IUCN/SCC Otter Specialist Group Bulletin
©IUCN/SCC Otter Specialist Group
Volume 25
Issue 1 Pages 1 - 74 (April 2008)
Citation: García Díaz,
P. (2008). Abundance
of the Eurasian Otter Lutra Lutra (Linnaeus, 1758) in
Two Areas from Central Spain (Province of Salamanca, River Tormes). IUCN
Otter Spec. Group Bull. 25 (1):
32 - 37
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Abundance
of the Eurasian Otter Lutra Lutra (Linnaeus, 1758)
in Two Areas from Central Spain (Province of Salamanca, River
Tormes)
Pablo García Díaz1
1Sociedad
para la Conservación de los Vertebrados (SCV), Box nº 270,
28080 Majadahonda, Madrid, Spain. e-mail: garciap@usal.es
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Abstract:The Eurasian
otter (Lutra lutra) is a widely distributed species
in central Spain. Studies about its occurrence and diet are abundant,
but data about population size are scarce. The density of the
species was estimated during consecutive winters in two contrasted
areas from central Spain by means of track censuses. The KAI
index (Kilometrical Abundance Index) varied between 0.14 otters/km
in the vicinity of the city of Salamanca and 0.25 otters/km in
a conserved area. These results fit well with moderate productivity
rivers and are similar to those obtained in other localities
from the Mediterranean basin. |
Keywords: Lutra lutra, population
size, track census |
Française | Español |
INTRODUCTION
The Eurasian otter Lutra lutra (Linnaeus, 1758) is nowadays
widely distributed in central Spain (Delibes, 1990; Morales
et al., 1998; Ruiz-Olmo and Delibes, 1998; Cortés et al., 1998; Palomo
et al., 2007), especially in riparian areas with certain water flow.
In the last decades an increase and a colonizing pattern in the species
range have been registered in this area after a worrying decrease in
the central decades of the 20th century (see previous references).
Although a large number of studies about distribution and trophic ecology
of the species have been carried out and an extensive monitoring
of some otter populations (Delibes, 1990; Morales
et al., 1998; Ruiz-Olmo
and Delibes, 1998) only one work concerning otter population size
has been published in reference to a naturally protected park (Bravo
et al., 1998) and thus density remains poorly known.
Data on otter abundance in central Spain are based in defecation
rates (Díez-Frontón,
1998; Morales et al., 1998; Pérez-Alonso, 1999) that can be used as an
indirect method for estimating population size (Mason and
MacDonald, 1987; Ruiz-Olmo
et al., 2001a; Guter et al., 2008; Lanzski
et al., 2008), but the application
of this rate as estimator depends on climatic factors, mainly rainfalls, availability
of defecation sites, season of the year and other factors (Conroy
et al., 1991;
Kranz, 1996; Strachan and Jefferies,
1996; Kruuk, 2006; Ruiz-Olmo
et al., 2001a)
making this spraint index not always adequate for abundance evaluation purposes.
In this communication some data about abundance and density of the
otter in two different areas from central Spain are discussed.
MATERIALS AND METHODS
Fieldwork was carried out in two localities of the river Tormes, one
of the major tributaries of the Duero basin, in the province of Salamanca,
central Spain (Fig. 1). Herein the occurrence of otter is well know
on the basis of large monitoring surveys using spraints but also registered
by direct observations from the later 1980s (Delibes, 1990; Ruiz-Olmo
and Delibes, 1998; Pérez-Alonso, 1999).
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Figure
1. Study area. A. Location
on the Iberian Peninsula. B. Digital Elevation Model of the
study area. C. Digital Elevation Model and hydrographic web
of the two localities surveyed; 1: Santa Teresa dam; 2: Salamanca.(click
for larger version) |
The first set of stretches studied is located downstream from the
Santa Teresa dam (GPS coordinates of the medium area point: 30T 280849,
4508295; 820 m. high) in a sedimentary plain intensively used as croplands
surrounded by oak forest (Quercus ilex),managed with extensive
livestock (called “dehesas”). The riparian forest is structured
in gallery where Salix sp., Populus sp., Ulmus
sp. and Fraxinus sp. are the dominant species, and with
high shrub cover in the inferior strata. Punctually, this forest is
removed and replaced for monospecific plantations of Populus nigra.
The water network is well developed, mainly by the beds of the rivers
Tormes and Alhandiga, which drains the flow of numerous rivers and
irrigation ditches. Moreover, gravel extraction activities create some
new lakes.
