The Impact of Commercial Exploitation on Sawfish and Shark Populations in Lake Nicaragua

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Abstract
The Lake Nicaragua-Rio San Juan System harbors two classical examples of freshwater adaptation by elasmobranchs, the bull shark, Carcharhinus leucas, and the largetooth sawfish, Pristis perotteti. The bull shark is heavily concentrated around the river mouth and reproduces along the coast. The sparser population in the lake is recruited almost entirely through upstream movements from the lower river. Relatively heavy, year-round commercial fishing around the river mouth since the late 1960's has sharply reduced the shark population in the lake. Since the shark fishery is primarily in Costa Rican waters, control and management can be effected only by a cooperative agreement between Costa Rica and Nicaragua, which has not yet been reached. The sawfish lives and reproduces primarily in the lake, where until 1970 a heavy concentration occurred, with relatively few being found in the lower river. Since 1970 heavy commercial fishing for sawfish has been carried on in Lake Nicaragua. A sharp reduction in the population became evident within two years. Early and continued warnings were sounded and attempts were made by the Division of Fisheries to control the operation. However, controlling interest in the fishery was held by individuals highly placed in the government. They continued to fish with no regard for the survival of the sawfish, but with the sole purpose of exploiting the resource until it was no longer profitable, and the population in the lake was reduced to a dangerously low level. The Fisheries Institute of the new Nicaraguan government has finally placed in effect a two-year moratorium on the fishing of both sharks and sawfish in Lake Nicaragua and has started a program of research and monitoring of the sawfish population to develop a management program. Time will tell if the unique resource of Nicaragua has been saved.

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