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Biodiversity of European Freshwater Fish - Threats and Conservation Priorities at the Catchment Scale

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Abstract and Figures

In the present thesis, the state and distribution of the European freshwater fish fauna was studied. For 161 river (sub-)catchments presence / absence records were retrieved from various sources. Spatial patterns of the fish fauna were analysed using GIS. Further, suggestions on how to reduce the loss of biodiversity are provided. A total of 400 freshwater fish species, including 32 species nonnative to Europe, were recorded. The European fish fauna is the most depauperate compared to other continents. Species richness of native European freshwater fish increases from west to east and from north to south. Species richness peaks in the Danube basin. Species richness of native species is strongly correlated to area and this relationship is best described by a power function. Within large river basins, however, the relationship between richness and subbasin area is weak. In contrast to native species, richness of introduced and extinct species is not related to area. Species introductions and -extinctions occur all over Europe. The proportion of introduced and extinct species can be 50%, or even higher. A high proportion of endemic and irreplaceable species occurs in southern European catchments. They are absent in catchments at latitudes > 50°N. Two species endemic in European catchments, are recorded as globally extinct. The most threatened and locally extinct species are long-migrating species (anadromous and catadromous species, such as sturgeons) These species travel along the river corridor and are thus especially vulnerable to river fragmentation. The “hot spots” of European freshwater fish, defined as areas with the highest proportion of irreplaceable and threatened species, occur in southern Europe (Iberian Rivers, rivers of the Balkan, and several rivers in Anatolia). Future conservation activities need to focus on those regions to prevent the future loss of irreplaceable species. “Hot spots” are not resistant against species introductions; they may contain high numbers of nonnative species. Since introduced species may pose a threat to the native fish fauna, their composition and ecological behaviour should be further analysed within all rivers that have been identified as conservation hot spots, and their abundances need to be managed.
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Diploma thesis presented by
Fabian Peter
Supervision:
Prof. Dr. (em.) Hartmut Leser (University of Basel)
Prof. Dr. Klement Tockner (Eawag)
Department of Geography, University of Basel
Physical Geography and Landscape Ecology
Eawag Aquatic Research
Department of Aquatic Ecology
Zürich, September 2006
Biodiversity of European Freshwater Fish
Threats and Conservation Priorities
at the Catchment Scale
Minor subjects:
Nature, Landscape and Environmental Protection
Hydrology
Geology
Major subject:
Geography
Contact:
fabianpeter@gmx.net
To be cited as:
Peter, F. (2006) Biodiversity of European Freshwater Fish - Threats and Conservation Priorities
at the Catchment Scale. Department of Geography, Basel.
Acknowledgements
This thesis is the outcome of an intensive data compilation of European freshwater fish. Taking
into account the vast spatial scale of this project and the manifold difficulties in finding the needed
information, it remains a surprising fact that information for so many rivers within the relatively
short time period available was found. To a very large extent this is due to the good collaboration
with scientists, public authorities and people from NGO’s all over the continent. My sincere
thanks therefore are addressed to all the researchers that are part of the book project “Rivers of
Europe”, for either direct delivery of data or forwarding my requests to the local specialists. I was
very lucky to work within a network of dedicated river and fish ecology scientists.
Many contributors are not part of this book project, but anyhow realised the importance of a
centralized continental freshwater fish database and their implications in ecology and
conservation and thus supported the data compilation. I am grateful for this extraordinary help to
(sorted alphabetically): Dr. Hans-Hermann Arzbach (Institut für Fischkunde, Kuxhaven, D), Prof.
Klaus W. Battes (University of Bacau, Bacau, RO), Dr. Vitaliy Bekh (Institute of Fisheries UAAS,
Kiev, UA), Marko Caleta (University of Zagreb, Zagreb, HR), Dr. Béla Csányi (VITUKI, Budapest,
H), Dr. Grigore Davideanu (Aquaterra, Iasi, RO), Dr. Markus Diekmann
(Fischereiforschungsstelle Baden-Württemberg, Langenargen, D), Stefan Gerster (Jagd und
Fischerei Solothurn, Solothurn, CH), Alexander Hegedis (Institute for Biological Research,
Belgrade, SCG), Dr. Josef Hoch (Fachberatung für Fischerei, Landshut, D), Ivan Jaric (Center for
multidisciplinary studies, Belgrade, SCG), Dr. Christian von Landwüst (Bundesanstalt für
Gewässerkunde, Koblenz, D), Dr. Maurice Kottelat (Cornol, CH), Dr. Mirjana Lenhardt (Institute
for Biological Research, Belgrade, SCG), Dr. Marcel Michel (Amt für Jagd und Fischerei
Graubünden, Chur, CH) Momir Paunovic (Center of multidisciplinary studies, Belgrade, SCR), Dr.
Armin Peter (Eawag, Kastanienbaum, CH), Georg Rast (WWF Deutschland, D), Gilla Rupp
(IKSMS-CIPMS, Trier, D), Dr. Zoltán Sallai (Hotobagy National Park, H), Dr. Stefan Schmutz
(BOKU, Vienna, A), Dr. M. Schramm (Verband für Fischerei und Gewässerschutz in Baden-
Württemberg e.V., D) Michael Schubert (Inst. für Fischerei Arbeitsbereich Fluss- und
Seenfischerei, Starnberg, D), Dr. Mircea Staras (Danube Delta National Institute, Tulcea, RO), Dr.
Eliza Uzunova (University of Sofia, Sofia, BG), Birgit Vogel (ICPDR, Vienna, A), Jakob Walter
(Fischereiaufsicht Schaffhausen, Schaffhausen, CH), Christine Weber (Eawag, Kastanienbaum,
CH), Claude Wisson (Fischereiaufsicht Basel-Stadt, Basel, CH).
Dr. Alcibiades Economou and Stamatis Zogaris (both Hellenic Institute for Marine research,
Institute of Inland waters, Athens, GR) gave important inputs for structuring the data collection.
Michael Vock and Nadja Fischbach offered to do the impressive cover illustration of this thesis -
thank you very much!
Especially grateful thanks to Diego Tonolla and Rosi Siber, who did the basic GIS work and to Dr.
Gabriel Piepke (all Eawag) who supported building up the database.
My supervisor, Prof. Hartmut Leser from the University of Basel, provided support to write this
thesis according to my personal interests and apart from my home university.
Prof. Klement Tockner, my supervisor at Eawag, was a helpful and visionary guide, who
contributed by both his enthusiasm and his ecological knowledge much to my motivation and the
success of this work.
My parents Elsbeth and Walter Peter supported my life in multifaceted ways. They conceded the
wish of a seven year old boy to dig a pond in their garden and raised like that my fascination for
life in and around water.
Dedicated to Maryna
Summary
Summary
In the present thesis, the state and distribution of the European freshwater fish fauna was studied.
For 161 river (sub-)catchments presence / absence records were retrieved from various sources.
Spatial patterns of the fish fauna were analysed using GIS. Further, suggestions on how to
reduce the loss of biodiversity are provided.
A total of 400 freshwater fish species, including 32 species nonnative to Europe, were recorded.
The European fish fauna is the most depauperate compared to other continents. Species richness
of native European freshwater fish increases from west to east and from north to south. Species
richness peaks in the Danube basin. Species richness of native species is strongly correlated to
area and this relationship is best described by a power function. Within large river basins, however,
the relationship between richness and subbasin area is weak. In contrast to native species,
richness of introduced and extinct species is not related to area.
Species introductions and -extinctions occur all over Europe. The proportion of introduced and
extinct species can be 50%, or even higher. A high proportion of endemic and irreplaceable
species occurs in southern European catchments. They are absent in catchments at latitudes >
50°N. Two species endemic in European catchments, are recorded as globally extinct. The most
threatened and locally extinct species are long-migrating species (anadromous and catadromous
species, such as sturgeons) These species travel along the river corridor and are thus especially
vulnerable to river fragmentation.
The “hot spots” of European freshwater fish, defined as areas with the highest proportion of
irreplaceable and threatened species, occur in southern Europe (Iberian Rivers, rivers of the Balkan,
and several rivers in Anatolia). Future conservation activities need to focus on those regions to
prevent the future loss of irreplaceable species. “Hot spots” are not resistant against species
introductions; they may contain high numbers of nonnative species. Since introduced species may
pose a threat to the native fish fauna, their composition and ecological behaviour should be further
analysed within all rivers that have been identified as conservation hot spots, and their abundances
need to be managed.
Table of Contents
Table of Contents
List of Figures .................................................................................................................................. I
List of Tables ................................................................................................................................. III
List of Maps ...................................................................................................................................IV
1 Introduction ............................................................................................................................. 1
1.1 Motivation............................................................................................................................ 1
1.2 Goals of this thesis.............................................................................................................. 2
1.3 Questions and hypotheses ................................................................................................. 2
2 Biogeographic Setting............................................................................................................. 4
2.1 The European Continent..................................................................................................... 4
2.2 Topography and climate ..................................................................................................... 5
2.3 Biogeographic regions ........................................................................................................ 7
2.4 River basins ...................................................................................................................... 10
2.5 River (sub-)catchments..................................................................................................... 11
3 European Freshwater Fish Biodiversity - Background.......................................................... 14
3.1 Legal foundations.............................................................................................................. 14
3.2 Natural distribution and dispersal of fish........................................................................... 14
3.3 Present knowledge ...........................................................................................................15
3.4 Nomenclature.................................................................................................................... 16
3.5 Ecological classification of fish.......................................................................................... 16
3.6 Biodiversity and conservation measures .......................................................................... 17
3.7 Threats to freshwater fish ................................................................................................. 18
3.8 Lack of information............................................................................................................ 19
4 Methods ................................................................................................................................ 20
4.1 Structure of the Diploma thesis......................................................................................... 20
4.2 Structure of the European Freshwater Fish Database...................................................... 20
4.3 Data collection ..................................................................................................................21
4.3.1 Freshwater fish distribution data ............................................................................... 21
4.3.2 Protection and conservation categories.................................................................... 22
4.3.3 Ecological guilds .......................................................................................................22
4.3.4 Peripheral / euryhaline species................................................................................. 23
4.4 Quality Assessment .......................................................................................................... 25
4.5 Data Analyses................................................................................................................... 26
4.5.1 General procedure .................................................................................................... 26
4.5.2 Species richness-area relationship ........................................................................... 27
Table of Contents
II
4.5.3 Species extinctions ...................................................................................................27
4.5.4 River fragmentation and local species extinction...................................................... 27
4.5.5 Migration behaviour of locally extinct species in relation to the degree of
fragmentation ............................................................................................................ 28
4.5.6 Degree of irreplaceability ..........................................................................................28
4.5.7 Conservation hot spots .............................................................................................28
4.5.8 Conservation hot spots threatened by species introductions.................................... 28
4.5.9 Maps and GIS analyses............................................................................................ 28
5 Results.................................................................................................................................. 30
5.1 Freshwater fish inventory.................................................................................................. 30
5.2 Fish distribution patterns in European Rivers ................................................................... 32
5.2.1 Species richness....................................................................................................... 32
5.2.2 Species relationships ................................................................................................ 34
5.2.3 Species Accumulation............................................................................................... 38
5.2.4 Latitudinal and longitudinal patterns in species richness .......................................... 39
5.2.5 Area-corrected species richness............................................................................... 40
5.3 Fish diversity patterns in the Volga, Danube, Rhine and Rhône Basins........................... 41
5.4 Threats to fish biodiversity ................................................................................................ 43
5.4.1 Introduced species.................................................................................................... 43
5.4.2 Extinction of species .................................................................................................45
5.4.3 Migration behaviour of extinct species...................................................................... 47
5.4.4 Fragmentation and Migration behaviour of extinct species....................................... 47
5.4.5 Irreplaceability and endemism ..................................................................................48
5.4.6 Conservation hot spots .............................................................................................50
5.4.7 Conservation hot spots threatened by introduced species .......................................51
6 Discussion ............................................................................................................................ 53
6.1 Fish inventory.................................................................................................................... 53
6.2 European Fish fauna in a global context........................................................................... 53
6.3 Richness patterns in European Rivers.............................................................................. 54
6.4 Threats to freshwater fish biodiversity .............................................................................. 55
6.5 Identifying priority sites for biodiversity conservation........................................................ 57
6.6 Proof of Hypotheses ......................................................................................................... 60
7 Conclusions and Outlook...................................................................................................... 62
8 Literature Cited .....................................................................................................................63
9 Appendix ............................................................................................................................... 71
List of Figures
I
List of Figures
Figure 2-1: Latitudinal area (km2) distribution of the investigated European river (sub-)
catchments............................................................................................................ 11
Figure 4-1: Relations among the tables used within the database. Blue fields indicate separate
tables which are connected with at least one parameter (primary key) in another
table. ..................................................................................................................... 20
Figure 5-1: Species-area relationship of native European freshwater fish. (S = 0.549A0.3703;
R2 = 0.5439) .......................................................................................................... 34
Figure 5-2: Species-area relationship for northern European Rivers (Rivers of the
fennoscandinavian, arctic and boreal regions) (S = 0.1645A 0.4645; R2 = 0.8325.) 35
Figure 5-3: Species-area relationship of rivers of the Iberian, Italian, Balkan and Anatolian
regions. ................................................................................................................. 35
Figure 5-4: Species-Area relationships of extinct (S = 0.6666A0.1275 ; R2 = 0.0439), endemic
(S = 0.3651A0.1652 ; R2 = 0.094) and introduced species (S = 1.9255A0.0852 ;
R2 = 0.0239). ......................................................................................................... 36
Figure 5-5: Native species richness of river (sub-)catchments (not corrected for area) to the
native species richness of the entire region (not corrected for area). .................. 36
Figure 5-6: Relationship between family richness and species richness (y = 1.7079x 1.2239 ;
R2 = 0.8908) .......................................................................................................... 37
Figure 5-7: Cumulative species richness and catchment area. (Sub-)catchments are ranked
from the most species rich to the least rich ones. ................................................ 38
Figure 5-8: Latitudinal distribution of native fish species richness (area-corrected; predicted
species per 10´000km2; see Figure 5-1) .............................................................. 39
Figure 5-9: Longitudinal distribution of native fish species richness (area-corrected; predicted
species per 10´000km2; see Figure 5-1) .............................................................. 39
Figure 5-10: Species-area relationships for four major European river basins. ........................ 41
Figure 5-11: Local species extinctions in the Rhine, Danube and Volga basins. Values are
presented for different scales (tributary to entire basin)....................................... 42
Figure 5-12: Extinct species-area relationship. Nested data from the sub catchments of the
Rhine, Danube and the Volga Rivers.(S = 17.596A -0.1654 ; R = 0.0923)
2.............. 42
Figure 5-13: Relative proportion of different migration behaviour guilds of a) all species
reported as locally extinct b) the species with highest local extinction records c)
the most threatened species (see Table 5-6)....................................................... 47
Figure 5-14: Comparison of migration behaviour guilds for extinction and occurrence records....
