Southeastern Naturalist
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K.A. Hecht, M.A. Nickerson, and P.B. Colclough
22001177 SOUTHEASTERN NATURALIST 16V(o2l).: 11567, –N1o6.22
Hellbenders (Cryptobranchus alleganiensis) May Exhibit an
Ontogenetic Dietary Shift
Kirsten A. Hecht1,2,*, Max A. Nickerson1,2, and Phillip B. Colclough3
Abstract - Organisms in lotic habitats often experience dietary shifts over their lifetime.
The diet of adult Cryptobranchus alleganiensis (Hellbender) is well studied throughout the
species’ range, but knowledge regarding the natural history of larval Hellbenders, including
dietary information, remains scarce. We obtained non-lethal diet samples from 23 larval
Hellbenders. Larval Hellbenders consumed primarily invertebrate prey including mayfly
(Ephemeroptera) and caddisfly (Trichoptera) nymphs. Since these items do not comprise
a large proportion of the adult diet, Hellbenders may undergo an ontogenetic dietary shift.
Therefore, future management and conservation decisions regarding the Hellbender should
consider the abundance and density of aquatic insect populations.
Introduction
Stream species that experience substantial changes in body size or type during
their life cycle commonly experience ontogenetic shifts in diet (Giller and
Malmqvist 1998, Petranka 1984). Cryptobranchus alleganiensis (Daudin) (Hellbender),
an imperiled lotic amphibian, grows rapidly in the first few years of
life (Smith 1907, Unger and Mathis 2013). Hatchlings emerge from eggs at approximately
20–30 mm total length (TL) with external gills and undeveloped
limbs (Bishop 1941, Smith 1907). Hellbenders develop fully formed limbs when
2 months old and reabsorb their external gills within 2 years of hatching (Bishop
1941). After 5–7 years, Hellbenders become sexually mature, and adults range from
300 to 740 mm TL (Nickerson and Mays 1973).
Over 15 papers examining the Hellbender diet found that crayfish and fish are
the main diet items of Hellbenders (e.g., Green 1933, 1935; Netting 1929; Nickerson
and Mays 1973; Peterson et al. 1989). Adult Hellbenders were the focus of
these previous studies, however, and the diet of wild Hellbender larvae remains
largely unknown with the exception of 2 anecdotal reports (Pitt and Nickerson
2006, Smith 1907). A sample from a single Hellbender larvae collected by Pitt and
Nickerson (2006) contained a mixture of aquatic insect remains including Megaloptera,
Ephemeroptera, and Diptera. Smith (1907) collected a second-year larvae that
regurgitated a smaller conspecific. In captivity, however, Hellbender larvae have
been reared successfully on Lumbriculus variegatus (Müller) (Blackworm), mayfly
nymphs (Stenonema spp.), cladocerans (Ceriodaphnia spp, Simocephalus spp.),
1PO Box 116455, School of Natural Resources and Environment, University of Florida,
Gainesville, FL 32611. 2PO Box 117800 Florida Museum of Natural History, University of
Florida, Gainesville, FL 32611. 3Zoo Knoxville, 3500 Knoxville Zoo Drive, Knoxville, TN
37914. *Corresponding author - kirstenhecht@ufl.edu.
Manuscript Editor: Kristen Cecala
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2017 Vol. 16, No. 2
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and chopped Lumbricus terrestris L. (Nightcrawler), with crayfish and small fish
added to their diet as they attain larger sizes (Unger and Mathis 2013). To increase
knowledge of wild larval Hellbender feeding habits, we investigated the diet of
larval Hellbenders in Little River, TN.
Methods
Due to the high number of larvae found during previous studies (Nickerson et al.
2003), we chose Little River as the study location (See Hecht-Kardasz et al. 2012 for
additional site information). We conducted diurnal skin-diving surveys in July and
August 2008, July and August 2009, and July, August, and September 2010 when
river conditions were suitable (390 total survey hours). During 21 survey events, we
located larval Hellbenders and secured them in moistened ziplock bags to measure
TL and snout–vent length (SVL). Individuals under 125 mm TL, both gilled and nongilled,
were classified as larvae (Bishop 1941, Nickerson and Mays 1973). Using an
Ohaus® CS2000 compact digital scale (accuracy ± 1.0 g; Ohaus Corporation, Parsippany,
NJ), we measured mass in grams. We collected non-lethal diet samples from
larval C. alleganiensis using a modified stomach flushing technique (Meehan and
Miller 1978) by inserting a 14.2-g (0.5-oz) capacity Easy Feeder Nipple Tip Syringe
(Four Paws Products, Ltd., Hauppauge, NY) filled with river water into the mouth
and depressing the syringe to flush out stomach contents. A plastic container was
placed under individuals to collect regurgitated stomach contents, which were then
preserved in either 70% ethanol or buffered 10% dilution of concentrated formalin.
We returned all Hellbenders to their capture site following sample collection. With
the aid of a 0.75–3.0x binocular microscope (Bausch and Lomb, Bridgewater, NJ),
we used a taxonomic key (Merritt and Cummins 1996) to identify diet items to the
lowest possible taxonomic level, usually order, depending on the condition of item.
We calculated numerical abundance and relative frequency of diet items in relation to
both total sampled diet items and sampled individuals.
