aquatic ecosystem health &...

This article was downloaded by:[Canadian Research Knowledge Network][Canadian Research Knowledge Network]

On: 15 June 2007Access Details: [subscription number 770938029]Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Aquatic Ecosystem Health &ManagementPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713393886

The freshwater habitats, fishes, and fisheries of theOrinoco River basin

To cite this Article: Rodríguez, Marco A., Winemiller, Kirk O., Lewis Jr., William M.and Baechle, Donald C. Taphorn , 'The freshwater habitats, fishes, and fisheries ofthe Orinoco River basin', Aquatic Ecosystem Health & Management, 10:2, 140 - 152To link to this article: DOI: 10.1080/14634980701350686URL: http://dx.doi.org/10.1080/14634980701350686

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf

This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction,re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expresslyforbidden.

The publisher does not give any warranty express or implied or make any representation that the contents will becomplete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should beindependently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings,demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with orarising out of the use of this material.

© Taylor and Francis 2007

http://www.informaworld.com/smpp/title~content=t713393886

http://dx.doi.org/10.1080/14634980701350686

http://www.informaworld.com/terms-and-conditions-of-access.pdf

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007

The freshwater habitats, fishes, and fisheriesof the Orinoco River basin

Marco A. Rodrıguez,1∗ Kirk O. Winemiller,2 William M. Lewis, Jr.,3

and Donald C. Taphorn Baechle41Departement de chimie-biologie, Universite du Quebec a Trois-Rivieres, 3351 boul. des Forges, Trois-Rivieres,

Quebec, G9A 5H7, Canada2Ecology and Evolutionary Biology, Dept. of Wildlife and Fisheries Sciences, Texas A&M University, 2258 TAMU

College Station, TX 778943-2258, USA3Professor and Director, Center for Limnology, Cooperative Institute for Research in Environmental Sciences,

University of Colorado, Boulder, Colorado, USA4UNELLEZ, BioCentro, Mesa de Cavacas, Guanare, Estado Portuguesa, Venezuela 3310

∗Corresponding author: Fax: (819) 376-5084; E-mail: [email protected]

The Orinoco River of Venezuela and Colombia is one of the great rivers of the world, ranking thirdby discharge after the Amazon and the Congo. In the Orinoco basin, riverine and floodplain habitats,including riparian forests, play key roles in the conservation of biodiversity and support commercial,sport, and subsistence fisheries. The basin’s three major floodplains regulate the amplitude and duration offloods, maintain fertile agricultural terrain, provide habitat for numerous terrestrial and aquatic species,and support the fishery. The fish fauna, which includes some 1,000 species, encompasses a great deal ofecological diversity in terms of geographic distributions, habitat affinities, functional morphology, andreproductive and feeding strategies. The Orinoco fishery is still multispecific, with around 80 differentspecies found in the fish markets at different times of year. Current estimates indicate that annual sustainableyield is 40,000 – 45,000 metric tons. Fish culture in the region is underdeveloped despite decades of researchand promotion. There is no serious commercial trade for ornamental fishes. Large regions of the Orinocobasin are still in a relatively pristine state, but aquatic resources are increasingly threatened by habitatdestruction, overharvesting, pollution, and hydrological perturbation. Scientific understanding of diversityhotspots, critical habitats, and conservation status of fishes in the basin is currently insufficient to satisfymanagement needs. Compliance to fishery regulations is low and fishing is drastically modifying the relativeabundance, population structure, and distribution of fish stocks. However, many sectors of the Orinoco basinare unexploited or only lightly exploited, and fish stocks can recover quickly if given the opportunity. Stricterenforcement of current fishery regulations would reduce the likelihood of stock collapses and other, possiblyirreversible, changes in the fishery.

Keywords: Aquatic resources, conservation, ecology, management, neotropical, floodplain, Venezuela

IntroductionThe Orinoco River basin is a vast reservoir of nat-

ural resources. Aquatic habitats in the basin support

commercial, sport, and subsistence fisheries, andharbor tremendous biodiversity, including variousspecies of emblematic value for conservation ini-tiatives, such as the Orinoco crocodile, the Arrau

140

Aquatic Ecosystem Health & Management, 10(2):140–152, 2007. Copyright C© 2007 AEHMS. ISSN: 1463-4988 print / 1539-4077 onlineDOI: 10.1080/14634980701350686

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007

Rodrıguez et al. / Aquatic Ecosystem Health and Management 10 (2007) 140–152 141

sideneck turtle, the Caribbean manatee, freshwa-ter dolphins, and the giant river otter. As well,the Orinoco basin is inhabited by many indigenouscultures that derive sustenance from its resources.Although vast areas within the basin have been his-torically subjected only to mild anthropogenic pres-sures and are still in a relatively pristine state, threatsfrom habitat destruction, overharvesting, pollution,and hydrological perturbation are rising.