.......................................................................................................................... 48
List of Figures
II
Figure 5-15: Latitudinal distribution of endemic species............................................................ 49
Figure 5-16: (Sub-)catchments ranked according to native species richness (from most to least
rich). Richness for endangered, endemic and irreplaceable species for the ranked
catchments............................................................................................................ 50
Figure 5-17: (Sub-)catchments ranked according to the relative proportion (%) of irreplaceable
species (from highest to lowest proportion). Relative proportion (%) of threatened
and introduced species for the ranked catchments.............................................. 50
List of Tables
III
List of Tables
Table 2-1: Area distribution of (sub-)catchments and river basins (subcatchments combined).
.............................................................................................................................. 12
Table 3-1: Some characteristics of freshwater fish populations which are especially relevant
to their communities and conservation, modified after Maitland (1995)............... 15
Table 3-2: A summary of the main pressures facing freshwater fish and their habitats,
modified after Maitland (1995). ............................................................................ 19
Table 4-1: Tables and description of tables used in the European Freshwater Fish Database.
.............................................................................................................................. 21
Table 4-2: Guild classification system used by the FAME project (Noble & Cowx
2002),modified. ..................................................................................................... 24
Table 4-3: Composition of analyses and the type of dataset used for each analysis. Data
groups excluded from analysis are annotated. .................................................... 26
Table 5-1: Native species richness of individual families. ...................................................... 30
Table 5-2: Native and introduced fish species that occur in most (sub-)catchments (ranked
from 1-20). Fish species highlighted in yellow are intracontinental displaced
species. These fish species might also occur in the native list, as they are native
to some parts of Europe........................................................................................ 31
Table 5-3: Subspecies added to the species list.................................................................... 32
Table 5-4: Reported species without verified names. These species are not included in the
analyses................................................................................................................ 32
Table 5-5: Number of river (sub-)catchments, percentage of area and cumulative species
richness (50%, 75%, 90%) of irreplaceable and introduced species. .................. 38
Table 5-7: The number of species per family and the proportion of species listed as extinct at
the local scale (extinct at least in one catchment / subcatchment). ..................... 46
Table 5-8: Species ranked according to their local extinction rate. The number of river (sub-
)catchments refers to the total of 102 river (sub-)catchments for which information
concerning extinction was available..................................................................... 46
List of Maps
IV
List of Maps
Map 2-1: Geographic setting and river regions of the present study...................................... 4
Map 2-2: Mean annual temperature of the study area. .......................................................... 6
Map 2-3: Mean annual precipitation (cm/year ) of the study area.
1......................................... 6
Map 2-4: Digital map of European ecological regions (DMEER). Based on vegetation cover,
climate and topography.......................................................................................... 8
Map 2-5: Ecoregions for rivers and lakes. Based on the distribution of the freshwater fauna.
................................................................................................................................9
Map 2-6: River regions, as used in this study. ....................................................................... 9
Map 2-7: Seasonal distribution of catchment runoff (l/sec/km ). Selected catchments across
Europe. Runoff includes the differences between precipitation, evapotranspiration
and the topography of the catchment.
2
.................................................................. 10
Map 2-8: River (sub-)catchments analysed within this study. .............................................. 13
Map 5-1: Native fish species richness in (sub)-catchments. ................................................ 33
Map 5-2: Native fish species richness of all river basins (sub-)catchments combined......... 33
Map 5-3: Area-corrected native species richness for all river basins (species predicted for a
catchment area of 10´000km ). For calculation see text.
2..................................... 40
Map 5-4: Relative proportion (%) of nonnative species per (sub-)catchment. ..................... 43
Map 5-5: Relative proportion (%) of the native species richness that is reported as extinct
locally. In total, information for 102 (sub-)catchments was available. .................. 45
Map 5-6: Relative proportion (%) of irreplaceable species compared to the total native fish
fauna in (sub-) catchments (peripheral species were excluded from analysis). ..... 49
Map 5-7: River (sub-)catchments with different conservation values (hot spot areas). Areas
are sorted according to their relative proportion of irreplaceable and threatened
species (four equally- separated groups; for further explanation see text).............. 51
Map 5-8: Hot spot areas sorted by their relative proportion of nonnative species (four equally
separated groups; for further explanation see text). .............................................. 52
Map 6-1: Percentage change in average annual water availability (natural discharge without
subtraction of consumptive water use) for European river basins as compared to
today’s levels, realized with two different models for the 2070s. ......................... 59
Introduction
1
1 Introduction
1.1 Motivation
Human activities are causing a biodiversity1 crisis with species extinction rates up to 1000 times
higher than background rates (Moyle & Yoshiyama 1994; Pimm et al. 1995; MEA 2005). In
particular natural rivers, including their riparian zones, are among the most diverse, dynamic and
complex ecosystems worldwide (Naiman et al. 1993; Tockner & Stanford 2002). These
ecosystems contain ~25% of the total global vertebrate biodiversity. At the same time, freshwater
biodiversity is declining faster than diversity in terrestrial and marine systems (Jenkins 2003).
With over 20% of endangered or extinct aquatic species and about 30% of threatened fish
species, freshwater habitats belong to the world’s most threatened ecosystems (Stiassny 1996;
Sala et al. 2000; Leveque et al. 2005).
In Europe, freshwater fish are the only vertebrate group that entirely depends on the presence of
water. However, its diversity is dramatically declining. Out of 252 endemic freshwater fish in the
Mediterranean basin 56% are threatened with extinction; the highest proportion of any regional
freshwater fish assessment worldwide (IUCN 2006). In particularly for inland waters, basic
information on species distributions and threatened status is highly deficient for conservation
planning purposes (Olson & Dinerstein 2002; Leveque et al. 2005).
Despite their high biodiversity and their major threat, freshwater ecosystems are receiving less
attention than terrestrial systems in present conservation templates (Myers et al. 2000; Brooks et
al. 2006). This lack of appropriate conservation and management strategies increases the risk of
permanent losses of aquatic biodiversity (Lundberg et al. 2000).
It is evident that there are neither the resources nor the time to protect all areas where species
are under threat. Therefore clear criteria are required for prioritising inland water sites for
conservation (Darwall & Vie 2005). It is thus essential to understand that the variety of life is non
uniformly distributed, and how biodiversity is distributed (Gaston 2000).
Central to conservation planning theory are measures of “irreplaceability” relative to “vulnerability”
(Margules & Pressey 2000). Different measurements are used to classify vulnerability of an area:
(i) environmental variables, (ii) land tenure, (iii) threatened species, and (iv) expert opinions
(Wilson et al. 2005). Irreplaceability refers to areas of high endemism because the species most
prone to extinction are often rare and exhibit restricted geographic distribution (Pimm et al. 1995).
The catchment area, the entire area drained by a river or by one of its tributaries (Revenga et al.
1998), is widely accepted as the most appropriate spatial unit to analyse, manage and conserve
(Pollard & Huxham 1998). However, information on species distribution is mostly reported per
country rather than per catchment.
1 Biological diversity or biodiversity is the variety of life, and refers collectively to variation at all levels of
biological organisation (Gaston et al. 2004).
Introduction
2
1.2 Goals of this thesis
The primary goals of the present thesis are: (i) to develop a catchment-based information base
for European freshwater fish, (ii) to identify continental distribution patterns, (iii) to compare
distribution records with existing data sets concerning threat, and (iv) to identify areas of high
conservation value and areas that experience high environmental stress.
The analysis contains three parts:
1. Spatial distribution patterns of freshwater fish across Europe: Within this part the
biogeographical patterns of species richness are analyzed.
2. Spatial distribution patterns of freshwater fish within large river basins. For selected large river
basins more detailed analyses were carried out at the sub-basin scale.
3. Threats to freshwater fish and identification of conservation priorities: Data are analysed
concerning river fragmentation, species introductions, and extinction patterns. Further,
irreplaceability and vulnerability records were used to identify areas of high conservation
priority.
1.3 Questions and hypotheses
Spatial distribution patterns of freshwater fish across Europe
Question 1: How is species richness distributed across Europe?
Hypothesis 1: Species richness increases from north to south and decreases from west to east.
Question 2: What is the species-area relationship?
Hypothesis 2: There is a distinct increase of species richness with catchment area.
Question 3: Which European catchments contain the highest species pool?
Hypothesis 3: A small number of catchments (less than 30%) contains more than 75% of all
European species.
Question 4: Do species distribution patterns of nonnative species differ from the distribution of
native species?
Hypothesis 4: Native and nonnative species exhibit very different distribution patterns.
Introduction
3
Threats to freshwater fish and identification of conservation priorities
Question 5: Does fragmentation of rivers have a visible effect on species extinctions?
Hypothesis 5: Most extinct species are sea - river migrating (anadromous and catadromous)
species and thus heavily affected by river fragmentation.
Question 6: Which rivers exhibit the highest proportion of irreplaceable species?
Hypothesis 6: The rivers with the highest proportion of irreplaceable species are found in the
Mediterranean area.
Question 7: Which are Europe’s highest priority conservation “hot spots” areas in respect to
threatened and irreplaceable species?
Hypothesis 7: They are found throughout the Mediterranean area.
Question 8: Do high priority conservation hotspots contain a high proportion of nonnative
species?
Hypothesis 8: Hot spot areas don’t contain many introduced species
Biogeographic Setting
4
2 Biogeographic Setting
2.1 The European Continent
Geologically, Europe is a subcontinent forming the western tip of Eurasia. It is surrounded by
nine sea basins: the Mediterranean Sea, Black Sea and Sea of Azov, the Caspian Sea, White
Sea, Barents Sea, Norwegian Sea, Baltic Sea, North Sea and the North Atlantic Ocean.
Compared with other continents, Europe has much more extensive and deeply penetrating
internal water bodies, and it is this feature above all others which has contributed to the rapid
development of its southern shores.
Map 2-1: Geographic setting and river regions of the present study.
Data sources: http://dataservice.eea.eu.int; http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
The Mediterranean Sea, together with the Black Sea and the Caspian and Aral Seas, is
essentially the surviving remnant of the great Tethys Sea which once separated Laurasia and the
Gondwanaland, the two successor-continents of Pangaea, of which Eurasia and Africa were
respectively parts. The open oceans, such as the North Atlantic Ocean, are still relatively
unaffected by human activities compared to coastal areas and enclosed or semi-enclosed seas,
which are also more dependent on the amount of freshwater input from precipitation and direct
runoff.
Biogeographic Setting
The western border of the continent is formed by the Atlantic Ocean, which divides Europe from
the Americas. The Mediterranean Sea marks the continental boundary in the south, separating
Europe and Africa. The south-eastern border with Asia is not universally defined. Most common
the boundary is being drawn through the Dardanelles, the Marmara Sea and the Bosporus,
fallowed by the Black Sea. The ridge of the Caucasus or alternatively the Kura river form the
adjacent border, while the Caspian sea, the Ural river and the Ural mountains are generally
accepted to mark the eastern divide between Asia and Europe. The northern boundary is the
Arctic Ocean.
5
In this thesis, the peripheral landmasses not situated on the European mainland but on the
continental shelf were included (e.g., British Isles, Sicily or Svalbard). Iceland is traditionally and
culturally seen as part of Europe, even if this island forms a landmass on its own, and it is not
situated on a continental shelf (Mid-Atlantic ridge). In addition, the landmasses of Anatolia
bordered by the national frontiers of Turkey and the Caucasus ridge and the Kura watershed
were included too (Map 2-1).
