township names omitted) for seven imperiled species. This work contributes to the understanding of Pennsylvania's herpetofauna and provides important baseline data for long-term monitoring and future research on amphibian and reptile species within Columbia County. [ J PA Acad Sci 90(1): 7-12, 2016 ]
Herpetological Review, 2016
Natural History Notes (Refereed) by Sean M Hartzell
Herpetological Review, 2021
blairi described herein is consistent with the category of eyeprotection described by Toledo et a... more blairi described herein is consistent with the category of eyeprotection described by Toledo et al (2011, op. cit.). Hypotheses of the adaptive function of eye-protection include changing the outline of the head to disorient a predator's search image (Channing and Howell 2003. Herpetol. Rev. 34:52); making an individual anuran appear larger or becoming motionless and inconspicuous as a variant of thanatosis (Brodie et al. 1998. J. Herpetol. 32:136-139); and being physically too large to swallow (Ferreira et al. 2019, op. cit.). Frogs from the Palearctic possibly use eye-protection during lower temperatures because hypothermic individuals have slower reactions and may be physically unable to escape (Harbel and Wilkinson 1997. Brit.
Herpetological Review, 2020
electromorphus are the only species of small Plethodon in Ohio. Their ranges throughout the state... more electromorphus are the only species of small Plethodon in Ohio. Their ranges throughout the state have intrigued biologists, as some areas have sharp boundaries between species, while in others, both species can be found under the same cover object. We report a hybrid individual in Brownhelm Township, Lorain County, Ohio, USA, near the northwestern-most extent of the range of P. electromorphus. To our knowledge, this is the first case of hybridization documented in Lorain County. The individual was recorded in Mill Hollow Bacon Woods Park (41.3811°N, 82.32103°W; WGS 84), which contains both species, and both color morphs of P. cinereus. Tail tissues were collected for population genetic studies, which assessed color polymorphism and mitochondrial clades using microsatellite DNA (Hantak et al. 2019. Ecography 42:1383-1394 Waldron et al. 2019. J. Herpetol. 53:144-153). Twenty-three tissues were collected, including P. cinereus (N = 20), P. electromorphus (N = 2), and the putative hybrid (N = 1). The hybrid's color morph was recorded in the field as red-striped, a coloration present in P. cinereus but not P. electromorphus. However, mitochondrial DNA was consistent with a P. electromorphus haplotype found in the two samples of P. electromorphus at this site, and known mtDNA sequences. Ten microsatellite loci designed for P. cinereus highly suggest that the individual is a hybrid; for the two samples of P. electromorphus, alleles were either completely unique from those of P. cinereus at this site (4 loci), or found in P. electromorphus and only one sample of P. cinereus (1 locus). The remaining loci failed to amplify for P. electromorphus (null alleles; 4 loci) or were fixed and shared between species (1 locus). The hybrid individual was heterozygous for the former five loci mentioned, possessing a diagnostic P. electromorphus allele, and an allele present in P. cinereus. For loci which failed to amplify in P. electromorphus, the hybrid sample exhibited only a P. cinereus allele, or in one case had an allele sampled in only that individual. The genotype is overall suggestive of an F1 hybrid.
Herpetological Review, 2020
Herpetological Review, 2020
Herpetological Review, 2020
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Papers by Sean M Hartzell
housed at Bloomsburg University of Pennsylvania (BU). Nine salamander species, encompassing a total of 132 individuals, were found, revealing a slightly greater diversity represented by historic vouchers within the BU herpetology collection (eight species). The most common species were
eastern red-backed salamanders (Plethodon cinereus) and Allegheny mountain dusky salamanders (Desmognathus ochrophaeus); the most uncommon were northern two-lined salamanders (Eurycea bislineata) and red salamanders (Pseudotriton ruber). Two species found in the recent survey (D. ochrophaeus and P. ruber) were not represented by historic vouchers in the BU collection. However, no spotted salamanders (Ambystoma maculatum) were found during this study, despite
historic voucher records for this species from this locality.
