African Tilapia in Lake Nicaragua Author(s): Kenneth R. McKaye, Joseph D. Ryan, Jay R. Stauffer, Jr., Lorenzo J. Lopez Perez, Gabriel I. Vega, Eric P. van den Berghe Source: BioScience, Vol. 45, No. 6 (Jun., 1995), pp. 406-411 Published by: University of California Press on behalf of the American Institute of Biological Sciences Stable URL: http://www.jstor.org/stable/1312721 . Accessed: 29/08/2011 17:58 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. University of California Press and American Institute of Biological Sciences are collaborating with JSTOR to digitize, preserve and extend access to BioScience. http://www.jstor.org African Tilapia in Lake Nicaragua Ecosystem in transition Kenneth R. McKaye, Joseph D. Ryan, Jay R. Stauffer Jr., Lorenzo J. Lopez Perez, Gabriel I. Vega, and Eric P. van den Berghe L ake Nicaragua contains more (1.17 x 105 km2) flow into the Car- than 40 species of fish, in- ibbean Sea and discharge an im- cluding 16 recognized spe- Swift, aggressive mense amount of fresh water (ap- cies (Thorson 1976) of native management of tilapia proximately 2.6 x 1011 m3) and cichlids and additional undescribed suspended sediments along the 450 cichlids.1 The lake is also inhabited is needed to mitigate km of coast. Ten biologically rich by several large marine predators, estuaries, whose waters oscillate be- such as the bull shark (Charch- the negative impacts of tween fresh in the rainy season to arhinus leucas), sawfish (Pristis moderately saline during the dry perotteti), tarpon (Tarpon atlan- their introduction season, act as nursery areas for many ticus), grunt (Pomadasys spp.), and marine species. These highly pro- snook ductive fisheries a livelihood (Centropomus parallelus; cated in a tectonic which provide Thorson Eleven of the 16 depression, for the of the 1976). extends northwest from the mouth people region. Popula- cichlid are confined to San tions of of the fish species of the Rio San to the Gulf of many species which contains the Juan extend into Lake and Juan Province, Fonseca in the Pacific. The Nicaragua, lake The most depres- hence that occurs (Miller 1966). heavily sion also includes the smaller Lake any perturbation resources have tra- in one can exploited fishery called system severely impact been the native Managua (also Xolotlan). the other. In order for a coastal ditionally cichlids, Numerous rivers flow into these two upon estimated to constitute 58% to be effective, it currently but the Rio San management plan of Lake fish biomass. lakes, only Juan must both the estuarine Nicaragua's drains this into the Carib- encompass Lake 1), the system systems and Lake Nicaragua (Ryan Nicaragua (Figure bean Sea. The Rio San Juan passes largest (8264 km2) tropical lake out- et al. 1993). through the productive Atlantic side of Africa (Incer 1976), is lo- The Lake Nicaragua ecosystem is Coast-region of Nicaragua. This of Lake Nicara- currently undergoing major ecologi- ecosystem cal changes. An extensive stocking is, therefore, intimately con- Kenneth R. McKaye is a professor of gua program introduced African tilapia and fisheries and coor- nected with the Caribbean Sea and tropical ecology (genus Oreochromis) into the lake dinator of international research pro- adjacent coastal habitats. The most in the 1980s. Native cichlid D. is a re- popula- grams, Joseph Ryan faculty famous result of this connection is tions have declined as introduced search Lorenzo Perez assistant, J. Lopez the migration of a shark, known as invade lake areas. The col- is a research assistant, and Eric P. van tilapia the freshwater shark of Lake Nica- of one of the world's den Bergheis a professor of fisheries at which in is the Carib- lapse unique Labo- ragua, reality freshwater is imminent the Appalachian Environmental bean bull C. leucus. ecosystems Center for Environmental and shark, if corrective measures are not taken. ratory, The Caribbean Coast of Nicara- Estaurine Studies, in the University of gua is biologically one of the most Maryland System, Frostburg, MD Historical 21532, and Universidad Centroamer- productive and speciose systems in perspectives Gabriel the world 1992, et al. icana, Managua, Nicaragua. (Ryan Ryan Lake Nicaragua and the Rio San I. Vega is an ecology student at 1993). It receives a large amount of have attracted the atten- Centroamericana. Juan long the Universidad Jay yearly rainfall, estimated at 4-6 m. tion of the world due to their strate- R. Stauffer is a of Jr. professor ichthyol- Fourteen primary rivers, drain- location for an in- at the School of Forest Resources, gic constructing ogy ing 90% of the country's watershed teroceanic canal. Such a Pennsylvania State University, Univer- project sity Park, PA 16802. ? 