2.2 Topography and climate
Europe is the second smallest continent covering 11´440´576 km2 (as delineated in the present
study). However, Europe has the longest relative coastline of all continents - an important factor
that partly explains the present distribution of freshwater fish. Average altitude of Europe is 300 m
a.s.l, compared to 600 m in North America and 1000 m in Asia. Only seven per cent of the
continent is above 1000 m. To the south and east, Europe is fringed by mountains; the highest
summits are in the Casucasus Mountains (Mount Elbrus, 5642 m) and in the Alps (Mont Blanc,
4808 m). North of the Pyrenees, the Alps, the Carpathians, the Balkan Mountains, and the
Caucasus an area of hilly uplands and of vast plains expands toward the eastern European
border. A second range of highlands borders the north-western continental areas (British Islands
and Norwegian scandes).
The extensive coastline and the variation in its relief lead to a variety of climate types over a
relatively small scale. According to the Köppen-Geiger-Pohl-System (Geiger & Pohl 1953) the
investigation area spans from polar to dry climate types: The moist subarctic climate in
Scandinavia and north-western Russia, the moist continental cool summer type in Eastern
Europe, and the moist temperate climate in western Europe predominate. Warm humid climates
are bordering the Mediterranean Sea, while the driest places are located in central Spain,
Anatolia and in the steppic regions bordering the Black and the Caspian Seas (Maps 2-2 and 2-3).
Biogeographic Setting
6
Map 2-2: Mean annual temperature of the study area.
Data sources: http://ipcc-ddc.cru.uea.ac.uk/obs/get_30yr_means.html; http://dataservice.eea.eu.int;
http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
Map 2-3: Mean annual precipitation (cm/year1) of the study area.
Data sources: http://ipcc-ddc.cru.uea.ac.uk/obs/get_30yr_means.html; http://dataservice.eea.eu.int;
http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
Biogeographic Setting
7
2.3 Biogeographic regions
Studies of biodiversity are often based on biogeographical units. Typically, these units are
defined a priori by specialist perception by the distribution of biodiversity. An “ecoregion”, one of
the most common classification scheme, is a “relatively large unit of land containing a
characteristic set of natural communities that shares a large majority of their species, dynamics
and environmental conditions” (Olson & Dinerstein 1998).
This definition leaves space to a wide range of interpretations. Thus ecoregions or biogeographic
regions are referring to different approaches based on different parameters considered and on
the spatial resolution. For Europe, mainly two classifications are common:
1. The map of European ecological regions (DMEER) is provided by the European Environment
Agency (EEA). It is based on potential vegetation, topographic, and climate data. It contains
69 regions, thus representing a high spatial resolution (http://www.eea.eu.int) (Map 2-4).
2. The ecoregions for rivers and lakes, first published by Illies (1978), is used for the
implementation of the Water Framework Directive (WFD) (http://www.eea.eu.int). The
ecoregions are based on the fauna living in European inland waters (Map 2-5).
Using these two maps combined, the European rivers were grouped into catchment based
regions. Map 2-6 shows the 17 different regions, some of them only consisted of a single large
river basin. It is thus rather a map of river regions than a map of ecoregions. Based on the large
continental scale, and the often coarse data resolution, this classification is justified.
Biogeographic Setting
8
Map 2-4: Digital map of European ecological regions (DMEER). Based on vegetation cover, climate and
topography.
Source: http://www.eea.eu.int
Biogeographic Setting
9
Map 2-5: Ecoregions for rivers and lakes. Based on the distribution of the freshwater fauna.
Source: http://www.eea.eu.int
Map 2-6: River regions, as used in this study.
Data sources: http://dataservice.eea.eu.int, http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
Biogeographic Setting
10
2.4 River basins
The European Continent is largely shaped by rivers, which are divided by their watersheds. In the
publication “Watersheds of the World” (Revenga et al. 1998), a watershed or river catchment is
defined as the entire area drained by a major river system or by one of its main tributaries.
A river basin consists of subcatchments, which are formed by tributaries or by upper, middle,
lower and deltic areas.
In this study, rivers are defined as superficial water courses having a steady gradient, creating
surface flow. Apart from the main channel a river also consists of a diverse and dynamic
patchwork of aquatic habitats that differ in flow velocity depth, physical, and chemical parameters.
According to their size, rivers are divided into large, medium, and small rivers. Large rivers are
characterized by basin areas of more than 50´000 km2; medium rivers by basin areas of 2000 -
50´000 km2, and small rivers, by basin areas less than 2000 km2. The lower boundary of a basin
area (50 km2) separating small rivers from creeks is ambiguous (Khublaryan 2004).
Rivers are shaped primarily by climate, i.e. the balance between precipitation and
evapotranspiration. Seasonal runoff variations are expressed by the hydrological regime, shown
in map 2-7. Inevitably, however, larger rivers cross several climatic zones, leading to complex
flow regimes (Pardé 1947).
Map 2-7: Seasonal distribution of catchment runoff (l/sec/km2). Selected catchments across Europe. Runoff
includes the differences between precipitation, evapotranspiration and the topography of the
catchment.
Source: (De Ureña 1999)
According to climate and topography there are also major gradients in runoff patterns across
Europe. Depending on their catchment area, rivers may be summer rain-, winter rain-, snowmelt-
or ice melt- fed, or contain a mixture of these regimes.
Biogeographic Setting
High seasonal runoff variability is typical for rivers in southern Europe, like the Duero, Ebro, Tajo,
Guadalquivir, among others. Low runoff variability is characteristic for North European rivers and
northern Russia (Babkin 2004).
2.5 River (sub-)catchments
The rivers included in this survey correspond to the rivers in the book “Rivers of Europe”
(Tockner et al. in prep.).
The rivers were selected due to three criteria:
1. the 20 largest European rivers are included
2. all ecoregions, therefore the entire continent, are covered
3. scientific information for these rivers is available
30
35
40
45
50
55
60
65
70
75
100 1000 10000 100000 1000000
River (sub-)catchment Area (km
2
) (log-scale)
Latitude °N
Figure 2-1: Latitudinal area (km2) distribution of the investigated European river (sub-)catchments.
Fish data were gathered for 129 river catchments (the book includes 160 catchments). These 129
catchments resemble the first dataset. In addition, fourteen rivers, mainly large ones and rivers with
very good data resolution, were split into 49 sub-catchments. The total dataset represents the finest
possible resolution. Including 161 river (sub-)catchments. From the Euphrates and Tigris Rivers
only the upper reaches were included within this study. These rivers drain into the Persian Gulf and
thus leave the investigation area. These 161 (sub-)catchments were used for analyses and
represent the second spatial dataset. Information for all (sub-)catchments, including size, perimeter,
mean latitude, mean longitude, and results of the data evaluation is included in Appendix 1.
11
Biogeographic Setting
The average size of the (sub-)catchments is 44’366 km
12
2; about the area of Switzerland. However,
few large catchments dominate in respect to area. Though, the mean area is of limited value
because it is heavily biased by the small number of very large basins (seven watersheds between
200’000 and 560’000 km2). Figure 2-1 shows the latitudinal distribution of rivers for basin area.
There is a higher number of (sub-)catchments in the southern than in the northern part of Europe.
Smaller basins are mostly missing in Central Europe (between 47°N and 56°N), because of the
vast and mostly flat central and eastern plains.
The ratio between the smallest (sub-)catchment (Geithellnaá, 187 km2) and the largest one (Dnjepr,
551’557 km2) is almost 3000! However the vast majority (77.6%) of all (sub-)catchments has an
area smaller than 50’000 km2 (see Table 2-1), while half of those small rivers are less than
10´000km2 (Map 2-8).
Table 2-1: Area distribution of (sub-)catchments and river basins (subcatchments combined).
Area range (km2) Number of (sub-)
catchments
Proportion (%)
of total area
Number of
river basins
Proportion (%)
of total area
50’000 125 25.6 67 11.9
50´000 - 100’000 18 17.2 19 18.6
100´000 - 150’000 8 13.3 4 7.0
150´000 - 200’000 3 7.6 2 5.1
200´000 - 250’000 1 3.5 0 0
250´000 - 300’000 1 4.0 3 7.4
300´000 - 350’000 2 9.2 1 4.7
350´000 - 400’000 1 5.0 1 4.9
400´000 - 450’000 0 0.0 1 6.0
450´000 - 500’000 0 0.0 0 0
500´000 - 550’000 2 14.6 1 7.1
550´000-1´000´000 0 0 1 10.7
>1´000´000 0 0 1 16.7
Total 161 100% 101 100%
Map 2-8: River (sub-)catchments analysed within this study. Hatched: Fish data not available.
European Freshwater Fish Biodiversity - Background
14
3 European Freshwater Fish Biodiversity - Background
3.1 Legal foundations
The loss of freshwater biodiversity caused by altered aquatic habitats reflects the poor legal
framework for protecting rivers, lakes and wetlands since the beginning of industrialisation. In
December 2000 the EU launched a new ambitious water policy by enacting the Water
Framework Directive (WFD). According to the WFD, Member States are obliged to protect,
enhance and restore all surface waters with the aim of achieving good ecological status by 2015.
For rivers, four biological indicator groups are used: phytoplankton, macrophytes and
phytobenthos, benthic invertebrates and fish. The principle of the assessment procedure is to
quantify the deviation of the ecological status of a site from type-specific reference conditions.
Thereby, reference conditions represent a status with no or only minor human alterations of all
quality elements included in the monitoring (EU 2000). It is evident, that a successful implication
of the WFD relies on well-structured spatial datasets. The data gathered within this study will
provide a central information base for the WFD.
3.2 Natural distribution and dispersal of fish
Europe’s freshwater fish fauna is studied for more than 450 years, more than twice as long as for
any other continent (Kottelat 1997). European freshwater fish belong to two zoological groups:
Cyclostomata are representatives of early primitive vertebrates from the super class Agnatha,
and Actinopergii (bony fish) belonging to the class Teleostei.
For fish, rivers can be considered as biogeographical islands since they are separated from each
other by barriers difficult to cross (sea, terrestrial area). Thus the number of species available to
colonize a given local habitat is the same as the number of species found in the catchment area
(Table 3-1) (Hugueny & Paugy 1995).
Many fish have low vagility because they are not migratory and are confined to freshwaters
(stenohaline species), whereas others can also live in the sea (euryhaline species). The present
natural distribution of fish species is determined by the post-glacial dispersal, the biological and
ecological requirements of each species, and the interactions with other species. At the broadest
scale, the natural pattern of fish distribution is determined by the prevailing climate, the
topography as well as the accessibility of a catchment. Within an individual catchment, the
distribution is controlled by local effects such as water temperature, flow velocity, productivity,
substrate type, gradient, among several others (Giles 1994; Maitland & Lyle 1996).
The diverse nature of habitats enables rivers to support a greater variety of fish species,
compared to lentic waters and canals. Morphology changes from the headwater to its mouth
European Freshwater Fish Biodiversity - Background
creating a succession of habitats, each of them supporting a different fish community (Huet 1949;
Maitland & Campbell 1992).
15
Table 3-1: Some characteristics of freshwater fish populations which are especially relevant to their
communities and conservation, modified after Maitland (1995).
1 Discreteness Fish are confined to their systems; this leads to independent populations with
individual stock characteristics developed since their isolation.
2 Numbers Because each population is often confined to a single (often small) aquatic system,
within which there is usually significant water movement, the entire population is
vulnerable to pollution disease, etc. Thus for any species, the number of populations is
of far greater importance than the number of individuals.
3 Migrations These are a feature of life cycle of many fish species and during migration they might
be particularly vulnerable. In particular, in diadromous riverine species, the whole
population has to pass through the lower reaches of their river at least twice in each
life cycle. If the river is polluted, obstructed or has many predators, the entire
populations of several species may disappear, leaving the community above
permanently impoverished.
4 Life cycles Large slow-growing species and small very short-lived species are very vulnerable to
fishing pressures can be fished to extinction.
5 Habitats Because they are often confined to discrete systems, all the life cycle requirements for
a species must be found within that system. Where this is not the case, species are
either migratory or do not establish permanent populations.
6 Communities Fish are typically key members of aquatic communities and food webs. As a
consequence, both fish populations and aquatic ecosystems can be disrupted by
changes in habitat or the introduction of new species which are predators or
competitors.
During the last ice age, the northern European fish fauna was eliminated by successive
glaciations. After deglaciation, areas were recolonized mainly from the Ponto-Caspian region and
the Danube basin. Post-glacial expansions of fish from the Iberian peninsula and the Adriatic
area were prevented by mountain ranges. Therefore the southern fauna is distinctly different than
the northern (Andersen & Borns 1994). Because of the glaciation, the freshwater fish fauna in
northern Europe is much poorer compared to the fauna in central and southern Europe (Noble &
Cowx 2002). Generally, Europe has the most depauperate freshwater fish fauna of all continents
(Mooi & Gill 2002).
3.3 Present knowledge
About 360 species are described in the most recent checklist, excluding the former USSR
(Kottelat 1997). Almost 36% of these species belong to the family Cyprinidae, 25% to the families
Salmonidae, Coregonidae and Gobiidae combined. Cobitidae, Petromyzontidae, Clupeidae and
Percidae add an additional 15%, and the rest is composed of several species-poor families. The
only endemic European fish family is the cyprinodontiform Valenciidae with two species
(Lundberg et al. 2000).
