Geoscience Reference
In-Depth Information
Detailed and comprehensive inventories such
as the one mentioned above are, however, both
expensive and time consuming. Most scientii c
studies have opted to focus on specii c wetland
sites, particular wetland types, or target groups
of organisms such as i sh, birds, and amphibians
(Brinson and Malvárez 2002; Tockner and Stan-
ford 2002; Deil 2005; Keddy et al. 2009). Such
detailed analyses provide a wealth of informa-
tion on unique habitat conditions, migratory
and threatened species, non-native invasive
species, and changing land-use conditions
within and around wetland sites.
Wetlands are crucial for supporting i sh popu-
lations. They provide food, shelter, spawning,
and nursery areas for both marine and inland
fresh-water species. Riverine wetlands are home
to a wide diversity of i sh species and these are
often uniquely adapted to survive l uctuations in
water levels and nutrient inputs based on l ood
events. For example, the seasonal l ood cycle of
southern Africa's Okavango River starting in
November drives a proportion of its 80 i sh
species from the main river channels into ephem-
erally l ooded areas (Merron and Bruton 1995;
Scott 2010). Similarly, the Sudd region of the
upper Nile River l oodplain spans across Sudan,
Ethiopia and Uganda and records some 118
species of i sh. Many of these species migrate
into nutrient-rich seasonally l ooded plains
and coincide their breeding and spawning
with the l oods to ensure adequate food for
juvenile i sh (Peck and Thieme 2010). Such l ood
pulses initiate ecological processes between
different components of a riverine ecosystem.
Other adaptations to variable salinity levels
allow migrating i sh such as salmon and trout to
move through fresh-water, estuarine and marine
habitats. The Chinook salmon (
Oncorhynchus
tshawytscha
), for instance, migrates hundreds of
kilometers from the Bering Sea to the upper
tributaries of the Yukon River in North America
to spawn (Burridge and Mandrak 2010).
Wetlands are also home to both resident and
migratory species of birds. Marsh habitats that
serve as migration stopover points for birds
traveling between wintering and breeding areas
provide vital food reserves. The conservation of
interconnected wetlands along major l yways is
critical to maintaining successful populations of
migrating bird species. This may be particularly
difi cult as the three major global l yways: the
Americas, the African-Eurasian and the East
Asia-Australasian, each span dozens of individ-
ual countries with unique sets of conservation
challenges.
The case of the Siberian crane (
Grus leuco-
geranus
), which once wintered in northern
India, provides one example. The migrating
population of the endangered Siberian crane
had been reduced to critical numbers in recent
decades. In most years just a handful of mating
pairs reached their wintering grounds in Keo-
ladeo National Park in Rajasthan, India. However,
the crane has not been spotted there since 2002.
The loss of wetland stopover sites along its
migratory route from central Siberia through
central Asian countries and Afghanistan into
northern India has been identii ed as one of the
main reasons for its disappearance (BirdLife
International 2010a). Other factors that have
been suggested as possible contributors to the
problem include the crane hunting tradition in
Afghanistan (a l yover country) and the decline
in forage areas within Keoladeo due to buffalo
grazing (Boojh, Patry and Smart 2008). With
vanishing wetlands, a few remaining areas
provide relief to large numbers of migrating
birds and are soon unable to sustain large visit-
ing populations. Moreover, such wetland oases,
in the absence of protection and active manage-
ment, may be particularly vulnerable to and
inl uenced by surrounding land-use change, sea-
sonal rainfall patterns, habitat fragmentation,
and changes to hydrological conditions. Organi-
zations such as BirdLife International target
these issues by working with local partners in
different countries to raise awareness, promote
conservation efforts, identify threatened bird
species, and develop comprehensive conserva-
tion action plans (BirdLife International 2010b).
Numerous physical, economic, political, and
socio-cultural factors contribute to the loss of
wetland habitat and consequentially a reduction
of their biodiversity. For any given region, it is
usually the combination of several different
factors that leads to habitat loss. These include
the following:
