Biologia, Bratislava, 59/Suppl. 14: 103—107, 2004
Body size and survivorship of the European pond turtle
Emys orbicularis in Central Poland
Slawomir Mitrus1* & Maria Zemanek2
Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, PL–30-387 Cracow,
Poland
2
Fiolkowa 7/36, PL–31-457 Cracow, Poland
*present address: Department of Environmental Protection, Faculty of Geology, Geophysics and Environmental Protection, AGH – University of Science and Technology, Aleja Mickiewicza 30, PL–30-059
Cracow, Poland; e-mail: [email protected]
1
MITRUS, S. & ZEMANEK, M., Body size and survivorship of the European pond turtle Emys orbicularis in Central Poland. Biologia, Bratislava,
59/Suppl. 14: 103—107, 2004; ISSN 0006-3088.
We used mark-recapture techniques to study survival rates of Emys orbicularis in the Borowiec Nature Reserve (Central Poland, Radom district). About
40 adult and 20 young (3–9 years old) turtles live there. Mean straight carapace length (SCL) and body mass (BM) of adult individuals were respectively:
SCL = 163.5 mm, BM = 0.67 kg for males (n = 14) and SCL = 181.8 mm,
BM = 0.97 kg for females (n = 21). Based on scute growth rings we estimated
that males mature on average with 11 years and females with 15 years. The
youngest gravid females were 12 years old. Mean annual survivorship was
close to 1.0 for adult turtles, and around 0.8 for young individuals.
Key words: Emys orbicularis, survival rate, body size, maturity, Poland.
Introduction
Populations of the European pond turtle Emys
orbicularis (L., 1758) are considered endangered
in several parts of its range, not only in northern areas (FRITZ & ANDREAS, 2000). However, about survival rates few data are available.
Thus, it is difficult to model population dynamics and to predict effects of conservation programmes.
Annual survival rate of adult individuals
of some freshwater turtle species is very high,
for example 0.96–0.98 for the Blanding’s turtle
Emydoidea blandingii (Holbrook, 1838) (CONGDON et al., 1993, 2000), and 0.95 for Kinosternon flavescens (Agassiz, 1857) (IVERSON, 1991).
The survival rate of adult individuals of E. or-
bicularis in France was about 0.9, but no exact
data were presented (SERVAN in GIRODONT &
PIEAU, 1993). In Brandenburg two individuals of
the species were observed 24 years after marking (SCHNEEWEISS & STEINHAUER, 1998). Age
records for wild E. orbicularis were 28 years for a
male and 29 years for a female (data from Spain:
KELLER et al., 1998).
In Central Poland, nine out of 15 turtles
(14 adults and one subadult) marked from 1986–
88 were observed in 1999, and three others were
watched for the last time in 1998 (MITRUS & ZEMANEK, 2000). Thus, E. orbicularis seems to be
a long-lived species with a high survival rate of
adults. In this study we summarize for a population in Central Poland information to calculate
survivorship.
103
Fig. 1. Location of the study area.
Material and methods
From 1998 to 2001 intensive fieldwork was conducted in
Borowiec Nature Reserve (BNR; Zwoleńka river valley,
Radom district, Central Poland; 51◦ 16 N, 21◦ 47 E)
(Fig. 1). The reserve (area 57.3 ha) contains aquatic,
marshy, and dry habitats (ZEMANEK, 1992). During
spring and summer (late April to late August), turtles
were caught by dip-netting. Depending on weather conditions, turtles were dip-netted from one or two rubber
dinghies several times per year (three to six consecutive days). In 2000 and 2001 baited traps (SERVAN,
1986) were used. Additionally, during each egg-laying
period (depending on weather: mid-May do mid-June),
females were observed on their way to nesting sites and
during nesting. With these methods we recorded each
year some new individuals.
In BNR, active protection of Emys orbicularis
has been carried out since 1989, including the release of headstarted juveniles (MITRUS & ZEMANEK,
2000). From 1991 onwards turtles were marked by
marginal notching (PLUMMER, 1979). Before 1991
numbers were engraved on the third vertebral (central)
scute (MITRUS & ZEMANEK, 1998).
Straight carapace (SCL) and plastron lengths
(PL) were obtained to the nearest 1 mm in 1998 and to
0.1 mm since 1999, and body mass (BM) was recorded
to the nearest 10 g using 1.5 kg Pesola scales. Sex was
identified according to male secondary sexual characters (ZUFFI & GARIBOLDI, 1995). The age of young
turtles was determined by counting annual growth
rings on the left pectoral scute. On scutes of adult
individuals, we observed two kinds of growth rings:
wide and narrows ones. In adults we counted only wide
rings. Turtles up to an age of nine years (based on wide
growth rings) were classified as “young”, older individuals as “adult”.
Survival rate and population size were estimated
by using the triple catch method (DONNELLY &
GUYER, 1994) for the periods 1998–2000 and 1999–
2001, for adults and young turtles separately. All turtles caught and/or observed during one year constituted one sample. The triple catch method is often
used for small samples, but the smaller the individual
number the greater the bias is (DONNELLY & GUYER,
1994).
15 turtles (12 adult females, 2 adult males,
and one young) were marked in BNR from 1986 to
1988 (MITRUS & ZEMANEK, 2000; ZEMANEK, unpubl.
data). We used these individuals to estimate the survival rate from 1986 to 1999.
Results
Emys orbicularis females reach in BNR greater
shell lengths and higher body masses than males
(t-test, for SCL: t = 4.95, df = 33, P < 0.001; for
PL: t = 9.53, df = 33, P < 0.001; for BM: t = 7.40,
df = 33, P < 0.001; Tab. 1).
