Capture Rate, Body Size, and Survey Recommendations for Larval Ambystoma cingulatum (Flatwoods Salamanders)
David C. Bishop, John G. Palis, Kevin M. Enge, David J. Printiss, and Dirk J. Stevenson
Southeastern Naturalist, Volume 5, Number 1 (2006): 9–16
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2006 SOUTHEASTERN NATURALIST 5(1):9–16
Capture Rate, Body Size, and Survey Recommendations for
Larval Ambystoma cingulatum (Flatwoods Salamanders)
DAVID C. BISHOP1,6,*, JOHN G. PALIS2, KEVIN M. ENGE3, DAVID J. PRINTISS4,
AND DIRK J. STEVENSON5
Abstract - Recovery of the federally threatened Ambystoma cingulatum (Flatwoods
Salamander) will require monitoring of known populations, as well as continued
searches for additional populations. In an effort to develop recommendations for
maximizing efficiency of future surveys of larval Flatwoods Salamanders, we combined
data from surveys conducted between 1990 and 2004 in Florida and Georgia.
Analysis of these data revealed variation in the number of larvae captured, survey
effort, capture rates, and larval body size among years and months. An average of 16
min or 45 one-m long dipnet sweeps was required to catch each larva. For wetlands
surveyed twice in a season, results (i.e., larval presence or assumed absence) were
consistent in 74% of consecutive surveys. We make recommendations for conducting
future surveys and the implementation of a coordinated research and monitoring
program for Flatwoods Salamanders.
In response to the apparent decline in many amphibian species (Halliday
1998, Pechmann and Wilbur 1994, Wake 1991), conservation efforts have
been focused on the development of survey techniques and monitoring
programs (e.g., Heyer et al. 1994, Smith and Petranka 2000, Welsh and
Droege 2001). Ideally, monitoring enables land managers to evaluate population
status over time and respond to potential threats with timely management
decisions. Before a monitoring program can be successful, however,
managers must first know the appropriate survey techniques and survey
schedule for the species of interest.
Ambystoma cingulatum Cope (Flatwoods Salamander) was listed as federally
threatened in 1999 (US Fish and Wildlife Service [USFWS] 1999).
Because of its protected status and the general perception that it has declined
in abundance over the last few decades (Means et al. 1996), greater effort
has been made recently to survey historical and potential sites for breeding
populations, primarily using larval dipnet surveys. Recovery of this species
will require monitoring of known populations as well as continued searches
1Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and
State University, Blacksburg, VA 24061. 2PO Box 387, Jonesboro, IL 62952.
3Florida Fish and Wildlife Conservation Commission, 5300 High Bridge Road,
Quincy, FL 32351. 4The Nature Conservancy, Northwest Florida Program, PO Box
393, Bristol, FL 32321. 5Fort Stewart Fish and Wildlife Branch, 1557 Frank Cochran
Drive, Building 1145, Fort Stewart, GA 31314. 6Current address - Spring Island
Trust, 40 Mobley Oaks Lane, Okatie, SC 29909. *Correspondening author -
10 Southeastern Naturalist Vol. 5, No. 1
for additional populations (L. LaClaire, USFWS,Jackson, MS, pers. comm.).
However, there has been no coordinated effort to combine data from past
surveys to identify trends in capture rates and capture repeatability. This
information would prove helpful to future surveyors wishing to maximize
We combined data from surveys of larval Flatwoods Salamanders conducted
between 1990 and 2004 in most known breeding wetlands in Florida
and Georgia. We report data on capture rates, capture repeatability, and
larval body size, and make recommendations for maximizing efficiency of
larval surveys for this species. In addition, we make suggestions for future A.
cingulatum monitoring programs.
Flatwoods Salamanders historically inhabited mesic flatwoods and savannas
within the Pinus palustris Miller (longleaf pine) and Aristida stricta
Michaux (wiregrass) ecosystem in South Carolina, Georgia, Florida, and
Alabama (USFWS 1999). Adults migrate at night to ephemeral breeding
wetlands from October to January during rainfall events associated with cold
fronts (Anderson and Williamson 1976, Means 1972, Palis 1997a, Safer
2001). Courtship and egg deposition have been observed on land (Anderson
and Williamson 1976, 1977; Safer 2001), but it has been suggested that
aquatic egg deposition also may occur (Ashton 1992). Eggs that are deposited
terrestrially within the wetland basin hatch quickly upon inundation (Anderson
and Williamson 1976). The larval period lasts 11–18 weeks from hatching
to metamorphosis (Palis 1995), with some individuals reaching sexual maturity
and returning to the breeding wetlands the following fall (Palis 1997a).
