nets are an even greater concern with a bycatch of up to 3000 dolphins per year. Dolphins that are bycaught often end up as shark bait for longline fisheries. There is not enough data to conclude total bycatch for the Philippines. Initial assessment indicates that bycatch is not sustainable. Monitoring of dolphin populations and fisheries is urgently needed. Yangtze River dolphins and finless porpoises The Yangtze River or Baiji dolphin (Lipotes vexillifer) is the most endangered cetacean and is only found in the Yangtze River, China. A survey conducted in 1997 found only thirteen dolphins. The Yangtze River finless porpoise (Neophocaena phocaenoides asiaeorientalis) also lives in the Yangtze River. Abundance has declined and there are fewer than 2000 dolphins left. This may be due, in part, to the construction of the Three Gorges Dam which covers a significant amount of the dolphin’s habitat. Both species are often subject to entanglement in gillnets. Vaquita The vaquita (Phocoena sinus) is highly endangered and is endemic to the upper Gulf of California, Mexico. They are killed in both gillnets and trawl nets from commercial and artisanal fishing. As of 2004 there are less than 100 vaquitas left in the Gulf of California. Mitigating bycatch Acoustic deterrent devices The use of acoustic alarms to mitigate by-catch and also to protect aquaculture sites has been proposed but has advantages and risks associated with the alarms. Acoustic deterrent devices, or pingers, have reduced the number of cetaceans caught in gill nets. Harbour porpoises have been effectively excluded from bottom-set gill nets during many experiments for instance in the Gulf of Maine, along the Olympic Peninsula, in the Bay of Fundy, and in the North Sea. All of these studies show up to a 90% decrease in harbour porpoise bycatch. Pingers work because they produce a sound that is aversive (20; 15). There has been a recent re-evaluation of the potential of pingers and their use in other fisheries due to their growing success. An experiment on the California drift gill net fishery demonstrated how acoustic pingers reduce marine mammal bycatch. It was shown that bycatch was significantly reduced for common dolphins and sea lions. Bycatch rates were also lower for other cetacean species like the Northern right whale dolphin, Pacific white-sided dolphin, Risso’s dolphin and Dall's porpoise. It is agreed upon that the more pingers on a net, the less bycatch. There was a 12-fold decrease