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A quantitative method for evaluating the importance
of marine areas for conservation of birds
Henrik Skova,*, Jan Durinckb, Mardik F. Leopoldc, Mark L. Taskerd
a
DHI Water and Environment, Agern Alle 5, DK-2970 Hørsholm, Denmark
Marine Observers, Svankjaervej 6, DK-7752 Snedsted, Denmark
c
Wageningen-IMARES, P.O. Box 167, Landsdiep 4, NRL-1797 SZ Den Hoorn (Texel), The Netherlands
d
Joint Nature Conservation Committee, Dunnet House, 7 Thistle Place, Aberdeen AB10 1UZ, United Kingdom
b
A R T I C L E I N F O
A B S T R A C T
Article history:
Objective criteria are needed for ranking marine sites when examining candidate areas for
Received 19 February 2006
protection measures. We suggest a Marine Classification Criterion (MCC) which allows the
Received in revised form
application of the widely used Ramsar 1% criterion for wetlands for seabirds with clustered
3 December 2006
distribution in offshore habitats. The maximum size of an area considered to be interna-
Accepted 6 December 2006
tionally important has not been defined by the Ramsar Convention. Terrestrial and coastal
sites generally have obvious hydrological or physical boundaries, whereas such boundaries
are less obvious at sea. The smallest unit which would pass the demands set by the MCC is
Keywords:
1% of the bio-geographic population of a particular species concentrated in an area (site)
Marine classification criterion
supporting a density exceeding a value equivalent of four times the average density of
Seabirds
the species in the investigated regional sea. The effect of choosing smaller or larger refer-
Marine protected areas
ence densities is tested. The results indicate that the chosen threshold density is a suitable
Identification of concentrations
requirement for the inclusion of the most important areas for seabird species with at least
25% of their bio-geographic population occurring in the studied regions of the North Sea
and the Baltic Sea. The test cases indicate that provided the MCC is based on geo-statistical
analyses of un-biased survey data the boundaries of areas holding large concentrations of
seabirds can be estimated with confidence. The MCC could be used to identify concentrations of seabirds and other marine animals of conservation priority and to rank marine
areas by their cumulative importance to different species.
Ó 2007 Elsevier Ltd. All rights reserved.
1.
Introduction
The IVth World Congress on National Parks and Protected
Areas held in Caracas, Venezuela, in 1992 (IUCN, 1993), highlighted the need for protected areas in marine as well as terrestrial environments in order to conserve biodiversity. In the
following years, scientifically-based methods (e.g. gap and
complementarity analysis) for prioritising conservation efforts have been developed and tested (Fjeldså and Rahbek,
1998; Williams, 1998). It has, however, been difficult to define
important marine areas, and relatively few marine protected
areas and integrated marine management zones exist today.
The lack of obvious boundaries, of quantitative information
and of jurisdiction has hampered the designation of areas
for conservation in offshore habitats. This paper discusses
the problems related to identifying and delineating areas for
conservation for seabirds, and it proposes a procedure which
ranks the conservation value of different marine areas for
* Corresponding author: Tel.: +45 45169220; fax: +45 45169292.
E-mail addresses: [email protected] (H. Skov), [email protected] (J. Durinck), [email protected] (M.F. Leopold), [email protected]
(M.L. Tasker).
0006-3207/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biocon.2006.12.016
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seabirds based on existing quantitative criteria for selecting
areas of international importance while taking the size of
the areas into consideration. The method is applicable to all
organisms for which reliable regional density and population
estimates exist, but seabirds were chosen to illustrate the procedure, as these are highly visible organisms for which relatively much information is available.
Over the last 15 years, scientifically-based methodologies
for identifying and prioritising conservation areas have been
developed. These methods define target areas based on species diversity or rarity, such as analyses of hotspots (Myers,
1990; ICBP, 1992) or more elaborately in analyses of complementarity (Vane-Wright et al., 1991; Fjeldså and Rahbek,
1998; Williams, 1998). However, these criteria may not be useful measures of the potential of sea areas for the conservation
of birds, as large numbers of birds can be concentrated in species-poor marine seascapes such as estuaries and upwelling
areas (Summerhayes et al., 1974). Kelleher and Kenchington
(1992) proposed a set of general, qualitative criteria to be used
for the selection of marine protected areas, but paid no attention to the specific conservation requirements of seabirds.
Full, effective protection of widely ranging animals like seabirds needs the co-operation between several countries.