Migrating adults can be captured in funnel or pitfall traps positioned next
to drift fences around the perimeter of breeding wetlands (Palis 1997a, Safer
2001). Because of relative inefficiency of sampling multiple sites for
Flatwoods Salamanders by these methods, most presence-absence surveys
focus on larval sampling by dipnet. Surveyors typically use 4-mm mesh
dipnets (Model SH-2 or SH-2D, Mid–Lakes Corporation, Knoxville, TN).
Larvae have been captured November to April (Means 1972, Palis 1996).
Larvae typically are captured in submerged herbaceous vegetation during
the day (Palis 1997b, Sekerak et al. 1996); therefore, most surveyors focus
their dipnetting efforts in vegetated areas (e.g., Palis 1997b).
Data collection and analyses
We combined data from previous surveys (N = 757) for larval Flatwoods
Salamanders at 176 different breeding wetlands in Florida and Georgia
(Table 1). We included only wetlands where at least one larva was captured
from 1990 through 2004. Each participant provided data on wetland location,
capture date, larval body size (total length [TL]), and survey effort.
Effort was reported as the total minutes spent dipnetting and/or the number
2006 D.C. Bishop, J.G. Palis, K.M. Enge, D.J. Printiss, and D. J. Stevenson 11
of 1-m long dipnet sweeps (Palis 1997b). Because we compiled data from
different sources, not all variables were collected for each individual captured;
hence, sample size differs among variables.
We calculated the total number of larvae captured, total effort (min. or
sweeps), and mean body size for 2-week intervals throughout the larval period
(Nov–Apr). We also calculated capture rates for positive surveys (i.e., those
where larvae were captured) by dividing the number of larvae captured in each
wetland by the total survey effort (min. or sweeps). Because some surveyors
stopped surveying after the first larva was captured, whereas others continued
dipnetting, capture rates should be interpreted as the average effort needed to
capture each larva. For records where surveyors recorded effort in both
minutes and sweeps, we used linear regression to examine the relationship
between the two methods.
For wetlands surveyed twice in a single season, we calculated the probability
of obtaining consistent results (i.e., larval presence or assumed absence) for
consecutive surveys. If a wetland was surveyed more than twice in a season, we
used only those data from the first two surveys in that year. We performed a ttest
to evaluate whether the mean number of days between consecutive surveys
differed between those that had consistent survey results those that did not.
Lastly, we looked at yearly variation in survey success for wetlands
dipnetted ≥ 5 different years (not necessarily sequential). We calculated the
percentage of successful years for each wetland and used these data to
estimate the minimum number of years potential or historical wetlands
should be surveyed to detect larval A. cingulatum. All analyses were conducted
using SPSS 11.0.
Table 1. Number of wetlands, surveys, and A. cingulatum larvae captured by location. NF =
National Forest, AFB = Air Force Base, SF = State Forest, NWR = National Wildlife Refuge.
Total Total Total
Location State Counties wetlands surveys larvae
Apalachicola NF FL Liberty, Franklin 54 351 234
Eglin AFB FL Okaloosa, Santa Rosa 28 163 116
(includes Hurlburt Field)
Fort Stewart (Army) GA Bryan, Evans, Liberty 14 72 142
Holley Field (Navy) FL Santa Rosa 1 1 1
Osceola NF FL Baker 3 9 7
Pine Log SF FL Washington 1 2 2
St. Marks NWR FL Wakulla 44 86 54
Private FL Baker 1 1 1
Private FL Calhoun 4 21 26
Private FL Holmes 1 1 1
Private FL Jackson 3 4 15
Private FL Jefferson 2 4 2
Private FL Liberty 4 12 9
Private FL Santa Rosa 4 9 8
Private FL Wakulla 9 18 10
Private FL Walton 1 1 1
Private FL Washington 2 2 2
Totals 176 757 631
12 Southeastern Naturalist Vol. 5, No. 1
Of the 757 surveys of known A. cingulatum breeding wetlands in our data
set, 348 (46.0%) resulted in the capture of one or more larvae (total larvae =
631). Larvae were captured from November 28 to April 23. The number of
larvae captured and the amount of survey effort varied by month (Table 2).
When data from all years and months were combined, larvae were captured at
a mean rate of 1 individual per 16.0 ± 23.9 min (range: 1–256, 95th percentile =
60.0, N = 296) or 1 individual per 44.6 ± 67.2 1-m long sweeps (range: 1–664,
95th percentile = 150.2, N = 231). There was a significant linear relationship
between the number of minutes spent surveying and the number of dipnet
sweeps (Sweeps = 4.292[min.] - 4.588, R2 = 0.7155, P < 0.001, N = 183).
Mean larval size and the range of sizes differed among months (Fig. 1).