This article summarizes the state of knowledgeon the freshwater habitats, fishes, and fisheries of theOrinoco River basin, with particular attention to theregion within Venezuela, which accounts for 71%of the total basin area. The focus is primarily on (1)the aquatic habitats of the Orinoco main stem, itstributaries, and their floodplains; (2) fish systemat-ics, ecology, and conservation; and (3) fisheries andfish culture, including current legislation.

Overview of freshwater resources,freshwater fish fauna, andfreshwater fisheries of theOrinoco basin

The Orinoco River of Venezuela and Colombiais one of the great rivers of the world, ranking thirdby discharge (38,000 m3 s−1) after the Amazon andthe Congo. The environmental and biotic compo-nents of the Orinoco River ecosystem are describedin Weibezhan et al. (1990), the proceedings of a sym-posium on large South American rivers published in1990 as a special issue of the journal Interciencia,Vol. 15(6), and Lewis et al. (2000).

The Orinoco River basin extends over 1.1 mil-lion km2 and covers 84% of Venezuela’s territory.The basin is bounded on its entire southern marginby the Rio Negro, a major Amazon tributary, and onthe north and west by coastal drainages of the Andes(Figure 1). The southern side of the drainage is al-most entirely accounted for by the Guayana Shield inthe states of Bolıvar and Amazonas, which consistsof thoroughly weathered crystalline basement rock.To the north and west, the Orinoco is flanked for adistance of several hundred kilometers by alluvialdeposits of Andean origin. Toward the periphery ofthe watershed, beyond these deposits, the northernand western headwaters of the Orinoco rise in theAndean montane zone at elevations above 3000 m.

The southern part of the Orinoco basin (GuayanaShield and western portion of Andean montane andalluvial zones) has high annual precipitation (1,000–

4,000 mm y−1), whereas the alluvial zones of thenorth are semiarid. The area-weighted precipitationof the entire basin (2,000 mm y−1) is approximatelyequal to that of the Amazon basin (Lewis et al.,1995). The wettest portions of the watershed (gen-erally to the south) consist of tropical moist forest,whereas the low-elevation portion of the northernhalf of the watershed is primarily savanna grassland(Figure 2). Precipitation in the Orinoco basin showsstrong seasonality. River discharges throughout thewatershed increase from approximately April toAugust and decrease thereafter to a plateau that lastsapproximately two months (February, March). Theannual range in water levels for the Orinoco lowermain stem is approximately 12 m.

The taxonomically rich fish fauna of the Orinocobasin encompasses a great deal of ecological di-versity in terms of geographic distributions, habitataffinities, functional morphology, and reproductiveand feeding strategies. The morphological diversityencompassed in local fish assemblages of the highplains (“Llanos”) is greater than that observed infish assemblages in comparable habitats in NorthAmerica, Central America, and Africa (Winemiller,1991). The latest published species lists (Taphornet al., 1997; Lasso et al., 2004a) include some1,200 freshwater fishes, most of them from theOrinoco basin. Machado-Allison (1993) provides anoverview of the natural history, ecology, and bio-geography of the fishes of the Venezuelan llanos.

Novoa (1982, 1989, 2002) reviewed the statusof commercial fisheries in the Orinoco River. Thelargest inland fishery in Venezuela is centered atSan Fernando de Apure in the western llanos. TheOrinoco River and its marginal lakes, wetlands, andtributaries also support commercial fisheries, withmajor markets located in Puerto Ayacucho, Guasdu-alito, Bruzual, Caicara del Orinoco, Maripa, CiudadBolıvar, Ciudad Guayana, and Barrancas. A greatvariety of species are exploited, with dominant fishesin the harvest varying according to region and timeof year.

The most important sportfishes in Venezuela arethe pavones, or peacock cichlids (Cichla spp.). Theirecology, distribution, and conservation challengeswere summarized by Winemiller (2001). Other pop-ular sport fishes include the payara (Hydrolycusarmatus) and large pimelodid catfishes includingthe bagres rayados (Pseudoplatystoma fasciatum,P. tigrinum), valenton (Brachyplatystoma filamento-sum), and cajaro (Phractocephalus hemioliopterus).These species remain common in rivers of the llanos,

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007

142 Rodrıguez et al. / Aquatic Ecosystem Health and Management 10 (2007) 140–152

Figure 1. Map of the Orinoco River basin, showing major geographic regions, tributaries, cities, and the three major types of floodplain(internal delta, fringing floodplain, and Orinoco delta). The extent of the inundation on the internal delta was kindly provided by S.K.Hamilton (Michigan State University).

Figure 2. Map of the Orinoco River basin, showing the distribution of major vegetation types.

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007


Guayana Shield, and Amazonas. Two migratorycharacids, the saltador (Salminus hilarii) and thepalambra (Brycon whitei), are also popular fish withanglers.