Site-based conservation of birds has a long history in terrestrial, limnic and coastal ecosystems, and has played an
important role in the development of today’s networks of protected areas worldwide. The overarching goal of site-based
conservation of birds has been to identify those sites that
are exceptionally important for birds at some period during
the year, – ones of significance both nationally and internationally, and to try to ensure the conservation of the features
that make these areas important. Examples of site-based bird
protection systems are the EU network of Special Protected
Areas (EU Birds Directive, 1979) and the global series of Important Bird Areas proposed by BirdLife International (Heath
et al., 2001). Quantification of the importance of coastal and
inland wetland areas for birds has long been based on a
widely agreed set of international criteria under the auspices
of the Convention on Wetlands of International Importance
especially as Waterbird Habitat (the Ramsar Convention). To
be considered internationally important for waterbirds, a
wetland site has to meet any one of two criteria (Ramsar Convention Bureau, 1988):
1. It regularly supports 20,000 waterbirds.
2. It regularly supports 1% of the individuals in a population
of one species or subspecies of waterbird.
The 1% criterion has been particularly useful because it is
comparatively easy to count waterbirds, and thereby derive
both site counts and global population estimates. There is
no biological reason to use 1% of a population as the threshold level for establishing international importance of a site.
However, this percentage has gained wide acceptance and
we see no reason to challenge it. The size of an area considered to be internationally important is, however, not defined.
A larger site is by definition likely to contain more birds than a
smaller site centred around the same location. Terrestrial and
coastal sites generally have obvious hydrological or physical
boundaries, whereas such boundaries are less obvious for
x x x ( 2 0 0 7 ) x x x –x x x
marine sites. Another restriction for the application of the
Ramsar Convention criteria to the open sea is that ‘wetlands’
are limited to areas that are no deeper than 6 m. Despite these
limitations, selection of conservation areas for birds by the
application of the Ramsar criteria has taken place in truly
marine areas, e.g. EU Special Protection Areas and Ramsar
sites in the Danish part of the Kattegat (Jensen, 1993). Other
approaches for selection of priority areas for conservation of
birds in marine waters include seaward extensions of nationally and internally important breeding colonies (e.g. United
Kingdom; Johnston et al., 2002), habitat features related to national marine sanctuary systems (e.g. Stellwagen Bank, USA;
http://sanctuaries.noaa.gov/) or analyses of tagging data (e.g.
Birdlife International’s ‘‘Ocean Wanderers’’ project (BirdLife
International, 2004).
The use of the 1% criterion requires the availability of estimates of total population size as well as estimates of the
Table 1 – Total estimates of selected seabird species
wintering in the Baltic Sea and the North Sea (1987–1995)
Species
Red-/black-throated diver
Gavia stellata/arctica
Great Northern Diver Gavia immer
Great Crested Grebe Podiceps cristatus
Red-necked Grebe Podiceps grisegena
Slavonian Grebe Podiceps auritus
Cormorant Phalacrocorax carbo
Shag Phalacrocorax aristotelis
Fulmar Fulmarus glacialis
Mute Swan Cygnus olor
Mallard Anas platyrhynchos
Pochard Aythya ferina
Tufted Duck Aythya fuligula
Scaup Aythya marila
Eider Somateria mollissima
Steller’s Eider Polysticta stelleri
Long-tailed Duck Clangula hyemalis
Common Scoter Melanitta nigra
Velvet Scoter Melanitta fusca
Goldeneye Bucephala clangula
Smew Mergus albellus
Red-breasted Merganser Mergus serrator
Goosander Mergus merganser
Coot Fulica atra
Great Skua Catharacta skua
Little Gull Larus minutus
Common Gull Larus canus
Herring Gull Larus argentatus
Great Black-backed Gull Larus marinus
Kittiwake Rissa tridactyla
Guillemot Uria aalge
Guillemot Uria aalge (Baltic form)
Razorbill Alca torda
Black Guillemot Cepphus grylle
Black Guillemot Cepphus grylle
(Baltic form)
Little Auk Alle alle
Puffin Fratercula arctica
Baltic Sea North Sea
56 700
49 000
<50
11 300
5500
1800
19 400
<2500
<150 000
108 000
227 000
31 200
319 000
145 700
1 048 000
6850
4 272 000
783 000
933 000
123 000
17 000
44 000
73 000
212 000
<280
2250
72 000
310 000
21 000
76 000
66 000
20 000
156 000
1250
27 000
900
14 000
2000
<50
14 000
29 000
1872 000
<1800
<50 000
<3500
<7500
14 000
463 000
<150
<47 000
570 000
121 000
16 000
<250
9850
3200
<15 000
1000
5400
176 000
918 000
300 000
1 034 000
1 562 000
<500
324 000
6600
<500
<3000
<14 000
853 000
75 000
Estimates are only mentioned for species occurring in the relevant
region in numbers exceeding 1% of the reference biogeographic
population.
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number of birds of the particular species in the studied area.
Population estimates for waterbirds inhabiting coastal environments have recently been reviewed (Wetlands International, 2002), while those for pelagic species of seabirds vary
from estimates with confidence limits to educated guesses.
Estimates of numbers of birds offshore and their distribution
are now becoming available through large-scale surveys using
line transect techniques (Tasker et al., 1984; Webb and Durinck, 1992). Due to the wide range of marine habitats occupied
by birds it is frequently necessary to merge data from multiple sources (e.g. counts from land, ships, aeroplanes) in order
to obtain a complete description of birds using an area based
on unbiased population estimates (e.g. Skov et al., 1995).