For wetlands surveyed twice in the same season, 107 out of 145 (73.8%)
yielded consistent results (i.e., larval presence or assumed absence) in consecutive
surveys. The mean number of days (± SD) between consecutive
surveys was 29.3 ± 18.1 (range: 1–101, N = 145). When separated, the mean
number of days between surveys was 27.2 ± 16.0 (range: 1–81, N = 107) for
those with the same results and 34.9 ± 22.3 (range: 3–101, N = 38) for those
with different results. This difference was statistically significant (t =
-2.279, df = 143, P = 0.024). For the 37 wetlands surveyed ≥ 5 years (mean:
6.7 ± 1.5 yrs, range: 5–11), the mean number of years needed to capture
larvae was 2.5 ± 1.3 (range: 1–8 yrs; 95th percentile = 5.3 yrs).
We made no attempt to account for geographic variation in capture rates,
capture repeatability, or larval size associated with latitude, years,
Table 2. Number of surveys, total captures, and capture rates for A. cingulatum by month.
Period 1 includes days 0–15 (0–14 for Feb). Capture rates were calculated using only data from
positive surveys (i.e., at least one larva was captured). Sample sizes vary between capture rate
categories because not all records had effort data in both minutes and sweeps. Mo. = month, Per.
= period, TS = total surveys, PS = positive surveys, TL = total larvae.
Capture rate (min/larvae) Capture rate (sweeps/larvae)
Mo. Per. TS PS TL Mean SD Range N Mean SD Range N
Nov 1 0 0 0 — — — 0 — — — 0
2 2 1 1 2.0 — — 1 7.0 — — 1
Dec 1 2 1 1 25.0 — — 1 — — — 0
2 1 1 2 10.0 — — 1 — — — 0
Jan 1 13 8 8 80.6 86.2 10.0–256.0 7 112.5 10.6 105.0–120.0 2
2 78 41 79 30.3 32.0 1.8–150.0 39 222.0 294.2 14.0–430.0 2
Feb 1 119 59 88 8.8 11.9 1.0–70.0 48 23.8 29.6 1.0–118.0 45
2 92 49 127 9.2 10.8 1.0–50.0 33 54.0 109.2 1.0–664.0 40
Mar 1 243 101 175 12.0 13.5 1.0–75.0 92 46.1 55.0 1.0–245.0 79
2 136 57 86 13.1 12.3 1.0–52.0 51 46.5 46.8 2.0–167.0 45
Apr 1 52 26 55 21.3 17.3 1.0–60.0 22 41.8 37.1 1.0–118.0 13
2 19 4 9 1.5 NA NA 1 29.5 29.8 1.5–60.0 4
2006 D.C. Bishop, J.G. Palis, K.M. Enge, D.J. Printiss, and D. J. Stevenson 13
hydroperiod, habitat, or weather. Likewise, we did not control for differences
in surveying methodology or larval measurements among individual surveyors.
Although surveyors used similar equipment and had comparable techniques,
individuals likely differed slightly in dipnetting methods. Despite
these problems, combining data sets provides useful information on capture
rates, capture repeatability, and body size of larval Flatwoods Salamanders.
When data were combined for all months, an average of 16 minutes or 45
one-m long sweeps was needed to capture each larval salamander. Larvae
were captured from November 28 to April 23, with the majority of surveys
occurring in February and March. Not surprisingly, the total number of larvae
captured increased with the number of surveys, both of which varied among
months. Assuming larvae were captured at rates relative to their abundance,
we can compare capture rates over time to estimate relative abundance each
month. Using this method, the data suggest that capture rates are similar in
February, March, and April. However, because the amount of effort spent
surveying varied among months, our analysis is limited.
Few surveys were conducted in November and December; hence, the
capture-rate data in Table 2 could be misleading if sample size is ignored.
Because ephemeral breeding wetlands often are not filled completely in
Figure 1. Size of larval A. cingulatum each month. Boxes display interquartile range.
The dark line is the median. Open circles are outliers. SVL = snout-vent length.
14 Southeastern Naturalist Vol. 5, No. 1
November or December, we do not recommend surveying during this time in
lieu of later months if the goal is to detect the species. In addition, because
larvae are small from November to January, they may be more likely to slip
through the netting of dipnets. As expected, mean larval size increased as the
larval season progressed, as observed by Whiles et al. (2004). Variation in
size reached a maximum in the middle of the larval season (February and
March), which likely can be attributed to multiple hatching dates (Palis
1995, Sekerak et al. 1996).