Fish culture centers on the cachama (Colos-soma macropomum) (reviewed in Ginelly, 1990),which dominates commercial production, and theexotic “tilapias” (includes Tilapia, Oreochromis,and Sarotherodon spp.). Cultivation of cachama andits hybrid with the morocoto (Piaractus brachypo-mus) has been practiced for many years.

There is no serious commercial trade for orna-mental fishes in Venezuela. Ornamental fishes havebeen harvested from the wild by a few companies,but these ventures have not persisted, probably be-cause of administrative hurdles to exportation. Tradestatistics are not reliable because an unknown andpossibly large proportion of all exportation is madeillegally via Colombia from the Amazonas region.However, overexploitation does not seem to be a ma-jor concern because operations are on a relativelysmall scale.

State of freshwater science in theOrinoco Basin

Habitats of the Orinoco Riverand its tributaries

Aquatic habitats available to fishes and otheraquatic organisms vary partly by climate and ge-omorphology and partly by stream order. Lakes arerare, except on floodplains; there is only one largereservoir (Guri, on the Caronı). The small streams ofthe Guayana Shield are predominantly canopied andhave relatively low gradient, with the notable excep-tion of streams and rivers that flow from the edgesof tepuys. The waters from the south are predom-inantly darkly colored by dissolved organic matterof terrestrial origin (”black waters”), although someare clear waters as well. Major tributaries emergefrom the canopy, but are generally deep because ofthe abundance of rainfall and, because they are pri-marily darkly colored, do not efficiently transmit ir-radiance to the substrate. Also the substrate is oftenfine and mobile, which reduces habitat diversity forboth fish and benthic invertebrates.

To the north, tributaries of small to intermediatesize flow at high gradient from the flanks of the An-des over substrate of moderate to high coarsenessbeneath waters that typically are highly transparent

except at times of highest flow, when turbidity in-tercepts light. Thus, the benthic habitat is suitablefor a diversity of both fishes and aquatic inverte-brates. On the alluvial plains, the gradients are low.The seasonal turbidity of these “white waters” canbe high (Saunders and Lewis, 1988), but the smalleramounts of runoff per unit area and the large amountof moving alluvial material in the channels promotesthe development of shallow stream channels that canproduce benthic algal growth at low flow and oftenare connected to off-channel waters that diversifyaquatic habitat.

The white waters contain large amounts of dis-solved and suspended solids produced by rapidweathering in the Andes. In contrast, the black wa-ters flow primarily through the Guayana Shield,which has been weathered so extensively that ityields only small amounts of suspended and dis-solved solids. Because it receives both white-waterand black-water tributaries, the Orinoco is a mix-ture of water types of sharply contrasting physical,chemical, and biological characteristics.

Floodplains are habitats of great consequence tothe aquatic fauna and flora of the Orinoco basin.There are three major types of floodplains withinthe Orinoco basin (Lewis et al., 1995; Figure 2).The Orinoco delta (∼21,000 km2) consists mainly offloodplain overlying deltaic deposits and dissectedby a large number of distributary channels. Aquaticgrasses predominate in the freshwater portions ofthis floodplain, about which very little is known.

Along the main stem, extending from the deltato the Apure (approximately 600 km), a fringingfloodplain (∼700 km2) encompasses both banksbut is considerably wider on the north than on thesouth. The fringing floodplain is approximately 79%canopied. The uncanopied portion of the fringingfloodplain corresponds to 2300 topographic depres-sions that can be called floodplain lakes. They arejoined with each other and with the surroundingcanopied areas at high water, but are isolated duringthe dry season. Within the uncanopied areas, Pas-palum repens, an aquatic C4 grass, is the dominantvascular plant, although other vascular plants arepresent as well. Paspalum provides critical physicalhabitat for floodplain invertebrates and fishes (Lewiset al., 2000; Valbo-Jørgensen et al., 2000). Althoughwater persists within the lakes during the prolongedseasonal drought (approximately 100 days), habitatspace shrinks at this time to a small percentage ofits annual maximum. Thus, fishes and other aquaticorganisms must contend with strictly lacustrine

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007


conditions of the dry season, but also may exploitresources on the floodplain at large during the in-terval of full inundation. Benthic environments ofthe Orinoco floodplain typically are oxygenated, andthus are more habitable than similar environmentsof the Amazon, which may become anoxic (Lewiset al., 1995). Accumulation of organic sediment isnegligible on the floodplain because of high oxida-tion rates; the substrates of the floodplain lakes areprimarily fine and inorganic.

The third floodplain of the Orinoco consists of anlarge internal delta near the Apure River (∼70,000km2) that forms as seasonal floodwaters moving to-ward the main stem are impeded by the high vol-ume of water in the main stem. Thus impounded,the water fills depressions and spreads over much ofthe landscape, where it provides temporary aquatichabitat over many thousand square km to the northof the Orinoco main stem. These shallow ephemeralhabitats are highly productive during the wet season.As rainfall and floodwaters subside drying poolsoften become anoxic, with struggling fishes pro-viding an abundant food resource for birds andcrocodilians.