2.
Materials and methods
2.1.
Study regions and survey data
This paper is based on European work, but the concept should
be applicable to all offshore marine areas including oceanic
and shelf seas, coastal zones and archipelagos. The methodology has gradually been developed and tested during a large
number of projects from feasibility studies in relation to marine conservation areas within the European Union (Durinck
et al., 1994), to analyses of marine important bird areas (Skov
et al., 1995, 2000) to designation of potential EU Special Protection Areas (SPAs, Johnston et al., 2002; ICES, 2006). In this
paper, the selection procedures used in Skov et al. (1995,
2000) have been refined and updated in order to strengthen
their general application. The revised selection procedures
have been tested on an international seabird database (ESAS,
European Seabirds at Sea database) containing winter distributions of waterbirds for the Baltic Sea and year-round seabird distributions for the North Sea at large (Stone et al.,
x x x ( 2 0 0 7 ) x x x –x x x
3
1995). Although the surveys contained in the ESAS database
were not specifically designed for this analysis, the use of it
made it possible to test the methods on a large, basin-wide
database that includes seabird densities in virtually all types
of habitats, including all coastal environments. The ESAS data
used here were collected by many observers between 1987
and 1995 (1993 in the Baltic Sea) using standard methods (Tasker et al., 1984). Although more recent data have been collected in the two regions, comprehensive coverage of both
regions was only achieved during the described period. All
data collected under relatively calm conditions (Beaufort sea
state 6 4) were processed to describe seabird distributions in
the Baltic Sea during winter and in the North Sea during the
whole year. Approximately 150,000 km of line transect
observations is represented in the data used for analysis. In
addition to offshore line transect data, information was obtained from national databases on birds in near-shore waters
during the same periods. These data mainly cover observations made from aerial or land-based surveys in connection
with the internationally co-ordinated Wetlands International
Midwinter Census of waterbirds. Information on numbers of
birds presumed to be associated with the breeding colonies
of seabirds in the region were derived from the United Kingdom Seabird Colony Register (Lloyd et al., 1991), Grimmett
and Jones (1989) and Hälterlein and Steinhardt (1993). No
extrapolation from these numbers into waters surrounding
the breeding colonies took place.
The distributions of the 30 most common species have
been analysed. Some species of seabirds are best surveyed
by one type of platform (e.g. aeroplane) while the distribution
of others may best be described using a combination of methods from several platforms. Thus, in order to achieve reliable
figures for the entire seabird fauna all data were combined
using a Geographical Information System (GIS) to produce
Fig. 1 – Study regions marked by solid lines; I: the North Sea and II: the Baltic Sea.
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Fig. 2 – Example variogram (spherical) used for description
of spatial variance for black guillemot (Cepphus grylle) in
the Baltic Sea.
x x x ( 2 0 0 7 ) x x x –x x x
integrated maps of bird numbers per unit area. The procedure
implied integration of densities obtained from aerial and
ship-based line transects with densities converted from total
counts (land-based and aerial total counts). Densities were
converted from total counts in near-shore areas by assuming
a detection range of 1 km during these counts. Densities obtained during aerial and different types of ship-based line
transects were standardised using correction factors for birds
missed in the searched area determined from estimated
detection probabilities in the software Distance (http://
www.ruwpa.st-and.ac.uk/distance/).
Comparison of the total numbers of all species of seabirds occurring in the whole Baltic Sea and the North Sea
was made for the winter season (December–February). During winter the total number of seabirds in the two regions
is of the same order of magnitude (106), but the communities
are clearly different (Table 1). The Baltic avifauna is dominated by benthic-feeding species (diving ducks), while in
the North Sea rather more pelagic-feeding species are dominant (fulmar, gannet, gulls and auks). Hence, the two study
areas provided a wide range of different habitats to test the
criteria on.
Fig. 3 – The effect of choosing different degrees of concentration reflected by density levels on the classification of areas of
importance to seabirds in the North Sea (a and b) and the Baltic Sea (c and d). The four graphs show the proportion of the total
estimated number of birds at sea covered by the classified areas in the two regions as determined by increasing minimum
densities from 2 to 7 times the average regional density of the species in question. The species selected are species for which
at least 25% of the total biogeographic population are estimated to occur in the North Sea and the Baltic Sea. In the North Sea,
the season has been chosen in which the largest number of birds in the region was found.
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2.2.
