The state of world inland fishery resources
Farming carp from a village pond
Fishes, lampreys, amphibians, crustaceans and molluscs constitute the broad groups of inland resources that directly or indirectly support fisheries. Some 11 500 fish species - 41 percent of all fishes - are exclusively freshwater and about one 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 two 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 monitoring 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.