In the main stem of the Orinoco itself, habitat forfishes and invertebrates is limited. If found in themain stem Orinoco at all, most fish species in thebasin seem to use this habitat for dispersal betweenbackwaters and tributaries. Nonetheless, a compar-atively small community of specialized fishes feedswithin lotic waters of the main stem (Lundberg et al.,1987; Barbarino Duque and Winemiller, 2003).

Multiple sources of carbon are available to pri-mary consumers on the Orinoco floodplain: phy-toplanktonic and periphytic algae, macrophytes,litterfall, and organic matter transported by theriver. Trophic flows from primary producers to topconsumers on the Orinoco floodplain have beenanalysed by means of estimation of P:B ratios com-bined with trophic-level analysis through stable iso-tope tracers (Lewis et al., 2001). Strikingly, althoughmacrophytes and litter jointly account for ∼98% oftotal available carbon, production of both fish and in-vertebrates on the floodplain is supported primarilyby algal carbon. Many fish of the Orinoco flood-plain have adaptations for feeding directly on al-gae, a nutritious source of carbon that accounts forapproximately 20% of fish production, or on her-bivorous invertebrates, which account for most ofthe remaining 80%. Fish production is thus derivedmostly from the 1st and 2nd trophic levels, ratherthan at and above the 2nd level as is more usual

for fishes in pelagic ecosystems. Food webs of theOrinoco floodplain and its major tributaries (Jepsenand Winemiller, 2002) therefore show marked foodchain compression, which is the only means of sus-taining high fish production on such a small fractionof the potentially available carbon.

Current state of knowledgeof Orinoco fishes

Venezuelan and Colombian ichthyologists havecollaborated on a complete revision and update ofthe list of freshwater fishes of the Orinoco basin, in-cluding lists for each major Orinoco tributary (Lassoet al., 2004b). The most current estimate places thespecies richness for the Orinoco basin at 995 fishspecies, of which 939 are found in Venezuela and627 in Colombia (Lasso et al., 2004a, b), but newspecies are being described every year. Nearly 85%of the species, including those most important tofisheries and aquaculture, fall within three majororders, the Characiformes, Siluriformes, and Per-ciformes (Table 1).

Within the Orinoco basin, two basic biogeo-graphic divisions of the ichthyofauna can be rec-ognized, each associated with a distinctive watertype. The first division is found in the sediment-and nutrient-rich whitewaters concentrated in thenorthern portion of the drainage, such as the Apureand Meta Rivers, whose watersheds originate in theAndes Mountains. The second division is foundin clear to blackwater rivers with low productiv-ity and biomass, but relatively high fish diversity,mostly in the southern portion of the drainage,in isolated pockets of sandy or lateritic soils inthe llanos, and draining the Guayana Shield. Pre-liminary attempts have been made to explain ob-served distributions (Chernoff et al., 1991; Lassoet al., 1991; Perez and Taphorn, 1993), but biogeo-graphical analyses for many groups are still limitedby poor knowledge of alpha taxonomy. The depthof taxonomic coverage varies considerably acrossgroups. Detailed monographs are available for somegroups, e.g., the caribes or piranhas (Machado-Allison and Fink, 1996), whereas the state of knowl-edge for other groups is poor even at the familiallevel.

Venezuelan fishes occupy a broad range ofecological niches that represent the full range ofconsumer trophic positions in aquatic food webs.Some species feed exclusively or opportunisti-cally on seeds/fruits, macrophytes, algae, wood,

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007


Table 1. Distribution of Orinoco fish species among orders, family, and genera (modified from Lasso et al., 2004b). Species importantto fishery or aquaculture are listed also.

Order Families Genera Species Fishery or aquaculture species

Anguilliformes 2 2 3Batrachoidiformes 1 1 1Beloniformes 2 5 8Characiformes 14 124 399 Brycon spp., Colossoma macropomum,

Hydrolycus armatus, Mylossoma spp.,Piaractus brachypomus, Prochilodus mariae,Semaprochilodus kneri, S. laticeps