Identification of concentrations
Different species of seabirds show different degrees of clustering within their preferred habitats depending on the scale
analyzed. Aggregating seabirds typically occur in few large
patches or more commonly in multiple smaller patches. In
this study the spatial variation of each species was analysed
by applying b-spline approximation techniques (North Sea,
see Skov et al., 1995 for details) and interpolations (Baltic
Sea, see Skov et al., 2000 for details) using kriging to the database of integrated densities from all survey platforms, see
(Fig. 1). In the case of multiple patches, our study shows that
gradients are found in the density between strata marking
the background density of birds and strata in which patches
of birds occur frequently at short relative intervals (extended
aggregations). The preferred scientific method for stratifying
areas of different densities of birds is fine-scale geo-statistical
analyses (kriging) and interpolation of sampled densities by
application of experimental variograms (Cressie, 1991). The
use of variograms allows for a model-based determination of
the scale of spatial autocorrelation (variogram range), which
can be used to inform about the chord length of extended
aggregations. In the analysis of the Baltic Sea the range was
also used to set the maximum distance of extrapolation away
x x x ( 2 0 0 7 ) x x x –x x x
5
from sample points. In this way the obvious danger of using
arbitrary borders, e.g. by expanding an area until numbers
within it reach 1%, was avoided. Further, the use of variograms
as a basis for kriging made it possible to determine nugget effects and the orientation of anisotropies in the data. For most
of the species of conservation concern (i.e. divers, grebes, seaducks and auks) radial and spherical variograms fitted best to
the sampled data, and strong anisotropies were apparent. A
sample variogram is depicted in Fig. 2.
2.3.
Identification of important areas per species – the
Marine Classification Criterion (MCC)
Geo-statistical analyses of the distribution of a seabird species can be coupled with two further parameters to determine
the importance of an area holding an aggregation of that species: the percentage of the bio-geographic population of the
bird living within the area and the degree of concentration
displayed by the aggregation. Due to characteristic pattern
of dispersal of many of the key marine bird species in the
two sea regions (species with more than 25% of the bio-geographic population occurring in either region), only a small
number of areas can be considered as of high importance to
seabirds and thus the target of conservation efforts. In the
Fig. 4 – Sketch of the GIS-procedure for merging boundaries of selected species areas into priority multi-species polygons.
The example is from Pomeranian Bay showing nine species areas meeting the MCC being merged into the multi-national
priority area for conservation marked with a blue line. EEZ boundaries for Germany, Poland and Denmark are indicated.
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North Sea, the six most important areas together account for
80% of the estimated total importance of areas to seabirds
(Skov et al., 2000), and in the Baltic Sea the ten most important areas, covering less than 5% of the Baltic Sea area, host
about 90% of the total estimated number of wintering seabirds in the region (Durinck et al., 1994). Accordingly, the
choice of the critical size of the reference basin-wide density
level (4*D, Fig. 3) was determined both by the requirement to
secure the inclusion of the globally important aggregation
areas and by the need to exclude peripheral areas characterised by moderate densities dispersed over wide areas.
The two parameters; percentage of the total bio-geographic population and the degree of concentration were
combined into a Marine Classification Criterion (MCC) for
selecting the most valuable sites. The percentage of the total
bio-geographic population living in the area was calculated
from figures provided by Rose and Scott (1994), Rose and Scott
(1997). In order to be considered ‘important’, this proportion
needed to be equal to or exceed one percent.
The degree of concentration displayed by the aggregation
should exceed four times the average basin-wide (North Sea/
Baltic Sea) density. Accordingly, the MCC can be written as
MCC : ðn=NÞ P 0:01;
and d > ð4 DÞ
where N is the total biogeographic population, n is the estimated number of birds within the aggregation, D is the regio-
x x x ( 2 0 0 7 ) x x x –x x x
nal average density and d is the local density of birds within
the aggregation.
2.4.
Selection of priority areas across species
The boundaries of the combined areas were computed by a
GIS procedure which (a) merged the borders of all overlapping
specific areas of international importance meeting the MCC
and (b) stratified merged areas by their total value calculated
as the sum of proportions of the total populations of the species meeting the MCC. The procedure for merging borders of
selected species areas according to the MCC into multi-species priority areas is outlined in Fig. 4.
3.
Results and discussion
Extended aggregations in the North Sea and the Baltic Sea
typically measured more than 500 km2 (Table 2). The total
number of birds within each stratum was estimated. The
amount of aggregation displayed by species of seabirds wintering in the Baltic Sea and the North Sea is indicated in Table
3. Contrary to common belief, benthivorous species like seaducks were generally not found to be more concentrated than
offshore, pelagic species. Species showing a high degree of
clustering were found among a wide range of groups from divers to auks and seaducks.
