Decline of freshwater fishes and fisheries in selected drainages of west-central Mexico

The unique freshwater fishes and fisheries of west-central Mexico are sharply declining because of environmental degradation. In the Lerma River basin, half of the localities that once supported fish communities either no longer have water or are so polluted that fish cannot survive. Of 44 native fishes, 3 are now extinct, and 23 are greatly reduced in range or abundance. In Lake Chapala, total fisheries production has actually increased despite major declines in water quantity and quality, but the fisheries for several valuable native species have declined or collapsed, and exotics now constitute a substantial portion of the catch. In the Ayuquila River, several species have been locally extirpated, and major untreated industrial and municipal discharges, coupled with substantial water withdrawals for irrigation, preclude fish life during the dry season in 20 km of river that once supported an important subsistence fishery. Conservation priorities include protecting localities that still retain native fish assemblages, reducing water withdrawals and pollution discharges, and controlling fishing effort and harvest better. These efforts in west-central Mexico would benefit from increased collaboration among Mexican, U.S., and Canadian fisheries professionals.