Charchariniformes 1 1 1Clupeiformes 3 12 20Cyprinodontiformes 4 12 27Elopiformes 2 2 2Gymnotiformes 5 24 59Lophiiformes 1 1 1Myliobatiformes 6 9 12Osteoglossiformes 1 1 2Perciformes 15 65 126 Cichla spp., Plagioscion squamosissimusPleuronectiformes 3 5 11Pristiformes 1 1 2Scorpaeniformes 1 1 1Siluriformes 12 150 314 Brachyplatystoma spp., Phractocephalus

hemioliopterus, Pseudoplatystoma fasciatum,P. tigrinum

Synbranchiformes 1 1 1Syngnathiformes 1 2 2Tetraodontiformes 1 2 3Total 77 421 995

zooplankton, terrestrial arthropods, fish fins, fishmucus, or blood. This high degree of feeding spe-cialization is assumed to allow for greater speciescoexistence during intervals of resource scarcity inseasonal aquatic habitats. Most fish assemblagesthat have been investigated at small spatial scalesalso reveal significant partitioning of space andtime (Arrington and Winemiller, 2003; Willis et al.,2005), and marked daily fluctuations in activity pat-terns have been documented for individual species(Rodrıguez et al., 1990). At larger spatial scales, fishassemblages are strongly patterned, with species dis-tributions segregating to varying degrees accordingto longitudinal position in river gradients (Hoeing-haus et al., 2003, 2004), lateral position in floodplainrivers (Barbarino Duque and Winemiller, 2003), orwater type (Rodrıguez and Lewis, 1997; Jepsen andWinemiller, 2002).

At the watershed scale, fish distribution pat-terns are strongly associated with landscape char-

acteristics and water quality features. Water typeis a particularly strong predictor of ichthyofaunalassemblages. Suites of species are affiliated withblackwater (low pH, low conductivity, intermediatetransparency), clearwater (variable pH and conduc-tivity, high transparency), or whitewater (high pH,high conductivity, low transparency) lakes, riversand streams. In some cases, geographic barrierslimit fish dispersal, but in many other cases wa-ter quality features appear to limit dispersal andgene flow (Turner et al., 2004). Taxonomic struc-ture of fish assemblages of the Casiquiare region(river connecting the headwaters of the Orinoco andNegro/Amazon basins) is significantly associatedwith a longitudinal clearwater-blackwater gradient(Winemiller et al., unpublished). Species primarilyrestricted to black waters of the Amazonian forestsin southern Venezuela (e.g., the cardinal tetra,Paracheirodon axelrodi and the Orinoco angelfish,Pterophyllum altum) are sometimes encountered as

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007


isolated populations in small blackwater tributariesof the Orinoco located hundreds of kilometers to thenorth in the vicinity of Puerto Ayacucho.

Fish assemblages of Orinoco floodplain lakes arestructured by causal relationships connecting pis-civory to transparency and transparency to lake mor-phometry (Rodrıguez and Lewis, 1997). During thedry season, fish with sensory adaptations to low lightare dominant in turbid lakes, whereas fish relying onvision predominate in clear lakes. Piscivores modifyassemblage structure by culling the most vulnerableprey species. Vulnerability in turn is strongly relatedto transparency and to the sensory and foraging ca-pabilities of individual species. Transparency at lowwater is predictably related to the depth and size oflakes: resuspension of sediment leading to turbidityoccurs at specific thresholds of depth and fetch. Inaddition to its role as a determinant of transparency,lake morphometry affects vulnerability through therelationship between lake relative depth and avail-ability of structural cover. Furthermore, prey speciesmay be able to use lake morphometry as an indica-tor of predation intensity, and predators may selectlakes that are most compatible with their mode ofpredation. Although assortment of fish among lakesseems largely unpatterned at the onset of the dryseason, assemblages are molded by predatory in-teractions that are intensified by the shrinking vol-ume of lakes during the dry season (Rodrıguez andLewis, 1994). Assemblage structure is thus stronglydeterministic in the dry season because lake mor-phometry channelizes the outcome of interactionsbetween predators and prey in the same way fromyear to year.

Most fishes move between aquatic habitats on aseasonal basis, and this behavioral pattern is par-ticularly prevalent in floodplain regions where an-nual flood pulses create and destroy shallow aquatichabitats (Arrington et al., 2005). Local fish assem-blages in floodplain creeks are influenced by local-scale movements in response to variation in waterquality and availability of habitats for feeding, shel-tering, and reproduction (Winemiller, 1996a; Wine-miller and Jepsen, 1998; Hoeinghaus et al., 2003).Fish assemblages in floodplain lakes show markedinterannual stability despite strong seasonal fluctua-tions in abundance that are driven by movements be-tween the lakes and adjacent floodplain (Rodrıguezand Lewis, 1990, 1994). Some of the most impor-tant fishery species perform seasonal, long-distancemigrations of several hundred kilometers (Saldanaand Venables, 1983). Most notable are the annual

migrations of the coporo between rivers draining theAndean piedmont and lowland rivers of the westernllanos (Lilyestrom, 1983). During the early wet sea-son, ripe coporos migrate from these rivers to thelowlands where they spawn in midriver and then re-main to feed in rain-swollen rivers and seasonal wet-lands. During the falling-water period (November-January), huge schools of coporos and several othermigratory species such as the mije (Leporinus frid-erici), morocoto, and bagres rayados, participate in“ribazones” (annual migrations at the end of theflood season) where they move upstream then grad-ually disperse within major tributary rivers (Bar-barino Duque et al., 1998).

