Changes in the occurrence and population trend of the Eurasian

NORTH-WESTERN JOURNAL OF ZOOLOGY 8 (1): 112-118
Article No.: 121105
©NwjZ, Oradea, Romania, 2012
www.herp-or.uv.ro/nwjz
Changes in the occurrence and population trend
of the Eurasian otter (Lutra lutra)
in Hungary between 1990 and 2006
Miklós HELTAI1,*, Éva A. BAUER-HAÁZ2, Róbert LEHOCZKI1 and József LANSZKI2
1. Institute for Wildlife Conservation, Szent István University, H-2103 Gödöllő, Páter K. u. 1,
Hungary. E-mail: [email protected]
2. Department of Nature Conservation, University of Kaposvár, H-7401 Kaposvár, P.O. Box 16,
Hungary. E-mail: [email protected]
*Corresponding author, M. Heltai, E-mail: [email protected]
Received: 18. February 2011 / Accepted: 12. December 2011 / Available online: 08. January 2012 / Printed: June 2012
Abstract. In order to determine the distribution of the Eurasian otter (Lutra lutra) in Hungary and to monitor
the changes in population trend, a questionnaire survey was sent out to Hungarian game management units
(GMUs) to complete between 1990 and 2006. The reliability of data coming from questionnaires was tested by
field survey in 92 areas of 10×10 km UTM cells. Both the mean response rate and the mean area covered by
responses was 42.4%. The otter population of Hungary might be considered to be stable. The otter
distribution area was found to be wide (approximately 72.000 km2, i.e. 77.5% of Hungary) and populations
were probably inter-connected; however, fewer occurrences were found in mountain areas and in dry plains
with little wetland. Distribution (permanent, occasional or negative presence of otter in different years) was
found to be constant. According to the questionnaire answers, the professional hunters seemed to slightly
underestimate the occurrence of the otter, which is strictly protected, but otherwise their responses were
reliable and usable. In order to conserve the otter and its aquatic habitats a standardized survey needs to be
established as soon as possible.
Key words: mail questionnaire survey, occurrence, population trend, field test, density.
Introduction
The Eurasian otter (Lutra lutra Linnaeus, 1758) is
listed as an animal species of Community importance (EEA 2009) and is widely distributed in
Europe (Chanin 1985, Mason & Macdonald 1986).
A study of the distribution started in the middle
1970s after the decline of the European population
was recognized (West 1975, Macdonald & Mason
1976). The decrease in populations in the 1960s
and the 1970s was probably caused by the cumulative effects of toxic chemicals (e.g. PCBs, DDT),
hunting and loss of habitat. Assessment of the otter populations from the 1990s showed a general
recovery in Europe (Conroy & Chanin 2002,
Reuther 2002, EEA 2009) which is believed to be
due to e.g. active and passive protection, general
improvement and rehabilitation of wetlands, and
a decrease in environmental pollutants. However,
the population recovery coincided with a resume
of the species persecution, due to real or suspected
damage caused by otters (Kranz 2000, Reuther
2002) mainly in Central Eastern Europe after privatization of fish ponds during that decade. The
treatments of fish ponds are getting more and
more intensive, which also contributes to this
problem (Gyalog et al 2011).
Information about the otter population in
Hungary from the time before they became protected in the country is only available from occasional observation and hunting statistics. According to the data of bags in the period before the
First World War, the otter occurred in every
county (325.000 km2) and the bag was of 526-1120
animals per year between 1884 and 1909 (Faragó
2009). These data show that the species was rare in
the Great Hungarian Plain (mainly in the counties
of Békés, Csongrád, Hajdú and Heves). Tankó &
Tassi (1978) calculated the population density
from the data of bags for the years right before the
species became protected (between 1969 and
1973). They estimated that the eastern part of the
country (the Plain) had the lowest density of otters
(0.002-0.02 animals per 1000 ha), while the highest
density (0.51-0.65 animals per 1000 ha) was in the
South Transdanubian counties (Baranya, Somogy
and Tolna). After protection came into force in
1974, information was collected from fisheries
through reports sent to the nature conservation
authority (instead of hunting statistics). Based on
reported damage caused by otters, Nechay (1980)
also estimated that the largest population inhabited the South Transdanubian region in those
years.