The second area studied was in the vicinity of the city of Salamanca
situated on the river Tormes and two of itd tributaries (GPS coordinates
of the medium area point: 30T 276181, 4537213; 800 m.). Here the
riparian habitat is largely degraded because the influence of the
human pressure on the river due to population size of the city and
recreational activities. Currently the forest is mainly reduced to
a series of islands in the middle of the river while banks are used
as a “river street” and parks for human activities.
In both territories helophyte vegetation (Phragmites australis, Typha
latifolia) covers up to a 10 % of the water surface, but in
some particular situations can reach more than 90 %.
The abundance of the otter in these areas where studied by means of
track censuses, a reliable indicator of real otter population in
a fixed surface (Sidorovich and Lauzhel, 1992; Reid
et al., 1987;
Ruiz-Olmo et al., 2001a; Sulkava,
2007; Sulkava and Liuko, 2007).
The banks of all water bodies included in any of the work
zones were intensively surveyed from November to February of several
consecutive winters (three in the first locality and two in the second)
searching for adequate points for track stamp. On the basis of the
adequate subtrate availability the length surveyed in Santa Teresa
was 15.7 kilometers but in Salamanca only seven kilometers were surveyed.
Only those fresh, clear and well-marked tracks on clay substrates
were used in the study (Hertweck et al., 1998; Mercier
and Fried, 2004).
Other signs found were not used to avoid biases. In those tracks
keeping these characteristics the total length including claws were
measured with a digital caliper (accurate: ± 1
mm.).
Results are expressed as Minimum Number of different Tracks (MNT) and
standardized by using a Kilometrical Abundance Index (KAI = MNT /
length of the stretch surveyed).
RESULTS AND DISCUSSION
In the first area studied, three MNTs were registered during the 2004-2005
winter and the winters of 2005-2006 and 2006-2007 registered four consistent
MNTs (Table 1). In the city of Salamanca only one MNT was estimated
during the two winters of study (Table 2). In both cases the low variation
MNT indicates a stable, although small, otter population.
Table
1:. Winter censuses of otter downstream of the Santa Teresa
dam.
MNT: minimum number of different tracks registered.
KAI:
Kilometrical Abundance Index (MNT / length surveyed).
|
ID |
Length surveyed (km) |
MNT |
KAI |
|
2005-2006 |
15.72 |
3 |
0.19 |
2006-2007 |
15.72 |
4 |
0.25 |
2007-2008 |
15.72 |
4 |
0.25 |
|
Table
2:. Winter censuses of otter in the river Tormes in the city of
Salamanca.
|
ID |
Length surveyed (km) |
MNT |
KAI |
|
2006-2007 |
15.72 |
1 |
0.14 |
2007-20087 |
15.72 |
1 |
0.14 |
|
Mean relative abundances (KAI) are higher in the floodplain downstream
the Santa Teresa dam (0.23 MNT) than in Salamanca (0.14 MNT), thus
reflecting a larger population in the first area than in the second.
Probably this can be related to a low habitat quality and productivity
of the river Tormes in the vicinity of Salamanca (Mason,
1995; Ruiz-Olmo
et al., 2001b) but the scarce sample size does not allows adequate
conclusions.
Otter spraints were also found during samplings, consistent with a
constant occupation of the stretches.
These short estimated abundances during fieldwork are in agreement
with a territorial mammal, which occurs in lineal habitats such as
rivers or streams (Kruuk, 2006). The obtained KAI belongs, in the Mediterranean
basin, with moderate or intermediate otter densities of the cyprinid
dominant area (Ruiz-Olmo, 1995; Ruiz-Olmo
et al., 2001a).
These KAI values were similar to those measured in Spain, Mediterranean
basin and northern Europe (about 0.20 otters/km; Sidorovich
and Lauzhel, 1992; Ruiz-Olmo, 1995; Bravo
et al., 1998; Sulkava et al., 2007),
high than in central and eastern Europe (Georgiev
and Stoycheva, 2006; Kalz et al., 2006; Lanzski
et al., 2008), but lower in comparison
with some populations from north Scotland, China or Germany where
densities higher as 1.66 otters/km are reported (Kruuk
et al., 1989;
Hung et al., 2004; Kruuk, 2006).
However it is necessary to take into account that the number of otters
estimated in winter was less than in summer (Ruiz-Olmo,
1995), although
this effect seems to be an effect of the water flow restriction during
this season (Prenda et al., 2001), bringing together a large number
of otters in areas with available resources.