If a wetland was dipnetted twice in the same season, there was a 74%
probability of obtaining consistent results in consecutive surveys. Discrepancy
in consecutive surveys could result from several factors: 1) larvae may
have metamorphosed between surveys, 2) habitat conditions may have
changed (e.g., wetland dry-down then refill), 3) differences in survey methodology
(e.g., different sections of the wetland were sampled, the amount of
effort varied, etc.), 4) differences in larval density between surveys, or 5)
larvae may have been too small to catch in the first survey, but large enough in
the second. Wetlands that yielded the same results and those that did not had a
mean difference of 7.7 days between consecutive surveys. Although this was
statistically significant, we believe this has little biological relevance.
Historical or potential A. cingulatum breeding wetlands may need to be
dipnetted for several years before larvae are captured. For the 37 wetlands
surveyed ≥ 5 years, an average of 3 (2.5) years of surveys were needed to
document the presence of larvae. However, some wetlands contained larvae
every year, whereas others had larvae only once in 8 years. Because we only
included those years for which dipnetting occurred, even more site visits
may be needed if drought years are included. Larvae were captured in 90%
of the wetlands after 4.6 years of sampling; therefore, we suggest a minimum
of 5 years of surveys be conducted in potential wetlands to document
the presence or assumed absence of A. cingulatum. Historical wetlands that
have not produced larvae in 5 years should continue to be dipnetted,
especially those located near other active breeding wetlands; Flatwoods
Salamanders likely occur in metapopulations, where wetland occupancy
varies over time.
Larvae were captured in 46% of the surveys. We do not have sufficient
data to determine why some surveys were successful and others were not;
however, casual observations indicated that locations and wetlands differed
annually in the relative abundance of salamanders. Little information is
available on how habitat modification (e.g., forestry operations, fire exclusion
and suppression [Bishop and Haas 2005]) or weather conditions (e.g.,
rain dates, rainfall, hydroperiod) affects the population dynamics of
Flatwoods Salamanders. If the species is declining, the scientific community
needs to determine the reasons and mitigate any anthropogenic causes.
Long-term annual monitoring programs should help identify the primary
factors that influence successful reproduction and recruitment; progress will
be faster if there is a coordinated effort by all management agencies to
2006 D.C. Bishop, J.G. Palis, K.M. Enge, D.J. Printiss, and D. J. Stevenson 15
standardize data collection. By simply evaluating the presence or assumed
absence of A. cingulatum in each wetland over a long period of time (e.g., 10
years) and coupling this information with data on weather patterns, habitat
changes (in uplands, wetlands, and ecotones), and survey efforts, we may
begin to understand the population dynamics. Even greater understanding
may be achieved through the development of quantitative techniques to
relate relative larval abundance to the aforementioned variables.
In summary, we recommend surveying from February to early April to
document the presence of A. cingulatum larvae. However, surveying in all
months of the larval period may be fruitful, and weather patterns may dictate
appropriate times. Larvae typically were captured in an average of 16 min or
45 one-m dipnet sweeps; however, there was significant variation in capture
rates, and we suggest that surveyors dipnet for longer periods. We recommend
each known breeding wetland be surveyed at least twice each season,
if the first survey was negative, preferably with several weeks between
surveys. Several years of surveys may be needed to document breeding
activity in potential wetlands. We encourage all Flatwoods Salamander
researchers and land managers to develop a consolidated plan for future
monitoring and research efforts.
Funding for this research was provided by Florida Fish and Wildlife Conservation
Commission, St. Joe Timberland Company, National Council for Air and Stream
Improvement, Inc., US Department of Defense, US Forest Service, and US Fish and
Wildlife Service. We thank Mark Bailey, Wendy Caster, Matthew Chatfield, David
Cook, Marquette Crockett, Angie Crook, Aubrey Davis, Debora Endriss, Michael
Evans, Sylvia Harris, Dan Hipes, Kelly Irwin, John Jensen, Joshua Jones, Will
Fields, Karen Lamonte, Joe McGlincy, Paul Moler, Katy NeSmith, Tom Ostertag,
Lourdes Oztolaza, Petko Petkov, Lou Phillips, Matthew Proett, Renee Ripley, Fred
Robinette, Carrie Sekerak, Gary Sprandel, Cathy Szymanski, Bob Walker, Lee
Walston, and Mike Wilson for field assistance. We also thank Jackson Guard (Eglin
Air Force Base), the Fort Stewart Fish and Wildlife Branch, and The Nature Conservancy
of Georgia for their assistance. Two anonymous reviewers provided helpful
comments on an earlier draft of this manuscript. Surveys were conducted under the
following permits: USFWS: TE008077, TE049502, TE051095-0, TE061051-0; FL
FWCC: WV00516A, WV01232, WV99431; GA DNR: 29-WMB-00-132.
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