The most recent biogeographical studies, which included the European fish fauna, were done by
Illies (1978) and Banarescu (1992). Both used different zoogeographical units and the data base
for both studies is vague and not related to river catchments. Within the WFD, an international
group of scientists collated a huge amount of fish distribution records from 2700 rivers and some
European Freshwater Fish Biodiversity - Background
15´000 sites. However these data are not accessable for the public and they only cover a small
proportion of the European continent (Schmutz 2004).
16
Biogeographical monographs of the European fish fauna are rare and cover only a limited
proportion of the subcontinent (Bemis & Grande 1991; Bemis & Kynard 1997). Several
compilations for the conservation of freshwater fish exist, mostly at the national level (Crivelli &
Maitland 1995; Kirchhofer & Hefti 1996) and at ecoregional scales (Smith & Darwall 2006)
3.4 Nomenclature
Nomenclature and systematics of European freshwater fish are currently based on Kottelat
(1997). It uses the “Phylogenetic Species Concept” (PSC), which is based on Hennig’s theory of
phylogenetic systematics (Hennig 1950). In contrast to other biological systematics, the PSC
does not require complete reproductive isolation, thus a species is “the smallest diagnosable
cluster of individual organisms within which there is a parental pattern of ancestry and descent"
(Cracraft 1983). Subspecies do not exist according to the rules of the PSC. Consequently there is a
tendency that the PSC creates more species than other concepts. However Kottelat noted: “The
aim of systematics is to describe nature as it is, not to find a simplified way; its task is not to
introduce order, but to understand the existing order” (Kottelat 1997).
For some families, the clear taxonomical state is still in discussion and not yet clarified (Crivelli &
Maitland 1995). The systematics of salmonids and coregonids has been notoriously difficult
because of real or perceived numbers of characters and because it was not possible to find
consistent morphological differences among populations (Lundberg et al. 2000). Thus the number
of species in those families seems to be highly underestimated. The revision of families is also the
most important reason why even in Europe new species are still described every year (Kottelat &
Barbieri 2004; Freyhof et al. 2005; Kottelat & Persat 2005).
3.5 Ecological classification of fish
Fish populations and communities are sensitive bioindicators of river habitat quality, because
they are at the high level of the aquatic food web and react to most anthropogenic disturbances
such as eutrophication, acidification, chemical pollution, flow regulation, physical habitat
alteration, and fragmentation (Pont et al. 2005).
Each fish species has characteristic tolerances or preferences for water quality, habitat condition
and other environmental properties. They have specific requirements for breeding, feeding,
growth, recruitment and survival. These characteristics have been used to classify fish species
according to the concept of ecological / functional guilds, which was developed to simplify
analyses and assist the prediction of community changes (Balon 1975, 1981; Karr 1981). The
European Freshwater Fish Biodiversity - Background
classification into functional groups or ecological guilds is used for ecological status assessment
for about 20 years (Hughes & Oberdorff 1999).
17
Because of this island-like character, the complete restriction to freshwater, and the subsequent
impossibility to spread through sea, rivers often exhibit a distinct fish composition. For analysing
their zoogeographic distribution, it is therefore necessary to classify taxa due to their origin.
Commonly three classes are used:
The native fauna consists of species, which established naturally in a geographical area,
with dispersal occurring independent of human intervention (Copp et al. 2005).
Endemic (or irreplaceable) species have a limited distribution area to which they are
endemic. For freshwater fish, usually the basin is the appropriate scale for endemism.
Endemic species form a subgroup of native species.
Introduced species intentionally or accidentally appeared in waters outside their native
range.
Regarding this classification, one difficulty exists concerning introduced species: Species may
have been introduced quite long ago and have naturalized in their new area (e.g. the common
carp, Cyprinus carpio, was already introduced by the Romans 2000 years ago into other rivers
and ponds (Balon 1995)). Thus, it is a general rule to treat alien species displaced before 1492
as native (Jungwirth et al. 2003).
If a species originally (native and endemic species) occurred in a river (sub-)catchment, but it is
no longer present, it is recorded as extinct.
3.6 Biodiversity and conservation measures
Most analyses of spatial variation in biodiversity used species numbers observed or estimated in
an area (species richness). This results from the widespread recognition of the significance of the
species as a biological unit and from the practical issues of the ease and magnitude of data
acquisition (Gaston 2000).
Species richness is generally related to area. This species-area relationship is expressed as a
power function, S = cAz, where S is the number of species, A is the area and c and z are
constants (Arrhenius 1921). To obtain realistic scores of relative diversity, the influence of area
has to be rescaled (Brummitt & Lughadha 2003). The species-area relationship is also an
important function to understand the link between habitat (area) and potential species loss
(Gaston & Spicer 2004).
Beside species richness, the number of irreplaceable, or endemic, species is commonly used.
Irreplaceability provides a key value for conservation measurements and for identifying “hot spots”.
European Freshwater Fish Biodiversity - Background
Central for conservation planning is also the degree of vulnerability. Different measurements of
vulnerability exist: (i) environmental variables, (ii) land tenure, (iii) threatened species and (iv)
expert opinions (Wilson et al. 2005).
18
The IUCN 1 red list of threatened species is the most comprehensive inventory of the global
conservation status of animals and plants (www.iucnredlist.org). The red list represents the
potential risk to extinction for more than 40’000 species. Species are classified in groups, set
through criteria such as rate of decline, population size, area of geographic distribution, and
degree of fragmentation.
The following categories, from highest to lowest threat are used (IUCN 2006):
Extinct
Critically Endangered, Endangered and Vulnerable: species threatened with global
extinction.
Near Threatened: species close to the threatened threshold or that would be threatened
without ongoing specific conservation measures.
Least Concern: species evaluated with low risk of extinction.
Data Deficient: no evaluation because of insufficient data.
Today, species extinctions are of global concern; in particular the loss of irreplaceable species
and biodiversity. Extinctions occur locally, regionally, and globally. It is being distinguished
between locally extinct and globally extinct species.
3.7 Threats to freshwater fish
The major threats are: overexploitation, water pollution, habitat degradation, flow modification,
water consumption and species introductions (Dudgeon et al. 2005). The main pressures and the
effects are listed in Table 3-2.
Overexploitation of fish resources by unsustainable fisheries is a major problem for species of
economic and recreational value. The four other threats have consequences for all fish species.
Pollution from organic and inorganic substances are pandemic - even if some western European
countries have achieved considerable progress in reducing water pollution.
Habitat degradation includes changed erosion and sedimentation patterns, channelisation and
habitat loss (Aarts et al. 2004).
Flow modifications are ubiquitous in running waters. Weirs, locks and dams alter flow,
sedimentation, and oxygen concentration in a river. Dams dissect rivers and prevent fish
migration. Europe’s rivers are the world’s most heavily affected rivers by fragmentation (Dynesius
& Nilsson 1994; Nilsson et al. 2005).
1 IUCN: International Union for the Conservation of Nature
European Freshwater Fish Biodiversity - Background
Water consumption by diversion or extraction for irrigation leads to flow reduction and habitat
loss.
19
Introduced species add to the physical and chemical impacts on freshwater. Introduced species
most likely invade these freshwaters that already had been modified or degraded by humans
(Bunn & Arthington 2002; Koehn 2004). Often these species have a success rate of around 50%
to establish in invaded habitats (Jeschke & Strayer 2005).
Table 3-2: A summary of the main pressures facing freshwater fish and their habitats, modified after
Maitland (1995).
Danger Effect
Industrial and domestic effluents Pollution, poisoning, blocking of migration routes
Acid deposition Acidification, release of toxic metals
Land use (farming and forestry) Eutrophication, acidification, sedimentation
Industrial development (including roads) Sedimentation, obstructions, transfer of species
Warm water discharge gradients Deoxygenation, temperature
River obstructions (dams) Blocking of migration routes, sedimentation of spawning beds
Infilling, drainage and canalization Loss of habitat, shelter and food supply
Water abstraction Loss of habitat and spawning grounds, transfer of species
Fluctuating water levels (reservoirs) Loss of habitat, spawning and food supply
Fish farming Eutrophication, introductions, diseases, genetic changes
Angling and fishery management Elimination by piscicides, diseases, introductions
Commercial fishing Overfishing, genetic changes
Introduction of new species Elimination of native species, diseases, parasites
Global warming Northward movement of southern species
Extinctions
3.8 Lack of information
Fish distribution studies and assessment of freshwaters are most commonly the duty of public
authorities. Consequently, data are available for political areas (nations). It is therefore much
easier to get information on fish living in a specific country rather than for a specific river and
catchment. But to analyse and compare the fish fauna of different catchments and to manage
and conserve them in a sustainable way a catchment-based database is indispensable.
Methods
20
4 Methods
4.1 Structure of the Diploma thesis
The Diploma thesis was developed in 3 stages:
Stage 1 - Orientation and build-up of contacts: In October 2005, the study of literature on fish
ecology and zoogeography started. Simultaneously, the book authors were contacted, the
general hypotheses were formulated, and the building of the database started.
Stage 2 - Data collection and evaluation: Presence / Absence data from various sources were
gathered and added to the database. It was very time-consuming to finding those data. All
data were carefully evaluated and checked for quality. In addition, a three week journey to the
Balkans (28 April - 17 May) was necessary to gather data from this region.
Stage 3 - Data analyses and thesis writing (July and August 2006).
4.2 Structure of the European Freshwater Fish Database
The vast amount of data compiled within this project required a special solution for central data
storing and handling. While for small databases simple spreadsheet analyses softwares (such as
Microsoft Excel) are sufficient, this was not the case in this study.
Figure 4-1: Relations among the tables used within the database. Blue fields indicate separate tables which
are connected with at least one parameter (primary key) in another table.
1 and refer to 1:n relationships. 1 indicates the table with the primary key, where n () marks the
table to which the data is distributed to (see text for further explanations).
Methods
There were different parameters referring to each other (example: threat status to species), and
values that refer to those again (example: species to river (sub-)catchments, river (sub-)
catchments to rivers and rivers to ecoregions). These relations advert to various interlinked tables.
Thus a relational database management system was needed. Such a database accepts values
only once for a certain connection and is therefore free of redundancy and values are not
duplicated (Brosius 1999). Microsoft Access software was used to build up the database. At the
beginning, the individual tables and relations among these tables were identified. All tables and
the related values were linked to each other, with at least one parameter in every table serving as
a defined key parameter (primary key; Figure 4-1).
21
Some data may occur more then once for the same relation. For example a river (sub-)catchment
can flow through different countries and thus does not only refer to one value in the country table.
For these cases a separate table had to be created, which links the river (sub-)catchment with
the country table (Table 4-1).
Table 4-1: Tables and description of tables used in the European Freshwater Fish Database.
Table name Description
Species In the species table are all species-related records stored. It contains the species
name in Latin, German and English, marks if a species is peripheral, includes
protection state from IUCN, Bern Convention, CITES as well as the FAME guild
classifications and zoogeographic distribution range, based on Illies (1978).
Collect The heart of the data base, in which all presence / absence data and site/species
related information like the origin state and the threat, are stored.
Riversection The Riversection is equal to river (sub)-catchments.
Here are all values concerning river (sub)-catchment (e.g. area, latitude, GIS ID,
results of the data evaluation, literature etc.) saved.
River Contains the river name, which it delivers to Riversection and the fragmentation
records of analysed rivers.
Main river region This is used for the book project. The rivers are divided in 17 chapters which are either
large river catchments or biogeographic regions.
Country Contains all countries in the investigation area.
Ecoregion Contains all ecoregions based on Illies (1978)
Ecoregion_x_Country Relates Country and Ecoregion together.
Riversection_x_Ecoregion Relates Riversection and Ecoregion to each other.
Riversection_x_Country Relates Riversection and Country to each other.
4.3 Data collection
4.3.1 Freshwater fish distribution data
The main goal was to collect data on the current distribution of the fish fauna in European
catchments. Up to now such a database is missing. Therefore, the data had to be compiled from
books, scientific literature, governmental reports, grey literature, and public agencies. In Europe,
Methods
it is difficult to collect these data because of the high number of states (45), the diversity of
languages, and the continuous divide between western and eastern European scientists. Thus
different approaches were necessary to compile the data:
22
1. Fish fauna distribution data for individual basins were collected from papers, books etc.
2. The chapter authors from the book “Rivers of Europe” (Tockner et al. in prep.) provided data.
A spreadsheet named “Freshwater Fish Data Entry Sheet”, including all European species,
was sent to the authors. Information on the status of origin of the species (native, endemic
and introduced) and on extinct fish was collected (including information on source of data;
see Appendix 2 for a version of this file). The species list of Kottelat (1997) was used. For
salmonids and coregonids the checklist of the EU-project FAME was used
(http://fame.boku.ac.at).
3. In cases when information was not available through the above mentioned sources,
environmental NGO’s and public authorities were contacted.
All data were entered into the European Freshwater Fish Database. The origin (native, endemic,
introduced) of each species in a (sub-)catchment was included. Further, information on extinct
species was included, if available.
There are differences between published and present (this study) species lists. Taxonomic
revisions and upgrading of subspecies to species are the reasons. Polymorphic species, such as
Salmo trutta fario and Salmo trutta trutta were not included as separate taxonomic units in the list
because recent results do not recognise them as distinct species (Hindar et al. 1991). Names
were always compared with the reference fish nomenclature (Kottelat 1997) and with the online
fish database www.fishbase.com (Froese & Pauly 2006).