Results
We collected a total of 33 Hellbender larvae, but failed to acquire stomach
contents from 30.3% of individuals that were therefore assumed to have empty
stomachs. Successfully sampled larvae (n = 23) ranged from 40–118 mm TL (mean
= 69.4 mm ± 13.95) and weighed 2–9 g (mean = 2.8 g ± 1.5). All but one Hellbender
appeared to be first-year larvae. The mean number of prey items per individual
was 1.96 ± 1.15, and ranged from 1 to 6. Aquatic insects and crayfish comprised
the majority of the 45 identifiable sampled diet items (Fig. 1). Ephemeroptera and
Trichoptera were the most commonly identified insect orders consumed by Hellbender
larvae (Table 1), with 43.5% and 26.1% of the sampled individuals in Little
River having consumed these prey types respectively. We found a single vertebrate
diet item, a Eurycea salamander, which is discussed further in Hecht-Kardasz and
Nickerson (2013). 27% of sampled individuals had incidentally ingested items
in their stomach, including plant matter and gravel. We were not able to identify
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2017 Vol. 16, No.2
17.8% of diet items, primarily aquatic insects, to order due to the digested state
of the specimens. We collected one additional sample, an Ephemeroptera nymph
(Heptageniidae), from a sub-adult (204 mm TL).
Discussion
Based on our results, an ontogenetic shift in the Hellbender diet appears likely,
although quickly digestible soft-bodied prey, such as fish, could have been missed
during the study. Consistent with the findings of Pitt and Nickerson (2006), aquatic
insects comprised 83.8% of identified dietary items collected from Little River
larvae. While previous studies found that adult Hellbenders occasionally consume
aquatic insects (Green 1935, Peterson et al. 1989), there is no evidence that insects
make up a significant proportion of the adult diet. Decapods, which generally
Table 1. Contents of diet samples collected from larval Cryptobranchus alleganiensis (Hellbender)
in Little River, TN (n = 23).
Number of stomachs Percentage of stomachs
Diet item containing item containing item
Insecta
Coleoptera (adult) 1 4.3%
Diptera 3 13.0%
Ephemeroptera 10 43.5%
Plecoptera 4 17.4%
Trichoptera 6 26.1%
Malacostraca
Decapoda 5 21.7%
Amphibia
Caudata 1 4.3%
Miscellaneous
Gravel 4 17.4%
Plant matter 3 13.0%
Figure 1. Composition of larval Cryptobranchus alleganiensis (Hellbender) diet samples
collected in Little River, TN. Percentages represent the number of identified food items
from each category in relation to the total number of identified food items from all samples.
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comprise the majority of adult Hellbender diets (Green 1933, 1935; Netting 1929;
Nickerson and Mays 1973; Peterson et al. 1989), were the third most numerous
prey group found in larval diet samples. Unger and Mathis (2013) noted that captive
Hellbender larvae readily consumed small crayfish when they attained 60 mm
TL. Decapods, however, only represented 13% of identified diet items in our study,
and consumed individuals were very small. While past studies of Hellbender prey
availability focused primarily on the abundance of crayfish populations (Bodinof et
al. 2012, Nickerson et al. 2003), aquatic insects and their habitat may be important
for the survival of larval Hellbenders, and should be considered in future management
and conservation actions.
Young larvae may have similar feeding mechanisms as adults, allowing them to
capture and swallow large prey items. While most prey items identified were small,
the consumption of a 40-mm TL Eurcyea sp. salamander by a 50-mm TL individual
suggests that Hellbender larvae are able to consume relatively large prey items.
Like adult Hellbenders that utilize suction-feeding strategies (Elwood and Cundall
1994), larvae lack vomerine tooth patches, which may be advantageous for swallowing
whole food items quickly via suction feeding (Greven and Clemens 2009).
According to Larghi (2013), immature Hellbenders exhibit a reduced bite force
compared to their larger conspecifics, but estimates of suction-feeding pressure
remain similar regardless of Hellbender size.
Stream macroinvertebrate communities are often dependent on water quality
and stream substrate characteristics (Erman and Erman 1984). The 3 aquatic insect
orders most commonly consumed by larval Hellbenders (Ephemeroptera, Trichoptera,
and Plecoptera) were abundant in benthic samples and regularly seen during
our surveys. Ephemeroptera and Trichoptera were also the most well-represented
invertebrate groups found during index of biological integrity (IBI) surveys conducted
downstream in adjacent Townsend, TN (Carter et al. 2008, 2009, 2010). As
these orders are known to be associated with high water quality, the abundance of
these organisms is used as a biological indicator of stream health through use of the
EPT (Ephemeroptera, Plecoptera, and Trichoptera) index (Weber 1973). While it is
not clear if Hellbenders require these dietary items or they were eaten more often
because they were more abundant, this study prompts further research into the importance
of stream quality in regards to larval Hellbender dietary requirements. As
communities of macroinvertebrates commonly change throughout the year (Giller
and Malmqvist 1998), diet studies on a longer time scale are necessary to determine
if Hellbender larval diet remains consistent throughout the year.
Acknowledgments
We thank Michael Freake, Marcy Souza, The Great Smoky Mountains Institute at
Tremont, Stephen Nelson, Shem Unger, Melrose Flockhart, Perran Ross, Andrea Drayer,
and all volunteers for assistance on this project. We also acknowledge Paul Super, Keith
Langdon, and the National Park Service. Financial support for this research was provided
by the Great Smoky Mountains Conservation Association Carlos C. Campbell Fellowship,
The Reptile and Amphibian Conservation Corp (RACC), and the Cryptobranchid Interest
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2017 Vol. 16, No.2
Group Jennifer Elwood Conservation Grant. Research was conducted under permits from
the National Park Service (GRSM-2008-SCI-0052) and University of Florida ARC Protocol
(#017-08WEC).
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