Table 2 – The proportion (%) of selected species of wintering seabirds in the Baltic and North Seas estimated to occur
within areas of different categories of size
<500 km2
500–1000 km2
1000–3000 km2
3000–10 000 km2
>10 000 km2
Baltic Sea
Red-/black-throated diver
Great Crested Grebe
Red-necked Grebe
Slavonian Grebe
Eider
Long-tailed Duck
Common Scoter
Velvet Scoter
Common Gull
Herring Gull
Great Black-backed Gull
Razorbill
Guillemot
Black Guillemot, Baltic
42.97
86.21
13.80
7.10
1.76
1.15
20.91
47.09
1.04
1.33
1.06
21.52
0.00
44.78
11.46
0.00
31.65
55.46
0.64
31.71
6.54
2.86
10.88
0.78
1.47
0.67
34.31
22.57
42.32
13.79
17.20
0.00
8.81
7.95
5.25
47.43
7.57
4.70
12.93
46.99
0.00
5.76
3.25
0.00
37.35
37.43
80.03
45.01
67.30
2.61
40.71
19.24
46.25
23.52
30.93
17.42
0.00
0.00
0.00
0.00
8.76
4.19
0.00
0.00
39.80
73.96
38.29
7.30
34.76
9.47
North Sea
Red-/black-throated diver
Great Northern Diver
Great Crested Grebe
Shag
Fulmar
Gannet Morus bassanus
Eider
Common Scoter
Common Gull
Herring Gull
Great Black-backed Gull
Kittiwake
Razorbill
Guillemot
Little Auk
8.59
85.23
30.17
68.99
0.50
0.00
19.11
10.16
0.11
0.00
0.00
0.21
0.00
0.26
0.03
22.31
14.77
0.00
1.13
0.00
2.09
2.60
6.18
12.61
0.00
0.00
0.86
0.00
0.56
0.04
22.89
0.00
0.00
20.09
0.13
33.90
1.09
31.23
20.55
15.57
12.99
8.15
72.23
5.32
0.09
21.31
0.00
69.83
9.79
0.67
17.54
57.31
51.99
38.29
18.25
9.08
9.95
21.50
13.87
1.52
24.90
0.00
0.00
0.00
98.70
46.47
19.89
0.43
28.44
66.18
77.94
80.83
6.27
79.99
98.32
Species
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Table 3 – The table shows the intensity of aggregation
among species of seabirds distributed in the Baltic Sea
and the North Sea during winter
Species
Intensity of aggregation
Baltic Sea
Red-/black-throated diver
Razorbill
Cormorant
Common Scoter
Long-tailed Duck
Scaup
Smew
Steller’s Eider
Guillemot
Velvet Scoter
Tufted Duck
Mute Swan
Pochard
Coot
Black Guillemot
Eider
Mallard
Great Crested Grebe
Red-breasted Merganser
Goosander
Herring Gull
Goldeneye
Common Gull
Red-necked Grebe
Little Gull
Great Black-backed Gull
Slavonian Grebe
8.15
12.14
17.29
18.12
18.35
21.97
24.38
25.00
25.06
28.30
29.89
30.49
31.42
32.84
35.90
37.32
47.59
51.54
54.62
56.19
56.27
62.71
73.44
83.81
84.43
84.79
92.83
North Sea
Razorbill
Little Auk
Velvet Scoter
Common Scoter
Fulmar
Goldeneye
Cormorant
Kittiwake
Red-breasted Merganser
Herring Gull
Scaup
Shag
Guillemot
Great Crested Grebe
Gannet
Eider
Great Black-backed Gull
Common Gull
Red-/black-throated diver
9.5
12.7
19.4
23.7
30.5
31.4
51.2
52.0
58.8
59.5
59.5
63.0
66.6
71.8
72.8
74.2
76.5
76.5
83.7
The intensity of aggregation is calculated as the proportion (%) of
the area of the sea surface inhabited by the 75& of the total
number of the species compared to the area of the sea surface
which embraces the total range of the species in the two regions.
In other words the measure of the intensity of aggregation
increases as the part of the range occupied by 75% of the population increases. The species are ranked by (descending) degree of
concentration.
In Fig. 3 it can be seen that the selection of key areas to
many of the globally important species with their main occurrence in offshore waters (red-/black-throated diver, long-
x x x ( 2 0 0 7 ) x x x –x x x
7
tailed duck in the Baltic Sea; great skua and common guillemot in the North Sea) are sensitive towards the application
of higher reference density levels than four times the regional
density. During the selection process it was further evident
that the 20,000 birds criterion (Ramsar Convention criterion
3a) is generally inapplicable in marine habitats, as any larger
unit of area within our study regions proved to meet the criterion at any one season!
Our study in the North Sea and the Baltic Sea showed that
most areas are of value to more than one species. The ranking
of selected marine areas in the North Sea by total conservation value is shown in Fig. 5a and for the Baltic in Fig. 5b.
The classified marine areas in the Baltic Sea and North Sea
cover large proportions (30% and 34% respectively, Fig. 5a and
b of the studied regions. Yet, of the 9.19 million seabirds
found wintering in the Baltic Sea the selected areas cover
8.40 million birds, – equivalent to 91.4%! In the Baltic Sea,
the ten most important areas covered only 5% of the region.
