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Tuesday, March 31, 2015

Lake Nicaragua shark

Posted to Maritime Musings (by on February 27, 2015

A wandering bull shark once common in a Central American lake

 The Lake Nicaragua shark is a common bull shark (Carcharhinus leucas) that has adapted to living, at least temporarily, in the fresh water of Lake Nicaragua and the San Juan River, which connects the lake to the Caribbean Sea.  Similar adaptive bull sharks have also been found in the Brisbane River (Queensland, Australia); in the Amazon River as far upstream as Iquitos, Peru; in the Ganges and Brahmaputra rivers of India and Bangladesh; in the Zambezi River in Mozambique; and in the St. Lucia Estuary of South Africa.  In the United States, bull sharks have been seen in the Mississippi River as far upstream as Alton, Illinois; in Lake Pontchartrain; and in the Potomac River.  The bull shark is categorized as a euryhaline fish, meaning that it can adapt to a wide range of salinities.  This category of fish, while in fresh water, excretes a reduced amount of sodium so as to maintain an acceptable level in its blood stream.  The Lake Nicaragua shark can grow up to eight feet in length and weigh up to 200 pounds, but this is uncommon.  Like other bull sharks, its upper portion is gray and its lower portion is white.  It prefers to eat bony fish, but will consume (or try to consume) almost any other animal that it encounters, including the occasional human.  During the Somoza regime in Nicaragua, a Japanese firm was granted a license to establish a shark-fin factory on the western shore of the lake near Grenada.  As a result, the number of sharks in Lake Nicaragua and the river was substantially reduced.  It has never recovered, even though the factory closed in the 1970s.  While sharks continue to be found in both the lake and the river, their presence is noticeably lower than during the pre-shark-fin era.  Targeting of sharks by fishing is now prohibited in the fresh waters of Nicaragua, but they continue to be incidental by-catch.

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