4.3.2 Protection and conservation categories
To identify the conservation status of all species and to identify hot spot areas for conservation the
IUCN Red List of Threatened Species (chapter 3.6) was applied to the 400 species. This
information was included in the European Freshwater Fish database (IUCN website accessed on
26th June 2006; http://www.iucnredlist.org).
4.3.3 Ecological guilds
Within the EU-founded FAME project a species guild approach was developed; Table 4-2 (Noble &
Cowx 2002). This information was entered into the European Freshwater Fish Database.
Since the present study covers entire Europe, in contrast to the FAME project, information for
~50% of species was not available.
Methods
23
4.3.4 Peripheral / euryhaline species
Very often, euryhaline or peripheral species were included. These species have a higher salt
tolerance and are adapted for living in fresh-, brackish- and salt water. Some species live along the
coastline or in estuaries, others are migratory between the river and the sea (e.g. eel, salmon,
sturgeons). The latter group is typical for fresh waters and is an important indicator of habitat quality
and river fragmentation. The first group of species that regularly enters freshwater, but is mostly
marine, has been classified as peripheral. After comparing all 400 species with the scientific
literature and expert opinions, finally 55 were included to belong to the ecological guild of
peripheral species (see Appendix 3). All peripheral species were kept in the database and in the
analyses; however, it was easier to exclude them from those analyses when only primary
freshwater fish were considered.
Methods
24
Table 4-2: Guild classification system used by the FAME project (Noble & Cowx 2002),
f
Methods
25
4.4 Quality Assessment
The data for this study were provided from many collaborators. If the original data source (e.g.
report, scientific paper) was unavailable, it was very difficult to assess the quality of those data.
For example, the number of extinct species, the origin species or the degree of endemism was
not available for all catchments, or only for specific countries.
It was therefore necessary to do an additional quality check. For each river (sub-)catchment the
following parameters had to be clarified:
1. Endemism applied for: River basin
Country
Ecoregion
2. Occurrence applied for: Main channel
River basin
3. Lacustrine species: Included in the list
Not included in the list
4. Extinct Species: Included in the list
Not included in the list
5. Assessment of literature: 1 Research was done in the last 10 years; a lot of
sample sites were included.
2 Research was done in the last 10 year; few sample
sites were included.
3 Research was done 10-20 years ago; a lot of sample
sites were included.
4 Research was done 10-20 years ago; few sample sites
were included.
5 Publication is older than 20 years.
An example of this evaluation table can be found in Appendix 4.
The results of this re-assessment were considered in the European Freshwater Fish database.
Methods
26
4.5 Data Analyses
4.5.1 General procedure
Two spatial data sets were used for the analyses (see Table 4-3):
1. Basin scale dataset: this dataset included the total number of species per basin.
Subcatchments were not analysed separately (in total 129 catchments).
2. River (sub-)catchment dataset: this dataset included all individual river (sub-)catchments
(Map 2-8). This dataset represents the finest spatial resolution in the present study (in total
161 (sub-)catchments).
Table 4-3: Composition of analyses and the type of dataset used for each analysis. Data groups excluded
from analysis are annotated.
Analysis type
Basin scale
dataset
River (sub)-
catchment
dataset
Excluded from analysis:
Longitudinal & latitudinal distribution of
species richness
X
Introduced species
Extinct species
Species-Area relationship X Introduced species
Extinct species (for the today occurring fishfauna)
Species richness compared to family
richness
X
Introduced species
Extinct species
Species accumulation X Extinct species
Species Introductions X Native species
Endemic species
Extinct species
Species Extinctions X Introduced species
(Native and endemic species if not extinct)
River (sub)-catchments where information concerning
extinct species was unavailable
Extinct migrating species X Introduced species
(Native and endemic species if not extinct)
River (sub)-catchments where information concerning
extinct species was unavailable
Species extinction and fragmentation X Introduced species
(Native and endemic species if not extinct)
River (sub)-catchments where information concerning
extinct species was unavailable
Irreplaceability X
Introduced species
Extinct species
Peripheral species
all species with >3 occurrence records
Conservation hot spots X Introduced species
Extinct species
Conservation hot spots threatened by
species introductions
X
Extinct species
Methods
27
4.5.2 Species richness-area relationship
For all catchments, the number of species was corrected for area. The power function of the
species-area relationship is:
S1 = cA1Z
Where S1 is the number of species, A1 is the area, and z and c are constants. The relative
species richness (S2) was standardized per 10´000km2 (A2). The transformed equation was:
(S2/S1) = (A2/A1)Z
S2 = (A2/A1)Z *S1
This equation was used to compare the latitudinal and longitudinal distribution of species
richness as well as to produce the map of area-corrected species richness.
4.5.3 Species extinctions
Following datasets were used:
a. the total of all species that are locally extinct in at least one river (sub-)catchment
b. Subset 1: The 20 species with the highest local extinction records
c. Subset 2: The 20 most threatened species.
Species belonging to subset 2 show only a small geographic distribution (compared to their
former distribution). The first subset contained common species with a wide geographic
distribution. These species suffer most from the decline at large spatial scales.
4.5.4 River fragmentation and local species extinction
Species were classified according to their migration behaviour. The guild classification was adopted
from FAME, although the number of classes was reduced. “Long anadromous” and “long
catadromous” guilds were combined (“Long diadromous migration”). Species classified as
“Intermediate anadromous migration” (mostly Alosa fallax) were included in the “Intermediate
Migration” guild.
Methods
28
4.5.5 Migration behaviour of locally extinct species in relation to the
degree of fragmentation
For degree of fragmentation, a dataset published by Dynesius et al. (1994) was used. Rivers were
classified as: (i) not affected, (ii) moderately affected, (iii) strongly affected. Degree of fragmentation
was related to subsets 1 and 2 of locally extinct species using the reclassified migration behaviour
guild as described above.
4.5.6 Degree of irreplaceability
Species were defined as irreplaceable when they were native and appeared in less than 4 (sub-)
catchments. Rare species and fish with a small remaining distribution area were included too. As
peripheral species could blur the irreplaceability patterns, they were excluded from the analyses.
4.5.7 Conservation hot spots
The datasets of “irreplaceability” and “vulnerability” were combined. Vulnerability was defined
according to the IUCN red list of threatened species.
Both datasets were combined as follows: The highest relative proportion of all river (sub-)
catchments for a) % irreplaceable species and b) % threatened species was divided through six.
Hence, six equally-sized classes were built (a 7th class included areas without threatened species).
The numbers of both classes were now added. In the case that the resulting sum of a river (sub-)
catchment increased, it was classified into one of the four equally-sized conservation hot spot
categories.
4.5.8 Conservation hot spots threatened by species introductions
For every (sub-)catchment the proportion of nonnative species was related to the result of the
conservation hot spots analysis. The highest relative proportion of introduced species for all river
(sub-)catchments was divided through six. Hence, six equally-sized classes were built. The
numbers of these classes were added to the classes of irreplaceble and threatened species. In the
case that the resulting sum of a river (sub-)catchment increased, it was classified into one of the
four equally-sized categories, indicating the threat of nonnative species to conservation hot sports.
4.5.9 Maps and GIS analyses
Fish distribution data were reported per (sub-)catchment. For the delineation of a catchment, data
provided by the European Environmental agency and the U.S. Geological Survey were combined
Methods
and adopted (http://dataservice.eea.eu.int, http://edcdaac.usgs.gov/gtopo30/hydro/index.asp).
Data from the 161 river (sub-)catchments were linked to the data reported in the European
Freshwater Fish Database. River (sub-)catchment area and perimeter were calculated using Arc
GIS 9 software. Longitude and latitude values were calculated as the geographic centre for each
river (sub-)catchment polygon.
29
Results
30
5 Results
5.1 Freshwater fish inventory
Data were collected for 400 species. The most species-rich families are the Cyprinidae, Gobiidae,
Cobitidae and Salmonidae (Table 5-1, Appendix 5). The most common fish species in Europe is
Salmo trutta. It is recorded from more than three quarters of all river (sub-)catchments (Table 5-2).
The most widespread introduced species, the rainbow trout (Oncorynchus mykiss), is recorded
from more than 50% of all river (sub-)catchments. It is also one of the most common freshwater
fish (Table 5-2). Several fish species are native to Europe but have been displaced to rivers
outside their original range (e.g. Sander lucioperca was introduced to the British Islands).
Table 5-1: Native species richness of individual families.
Family Total number of species % of total fish fauna
Cyprinidae 156 42.4
Gobiidae 40 10.9
Cobitidae 32 8.7
Salmonidae 22 6.0
Clupeidae 13 3.5
Percidae 12 3.3
Balitoridae 11 3.0
Petromyzontidae 11 3.0
Acipenseridae 9 2.4
Coregonidae 9 2.4
Cyprinodontidae 8 2.2
Mugilidae 6 1.6
Gasterosteidae 5 1.4
Cottidae 3 0.8
Osmeridae 3 0.8
Siluridae 3 0.8
Syngnathidae 3 0.8
Atherinidae 2 0.5
Blenniidae 2 0.5
Sisoridae 2 0.5
Valenciidae 2 0.5
Anguillidae 1 0.3
Ariidae 1 0.3
Bagridae 1 0.3
Citharidae 1 0.3
Clariidae 1 0.3
Esocidae 1 0.3
Gadidae 1 0.3
Mastacembelidae 1 0.3
Odontobutidae 1 0.3
Pleuronectidae 1 0.3
Serranidae 1 0.3
Umbridae 1 0.3
Total 366 100
Results
31
Table 5-2: Native and introduced fish species that occur in most (sub-)catchments (ranked from 1-20). Fish
species highlighted in yellow are intracontinental displaced species. These fish species might
also occur in the native list, as they are native to some parts of Europe.
Top 20 native species Top 20 introduced species
Species Name
# River (sub-)
catchments
Proportion (%) of river
(sub-)catchments
Species Name
# River (sub-)
catchments
Proportion (%) of river
(sub-)catchments
Salmo trutta 126 78.3 Oncorynchus mykiss 81 50.3
Leuciscus cephalus 116 72.0 Lepomis gibbosus 60 37.3
Perca fluviatilis 110 68.3 Pseudorasbora parva 48 29.8
Anguilla anguilla 110 68.3 Ctenopharyngodon idella 42 26.1
Esox lucius 108 67.1 Salvelinus fontinalis 40 24.8
Rutilus rutilus 102 63.4 Carassius auratus 38 23.6
Phoxinus phoxinus 101 62.7 Ameiurus melas 35 21.7
Gobio gobio 100 62.1 Hypophthalmichthys molitrix 34 21.1
Tinca tinca 98 60.9 Sander lucioperca 33 20.5
Alburnus alburnus 98 60.9 Carassius gibelio 29 18.0
Scardinius erythrophthalmus 95 59.0 Aristichthys nobilis 26 16.1
Cyprinus carpio 91 56.5 Gambusia affinis 25 15.5
Cottus gobio 90 55.9 Carassius carassius 22 13.7
Abramis brama 86 53.4 Silurus glanis 22 13.7
Lota lota 82 50.9 Micropterus salmoides 22 13.7
Leuciscus leuciscus 80 49.7 Cyprinus carpio 18 11.2
Gasterosteus aculeatus 79 49.1 Gambusia holbrooki 13 8.1
Blicca bjoerkna 78 48.4 Ameiurus nebulosus 12 7.5
Barbatula barbatula 77 47.8 Ictalurus punctatus 10 6.2
Gymnocephalus cernuus 77 47.8 Coregonus lavaretus 10 6.2
Two species are extinct from Europe: Chondrostoma scodrense and Leuciscus montenegrinus.
Both were endemic Cyprinid species in the Drin River. Chondrostoma scodrense is also classified
extinct by the IUCN, while for Leuciscus montenegrinus no information on its status is recorded by
IUCN (IUCN 2006) (http://www.iucnredlist.org). Sixty eight species are at least recorded as extinct
at the local (sub-)catchment scale.
Fifty five species are considered as peripheral species. Knipowitschia ephesi is endemic to Smaller
Meander River and Knipowitschia thessala to the Pinios River. For seven species the currently
valid name could only be found at the subspecies level. Even if the strict use of the PSC does not
allow the use of subspecies names, a consultation of systematists is needed to clarify their status.
Thus these seven species were included in the list (Table 5-3).
Results
32
Table 5-3: Subspecies added to the species list.
Subspecies Family Authority
Alburnus alburnus hohenackeri Cyprinidae Kessler, 1877
Barbus brachycephalus caspius Cyprinidae Berg, 1914
Barbus tauricus kubanicus Cyprinidae Berg, 1913
Capoeta capoeta capoeta Cyprinidae (Güldenstädt, 1772)
Cobitis vardarensis kurui Cobitidae Erkakan, Atalay-Ekmeçi & Nalbant, 1998
Neogobius cephalarges cephalarges Gobiidae (Pallas, 1814)
Neogobius cephalarges constructor Gobiidae Nordmann, 1840
However, for nine species from rivers in Anatolia and the Caucasus no information concerning their
present nomenclature was found. Their names could either be misspellings, outdated, or synonyms
for other species. Therefore these fish were not included in the present analysis (Table 5-4).
Table 5-4: Reported species without verified names. These species are not included in the analyses.