1995 American would require deepening portions Institute of Biological Sciences. 1K. R. McKaye, personal observation. of the river and lake and cutting 406 BioScience Vol. 45 No. 6 . T6; ig, ~"- . ..~'=*, ........ ''.'o.,,:,.--'-... CH!C i.:''~' . ..'-"? ;..,,,~. ~,.,..?~,:e,.,:,:=:....;:::....=> ' ~ _ -, BRITIMECANAL CE. R,No CAqGC-oF CRA 1902X Figure 1. Map of the proposed canal route through Lake Nicaragua in 1902. through the low-lying mountains of and thus a tempting target for pi- kilometer road was constructed to the Isthmus of Rivas (20 km wide at rates. his new port of San Juan del Sur on its narrowest section) to the Pacific After the end of the colonial era, the Pacific coast. Greytown (San Ocean (Figure 1). The project, how- the possibility of an interoceanic Juan del Norte), located at the mouth ever, never materialized. In 1903 connection and the emergence of of the San Juan River, was to remain Panama, with help from the United the United States as a commercial the most important port in Nicara- States, achieved independence from power generated renewed interest in gua until the turn of the century Columbia. The United States then Nicaragua. With the discovery of (Incer 1976). took control of the construction of gold in California in 1848, a rapid With the enhanced importance of the Panama Canal and was no longer route to the gold fields was required, the canal route came increased po- interested in a possible second ca- and Commodore Cornelius Vander- litical interest by the great powers nal. bilt, the US shipping tycoon, real- of the day-Great Britain and the During the Spanish colonial rule ized immediately the importance of United States. William Walker, a (1520-1821), Lake Nicaragua and a Nicaraguan route. He organized filibuster invited by the Nicaraguan the Rio San Juan served as the pri- the Accessory Transit Company Liberals, arrived in Nicaragua in mary highway through which gold, (ATC) and paid the Nicaraguan gov- 1855 and shortly thereafter declared cacao, indigo, and other products of ernment $10,000 for the right to himself president of Nicaragua. Central America reached the Span- cross the country by river and lake. Walker's goal, with the support of ish galleons, which were constantly The creation of this new route would men and material from the slave- being pursued by British and other cut 800 km and several days off the owning US South, was to annex European buccaneers. Several times trip of the anxious prospectors. Nicaragua to the United States. His these pirates, including Sir Francis The first man-made alteration to presidency was initially recognized Drake, sailed up the Rio San Juan to Lake Nicaragua's ecosystem oc- by the US ambassador in Nicara- attack Granada (located on the fur- curred at this time as Vanderbilt gua. This initial recognition was sub- thest northwestern shore of the lake), arranged for portions of the Rio San sequently withdrawn from Wash- where our primary study sites are Juan to be dredged and for large ington, DC, due to pressure from now located (Figure 1). During co- boulders, sand bars, and other ob- Great Britain and the Central Ameri- lonial times Granada was a world- stacles to be blasted away. Docks can governments that recognized the renowned and exceedingly rich port, were built on both coasts and a 20- Nicaraguan Conservative govern- June 1995 407 of the Sandinista revolution in 1979. Both Japanese and Soviet interest in a canal route in the 1980s stimu- lated research on the lake ecosys- tem, the results of which remain unpublished in the scientific litera- ture2 (MEPURSS1983). A plan for a canal, however, was eventually pre- sented by the Japanese with an esti- mated cost of $25 billion (Estrada et al. 1994). The US government be- gan to view with alarm these initia- tives for developing another canal outside of US control and continued to arm and aid the contra movement in its efforts to overthrow the Sandinista government. Many proposals are still being considered, and even today the pos- sibility of a canal through Lake Nica- Figure 2. Common cichlids of Lake Nicaragua. The two large individuals on the ragua and the Rio San Juan is a right are African Oreochromis spp. All others are native to Lake Nicaragua. continuing dream of many Nicara- guans (Estrada et al. 1994). Any ment. Nevertheless, it was to be the the army of Honduras when he tried such project, be it a sea-level canal beginning of a long period of inter- to reconquer Central America. that turns Lake Nicaragua into a vention of the United States in Nica- At the end of the nineteenth cen- marine ecosystem or one that uses raguan affairs.