Otter distribution in Hungary
In the last two decades the otter population in
Hungary was investigated by several methods.
The first systematic field survey was carried out
between 1987 and 1990 (Kemenes 1991, Kemenes
& Demeter 1995) and covered several regions of
the country using the IUCN current minimum
standard method (3-5 sites are examined per
10×10 km UTM cell and 600 m long shoreline per
site; Macdonald 1984, Reuther 1984). The presence
or absence of otters was determined by otter specialists for 369 sites. The survey showed positive
records at 52% of the sites which was a good result
in comparison with other regions of (Central)
Europe (Reuther 2002). However, the distribution
of the species was not uniform.
Field surveys using these standard IUCN
methods have not continued. Various countrywide surveys have been carried out between 19951996 by the NGO ‘Foundation for Otters’ (Gera
2004) following only partially the IUCN minimum
standard method. Observations from numerous
volunteers with different levels of interest and
skills (anglers, fishermen, students, amateur naturalists, rangers) were recorded in the survey. The
reliability of this unpublished data was not within
our control.
The Institute for Wildlife Conservation, Szent
István University carried out 16 questionnaire surveys among Game Management Units (GMUs) in
Hungary with regard to carnivores between 1987
and 2006 (with 10 of the surveys regarding otters).
This method was used in studies of endangered,
recovering native and invasive carnivore species
(e.g. Heltai et al. 2000a, 2006, Bihari et al. 2007,
Heltai 2010), and during the present study. It is
difficult to evaluate any change in the otter population in Hungary since results of different surveys
in the country can be hardly compared (overview:
Kemenes et al. 2005). Also they cannot be compared to data from other European countries
(Reuther & Krekemeyer 2003), so it is not possible
to be certain of any changes in population trends
over the last 20 years as there was no countrywide
field survey carried out by experts according to
the standardized method (e.g. Reuther et al. 2000,
Chanin 2003).
Our aim in this study was to examine whether
a simple, quick and cheap mail questionnaire survey (Filion 1980, Dillman 1983, Sheatsley 1983) using independent and competent respondents
(GMUs) could be used to describe the countrylevel distribution and to monitor the population
trend of the strictly protected otter.
113
Materials and methods
Mail questionnaire survey and data processing
Data on otter distribution and occurrence in Hungary
were collected annually between 1990 and 2006 by mail
questionnaires and were based on the voluntary responses of Game Management Units (GMUs). Questions
were asked about the occurrence of the species (presence
or absence) and in the case of a positive answer, whether
the presence was permanent (i.e. the otter appeared regularly during the given period) or only occasional. If the otter presence was permanent, the estimated number of
animals was asked to be listed in one of the following
categories: 1, 2-4, 5-7, 8-10, 11-13, or more. Otter density
for a GMU was calculated based on the responded value
and area of a given GMU. The average otter density per
year (both at the country level and within the distribution
area) was calculated by averaging the data of respondents. Respondents were professional hunters who have
at minimum an intermediate level professional qualification and one-third of them have higher education (wildlife management BSc). GMU areas cover the entire territory of Hungary and they must employ a minimum of
one professional hunter per 3000 hectares.
According to the Atlas of European Mammals
(Mitchell-Jones et al. 1999), 10x10 km units of the universal transverse mercator (UTM)-based distribution map
are appropriate for revealing the maximum distribution
area of the otter.
In order to convert the questionnaire data into UTM
grid cells, the percentage of a UTM cell (10.000 ha) covered by GMU reporting otter presence was calculated using ArcGIS 9.1. If the otter occurred in a GMU covering at
least 625 ha of a UTM cell then the cell was regarded as
showing a presence. The reason for using the value of 625
ha was that the minimum required size of a GMU area is
3000 ha (although the authority for hunting can allow it to
be reduced to 2500 ha). Thus if 625 ha is used as a basis,
no positive data losses will occur even in a smaller GMU
area of 2500 ha if the GMU area is divided into four by
the UTM net. The summarized UTM map is based on the
various annual (1990, 1994, 1995, 2000, 2001, 2002, 2003,
2004, 2005, 2006) UTM nets, where the UTM cells show
different values from 0 to 10 depending on the number of
years which responded positive. In order to quantify the
potential otter distribution area size we calculated the
percentage of UTM cells over the whole country (1060
UTM cells) which provided positive values during the
study period. If a particular UTM cell showed a positive
value for at least one year than it was included in the
summary. The received data was archived by using Paradox 8 and Quattro Pro 11.0 database programs (Corel
Corporation, Ottawa, Canada).