Each year 14–25 adult and 5–15 young turtles were caught. About 40 adult and 20 young
turtles live in BNR. Survivorship of the adult turtles (males and females together) is close to 1.0
(Tab. 2).
Twelve of the 14 adult turtles marked in the
years 1986–1988 were recaptured from 1999–2001
(one adult female marked in BNR was caught in
Barycz region – about 10 km from BNR; Fig. 1).
This indicates a minimal annual survival rate of
about 0.98–0.99 from 1986–1999.
Adult males have 10.1 wide growth rings (SD
= 3.1, range: 4–15, n = 14). Adult females have
an average of 14.2 wide growth rings (SD = 2.2,
range: 11–17, n = 19); the narrow rings are impossible to count accurately. Two individuals were
12 winters old (based on growth rings) in 2000
and 2001, respectively. In these years they were
watched during nesting. In previous seasons they
were not observed on land during the egg-laying
period.
Table 1. Measurements and body mass of Emys orbicularis in Borowiec Nature Reserve, Central Poland (mean,
standard deviation, range).
Males (n = 14)
Females (n = 21)
104
Straight carapace length [mm]
Plastron length [mm]
Body mass [kg]
163.5 (15.1) 124.1–179.4
181.8 (6.4) 170.4–191.9
146.0 (11.1) 120.2–162.8
173.6 (6.1) 163.8–187.5
0.671 (0.145) 0.33–0.84
0.969 (0.094) 0.83–1.13
Table 2. Estimations of population size and survival rate of adult and young (3–9 years old) Emys orbicularis
in Borowiec Nature Reserve, Central Poland (mean ± standard error = SE).
Study period
Age class
Population size
Mean annual survivorship
1998–2000
Adult
1.00 ± 0.16
1998–2000
Young
1999–2001
Adult
1999–2001
Young
33.1 ± 4.9
(estimation for 1999)
14.4 (no SE estimation)
(estimation for 1999)
52.9 ± 15.3
(estimation for 2000)
25.2 ± 8.0
(estimation for 2000)
Discussion
Emys orbicularis lives in Poland near its northern
distribution border (FRITZ, 1998). Body sizes of
the turtles from BNR resemble other populations
from the northern part of the range (FRITZ, 1998;
FARKAS et al., 1998). In the south, individuals are
smaller (SHCHERBAK, 1966; FRITZ, 1998; KELLER
et al., 1998).
It is generally accepted that the mortality
of freshwater turtles occupying higher latitudes is
highest during overwintering (e. g. ULTSCH, 1989;
BODIE & SEMLITSCH, 2000). This suggests that
mortality is low during spring and summer, and
individuals caught during these seasons probably
survive throughout the activity period.
Most authors assume that survival rates of
adults of both sexes are equal (FRAZER et al.,
1990; IVERSON, 1991; CONGDON et al., 1993,
2000). However, mortality could be different for
males and females (WILBUR, 1975; ZWEIFEL,
1989). Due to small sample size, we combined in
this study males and females. Dispersal of turtles to areas that were not dip-netted could bias
our survivorship estimates. Theoretically, both
young and adult turtles could emmigrate. However, in other species long distance dispersal of
young freshwater turtles is rare (GIBBONS et al.,
1990). Although fieldwork has been carried out in
BNR since the mid-1980s and in the Barycz region since 1993, only one long distance dispersal
was recorded (see Results).
An active protection programme could influence the estimation of survival rate of young turtles. In the years 1990–1997 released headstarted
turtles were not marked (MITRUS, 2000). Thus,
among the group of “young” turtles might be also
headstarted individuals. However, we believe the
influence of artificial rearing on survival rate is low
after several years in the wild.
Females of E. orbicularis from BNR have on
0.80 ± 0.22
1.38 ± 0.39
1.00 ± 0.38
average 14.2 wide growth rings and a series of narrow ones (this study). Similar growth ring patterns
were described from France (BARON & DUGUY,
2000; NAULLEAU, 2000). These patterns might be
associated with sexual maturity age (ZUG, 1991)
in that the narrow rings are formed after maturity, the wide ones before. If this is applied to
BNR turtles, males mature there on average with
11 years and females with 15 years. Egg-laying females were at least 12 years old (11 growth rings).
Similar data are known from Central France: 12
and 17 years for males and females, respectively,
were recorded there as maturity ages (GIRONDOT
& PIEAU, 1993). These ages exceed the data for
other parts of the species’ range (e. g. southernmost Russia: 6–8 years, BANNIKOV, 1951; Spain:
more than 6 years, KELLER et al., 1998; Ukraine:
6–8 years, SHCHERBAK, 1966). In the south of the
range, adults attain a smaller body size. This is
could be associated with an earlier sexual maturity.
Growth rings may not be always produced
annually (ZUG, 1991; KELLER et al., 1998), thus
our estimations could be imprecise. However, we
observed annual production of growth rings in
young turtles from the Zwoleńka river valley
(MITRUS & ZEMANEK, unpubl. data).
In this study, mean annual survivorship of
adult E. orbicularis was about 1.0. Due to small
sample size, this estimate might be not exact. In
any case, our data from Central Poland suggest a
very high adult survivorship. At least the northern E. orbicularis seem to belong to the freshwater
turtles with the highest known survival rates.
Acknowledgements
We are very grateful for the constructive comments
of two anonymous referees. Thanks to all friends who
helped during fieldwork, especially to A. KOTOWICZ
and M. R˛
EBIŚ. Data of this study were collected dur-
105
ing a programme of active protection of the European pond turtle, supported by Environment and Agriculture Division, Mazovian Voivodship Office in Warsaw, EcoFund – Polish Debt for Environment Swap,
Global Environment Facility – GEF/SGP UNDP, and
Kozienice Landscape Park.
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