Species name
Alburnus coeruleus
Barbus plebejus escherichi
Barbus rajanorum rajanorum
Capoeta capoeta angorae
Capoeta capoeta bergamae
Capoeta capoeta kosswigi
Capoeta capoeta umbla
Garra rufa obtusa
Gobius (Ponticola) ratan
5.2 Fish distribution patterns in European Rivers
5.2.1 Species richness
The number of native freshwater fish per river (sub-)catchment varied from 0 (Bayelva) to 64 (Don).
If subcatchments were combined, the Danube contains a quarter of all European freshwater fish
species (98 species; Appendix 6, Maps 5-1, 5-2). For most analyses, river Bayelva, which was free
of fish species, was excluded.
Results
33
Map 5-1: Native fish species richness in (sub)-catchments.
Data sources: http://dataservice.eea.eu.int, http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
Map 5-2: Native fish species richness of all river basins (sub-)catchments combined.
Data sources: http://dataservice.eea.eu.int, http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
Results
34
5.2.2 Species relationships
Species richness was significantly related to basin area (Power function, R2 = 0.55, z = 0.3703,
Figure 5-1). The species-area relationship for the autochthonous fauna (including native, endemic
and extinct species) exhibited a very similar z-value (R2 = 0.5543, z = 0.3739). Relationship was
very high for Nordic rivers (Rivers of the Fennoscandinavian, Arctic and Boreal upland river regions
Figure 5-2). For the southern rivers (Iberian Peninsula, Italy, the Balkans and Anatolia and the
Caucasus), no significant relationship was found (R2=0.1949, Power Function; Figure 5-3). Species
richness was only weakly related to area.
Significant species-area relationships were only found for native species (endemic and native
species). No significant correlation for endemic-, introduced- or extinct species to area was found
(Figure 5-4). Strong differences were found between local ((sub-)catchment-scale) and regional
(river region-scale) species richness, as well as among the different regions (Figure 5-5). A highly
significant correlation existed between species and family richness within a specific catchment (R2
= 0.8908, Figure 5-6).
1
10
100
100 1000 10000 100000 1000000 10000000
River (sub-)catchment Area (km2) (log-scale)
Species Richness (log-scale)
Figure 5-1: Species-area relationship of native European freshwater fish. (S = 0.549A0.3703; R2 = 0.5439)
Results
35
1
10
100
100 1000 10000 100000 1000000
Basin Area (km
2
) (log-scale)
Species Richness (log-scale)
Figure 5-2: Species-area relationship for northern European Rivers (Rivers of the fennoscandinavian,
arctic and boreal regions) (S = 0.1645A 0.4645; R2 = 0.8325.)
Figure 5-3: Species-area relationship of rivers of the Iberian, Italian, Balkan and Anatolian regions.
(S = 2.2476A 0.2392; R2 = 0.1852)
Results
36
1
10
100
100 1000 10000 100000 1000000
River (sub-)catchment Area (km2) (log-scale)
Species Richness (log-scale)
Extinct species Endemic species Introduced species
Figure 5-4: Species-Area relationships of extinct (S = 0.6666A0.1275 ; R2 = 0.0439), endemic (S = 0.3651A0.1652 ;
R
2 = 0.094) and introduced species (S = 1.9255A0.0852 ; R2 = 0.0239).
Figure 5-5: Native species richness of river (sub-)catchments (not corrected for area) to the native species
richness of the entire region (not corrected for area).
Results
37
0
20
40
60
80
100
120
0 5 10 15 20 25
Family richness
Species richness
Figure 5-6: Relationship between family richness and species richness (y = 1.7079x 1.2239 ; R2 = 0.8908)
Results
38
5.2.3 Species Accumulation
To find out, which European river (sub-)catchments contributed most to total species richness, all
river (sub-)catchments were arranged according to their species richness (Figure 5-7).
Fifty per cent of all native species were found in only 17 river (sub-)catchments which cover 16% of
the total surface area. Seventy five per cent were found in 38 out of 161 river (sub-)catchments,
covering 35% of the total area.
0
10
20
30
40
50
60
70
80
90
100
1 21 41 61 81 101 121 141 161
Number of river (sub-)catchments
C
umu
l
at
i
ve
(%)
spec
i
es r
i
c
h
ness
and catchment area
%All catchments %Native Species
%Introduced Species %Irreplaceable Specie
s
However, all river (sub-)catch-
ments that contain 50% of all
species combined, included
less than 30% of irreplaceable
and 40.4% of introduced
species (see Table 5-5).
Introduced and irreplaceable
species did not accumulate as
fast as native species richness.
Introduced and irreplaceable
species were therefore less
related to total species rich-
ness.
Figure 5-7: Cumulative species richness and catchment area. (Sub-)catchments are ranked from the most
species rich to the least rich ones.
Table 5-5: Number of river (sub-)catchments, percentage of area and cumulative species richness (50%, 75%,
90%) of irreplaceable and introduced species.
% Species
Richness
Nr of river (sub)-
catchments incl.
% Area covered
%Irreplaceable
Species
%Introduced Species
50 17 16 29 40
75 38 35 61 59
90 93 86 85 99
Results
39
5.2.4 Latitudinal and longitudinal patterns in species richness
Area-corrected values were used to assess latitudinal and longitudinal gradients in species
richness (S = 0.549*A 0.3703). Latitudinally, species richness decreases continuously from South to
North (Figure 5-8). Spatial variation, however, was very high in southern Europe.
Longitudinally, species richness increased from West to East (Figure 5-9). Very low numbers were
recorded for the most western rivers, high numbers for eastern European and Russian rivers. The
variation in species richness increased as well from West to East.
0
10
20
30
40
50
60
30 40 50 60 70 80
Latitude (°N)
Species richness (area corrected)
Figure 5-8: Latitudinal distribution of native fish species richness (area-corrected; predicted species per
10´000km2; see Figure 5-1)
0
10
20
30
40
50
60
-30 -20 -10 0 10 20 30 40 50 60 70
Longitude (°E)
Species richness (area corrected)
Figure 5-9: Longitudinal distribution of native fish species richness (area-corrected; predicted species per
10´000km2; see Figure 5-1)
Results
40
5.2.5 Area-corrected species richness
The power function from the species-area relationship (Figure 5-1) was used to create an area-
corrected map of species richness (Map 5-3). The most species rich catchments are situated in
Southern Europe, with catchments smaller than 10´000 km2. With exception of the Rhine and the
Thames Rivers, the larger catchments with high richness are all situated in southern and south-
eastern Europe.
Map 5-3: Area-corrected native species richness for all river basins (species predicted for a catchment area
of 10´000km2). For calculation see text.
Data sources: http://dataservice.eea.eu.int, http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
Results
41
5.3 Fish diversity patterns in the Volga, Danube, Rhine and Rhône
Basins
The species-area relationship within the Rhône, Rhine, Danube and Volga basins resulted only in
significant relations for the Danube and Rhine Basin (Figure 5-10). Locally extinct species were
compared between the Volga, Danube and Rhine Basins (for the Rhône Basin no data on species
extinctions were available). In general, the proportion of extinct species decreased with increasing
area of sub-catchments. Less than two extinct species were recorded from each of the three River
basins (Figure 5-11). However, no relationship between extinct species number and area of
subcatchments was detected (Figure 5-12).
Figure 5-10: Species-area relationships for four major European river basins.
Volga: S = 42.646A-0.0129; Rhône: S = 8.1184A0.1083; Rhine: S = 0.0368A0.6941; Danube: S =
0.6458A0.4117
Results
42
0
5
10
15
20
25
30
35
Rhine Main channel
Rhine Basin
Average of all tribuitaries (Rhine)
Average of all parts of the main
channel (Rhine)
Average of tributaries and parts
of main channel (Rhine)
Danube Basin
Danube Main channel
Average of all tribuitaries
(Danube)
Average of all parts of the main
channel (Danube)
Average of tributaries and parts
of main channel (Danube)
Volga Basin
Volga Main channel
Average of all tribuitaries (Volga)
Average of all parts of the main
channel (Volga)
Average of tributaries and parts
of main channel (Volga)
Per cent extinct species
Figure 5-11: Local species extinctions in the Rhine, Danube and Volga basins. Values are presented for
different scales (tributary to entire basin).
1
10
100
1000 10000 100000 1000000 10000000
River (sub-)catchment Area (log-scale)
Extinct species (log-scale)
Figure 5-12: Extinct species-area relationship. Nested data from the sub catchments of the Rhine, Danube and
the Volga Rivers.(S = 17.596A -0.1654 ; R2 = 0.0923)
Results
43
5.4 Threats to fish biodiversity
5.4.1 Introduced species
Most river (sub-)catchments are colonised by nonnative species (Map 5-4). On average about 15%
of introduced species occur per river (sub-)catchment, with exceptionally high proportions for
Iberian rivers, the Loire River (France), parts of the Rhine catchment, the Po and Tebere rivers
(Italy) and rivers in the southern Balkans. The Spey River in Scotland as well as the Mandalselva
and Namsen Rivers (Norway) are the only rivers in northern Europe that contained high proportions
of nonnative species (Table 5-6). There was no distinct latitudinal gradient in nonnative species
richness.
Map 5-4: Relative proportion (%) of nonnative species per (sub-)catchment.
Data sources: http://dataservice.eea.eu.int, http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
Results
44
Table 5-6: The top twenty river (sub)-catchments ranked according to species distribution (see text).
* Values refer to river basins (subcatchments combined), not river (sub-)catchments
Results
45
5.4.2 Extinction of species
For 102 river (sub-)catchments information on local extinctions was available (Map 5-5). For these
rivers (48 in total), no species were reported as extinct. In total, 68 species disappeared locally (at
least in one river (sub-)catchment). Two species were extinct from European rivers.
Among the families that contained higher species numbers, the Acipenseridae, Petromyzontidae
and Salmonidae included the highest number of threatened species (Table 5-7). Ten species
appeared in both subsets (indicated with “X” in Table 5-8). These are very common fish species
with a wide geographic range but with a decreasing population density. Five species belonged to
the family Acipenseridae (sturgeons) including the largest European fish species (Huso huso).
Map 5-5: Relative proportion (%) of the native species richness that is reported as extinct locally. In total,
information for 102 (sub-)catchments was available.
Data sources: http://dataservice.eea.eu.int, http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
Results
46
Table 5-7: The number of species per family and the proportion of species listed as extinct at the local scale
(extinct at least in one catchment / subcatchment).
Families Native &Extinct
species richness
Number of locally
extinct species
Proportion (%) of
species reported as
locally extinct
Acipenseridae 9 7 77.8
Anguillidae 1 1 100.0
Balitoridae 11 1 9.1
Blenniidae 2 1 50.0
Clupeidae 13 5 38.5
Cobitidae 32 2 6.3
Coregonidae 9 3 33.3
Cottidae 3 1 33.3
Cyprinidae 158 26 16.5
Esocidae 1 1 100.0
Gadidae 1 1 100.0
Gasterosteidae 5 1 20.0
Gobiidae 40 1 2.5
Percidae 12 3 25.0
Petromyzontidae 11 4 36.4
Pleuronectidae 1 1 100.0
Salmonidae 22 7 31.8
Umbridae 1 1 100.0
Valenciidae 2 1 50.0
Table 5-8: Species ranked according to their local extinction rate. The number of river (sub-)catchments
refers to the total of 102 river (sub-)catchments for which information concerning extinction was
available.
Left panel: species with highest local extinction records; right panel: most threatened species
(species with the smallest relative distribution area (%) they still live in). Highlighted species are
extinct on the continental scale (according to this data compilation). C. oxyrinchus and B.
borysthenicus still appear in other rivers for which no information concerning extinct species was
available.
Species marked with "X" appear in both panels.
Twice
listed
Species name Number of river
(sub-)catchments
with extinction
records
Species name % analyzed river
(sub-)catchments
this species still
occurs in
X Acipenser sturio 27 Barbus borysthenicus 0
X Huso huso 12 Chondrostoma scodrense 0
X Acipenser stellatus 10 Coregonus oxyrinchus 0
X Petromyzon marinus 10 Leuciscus montenigrinus 0
X Acipenser gueldenstaedtii 9 Acipenser sturio 16
Anguilla anguilla 6 Huso huso 33
Salmo salar 6 Barbus comizo 33
X Alosa alosa 5 Acipenser gueldenstaedtii 40
Lampetra fluviatilis 5 Acipenser stellatus 41
X Acipenser nudiventris 4 Alosa alosa 44
Acipenser ruthenus 4 Acipenser nudiventris 50
Alosa fallax 4 Rutilus meidingeri 50
Lota lota 4 Valencia hispanica 50
Salmo trutta 4 Petromyzon marinus 57
Alburnoides bipunctatus 3 Stenodus leucichthys 57
Chalcalburnus chalcoides 3 Alosa kessleri 60
X Coregonus oxyrinchus 3 Rutilus frisii 63
Lampetra planeri 3 Alosa immaculata 67
X Rutilus frisii 3 Caspiomyzon wagneri 67
X Stenodus leucichthys 3 Gobio elimeius 67
Results
47
5.4.3 Migration behaviour of extinct species
Migration behaviour of extinct species was analysed using the main dataset of all locally extinct
species and the two subsets. Within the main dataset of all species locally extinct in at least one
river (sub-)catchment, short-migrating species dominated (36%), followed by intermediate migrating
species (ca. 25%; Figure 5-13). Within both subsets, short-migrating species decreased distinctly
(25% for the subsets of the species with the highest local extinction records and 5% for the subset
of most threatened species). Simultaneously, the proportion of diadromous species was higher
(40% for subset 1 and 55% for subset 2). The proportion of species without migration behaviour
evaluation was most distinctly increasing in subset 1 (45%).
