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Fishes, lampreys, amphibians, crustaceans and
molluscs constitute the broad groups of inland
resources that directly or indirectly support
fisheries (see FAO Fisheries Species
Identification and Data Programme and the
ASFIS list of species for statistics). Some
11 500 fish species - 41 percent of all fishes
- are exclusively freshwater and about 1 percent
are diadromous.
A relatively large body of knowledge about
taxonomies and life histories of many individual
species exists and much of it has been compiled and
disseminated as FishBase. However, as many
countries do not individually identify species or
species groups when reporting inland capture
statistics, there are no geographically
comprehensive estimates of the state of inland
water resources. Overall, some 45 percent of inland
fish capture is unidentified; similarly, this
figure stands at 7 percent for molluscs and 6
percent for crustaceans.
Underreporting is another significant problem.
Failure to account fully for inland capture is
costly in terms of decreased, or lost,
opportunities to increase food security and
other social and economic benefits from inland
fisheries.
Due to statistical problems, the state of inland
water resources must be implied from other
information. Trends in annual capture data provide
one line of evidence. Globally, the trend for
capture has been for modest annual increases of
about 2 percent during the last two decades of the
twentieth century. From a continental perspective,
trends show increases in Asia, Africa and Latin
America, decreases in the Commonwealth of
Independent States and Baltic States (former USSR),
North America and Europe, and stability in
Oceania.
Another line of evidence on the state of inland
resources comes from the status and trends of
ecosystems. Generally, it can be inferred that
aquatic ecosystems are in a state of decline
throughout most of the world. How can this be
reconciled with an apparent trend for increases in
capture output from inland resources?
One reason is a human-induced enriching of
aquatic systems from agriculture and urban sources
to produce more fish. Another is that that the
combined effects of fishing and physical and
chemical changes in inland waters have caused a
shift to species that are more productive per unit
of area, weight-wise, but may be of lesser economic
value. Better governance -- with attention to
aquatic ecosystem management such as
habitat enhancement and stocking
interventions -- along with broad approaches to
management, such as integrated watershed
management, also increase inland output.
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