Current status of freshwater fisheriesand fish culture

The Orinoco fishery is still multispecific, witharound 80 different species found in the fish mar-kets at different times of year, but the bulk of theharvest consists of prochilodontids and pimelodidcatfishes. Novoa (1989) reported that commercialfisheries of the Orinoco basin expanded during the1980s accompanied by shifts from large pimelodidcatfishes to greater proportional reliance on migra-tory prochilodontids. Novoa previously calculatedan estimated annual yield of 40,000–45,000 metrictons for the Orinoco River and noted that yields ap-pear to be correlated with intensity of annual floods.The multispecies fishery yields were estimated atabout 12,000 metric tons in the mid 1980s. Between1984 and 2000, INAPESCA, the Venezuelan na-tional fishery agency, reported annual harvests of16,000–60,000 tons, representing between 3–12%of the country’s total fishery production (Novoa,2002). A comprehensive foodweb analysis yieldedan estimate of 79,000 metric tons for total fish pro-duction on the Orinoco floodplain (Lewis et al.,2001). This value supports Novoa’s estimate of an-nual yield, which represents just over half of totalfish production, as an upper limit for harvests in theOrinoco fishery.

The western llanos of Venezuela is an impor-tant nursery area for major commercial species suchas the coporo, bagres rayados, mije, and moro-coto. Coporos and bagres rayados dominate fish-eries in San Fernando and other areas in the west-ern llanos (Apure-Arauca basin). The main stemOrinoco River yields large catches of catfishes(Brachyplatystoma spp.), morocoto, palometas (My-lossoma spp.), payara, palambra (Brycon spp.), and

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007


prochilodontids. The fishery of the Caura River isdominated by the morocoto and bagres rayados, butat least 27 species comprised an estimated 250 met-ric tons of fishe harvested annually (Vispo et al.,2003). Slightly less than half of the annual harvestwas taken by subsistence fishers.

The fishery has drastically modified the rela-tive abundance, population structure, and distribu-tion of fish stocks in the Orinoco basin. Overhar-vesting of large fishes began with the arrival ofnylon seines over 30 years ago and has been com-pounded recently by habitat destruction and the dou-bling of Venezuela’s population in the last 25 years.Patterns of human consumption have respondedto selective reduction or depletion of fish stocks.Caribes, doradid catfishes, and payara, once con-sidered “trash” fish and discarded from catches, arenow common in markets because previously pre-ferred species have disappeared or become rare andexpensive.

Spatial shifts in the fishery have occurred at sev-eral scales. Near fishing centers, the largest speciesof commercial fishes are now scarce or absent, andfishers are required to make longer journeys and stayout more days to fill their boats. At larger scales, thecommercial fishery for prochilodontids has shiftedand is now concentrated in the lower portions ofthe Orinoco tributaries. Highland rivers with damsor dykes and irrigation canals that block migrationhave lost significant portions of their prochilodontidpopulations (Barbarino Duque et al., 1998). Agricul-tural development has led to extensive deforestationand concomitant sedimentation of the upper sectionsof rivers draining the Andes mountain range. Thedry season is more severe and extended, permittingfishers to completely fish out these smaller rivers.These conditions, along with peak demand for fishfor Holy Week during the dry season, have causedsevere overexploitation. The practice of blockingrivers downstream with large seines to harvest theblocked migrators with cast nets has contributed todeclines in population sizes and earlier maturationin the prochilodontids.

The effects of overharvesting generally are mostnotable in the upper sections of the Orinoco basin.On the delta, catch per unit effort has actually in-creased in the last 25 years, but the composition ofthe catch has changed over the same period (Novoa,2002). The largest predatory species are now caughtat much smaller sizes or have disappeared com-pletely from the commercial harvest, but stocks of

smaller detritivores and herbivores are still healthyin the delta.

Most sport fishing in Venezuela centers on thepavones. Five Cichla species occur in the country,but only three (C. intermedia, C. orinocensis, andC. temensis) appear to be widespread. Pavon popu-lations appear to be highly sensitive to overharvest,and this is probably a function of their occupation ofunproductive ecosystems, their reproductive strat-egy involving nesting and parental care, and theirtrophic position as top predators. Overharvest hasbeen a serious problem in all areas with good accessto anglers and net fishers. In recent years, pavon pop-ulations in remote areas in Amazonas (Casiquiareregion) and the Guayana Shield (Caura and Caronırivers) have begun to be exploited more heavily. Im-pressive pavon fisheries in the Aguaro River and LasMajaguas Reservoir were destroyed after only abouta decade of illegal fishing activity.