Figure 5-13: Relative proportion of different migration behaviour guilds of a) all species reported as locally
extinct b) the species with highest local extinction records c) the most threatened species (see
Table 5-6).
5.4.4 Fragmentation and Migration behaviour of extinct species
Fragmentation records were available for 41 river (sub-)catchments. Two rivers were unaffected, 8
moderately affected, and 31 strongly affected by fragmentation. The findings of the analysis
concerning the coherence between river fragmentation and the migration behaviour of extinct
species are shown in Figure 5-14.
Extinction records for the most threatened species (subset 1) were related, except for long
diadromous species, to strongly affected rivers. However, also most occurrence records were
related to strongly affected rivers. But the highest proportion of occurrence records for short
migrating species was reported from rivers moderately affected by fragmentation.
For subset 2 (species with highest local extinction records), most extinction records were from
strongly affected rivers. The occurrence records are more diverse: For three migration guilds, the
species appeared in rivers of all three fragmentation classes.
Results
48
Figure 5-14: Comparison of migration behaviour guilds for extinction and occurrence records.
Figures A and B compare the 20 most threatened species, Figures C and D compare the species
with highest local extinction records. Bars show the fragmentation status of the river (sub-)
catchment, the record is belonging to.
5.4.5 Irreplaceability and endemism
Endemic species are restricted in their occurrence to rivers between 37 and 49°N (Figure 5-15).
Distribution of irreplaceable species (species that occur in 4 river (sub-)catchments) is shown in
Map 5-6. High degree of irreplaceability occurred in Anatolian rivers, in catchments at the western
fringe of the Ural Mountains (Pechora, Kara and Ural), in rivers of the Balkans, and at the Iberian
Peninsula.
Results
49
0
2
4
6
8
10
12
30.00 40.00 50.00 60.00 70.00 80.00
Latitudinal distribution of catchments (°N)
Number of endemic species
Figure 5-15: Latitudinal distribution of endemic species.
Map 5-6: Relative proportion (%) of irreplaceable species compared to the total native fish fauna in (sub-)
catchments (peripheral species were excluded from analysis).
Data sources: http://dataservice.eea.eu.int, http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
Results
50
5.4.6 Conservation hot spots
No correlation was found between total species richness and the numbers of endemic,
irreplaceable, and threatened species (Figure 5-16). No correlation was also found between
irreplaceable and threatened species (Figure 5-17). This finding is important since both parameters
were used for the creation of conservation hot spots (Map 5-7). The results demonstrated that the
southern European rivers posses highest conservation priority.
0
10
20
30
40
50
60
70
1 21416181101121141161
0
5
10
15
20
25
30
35
Native Species Endangerd species
Endemic species Irreplaceable species
Rank of river (sub-)catchments
Relative proportion of species
Number of endemic,
endangered and irrepl. species
Figure 5-16: (Sub-)catchments ranked according to native species richness (from most to least rich). Richness
for endangered, endemic and irreplaceable species for the ranked catchments.
0
10
20
30
40
50
60
70
80
1 21 41 61 81 101 121 141 161
Rank of river (sub-)catchment
Realtive proportion of species
%Introduced species %Irreplaceable Species %Threatened Species
Figure 5-17: (Sub-)catchments ranked according to the relative proportion (%) of irreplaceable species (from
highest to lowest proportion). Relative proportion (%) of threatened and introduced species for
the ranked catchments.
Results
51
Map 5-7: River (sub-)catchments with different conservation values (hot spot areas). Areas are sorted
according to their relative proportion of irreplaceable and threatened species (four equally-
separated groups; for further explanation see text).
Data sources: http://dataservice.eea.eu.int, http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
5.4.7 Conservation hot spots threatened by introduced species
There was no relationship between irreplaceable species richness and nonnative species richness
(Figure 5-17). The Iberian rivers (except Segura) and the Balkan Rivers Neretva, Acheloos,
Arachthos and Alpheios on the Balkans are among the hot spot areas that were most heavily
affected areas by species introductions (Map 5-8).
Results
52
Map 5-8: Hot spot areas sorted by their relative proportion of nonnative species (four equally separated
groups; for further explanation see text).
Data sources: http://dataservice.eea.eu.int, http://edcdaac.usgs.gov/gtopo30/hydro/index.asp
Discussion
53
6 Discussion
6.1 Fish inventory
Distribution records for 400 freshwater fish species were found. Kottelat (1997) listed only 358
species. However, out of the 400 species, 32 species are of non-European origin. In addition, the
present investigation included also the European areas of the former USSR as well as the
Caucasus area and Turkey. Due to its transitional character between Mediterranean and south
Asian faunal elements (Banarescu 1992) the Turkish and Caucasian rivers added 86 new species
to the European freshwater fish list. Thus the present species list contains less species than
expected.
For two families, the Salmonidae and the Coregonidae, the present list deviates from Kottelat’s
checklist (Kottelat 1997). Kottelat lists 27 species within the genus Salmo and 44 species within the
genus Coregonus, compared to 22 salmonid and 9 coregonid species listed in the present study.
Kottelat (1997) proposed an extreme splitting of these families. This splitting is not generally
accepted among ichthyologists, because its systematics is still in move (Maitland 2000; Griffiths
2006). Another gap occurred because freshwater fish are not the same than riverine fish. Species
may be very rare or endemic in lakes, which were not included in the catchments of this study or
which were not reported within the analyzed publications.
6.2 European Fish fauna in a global context
The 368 native species in Europe represent a rather poor community compared to the 10´000
freshwater fish known worldwide (Eschmeyer 1998). Even Australia contains a richer fauna with
500 species. North America contains around 1´050 species. The most diverse fish fauna is found
throughout the tropics; tropical Asia and Africa contain about 3´000 species each, while in South &
Central America more than 5´000 species occur (Lundberg et al. 2000).
Many studies have shown that species richness increases towards the equator (Oberdorff et al.
1995; Kaufmann & Willig 1998; Gaston et al. 2000; Enquist & Niklas 2001). This is probably the
oldest and best documented global pattern in biogeography (Humboldt & Bonpland 1807; Wallace
1878). The most common explanations refer to climatic reasons (higher energy availability, lack of
glaciations), to time (more effective evolutionary time for speciation), and to area-effects (larger
areas are found in the tropical regions than in the temperate ones).
Within the temperate zone, North America contains 2.5 times more freshwater fish species than
Europe. This difference can not be explained by a higher extinction in Europe due to the longer
human impacts. Energy availability is similar for both continents. However, North America
(24´480´000 km2) covers more than twice the area of Europe (11´440´576 km2). But even if the
Discussion
diversity is area corrected (10´000 km
54
2), the North American fish fauna is still two times richer
(58.3 species/10´000km2) than the European fauna (27.1species/10´000km2).
Possible explanations include: (i) North America received many species from very diverse
regions (e.g. Central and South America) and (ii) the recolonization after glaciations was faster.
The second explanation is supported by the location of the North American mountain ridges. In
contrast to Europe, where most mountains form north-south barriers, the Rocky Mountains or the
Appalachian Mountains are west-east barriers. This effect might have been fundamental for the
retreat of fish from advancing glaciers and for the subsequent recolonization after deglaciation.
Further, there might also be a stronger influence from the catchments draining into the Gulf of
Mexico, where a rich sub-tropic fish fauna is present (Lundberg et al. 2000).
6.3 Richness patterns in European Rivers
A distinct west-east and a north-south increase in richness was observed. Species richness also
increased with catchment area. However, in southern Europe richness did not correlate to
catchment size. Relatively low species numbers are reported from the Iberian rivers as well as from
the Kura-Aras drainage in the southern Caucasus area (despite its high proportion of endemic
species). Oberdorff et al (1995) found that fish species richness is not only related to catchment
area but also to mean annual discharge. As discharge is a function of precipitation and
evapotranspiration and fish are highly sensitive to low water levels and droughts, there might be a
considerable influence of the dry inland areas of Spain and Anatolia to the low species richness in
these areas. These regions also suffer most from severe water stress (Henrichs & Alcamo 2001)
and especially the Iberian rivers exhibit large seasonal and interannual flow variability (Babkin
2004).
For the four large river basins of the Volga, Danube, Rhine and Rhône Rivers significant species-
area relationships were only found for the Rhine and Danube Rivers. Data resolution was probably
too coarse and the catchment areas too large to detect a significant relationship for two of these
rivers. Studies on the Garonne River in France have shown that until the river’s mid stretch species
richness is significantly related to area, while with distance to source species richness is generally
increasing (Mastrorillo et al. 1998; Ibarra et al. 2005). Thus, within a large river basin climate and
physiography as well as discharge influence species richness more than area itself. In the Danube
basin the Inn River (glacial-nival regime), with an area of 26’128 km2, contains 22 native species,
while the Morava River (nival-pluvial regime), with an area of 27’267 km2, contains 50 native
species)
Harte and Kinzig (1997) propose a distinct relationship between endemism and area. The
argument is that at the largest scale (the planet), all species must be endemic and the degree of
endemism therefore declines with area. Thus, endemism should increase faster than the number of
Discussion
species with increasing area and increasing species. Recent studies have shown that the
correlation between biodiversity and endemism is generally low (Ricketts 2001; Lamoreux et al.
2006). This is supported by the present study. Further no correlation between species richness
and the proportion of irreplaceability was observed. Interestingly, the study by Oberdorff, Lek and
Guégan (1999) found exactly opposite results when comparing riverine fish of the Northern
hemisphere. According to these authors, species richness is the strongest significant predictor of
the number of endemic species, among other parameters like area or latitude. The understanding
of this (lack of) correlation is crucial in biogeographical studies and especially valuable for the
preservation of biodiversity. It is also important to mention that in the present study neither species
introductions nor extinctions are correlated to area. Thus, since species richness is faster declining
in smaller catchments with decreasing area, the proportions of extinctions and species
introductions become more intense.
55
Hence, species richness is not related to extinction rate and degree of endemism. In respect to
conservation, it means that not the most diverse catchments are the most valuable ones. A positive
correlation between family and species richness, as demonstrated for freshwater fish, is a well
known phenomena (Roy et al. 1996). Family richness is therefore frequently used as a surrogate
for species richness in particular for less studied areas (for example (sub-)tropical catchments)
(Kretschmar 2002).
Species diversity was highest in the Danube basin. Griffiths (2006) also found most species in the
Ponto-Caspian region including the lower courses of the Danube, Dniestr, Dnjepr and Southern
Bug rivers. Banarescu (1992) also identified the Danube as the center of European fish species
richness. The latter author also pointed out that most fish recolonized deglaciated regions from the
Ponto-Caspian region, particularly from the lower and middle Danube (Banarescu 1992).
The Danube Basin contains 98 fish species, which is about 1/4 of the European fish fauna. In North
America, the Mississippi has 375 species, the Amur River in south-eastern Russia contains 120
fish species, and the Yangtse River 322. In the tropics; the Congo contains 700, the Parana River
355, the Orinoco River 318, the Mekong River 1200-1700 and Amazon River around 3000 species
(Revenga et al. 1998).
6.4 Threats to freshwater fish biodiversity
Nonnative species are very common in most rivers. In two river (sub-)catchments (Vorderrhein and
Segura), introduced species exceed native richness. Generally, the number of nonative species is
underestimated, since interbasin displacements are often ignored. In addition national species lists
are mostly used. For example, Cobitis taenia is native to the Swiss rivers draining into the
Mediterranean Sea (Zaugg & Stucki 2003). However, it is listed as native to Switzerland in national
fish lists. But the same species has been introduced to catchments north of the Alps. There it has to
Discussion
be treated as a nonnative species. Freshwater fish translocations have been very common in some
countries (e.g. Italy, UK) for decades to centuries which makes it difficult to determine the natural
post-glacial ranges of several species (Copp et al. 2005).
56
In the present study, presence / absence records are used. Therefore, the influence of species
introductions on the native fauna can not be assessed. Jeschke and Strayer (2005) found that
about 50% of all introduced species become successful invaders, which is in contradiction to the so
called “tens rule”, that 10% of the introduced species establish themselves and that 10% of
established species spread (Williamson 1996).
An other study on invasive grass species has shown, that introduced species become more
invasive if they are genetically not closely related to native species (Strauss et al. 2006). It should
be expected that species with low phylogenetic relatedness are more successful than closer related
introduced species. However, to find such a correlation, abundance data and information
concerning the invasiveness are needed. Even if such a correlation can be found, fish introductions
are widely supported by intensive stockings and thus often consist of artificially maintained
communities, blurring the invasion success.
Long migrating species exhibit the highest degree of local extinctions. These species are highly
vulnerable during their migration period. Pollution, predation, overfishing and fragmentation may
alter communities (Maitland 1995). Sturgeons, salmonids, lampreys, the eel and Allis shad are
represented by this group. Especially sturgeons (Huso huso, Acipenser sturio, A. stellatus, A.
gueldenstaedtii and A. nudiventris) belong to the most locally extinct species and are among the
most threatened species. Allis shad (Alosa alosa), Petromyzon marinus, Coregonus oxyrinchus
and Rutilus frisii (all four are long migrating species) and Stenodus leucichthys (not evaluated) are
also heavily threatened.