For the species with clustered distribution of high regional
importance found wintering in the Baltic Sea more than
70% of the estimated total number of individuals occur within
the proposed areas, and in the North Sea more than 40–80% of
key species occur within the proposed areas. Another striking
general feature about the selected areas is that for the majority of species, more than half of the cumulated sum of proportions is held within the top four (Baltic Sea) or five (North Sea)
areas. In addition, more than 75% of the cumulative sum of
proportions is held within the top ten areas in both regions.
Thus, the case studies indicate that the areas selected on
the basis of the Marine Classification Criterion possess large
conservation potentials. This is corroborated by Hägerhäll
and Skov (1998) who showed that a satisfactory level of protection of many seabird species in the Baltic Sea may be
accomplished by conserving a smaller part of the classified
areas which overlaps coherent concentrations of other predators or other biota. It should be noted however, that our analyses refer to complete basins and do not take national
jurisdictions into account. Obviously, within an international
sea, important seabird areas may not be distributed equally
over the respective waters of the different countries around
that sea. Although from a biological perspective, selecting
the most important areas within a whole basis, or even within
larger, coherent biogeographical regions is clearly defendable,
this approach is currently not followed by the EU Bird Directive, which only considers national jurisdictions.
Our analysis did not include assessments of the fine-scale
temporal variability of selected areas or the distributions of
individual species. Although not a requirement for selection
of potential areas for conservation of seabirds, analysis of
the variability of the number of birds related to the selected
areas between seasons and years would form an important
prerequisite for drafting detailed management plans for these
areas.
In spite of the fact that the suggested Marine Classification
Criterion (MCC) is a modified version of the MCC criteria
implemented by Skov et al. (1995, 2000) the differences in
the resulting selection of areas are minor. Most areas selected
using the early version of the MCC were retained during this
analysis, and the boundaries were only modified slightly as an
effect of adding or deleting the boundary of a few concentra-
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B I O L O G I C A L C O N S E RVAT I O N
x x x ( 2 0 0 7 ) x x x –x x x
Fig. 5 – The location and extent of areas of international importance for seabirds selected on the basis of the MCC in (a) the
North Sea and (b) the Baltic Sea. The numbers refer to the priority ranking of the areas based on the sum of proportions of
total populations of seabirds supported.
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tions of moderate importance. As can be seen in Fig. 3, adjustments of the acceptance criteria for defining a concentration
of seabirds (2–7*D) have only a limited impact on the selection
of the top ten areas to seabirds in both study regions. This reflects the fact that the gradients in area importance and thus
in seabird densities play a significant role in shaping the
boundaries of the selected areas. It should be underlined,
however, that picking a value of four times the average density has been based on practical site selection processes
rather than scientific approaches. Hence, this element of
the MCC follows the history of selection of wetlands of international importance, in which an arbitrary 1% criterion has
proven a practical tool in wetland management.
The MCC was developed in view of the protected areas systems and seabird databases available or potentially available
for shallow shelf seas, like the North Sea and the Baltic Sea.
Thus, although the MCC is applicable for similar environments provided seabird line transect data are available, for
most marine areas, and certainly the deeper parts of the
ocean outside the shelf seas the MCC needs to be supplemented by techniques like habitat modeling based on tracking data. With the recent development of spatial prediction
modeling methods and the increasing electronic access to
vast sets of oceanographic and occurrence records from satellite tracking and other seabird telemetry studies, as illustrated by the Birdlife International’s ‘‘Ocean Wanderers’’
project (BirdLife International, 2004), the potential for achieving reliable estimates of gradients in some seabird distributions for vast expanses of ocean is rapidly increasing. Novel
habitat modeling methods, including both data-driven and
machine-learning methods, have the capacity to use presence-only records as tracking data and clearly outperform
more established statistical methods for eco-geographical
predictions (Elith et al., 2006). Thus, an application of the
MCC in ocean areas might be developed for tracking data
using statistics on time budgets rather than bird densities.
In 1990, BirdLife International launched the Dispersed Species Project with the aim of developing wide-scale habitat
conservation measures for European bird species that are in
need of conservation action. Seabird species of conservation
concern were identified by Tucker and Heath (1994) and strategies for the integration of habitat conservation and management have been drawn up for these species (Tasker and
Canova, 1997). Ours and other studies show that although
seabirds have large or very large ranges of occurrence at
sea, only a minority of species show truly dispersed distributions throughout their range, at least in shelf seas. The size of
aggregations and the difficulty of enforcement in offshore
waters, however entail that rather than establishing networks
of strict reserves, a realistic goal would be to develop networks of integrated management zones.
Acknowledgements
A significant part of the field work on which the initial MCC
tests were based was carried out within the frames of the
EPAS (Establishment of a Protected Areas network at Sea) project, funded through the European Union Directorate General
XI, ACE Contract No. 2242/90-09-011994. Additional funding
came from Netherlands Institute for Sea Research, the Nordic
x x x ( 2 0 0 7 ) x x x –x x x
9
Council of Ministers and the National Environmental Research Institute, Denmark. The study on the ESAS database
was funded by BirdLife International.