The saltador, a predatory characid, is a sport fishthat was once common in rivers of the Andean pied-mont but has now been nearly eliminated by over-fishing, deforestation and siltation, and dam con-struction (Winemiller et al., 1996). The saltador hasa migratory life history similar to the coporo in thisregion. Blockage of migration routes by dams isparticularly damaging to these species. The palam-bra, another migratory characid, has been reducedin numbers due to dams and other human impacts inthis heavily populated region of Venezuela (Lilye-strom and Taphorn, 1983).

Cachama hatcheries have been in existence inVenezuela since the 1970’s (Ginelly, 1990). Moststations use earthen ponds to cultivate the cachama,but cage culture has also produced positive experi-mental results. Artificial feeds incorporating indus-trial byproducts and locally produced ingredients arethe key to successful commercialization.

Several species of cultivated tilapia have escapedinto the wild. Use of these exotics poses a seriouspotential threat to native species and the integrityof the ecosystems on which they depend. Expect-ing extraordinary profits and high production, manyfarmers abandoned the cachama in favor of tilapia.Unfortunately, there was little appreciation for thepitfalls associated with tilapia culture: reproductionof commercial numbers of these mouth-brooders isexpensive, labor intensive, and time consuming. Al-though tilapias were first introduced into Venezuelain 1959, the currently cultivated variety, red tilapia,is a relative newcomer.

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007


Survey of freshwater managementin the Orinoco basin

Water quality and fisheries lawsin Venezuela

A regional development agency, the Corpo-racion Venezolana de Guayana (CVG), is a majorplayer in environmental management in the lowerOrinoco basin. The agency is responsible for plan-ning, promoting, and implementing projects in agri-culture, forestry, mining, tourism, urban develop-ment, and water resources. Historically, there hasbeen a lack of concerted efforts by CVG and othergovernmental institutions to manage water qual-ity and discharges with conservation as an ex-plicit aim. In 1995, new regulations were createdthat tightened the standards for treatment of efflu-ents (BOD; solids) prior to release into natural wa-ters. However, these regulations contain a “grandfa-ther” clause which provides exemptions from en-vironmental rehabilitation and the aluminum in-dustry, among others, has legally discharged ef-fluents into natural lakes. Without remedial treat-ment, the pollutants accumulated in the lakes maybe sporadically washed into the river by extremefloods.

The Ministry of Agriculture (MAC) is responsi-ble for management of the fisheries in Venezuela,including stock assessment, issuing of permits, andregulation of fishing gear and effort. Unfortunately,harvest regulations are often violated by all sec-tors of society throughout the country. Law en-forcement entities make occasional citations andarrests of illegal netters, often confiscating netsand boat motors, but these are too few and in-frequent to create an environment of widespreaddeterrence.

Although more than 70% of all fishery harvestsin Venezuela are captured by rural fishers using tra-ditional gear, the relatively low value of these fish-eries has led to official neglect. Both the MAC andthe Ministry of the Environment (MARNR) have as-sumed roles in regulating the harvesting of fishes,sometimes with conflicting objectives and ineffec-tive results. Between 1999 and 2001, legislators es-tablished regulations that permitted harvests duringreproduction and migration phases and were thushighly detrimental to the fishery. This undesirablesituation might be corrected under the newly en-acted fishery law (Novoa, 2002).

Linkages with biodiversity conservationand ecosystem management

Riverine and floodplain habitats, including ri-parian forests, play a key role in conservation ofbiodiversity in the Orinoco basin. For example, thefloodplain regulates the amplitude and duration offloods, maintains fertile agricultural terrain, pro-vides refuge and feeding or breeding grounds fornumerous terrestrial and aquatic species, and sup-ports the fishery. Strategies for preserving aquatichabitats and biota in the basin will be more likely tosucceed if they account for and adapt to local needsand constraints. In the llanos, the development ofecotourism ventures on private lands managed forranching of cattle and capybaras (large cavimorphrodents) has proven economically viable. Similarmanagement schemes, encouraging conservation bythe landowners, could be promoted to maintain keyaquatic habitats in a natural state even as economi-cally profitable activities develop around these areas.

Conservation of aquatic habitats in Venezuela isfostered by the existence of a network of protectedareas (ABRAE, or areas under special administra-tion regime), which collectively cover two thirds ofthe country’s territory. Most of these areas, though,afford only nominal protection because they are notactively managed or monitored. The categories ofprotected areas most relevant to conservation, Na-tional Parks, Natural Monuments, Faunal Refuges,Faunal Reserves, and Biosphere Reserves (26% ofVenezuelan territory), are concentrated in the south-ern part of the Orinoco basin and the Orinoco delta.With some exceptions, surveillance and control offishing in protected areas is minimal or altogetherlacking, even within the National Parks. Protectedareas therefore probably contribute to the mainte-nance of aquatic biodiversity mostly by prevent-ing large-scale degradation of the watersheds fromforestry, urban development, and mining.