Anyway, the variability in the length studied in both areas (see Tables
1 and 2) could influence the results obtained and makes comparisons
among localities hard to interpetrate. An appropriate length for surveying
otters was estimated as ten kilometers in Spain (Ruiz-Olmo,
1995) but
this were not accomplished in Salamanca and the results then should
be interpreted cautiously.
Despite the reported increase in otter range in central Spain a need
for increasing the knowledge on population size could be important
for implementing conservation measures.
ACKNOWLEDGMENTS - I want to acknowledge
the selfless collaboration of some people that made this work possible,
especially with Alicio García, Josefa García and Isabel
Mateos. Thanks to Miguel Lizana and Javier Morales who lead the work
about this species.
REFERENCES
Bravo, C., Bueno, F. and Sánchez-Aguado,
F. (1998). I
Censo visual de nutria (Lutra lutra) y visón americano
(Mustela vison) en el Parque Natural de las Hoces del Duratón
(Segovia). Galemys 10 (N.E.): 89-96.
Cortés, Y., Fernández-Salvador,
R., García,
F.J., Virgos, E. and Llorente, M. (1998). Changes in otter
(Lutra
lutra) distribution in central Spain during the 1984-1995 period.
Biol. Conserv. 86: 179-183.
Conroy, J.W.H. and French,
D.D. (1991). Seasonal patterns
in the sprainting behaviour of otters (Lutra lutra L.) in
Shetland. Habitat 6: 159-166.
Delibes, M. (ed.) (1990). La
nutria (Lutra lutra)
en España. Serie Técnica, ICONA, Madrid.
Díez-Frontón, D.
(1998). Ecología
trófica, distribución y competencia del visón
americano (Mustela vison) y la nutria (Lutra lutra)
en el río Moros, Segovia. Degree Thesis, University of Salamanca,
Salamanca.
Georgiev, D. G.
and Stoycheva, S. (2006). Habitats,
distribution and population density otter survey in western Rhodopes
mountains (Southern Bulgaria). IUCN
Otter Spec. Group Bull. 23: 36-43.
Guter, A., Dolev, A., Saltz,
A. and Kronfeld-Schor, A. (2008). Using
videotaping to validate the use of spraints as an index of Eurasian
otter (Lutra lutra) activity. Ecol. Indic. 8:
462-465.
Hertweck, K., Klenke, R., Henle, K. (1998). Estimating
the density of otter Lutra lutra population using individual
analysis of tracks. IUCN Otter Spec. Group Bull. 19:
118-122.
Hung, C.M., Li, S.-H., Lee, L.-L. (2004). Faecal
DNA typing to determinate the abundance and spatial organisation of
otter (Lutra lutra) along two stream systems in Kinmen. Anim.
Conserv. 7: 301-311.
Kalz, B., Jewgenow, K., Fickel, J. (2006). Structure
of an otter (Lutra lutra) population in Germany – results
of DNA and hormone analyses from faecal samples. Mamm. Biol. 71:
321-335.
Kranz, A. (1996). Variability and seasonality in sprainting
behaviour of otters Lutra lutra in a highland river in central
Europe. Lutra 38: 33-44.
Kruuk, H. (2006). Otters. Ecology, behaviour and conservation.
Oxford University Press, Cambridge.
Kruuk, H., Moorhouse, A., Conroy, J.W.H., Durbin, L., Fears,
S. (1989). An estimate of numbers and habitat preferences
of otters Lutra lutra in Shetland, UK. Biol. Cons. 49:
241-254.
Lanszki, J., Hidas, A., Szentes, K., Révay, T., Lehoczky,
I., Weiss, S. (2008). Relative spraint density and genetic
structure of otter (Lutra lutra) along the Drava River in
Hungary. Mamm. Biol. 73: 40-47.
Mason, C.F., MacDonald, S.M. (1987). The use of spraints
for surveying the otter Lutra lutra populations: an evaluation. Biol.
Cons. 41: 167-177.
Mason, C.F. (1995). Habitat quality, water quality
and otter distribution. Hystrix 7: 195-207.
Mercier, L., Fried, G. (2004). Preliminary
study of the tracks of captive otters (Lutra lutra) as a tool
for field research. IUCN Otter Spec. Group Bull. 21:
94-99.
Morales, J.J., Lizana, M., Gutiérrez, F.J., Pedraza,
E. (1998). Distribución espacial y ecología
trófica de la nutria euroasiática y el visón americano
en el Parque Natural de las Hoces del Duratón (Segovia). Colección
Naturaleza y Medio Ambiente, Obra Social y Cultural de Caja Segovia,
Segovia.
