In freshwater (and estuarine) ecosystems, more so than in coastal or oceanic systems, such basic elements are finite and may be completely regulated, modified, or destroyed by human activities. Unlike marine cetaceans, many freshwater animals live in environments where the very availability of water can be in doubt.Īll freshwater cetaceans require adequate water flow and water quality within their range as basic elements of suitable habitat to support their physical health, mobility, and ability to forage efficiently and find prey. Some of these factors kill animals outright, and others impair their health or undermine their reproductive capabilities and social behavior. Vessel strikes, under-water explosions, the shock from electro-fishing, and entrapment in water management structures, notably irrigation canals, can cause injury or death. Freshwater cetaceans are also vulnerable to habitat modification and degradation (e.g., noise, chemical pollution, dams, lack of stream volume), and they compete with humans for prey.
Bycatch in fishing gear (entanglement or entrapment, usually leading to death) is the most serious and immediate problem for most populations, and gillnets are the greatest currently recognized cause of human-induced mortality. The threats to freshwater cetaceans are diverse, longstanding, and difficult to assess and manage. The Yangtze River dolphin (Lipotes vexillifer) was finally driven to extinction in the last two decades. Provisions for Managing Fisheries Interactionsįreshwater cetaceans (including six dolphin species and a porpoise) have declined dramatically in numbers and range, especially in Asia.Marine Mammal Commission: An Independent Agency of the U.S.
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