and Faxonius obscurus exhibit an ontogenetic shift in color change, with greener coloration in younger individuals of both species diminishing with age in larger specimens. However, this hypothesis has
never been quantitatively tested. This work incorporated digital image analysis to quantify colorationof samples of C. b. bartonii and F. obscurus collected from two locations, respectively, in an eastern
Pennsylvania stream. Examination for relationships between coloration (percent “green dominance”, i.e., the proportion of green in comparison to blue and red in photographs) and body size did not reveal
any significant relationship between these variables in either crayfish species. Therefore, this study does not support the presence of ontogenetic color change in C. b. bartonii and F. obscurus, and
this watershed; however, recent point surveys have documented the presence of the nonindigenous crayfish O. obscurus. We sampled crayfish in 15 sites from the lower reaches of Fishing Creek through its headwaters and major tributaries. We collected a total of 484 crayfish, representing the species O. obscurus and C. bartonii. We found O. obscurus within much of Fishing Creek and some tributaries, but absent from the upper reaches of the watershed, possibly due to a series of
dams. C. bartonii were primarily found in the upper portions of the Fishing Creek watershed, but also found at low abundance with O. obscurus in the central portions of the watershed and in a
small, first order tributary. We collected no O. limosus specimens in our samples, suggesting local extirpation via displacement by O. obscurus, as has been reported elsewhere.
Natural History Notes (Refereed) by Sean M Hartzell
housed at Bloomsburg University of Pennsylvania (BU). Nine salamander species, encompassing a total of 132 individuals, were found, revealing a slightly greater diversity represented by historic vouchers within the BU herpetology collection (eight species). The most common species were
eastern red-backed salamanders (Plethodon cinereus) and Allegheny mountain dusky salamanders (Desmognathus ochrophaeus); the most uncommon were northern two-lined salamanders (Eurycea bislineata) and red salamanders (Pseudotriton ruber). Two species found in the recent survey (D. ochrophaeus and P. ruber) were not represented by historic vouchers in the BU collection. However, no spotted salamanders (Ambystoma maculatum) were found during this study, despite
historic voucher records for this species from this locality.
and Faxonius obscurus exhibit an ontogenetic shift in color change, with greener coloration in younger individuals of both species diminishing with age in larger specimens. However, this hypothesis has
never been quantitatively tested. This work incorporated digital image analysis to quantify colorationof samples of C. b. bartonii and F. obscurus collected from two locations, respectively, in an eastern
Pennsylvania stream. Examination for relationships between coloration (percent “green dominance”, i.e., the proportion of green in comparison to blue and red in photographs) and body size did not reveal
any significant relationship between these variables in either crayfish species. Therefore, this study does not support the presence of ontogenetic color change in C. b. bartonii and F. obscurus, and
this watershed; however, recent point surveys have documented the presence of the nonindigenous crayfish O. obscurus. We sampled crayfish in 15 sites from the lower reaches of Fishing Creek through its headwaters and major tributaries. We collected a total of 484 crayfish, representing the species O. obscurus and C. bartonii. We found O. obscurus within much of Fishing Creek and some tributaries, but absent from the upper reaches of the watershed, possibly due to a series of
dams. C. bartonii were primarily found in the upper portions of the Fishing Creek watershed, but also found at low abundance with O. obscurus in the central portions of the watershed and in a
small, first order tributary. We collected no O. limosus specimens in our samples, suggesting local extirpation via displacement by O. obscurus, as has been reported elsewhere.
communities are well documented, the broader implications of this invasive species regarding Pennsylvania's freshwater ecosystems are largely unknown. While options are limited for the control of NZMS once introduced, rapid response actions taken by the Pennsylvania Fish and Boat Commission and partners have focused on educational strategies to prevent further spread, such as posting warning signs along infested waters.
crayfish due to increased activity (defined as time spent outside of
cover) in invaded environments, allowing for the acquisition of
greater resources. We conducted an ex situ study to determine if total
exposure time (a proxy for activity and defined as time spent outside
of shelter regardless of behavior) and behavior (i.e., walking;
immobile) differed between native spiny-cheek crayfish (Orconectes
limosus) and invasive rusty crayfish (Orconectes rusticus) from the
Susquehanna River drainage in Pennsylvania. We conducted the
study in raceways modified to simulate a typical stream within the
Susquehanna River drainage, inclusive of a native, nocturnal
predator, the eastern hellbender (Cryptobranchus alleganiensis
alleganiensis). We recorded video in each raceway and collected data
from the video including total exposure time and duration of walking
and immobile crayfish behaviors. There were no significant nocturnal
differences between crayfish species in total exposure time
(w=13668, df=338, p=0.44), walking behavior (t=0.4478, df=160,
p=0.65), or immobile behavior (t=-1.5687, df=176, p=0.11),
suggesting both species behave similarly at night. Diurnally, rusty
crayfish had significantly greater total exposure time (w=235.5,
df=70, p<0.01) and spent significantly more time walking (t=-4.4424,
df=30, p<0.01) and immobile (t=-4.350, df=37, p<0.01) than
spiny-cheek crayfish. This suggests invasive rusty crayfish may have
an indirect competitive advantage over native spiny-cheek crayfish
due to differences in diurnal behavior.