Palomo, L.J., Gisbert, J., Blanco, J.C. (eds.) (2007). Atlas
y libro rojo de los mamíferos terrestres de España. DGCN-SECEM-SECEMU,
Madrid.
Pérez-Alonso, J.C. (1999). Distribución
y ecología trófica de la nutria (Lutra lutra Linneo,
1758) en el río Tormes (Salamanca). Degree Thesis, University
of Salamanca, Salamanca.
Prenda, J., López-Nieves, P., Bravo, R. (2001). Conservation
of otter (Lutra lutra) in a Mediterranean area: the importance
of habitat quality and temporal variation in water availability.
Aquat. Cons. 11: 343-355.
Reid, D.G., Bayer, M.B., Code, T.E., McLean, B. (1987). A
possible method for estimating river otter, Lutra canadiensis,
populations using snow tracks. Can. Field Nat. 101:
576-580.
Ruiz-Olmo, J. (1995). Estudio bionómico sobre
la nutria (Lutra lutra L., 1758) en aguas continentales de
la península Ibérica. Ph. D. Thesis, University of Barcelona,
Barcelona.
Ruiz-Olmo, J., Delibes, M. (eds.) (1998). La nutria
en España ante el horizonte del año 2000. SECEM, Málaga.
Ruiz-Olmo, J., Saavedra, D., Jiménez, J. (2001a.) Testing
the surveys and visual and track censuses of Eurasian otters (Lutra
lutra). J. Zool. 253: 359-369.
Ruiz-Olmo, J., López-Martín, J.M., Palazón,
S. (2001b). The influence of fish abundance on the otter (Lutra
lutra) populations in Iberian Mediterranean habitats. J. Zool. 254:
325-336.
Sidorovich, V.E., Lauzhel, G.O. (1992). Numbers of
otters and approach to population estimation in Byelorrusia. IUCN
Otter Spec. Group Bull. 7: 13-16.
Strachan,
R. and Jefferies, D. (1996). Otter Survey of England 1991–
1994. A report on the decline and recovery of the otter in England
and on its
distribution, status and conservation in 1991–1994. Vincent Wildlife
Trust, London
Sulkava,
R. 2007. Snow
tracking: a relevant method for estimating otter Lutra lutra populations. Wildlife
Biol. 13: 208-218.
Sulkava, R., U.M. Liukko, U.M. (2007). Use
of snow-tracking methods to estimate the abundance of otter (Lutra lutra)
in Finland with evaluation of one-visit census for monitoring purposes. Ann.
Zool. Fenn, 44: 179-188.
Sulkava, R., Sulkava, P.O., Sulkava, P.E. (2007). Source
and sink dynamics of density-dependent otter (Lutra lutra)
populations in rivers of central Finland. Oecologia 153:
579-588
Résumé : Repartition
de la loutre eurasienne Lutra lutra (Linnaeus, 1758) dans
deux regions du centre de l’Espagne (Province de Salamanque,
Rivière Tormes)
La loutre eurasienne (Lutra lutra) est une espèce
particulièrement abondante dans le centre de l’Espagne.
Il existe de nombreuses études sur sa répartition et
son alimentation. Cependant, des données sur l’importance
de la population sont rares. La densité de l’espèce
a été estimée par inventaire des traces durant
deux hivers consécutifs dans deux régions différentes
du centre de l’Espagne. L’Indice d’Abondance Kilométrique
(IAK) varie entre 0.14 loutre/km dans les environs de la ville de
Salamanque et 0.25 loutre/km dans une région préservée.
Ces résultats correspondent bien aux rivières de productivité moyenne
et sont similaires à ceux obtenus dans le bassin méditerranéen.
Revenez au dessus
Resumen:Abundancia
de la nutria paleártica Lutra lutra (Linnaeus, 1758)
en dos áreas de España central (provincia de Salamanca,
río Tormes)
La nutria paleártica (Lutra lutra) es una especie
bien distribuida en España central. Los estudios sobre presencia
y dieta son abundantes, pero apenas existen datos sobre el tamaño
poblacional. Se estimó la abundancia de la especie en dos áreas
contrastadas de España central mediante el censo de huellas
durante varios inviernos. El índice KAI (Índice Kilómetro
de Abundancia) varió entre 0.14 nutrias/km en las cercanías
de la ciudad de Salamanca y 0.25 nutrias/km en un área mejor
conservada. Estos resultados son concordantes con ríos de
productividad media y similares a los obtenidos en otras localidades
de la cuenca mediterránea.
Vuelva a la tapa
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