The EPAS surveys were undertaken by Ornis Consult A/S,
Netherlands Institute for Sea Research and the National Environmental Research Institute, Denmark, in collaboration with
the following coordinators of seabird surveys in the Baltic and
North Seas: Leif Nilsson and Per Andell, University of Lund,
Sweden, Martti Hario, Finnish Game and Fisheries Research
Institute, Finland, Andres Kuresoo, Institute of Zoology and
Botany, Estonia, Patrick Meire, Belgium Institute of Nature
Conservation, Antra Stipniece, Institute of Biology, Latvia,
Saulius Svazas, Institute of Ecology, Lithuania, Wlodzimiers
Meissner, University of Gdansk, Poland, Hans Wolfgang
Nehls, Rostock Zoological Garden, Germany and Jan Meissner,
University of Kiel, Germany. We greatly acknowledge their
help and support during the whole project. The surveys would
not have been possible without the support from hundreds of
observers participating in the International Waterfowl Census
around the Baltic Sea. Furthermore, a number of ornithologists from most Baltic and southern North Sea countries took
part in the air and ship surveys. We thank them all for their
great effort during the long and often cold surveys. We also
acknowledge the assistance and support from Wetlands
International.
The North Sea data were kindly supplied by the European
Seabirds at Sea database (ESAS) Danish National Environmental Research Institute, The Dutch National Institute for
Coastal and Marine Management, Norwegian Institute for
Nature Research, University of Lund, Sweden, Institut für
Vogelforschung, Germany, Free University Brussels, Belgium,
Institute for Nature Conservation, Belgium, Netherlands
Institute for Sea Research, Joint Nature Conservation Committee, Central Institute for Waterfowl Research and Wetland Protection, Germany, Ligue pour la Protection des
Oiseaux, France, Office National de la Chasse, France, The
Wildfowl & Wetlands Trust, United Kingdom, Samenwerkende Organisaties Vogelonderzoek Nederland (SOVON), The
Netherlands and Institut für Meereskunde an der Universität
Kiel, Germany.
An early version of the manuscript was improved by Professor Jon Fjeldså, Zoological Museum, Copenhagen and Ole
Norden Andersen, Danish Forest and Nature Agency.
R E F E R E N C E S
BirdLife International, 2004. Tracking ocean wanderers: the global
distribution of albatrosses and petrels : results from the Global
Procellariiform tracking workshop, 1–5 September, 2003,
Gordon’s Bay, South Africa, Cambridge.
Cressie, N.A.C., 1991. Statistics for Spatial Data. John Wiley and
Sons Inc., New York.
Durinck, J., Skov, H, Jensen, F.P., Pihl, S., 1994. Important Marine
Areas for Wintering Birds in the Baltic Sea. EU DG XI research
contract no. 2242/90-09-01. Ornis Consult Report.
Elith, J., Graham, C.H., Anderson, R.P., Dudik, M., Ferrier, S.,
Guisan, A., Hijmans, R.J., Huettmann, F., Leathwick, J.R.,
Lehmann, A., Li, J., Lohmann, L.G., Loiselle, B.A., Manion, G.,
Moritz, C., Nakamura, M., Nakazawa, Y., Overton, J.McC.,
Please cite this article in press as: Skov, H. et al., A quantitative method for evaluating the importance ..., Biol. Conserv.
(2007), doi:10.1016/j.biocon.2006.12.016
ARTICLE IN PRESS
10
B I O L O G I C A L C O N S E RVAT I O N
Peterson, A.T., Phillips, S.J., Richardson, K.S., Scachetti-Pereira,
R., Schapire, R.E., Sobéron, J., Silliams, S., Wisz, M.S.,
Zimmermann, N.E., 1998. Novel methods improve prediction
of species’ distributions from occurrence data. Ecography 29,
129–151.
EU Birds Directive, 1979. Council Directive of 2 April 1979 on the
conservation of wild birds (79/409/EEC). Official Journal of the
European Communities No. L103, 25-04-1979.
Fjeldså, J., Rahbek, C., 1998. Continent-wide conservation
priorities and diversification processes. In: Mace, G.M.,
Balmford, A., Ginsberg, M. (Eds.), Conservation in a Changing
World. Conservation Biology Series, Cambridge.
Grimmett, R.F.A., Jones, T.A., 1989. Important Bird Areas in
Europe. International Council for Bird Preservation,
Cambridge.
Hägerhäll, B., Skov, H. 1998. Proposal for offshore Protected Areas
(BSPAs). Report to HELCOM EC Nature. Ornis Consult report.
Hälterlein, B., Steinhardt, B., 1993. Brutvogelbestände an der
deutschen Nordseeküste im Jahre 1991 – fünfte Erfassung
durch die Arbeitsgemeinschaft ‘‘Seevogelschutz’’. Seevögel 14
(1), 1–5.
Heath, M.F., Evans, M.I., Hoccum, D.I., Payne, A.J., Peet, N.B., 2001.