There is a large amount of literature describing the negative effects of dam constructions on
migrating fish (Busnita 1961; Jungwirth 1984; Jankovic 1994; Jurajda 1995; Holcik 1996; Bloesch &
Sieber 2003; Holcik 2003; Reinartz et al. 2003). However, this effect is easier to prove on the reach
scale when comparing fish communities before and after the construction of a power plant then on
the catchment scale. Species still appear in the lower reaches of a river but are locally extinct in
upper courses due to fragmentation. Comparing the effect of fragmentation on species extinction
could therefore not have been proved satisfactory. The other reason is that there are only few
unaffected rivers left in Europe for comparison.
Discussion
57
6.5 Identifying priority sites for biodiversity conservation
No correlation between species richness and degree of endemism and irreplaceability was found
(Figures 5-7 and 5-16). Thus, protecting the sites with the highest number of species does not
include the conservation of species most prone to extinction. Species richness is mainly a result of
common, widespread species; therefore, strategies that focus on species richness tend to miss
exactly those biodiversity features most in need for conservation (Orme et al. 2005). Information on
state of endemism is heavily dependent on expert judgement. Based of the quality assessment,
these data were not very uniform. Some endemic species occurred in more than one river and
species endemic to one catchment were listed as native in another catchment. In contrast,
irreplaceability is based on the fact that a species does not occur in more than three (sub-)
catchments. Therefore it seems to be more reliable to use irreplaceability for prioritising
conservation sites. The use of irreplaceability may include a systematic error by excluding species
from large catchments; if these catchments were split into several sub-catchments (like Rhine or
Danube Basin) a species endemic to this area may appear in more than 3 (sub-)catchments and
thus may not be listed as irreplaceable (e.g. Hucho hucho for Danube). Since these species occur
in at least 4 river (sub-)catchments they are probably not so rare.
In the present study, irreplaceability included information only for European freshwater fish species.
Therefore, many rivers at Europe’s eastern boarder exhibit a high degree of irreplaceability. In
Russian rivers, such as Pechora, Kara and Don Rivers, Siberian fish species show their western
distribution range. Therefore these species appear as irreplaceable for Europe, however they are
not endemic to these rivers (see also Figure 5-15).
A high degree of irreplaceability is also found in Anatolian and Caucasian rivers. This area
represents a transition zone between the European and Asian fish fauna and thus includes species
found nowhere else in Europe (Banarescu 1992). Especially the Euphrates and Tigris rivers, of
which only the upper parts were included in the present study, contain a high number of faunal
elements from outside of Europe. Even though, Anatolia is known for its large and most probably
underestimated number of endemic fish. The database includes 80 fish species, which are found
nowhere else in Europe. To clearly estimate the degree of irreplaceability in this area, it would be
necessary to compile fish data from adjacent areas as well.
The remaining catchments with high degree of endemism are situated in southern Europe. Rivers
of the Iberian Peninsula and of the Balkan contain a high proportion of irreplaceable species.
However, Italian rivers did not contain a high number of irreplaceable species, which is in contrast
to a study concerning endemic freshwater fish of the Mediterranean basin (Smith & Darwall 2006).
The reason might be that species endemic to Italian rivers were widely introduced to other rivers
(see also Copp et al (2005)). However, in the present database these species were often not
marked as introduced and thus blurred the pattern of irreplaceability. Also, the Italian peninsula
Discussion
contains a unique fish fauna but it is distributed over more than three river (sub-)catchments (the
Po River was split into three subcatchments).
58
When comparing irreplaceable and threatened species, no clear patterns were found (Figure 5-17).
The 71 species classified as threatened (including the categories critically endangered,
endangered and vulnerable) by the IUCN are not only endangered because of their small
distribution area. Species like sturgeons declined in their distribution area and population density.
On the other hand, irreplaceable species may, for reasons mentioned above, not be rare at the
global scale and thus not be listed by the IUCN, or data on their status are not available.
The highest proportion of threatened species (up to 40%) is found in southern European rivers,
primarily in Iberian rivers (Table 6-6). When merging irreplaceable and threatened species, one can
identify areas of high conservation value. Rivers in southern Europe require urgent attention for
conservation planning. Otherwise, a unique biodiversity will be lost (Margules & Pressey 2000).
Since money in biodiversity conservation is short (Myers et al. 2000), one need to concentrate on
maintaining the rare and threatened species of the Iberian, Balkan and Anatolian rivers; in order to
avoid mass extinction in the European conservation hot spots.
The rivers Acheloos and Neretva in the Balkans and most Iberian rivers are at the same time
heavily threatened by species introductions (Maps 5-4 and 5-8). Often, the introduced species are
more successful in altered river systems (Bunn & Arthington 2002; Koehn 2004). It seems to be
surprising to find high proportion of nonnative species in the same rivers that have a high proportion
of threatened and irreplaceable species. Species introductions is one stress factor analysed here
which is often reported to have severe consequences on the native fauna. It is also the
Mediterranean rivers that face the highest discharge variability (Babkin 2004). Water stress,
characterized by the withdrawals-to-availability ratio is high in the Mediterranean region. Henrichs
and Alcamo (2001) identified that river basins in Southern Italy, Spain, Greece and Turkey
experience high water stress. For the dry southern European regions, especially for Southern
Spain, water is mainly extracted for irrigation. The Mediterranean Basin faces a growing human
population, with 450 million people at present, and it is the world’s main tourist destination with
around 175 million visitors a year (Smith & Darwall 2006). The demand for drinking water and water
for recreational reasons (e.g. golf courses) will further increase, in particular in summer, when water
availability is limited.
For successful conservation planning and the protection of the southern European fish fauna it will
be also inescapable to consider the forecasted scenarios for climatic change. In its most recent
assessment the IPCC (Intergovernmental Panel on Climate change) warns, that “projected change
could further decrease streamflow and groundwater recharge in many water stressed
countries“ (IPCC 2001). Furthermore, the IPCC highlights that the effect of climate change on water
availability will vary regionally and largely follow projected changes in precipitation. Henrichs and
Alcamo (2001) analysed future precipitation trends for Europe using two different models. For long-
Discussion
term forecasts (for the year 2070), they found a tendency, that climate change will increase water
availability in northern and north-eastern Europe and decrease availability in large parts of southern
and south-eastern Europe (Map 6-1).
Map 6-1: Percentage change in average annual water availability (natural discharge without
subtraction of consumptive water use) for European river basins as compared to today’s levels,
realized with two different models for the 2070s.
Source: (Henrichs & Alcamo 2001)
It is thus even more important to take action in conservation planning in Southern European river
systems. Otherwise, it will not be possible to fulfil the goal of the EU-WFD (Water Framework
Directive) to halt the loss of biodiversity in freshwater ecosystems until 2015. Altered river systems,
especially “hot spots” must be restored to stop species loss. Reaching this target will only be
possible if the catchment is considered as the spatial unit for which management strategies must
be developed. Local and national authorities must avoid treating river within their political
boundaries, but interact with the people in charge from the source to the river’s mouth. For example,
the Danube drains parts of 18 European countries. Worldwide it is the most international river
system.
59
Discussion
60
6.6 Proof of Hypotheses
Question 1: How is species richness distributed across Europe?
Hypothesis 1: Species richness increases from north to south and decreases from west to east.
This hypothesis is in general correct. Clear longitudinal and latitudinal trends were found (Figures
5-8 and 5-9).
Question 2: What is the species-area relationship?
Hypothesis 2: There is a distinct increase of species richness with catchment area.
This hypothesis is correct. A significant species-area relationship was identified for native species
richness per river basin. Relationship was very strong for Nordic rivers. However, for southern
European rivers, and for endemic, extinct and introduced species, no significant correlation
between richness and area was found.
Question 3: Which European catchments contain the highest species pool?
Hypothesis 3: A small number of catchments (less than 30%) contains more than 75% of all
European species.
Seventy five percent of native species richness were found in 38 river (sub-)catchments (23.6%
of all (sub-)catchments). These catchments cover a total area of 35.3% of the total area
considered in this study. This hypothesis is therefore correct.
Question 4: Do species distribution patterns of nonnative species differ from the distribution of
native species?
Hypothesis 4: Native and nonnative species exhibit very different distribution patterns.
Nonnative or introduced species are distributed all over Europe. Their richness is not correlated
with area. This hypothesis is therefore correct.
Question 5: Does fragmentation of rivers have a visible effect on species extinctions?
Hypothesis 5: Most extinct species are sea - river migrating (anadromous and catadromous)
species and thus heavily affected by river fragmentation.
Discussion
61
It is correct, that the most locally extinct species are long-migrating species. However, due to lack
of data on river fragmentation, a distinct correlation between fragmentation and extinction could
not be detected.
Question 6: Which rivers exhibit the highest proportion of irreplaceable species?
Hypothesis 6: The rivers with the highest proportion of irreplaceable species are found in the
Mediterranean area.
The hypothesis is partly correct. Most rivers around the Mediterranean basin contain a high number
of irreplaceable species, however also the Anatolian and Caucasian rivers as well as the Russian
rivers also contain high proportion of irreplaceable species (at least, if only the European continent
is being considered).
Question 7: Which are Europe’s highest priority conservation “hot spots” areas in respect to
threatened and irreplaceable species?
Hypothesis 7: They are found throughout the Mediterranean area.
Europe’s fish biodiversity “hot spot” areas are found mainly on the Iberian peninsula. In addition,
rivers along the western coastline of the Balkans, in Anatolia and in the middle part of the
Danube are important conservation areas. All hot spots are found in southern Europe and mostly
around the Mediterranean basin; some rivers flow into other sea basins (Euphrates and Tigris
into the Persian Gulf; Danube, Sakarya and Coruh into the Black sea). Therefore the hypothesis
is partly correct.
Question 8: Do high priority conservation hotspots contain a high proportion of nonnative
species?
Hypothesis 8: Hot spot areas don’t contain many introduced species
This hypothesis is not correct; especially the Iberian rivers and rivers on the Balkan contain also
high numbers of introduced species.
Conclusions and Outlook
62
7 Conclusions and Outlook
There is a lack of catchment-based European datasets of freshwater fish, which limits the
understanding of species distribution patterns and developing conservation strategies. Therefore, a
catchment-scale database was built. The distribution of 368 native and 32 nonnative freshwater fish
has been recorded. Native fish species richness is increasing from west to east and from north to
south. Species richness is increasing with catchment area, best described by a power function.
Although species richness is related to area, it is not the most species rich catchments that contain
the highest proportion of species in need for conservation. Prioritization of catchments with a high
degree of threatened and irreplaceable species is urgently needed for halting species loss. Such
“hot spot” areas were identified for Iberian and Anatolian rivers as well as for rivers of the Balkan.
The data compiled for this study provides the basis for the knowledge of European freshwater fish
and for developing conservation strategies. Data resolution and information can be improved in the
future.
The present knowledge about extinct species is still poor. Also, species introductions and
translocations of European species are poorly known - a fact which might blur the fish fauna
distribution patterns. This is needed for a better knowledge of the native fish, which is important to
evaluate, manage, and enhance riverine species richness and to set up appropriate conservation
and protection strategies.
From a biogeographical point of view additional information about the distribution of other
vertebrates (amphibians, water birds) and aquatic invertebrates would be necessary in order to see
if distribution patterns differ among taxonomic groups.
Conservation strategies based on priority areas are more useful if not only focused on fish
(Rodrigues et al. 2004; Lamoreux et al. 2006). Such an approach should take into account the
existing protected areas along the river corridors. To get a better knowledge an how big the human
footprint on a river catchment is, we need better spatial information about fragmentation, flow
regulation, habitat destruction, water pollution, waste water treatment, population density, land use,
and water stress (Sanderson et al. 2002). As climate change could become an overwhelming threat
to freshwater biodiversity in the future (Xenopoulos & Lodge 2006), future studies should include
scenarios of changing patterns of precipitation and evapotranspiration (and therefore river
discharge) into their analyses. Such approaches may lead to stronger predictive models necessary
for successfully conserving freshwater biodiversity.
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Appendix
71
9 Appendix
Appendix 1: River (sub-)catchments: Spatial parameters and the results of the quality assessment.
Quality assessment
River (sub-)catchments
River Region
Perimeter (km)
Area (km2)
Longitude (catchment
center)
Latitude (catchment
center)
Endemism applied for
Occurrence applied
for
Lacustrine species
ExtInct species
Assessment of
Literature
Aare BE Rhine 760 7883 7.28 46.71 RB RB Inc NotInc 5
Aare Lake Biel -
Mouth Rhine 823 9723 8.30 47.08 RB MC Inc Inc 5
Acheloos Rivers of the Balkan 853 6472 21.46 38.96 RB RB Inc Inc 5
Adige Low Italian Rivers 487 1674 11.18 45.44 Eco MC NotInc Inc 4
Adige up Italian Rivers 955 10650 11.30 46.54 Eco MC NotInc Inc 4
Ain Low Rhone 532 2536 5.58 46.24 RB MC NotInc NotInc 4
Ain upstream
Vouglan reservoir Rhone 233 1005 5.92 46.67 RB MC NotInc NotInc 4
Ain Vouglan