Field survey
An assessment of otter distribution and quality of otter
habitats was carried out in the South Transdanubian Region, mainly in the Dráva, Kapos and Danube river basins, using the methodology determined by Reuther et al.
(2000). The study was undertaken between November
2006 and April 2008 in 390 sites (n= 92 pc of 10×10 km
Heltai, M. et al.
114
UTM cell) (Lanszki 2008a, 2008b, 2008c). The testing of responses received from GMUs on the given area was
based on these detailed field surveys.
Statistical analysis
Examination of differences in estimated (countrywide
and in the distribution area) population density (animals
per 1000 ha) during the periods (1: 1990-1995, 2: 2000-2002
and 3: 2003-2006) was tested by ANOVA (dependent
variable was the estimated population density and independent variable was the period, Bonferroni post hoc
test). The estimated population data in the distribution
area was considered only in GMU sites where occurrences were recorded as permanent. Chi-square test was
used for distribution analysis of permanent, occasional, or
negative presence of otter (number of 10-km UTM cells)
in different years. Variation of UTM cells number per
year, where the occurrence was considered positive or
negative by GMUs or where no responses were received,
was tested separately by univariate logistic regression
analysis to reduce the probability of a false positive trend
(Marcelli & Fusillo 2009).
Those cells from the total of 92 cells included in the
field survey were considered only where the answer of
GMUs in the questionnaire survey was positive or negative (excluding UTMs with no replies). Consequently, to
test the distribution of negative and positive cells, 69 cells
from 2006 were considered using Chi-square test. Results
of field surveys were compared with data of responses
received from GMUs in 2006 (season 2006/2007, which
means that the same period was used in both surveys).
The SPSS (1999) statistical package was used for the processing of the data obtained.
Results
Between 743 and 1202 questionnaires were distributed each year. The response rate varied between 26% and 51% (mean 42.4%) and the mean
area covered by responses was 42.4% of the total
(Table 1). According to assessment based on questionnaire surveys, the average countrywide density of otters was between 0.46 and 0.80 individuals per 1000 ha since 1990. The population density
slightly increased until 2002 and 2003 and since
then it is regarded as stable (Fig. 1). The estimated
average density (0.44 animals per 1000 ha) of the
initial period (1990-1995) did not differ significantly from the average value (0.56 ind. per 1000
ha) of the next decade (2000-2002). In comparison
(ANOVA, F2= 23.07, p<0.001) the density increased to 0.77 individuals per 1000 ha in the latest
period (2003-2006). The same trend can be seen in
the otter distribution area, where the estimated
density of 0.99 individuals per 1000 ha in 1990 increased to 1.82 individuals per 1000 ha in 2003,
and since then the density has remained roughly
constant. The differences in all three periods were
significant (in order 1.14, 1.45 and 1.80 ind. Per
1000 ha, ANOVA, F2= 16.51, p<0.001).
Whereas the density data showed an increasing trend, the more accurate distribution data
(permanent, occasional or negative occurrence,
Fig. 2) hardly changed since 1990 (Chi-square-test,
χ218= 12.97, p= 0.793). The number of UTM cells
with no responses decreased (Fig. 3) (logistic regression, r2= 0.635, p<0.05), the number of negative
response cells slightly decreased also (r2= 0.155, p=
0.401), and the number of positive cells increased
considerably (r2= 0.644, p<0.05). According to the
total number of positive UTM cells between 1990
and 2006, the distribution of otters (extension of
area inhabited by otters) was approximately
72.000 km2, which represents 77.5% of the country
(Fig. 4). The species is rare in the mountains, in the
arid and sandy region between the rivers Danube
and Tisza and in a part of the Small Hungarian
Plain (Fig. 4). Continuous otter distribution features in other parts of the country as along the
Middle-Tisza, the lower part of the rivers Danube
and Tisza, around Lake Balaton, in the south
Transdanubian region, along the river Rába and in
the river Drava plains region. Blocks of distribution areas are connected to each other and on the
basis of applied 10×10 km resolution the otter
population seems not to be fragmented.