Important Bird Areas in Europe: Priority Sites for
Conservation. BirdLife Conservation Series No. 8. vol. 2.
BirdLife International.
ICBP, 1992. Putting biodiversty on the map: priority areas for
global conservation. International Council for Bird
Preservation, Cambridge.
ICES, 2006. Current approached for identifying offshore seabird
aggregations and delineating Important Bird Areas (IBAs) and
Special Protection Areas (SPAs). Report of the Working Group
on Seabird Ecology (WGSE). ICES CM 2006/LRC:08.
IUCN, 1993. Parks for Life: Report of the IVth World Congress on
National Parks and Protected Areas. IUCN, Gland, Switzerland.
Jensen, F.P., 1993. EU Special Protection Areas and Ramsar sites.
Danish Ministry of Environment and Energy. Ornis Consult
Report (In Danish).
Johnston, C.M., Turnbull, C.G., Tasker, M.L., 2002. Natura 2000 in
UK Offshore Waters. JNCC Report 325. Joint Nature
Conservation Committee, Peterborough.
Kelleher, G., Kenchington, R., 1992. Guidelines for Establishing
Marine Protected Areas. A Marine Conservation and
Development Report. IUCN, Gland, Switzerland.
Lloyd, C., Tasker, M.L., Partridge, K., 1991. The Status of Seabirds
in Britain and Ireland. T&AD Poyser, London.
Myers, N., 1990. The biodiversity challenge: expanded hot-spots
analysis. Environmentalist 10, 243–256.
x x x ( 2 0 0 7 ) x x x –x x x
Ramsar Convention Bureau, 1988. Convention of Wetlands of
Internatinal Importance especially as waterfowl habitat. In:
Proceedings of the third meeting of the Conference of the
Contracting Parties. Regina, Saskatchewan, Canada; 27 May to
5 June 1987. Ramsar Convention Bureau, Switzerland.
Rose, P.M., Scott, D.A. 1994. Waterfowl population estimates.
IWRB Rapport No. 29.
Rose, P.M., Scott, D.A., 1997. Waterfowl Population Estimates,
second ed. Springer. p. 44.
Skov, H., Durinck, J., Leopold, M.F., Tasker, M.L., 1995. Important
Bird Areas for seabirds in the North Sea, including the Channel
and Kattegat. BirdLife International, Cambridge.
Skov, H., Vaitkus, G., Flensted, K.N., Grishanov, G., Kalamees, A.,
Kondratyev, A., Leivo, M., Luigujõe, L., Mayr, C., Rasmussen,
J.F., Raudonikis, L., Scheller, W., Sidlo, P.O., Stipniece, A.,
Struwe-Juhl, B., Welander, B., 2000. Inventory of Coastal and
Marine Important Bird Areas in the Baltic Sea. BirdLife
International, Cambridge.
Stone, C.J., Webb, A., Barton, C., Ratcliffe, N., Reed, T.C., Tasker,
M.L., Camphuysen, C.J., Pienkowski, M.W., 1995. An atlas of
seabird distribution in north-west European waters. Joint
Nature Conservation Committee. Peterborough.
Summerhayes, C.P., Hofmeyr, P.K., Rioux, R.H., 1974. Seabirds off
the southwestern coast of Africa. Ostrich 45, 83–109.
Tasker, M.L., Canova, L., 1997. Marine habitats. In: Tucker, G.M.,
Evans, I.M. (Eds.), Habitats for Birds in Europe. BirdLife
International, Cambridge, pp. 59–91.
Tasker, M.L., Jones, P.H., Dixon, T.J., Blake, B.F., 1984. Counting
seabirds at sea from ships: a review of methods employed
and a suggestion for a standardized approach. Auk 101,
567–577.
Tucker, G.M., Heath, M.F., 1994. Birds in Europe: Their
Conservation Status. BirdLife International, Cambridge, UK.
Vane-Wright, R.I., Humphries, C.J., Williams, P.H., 1991. What to
protect? – Systematics and the agony of choice. Biol. Conserv.
55, 235–254.
Webb, A., Durinck, J., 1992. Counting birds from ship. In: Komdeur,
J., Bertelsen, J., Cracknell, J. (Eds.), Manual for Aeroplane and
Ship Surveys of Waterfowl and Seabirds, vol. 19. IWRB Special
Publication, pp. 24–34.
Wetlands International, 2002. Waterfowl population estimates.
Wetlands International Global Series 12, third ed. The
Netherlands, Wageningen, p. 220.
Williams, P.H., 1998. Key sites for conservation: area-selection
methods for biodiversity. In: Mace, G.M., Balmford, A.,
Ginsberg, M. (Eds.), Conservation in a Changing World.
Conservation Biology Series, Cambridge.
Please cite this article in press as: Skov, H. et al., A quantitative method for evaluating the importance ..., Biol. Conserv.
(2007), doi:10.1016/j.biocon.2006.12.016