Presence of otter was positive in 344 sites out
of the 390 sites examined through field survey
(88.2%) and in 91 cells out of the total 92 UTM cells
covered (98.9). In 2006, based on the 69 cells for
which there were responses (negative or positive)
from the GMUs, the otter occurred in 68 UTM cells
for the field survey (98.6%), and in 56 cells for the
mail questionnaire survey (81.2%). The difference
in distribution of the positive and negative presence between the results of the two surveys was
significant (χ21= 11.45, p<0.01).
Discussion
The total country area is covered by 1060 UTM
cells of which 778 cells (73.4%) showed positive
occurrences according to the total number of responses during the period 1990-2006 of the present
study. In other studies 239 cells (23.6%) were
found to be positive by Kemenes and Demeter
(1995), 335 cells (33.0%) in the period 1995-1996,
407 cells (40.1%) in 2001 and 579 cells (54.6%) in
2004 by Gera (2004). The higher rate of occurrence
Otter distribution in Hungary
115
Table 1. GMU response rate, area covered and number of positive and negative UTM cells
between 1990 and 2006 in Hungary.
Questionnaires sent
Number of responses
Response rate (%)
Area covered by response (1000 km2)
Positive UTM cells (otter presence)*
Negative UTM cells*
1990
743
193
26.0
46.5
204
297
1994
838
352
42.0
33.5
273
305
1995
792
404
51.0
40.0
407
277
2000
1161
557
48.0
46.5
410
268
2001
1161
511
44.0
43.7
406
278
2002
1169
568
48,6
47.0
457
322
2003
1181
556
47,0
46.6
424
311
2004
1181
550
46,6
46.0
442
397
2005
1185
557
47.0
46.5
446
303
2006
1202
467
38.9
40.0
400
273
Permanent
2.0
Occasional
Negative
100%
Otter presence
Estimated otter density
(ind./1000 ha)
*from the total number of 1060 10×10 km UTM cells.
1.5
1.0
0.5
75%
50%
25%
0%
0.0
1990 1994 1995 2000 2001 2002 2003 2004 2005 2006
Figure 1. Change of mean (1SE) estimated otter
density at country level (white column) and in the
distribution area (dark column) between 1990 and
2006 (calculated on the responses of GMUs).
1990 1994 1995 2000 2001 2002 2003 2004 2005 2006
Figure 2. Change of distribution of otter presence in
Hungary between 1990 and 2006 (calculated on the
responses of GMUs).
1995
1990
2006
2000
Figure 3. Occurrence of otter in 1990, in 1995, in 2000 and in 2006
based on the result of questionnaire surveys in Hungary. Black points marks presence.
shown by the present work is highly owed to the
fact that more years were summarized; there was
a high level of readiness to reply and greater coverage. Due to differences in reliability and coverage of different surveys in Hungary, we have not
compared our detailed data to others.
Questionnaire surveys have frequently been
used for otter surveys (e.g. Kauhala 1996, Paunović & Milenković 1996, Cortés et al. 1998) sometimes together with field survey data. This mail
Heltai, M. et al.
116
Figure 4. Occurrence of otters in Hungary based on the total responses
of questionnaires survey between 1990 and 2006.
[Legend: 1- if otter occurred in a given 10×10 km UTM cell only in one year, 10- if otter occurred in a cell in all the ten years.
Regions: I – Great Hungarian Plain, II – Northern Medium Mountains, III – Transdanubian Medium Mountains,
IV – Little Hungarian Plain, V – Alpokalja (or Feet of the Alps), VI – Transdanubian Hills and Mecsek.]
questionnaire survey became an accepted method
in the National Biodiversity Monitoring Program
(Török et al. 2001) and was used in the case of
several carnivore species, like the strictly protected
wolf (Canis lupus) and lynx (Lynx lynx) (Szemethy
et al. 2004a, 2004b), the non-native raccoon dog
(Nyctereutes procyonoides) and raccoon (Procyon
lotor) (Heltai et al. 2000a, 2003), the recovering
golden jackal (Canis aureus) (Heltai et al. 2000a,
Szabó et al. 2009) and other small- or mediumsized carnivores (Heltai et al. 2000b, 2005, 2006).
Data from the present study provided by responses from GMUs have been used not for determining the exact number or density (or distribution) of otters in a given year but for establishing a more accurate population trend (Reuther et
al. 2000, Reuther 2002, Heltai 2010). The distribution area of the species (Fig. 3, Table 1) has been
seen to change and there has been an increasing
number of responses in the period 1990-2006;
therefore the growth in distribution area was only
apparent and it might mask a false presence or absence (Marcelli & Fusillo 2009). Consequently, the
size of distribution area, in contrast with the estimated density, probably did not change over the
last two decades. According to the results of the
field survey, the GMUs slightly under-estimated
the occurrence of this strictly protected species.
The existence of a considerable and stable Hungarian otter population is indicated by 1) the distribution area covers three quarters of the whole coun-
try, and otters can be found in almost every potential habitat, 2) there are large blocks in the distribution area, which are believed to be connected to
each other. Results of the questionnaire survey are
supported by the results of detailed field surveys
(Kemenes 1991, Kemenes et al. 2005, Lanszki
2008a, 2008b, 2008c, Sike & Márk-Nagy 2008),
however the scale size (10×10 km) used in surveys
is much greater than the home-range size of otters
measured by radio-telemetry examinations in
Central Europe (1.2-2.6 km2, Dulfer et al. 1998).
This resolution (and mail questionnaire survey) is
not enough to monitor smaller-scale changes
(Reuther et al. 2000).
According to historical data (Faragó 2009) and
to results of different otter surveys summarized by
Kemenes et al. (2005), in contrast with numerous
other European regions (West 1975, Macdonald &
Mason 1976), no decline has been observed in otter
populations in Hungary. The present population
is showing an increase which is similar to other
European trends (EEA 2009). The stability of the
otter population is confirmed also by field studies
and post mortem examinations which showed that
concentrations of metals in tissues were usually at
a low or medium level (Lanszki et al. 2009). Furthermore, the reproduction parameters were similar to European averages (Lanszki et al. 2008b),
condition indices were generally good (Lanszki et
al. 2007), the genetic diversity was high, and the
population was not fragmented at a regional level
Otter distribution in Hungary
(Lanszki et al. 2008a, 2010, Mucci et al. 2010). According to data of distribution and estimated density from the present work and the local and regional molecular genetic studies, otter numbers
are estimated in the order of thousands of individuals in Hungary (estimated density in fish
ponds: minimum 1.8-4.6 animals per 100 ha of
wetland, along the rivers and backwaters: minimum 0.17 animals per km of riverside section;
Lanszki et al. 2008, 2010). The difficulty of observation and the elusive habits of the species, the
problematic estimation of density calculated by
life signs (footprints, burrows, scats) make it very
difficult to assess and/or estimate actual numbers
of individuals (Jefferies 1986, Kruuk et al. 1986,
Kruuk & Conroy 1987, Conroy & French 1991,
Reuther et al. 2000). Therefore an exact population
number cannot be determined by the available
data received from these surveys.
In conclusion, according to the results of questionnaire surveys the otter is widely distributed in
Hungary and its population has been stable over
the last two decades. A field test of the questionnaire survey shows that the professional hunters
slightly underestimate occurrences, but their answers are reliable with regard to determination of
distribution area and are useful for monitoring
population changes. The smaller negative population changes are not detectable because of a lack of
accurate (standardized, using appropriate resolution) surveys (Barbosa et al. 2003, MacKenzie et al.
2005, Marcelli & Fusillo 2009, Cianfrani et al.
2010). In order to conserve the species and the viable wetlands, the introduction of standardized
surveys over the whole country or in selected regions (especially where a decline has occurred)
and/or in Natura 2000 sites (Reuther et al. 2000,
Chanin 2003) is required as soon as possible.
Acknowledgements. Thanks to Grace Yoxon, Manlio
Marcelli, Romina Fusillo and the two anonymous
reviewers for their helpful comments. This work was
supported by the Department of Game Management and
Fishery of the Ministry of Agriculture and Rural
Development for financial support and by the Bolyai
János Scholarship (JL).
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