Although most of the Orinoco basin is rela-tively unaltered physically, the conservation statusof fishes and the state of local fisheries is corre-lated with human presence. The most deterioratedregions in the Orinoco basin are the once exten-sively forested Andean piedmont regions and highplains regions in the states that border the Andesmountains in the north, Apure, Barinas, Portuguesa,Cojedes, and Guarico, and the eastern plains ofAnzoategui, Monagas, and Delta Amacuro. Agri-culture and cattle ranching are extensive in these

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007


regions and deforestation has reached over 80% oforiginal existing forests (Winemiller et al., 1996).In the still sparsely settled southern Apure state andthe rivers draining the Guayana Shield, the vegeta-tion has suffered less and rivers are in better shape.However, gold mining in many rivers of Bolıvarand Amazonas has contaminated the water and theaquatic food chain with mercury.

Conservation of biodiversity has been hinderedby an almost exclusive focus by fisheries managerson harvest, with little attention to preservation ofa diversified fishery, genetic integrity, and balancedtrophic structure (including large predators).Although maximum sustainable yield perhaps hasnot been attained in the Orinoco fishery, variousindicators point to overexploitation for almostall of the large predatory catfishes. Though stillclassified as a low technology fishery, the use ofnylon seines pulled by small boats or canoes withoutboard motors and cast nets has greatly increasedfishing efficacy and contributed to the decline ofstocks of large catfishes. Declining mesh sizesin the commercial seines indicate that the largerindividuals are no longer present in commerciallyattractive quantities. There is evidence that com-mercial netting is also causing reductions in theaverage size and age at maturity. In the Orinocodelta, threats to biodiversity include trawling ofchannels and use of unselective fishing gear, whichresult in habitat destruction and high by-catchesand discarding of non-commercial species.

Management success stories

Regrettably, Venezuela provides few examples ofspecific management practices that have protected orenhanced stocks of freshwater fishes or their naturalhabitats. We are only able to cite a couple of ex-ceptions: the pavon sport fisheries of the CinarucoRiver, forming the border of Santos Luzardo Na-tional Park, and Guri Reservoir, where access iscontrolled by EDELCA, a government-run miningand power company. In both cases, local sportfish-ing interests were sufficiently motivated to requestincreased enforcement of fishing laws. Protection ofpavon stocks was the primary concern. Sometimesaided by donations of boats, motors, and fuel fromsportfishing groups, the Guardia Nacional was ableto periodically patrol these areas, which provideda degree of deterrence. Following recent politicaland social conflicts in Venezuela, these patrols haveall but stopped, and illegal net fishing has increased

in both areas. The law was recently changed to al-low commercial fishing of pavon for the first timein Venezuela, and this is certain to have negativeimpact on populations.

The creation of dams, while devastating to mi-gratory fishes, has created new habitat for lentic-adapted sport fishes, especially the pavones. Newpavon fisheries have been established in reservoirswithin piedmont regions of the Andean and Coastalmountain ranges. These reservoirs bring a valuablenew fishery resource to people in areas having thehighest human population densities. Unfortunately,these fisheries are no better regulated than thoseof the rivers, and, following the initial productionburst after reservoir formation, pavon populationshave been depleted by illegal fishing over intervalsas short as a decade (e.g., Las Majaguas Reservoirin Cojedes state).

Conclusions

Science and management: Summaryoverview and priority gaps and needs

Scientific understanding of diversity hotspots andcritical habitats in the Orinoco basin, including theirdistribution and the ecological processes that main-tain them, is currently insufficient to satisfy man-agement needs. Various knowledge gaps hamper themanagement of freshwater resources in the Orinocobasin. For example, basic data on population sta-tus, demographic parameters, and genetic structureare unavailable for most fish species. Only 13 fishesare listed (all risk categories combined) in the sec-ond edition of the Venezuelan Red List of threat-ened animals (Rodrıguez and Rojas-Suarez, 1999),up from five in the 1995 edition. A minority of the13 species is from the Orinoco basin and the rest arefrom densely populated areas near the coast. Thesparse representation of Orinoco fishes in the RedList probably reflects current lack of knowledge onpopulation status rather than true absence of risk.Various potentially effective and relatively inexpen-sive tools for evaluating and managing freshwaterresources, such as biotic metrics of habitat quality(indicator species; indices of biotic integrity) andrapid assessment protocols, still await developmentand implementation in Venezuela. The feasibility ofrapid biological appraisals to map diversity and as-sess management needs is illustrated by the AquaticRapid Assessment Program (AquaRAP) conductedrecently (2000) in the Caura River basin.

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007


Management priorities for fishes in the Orinocobasin are associated with four major threats: defor-estation, dams, overfishing, and pollution (summa-rized in Winemiller et al., 1996). The introductionof exotic species, such as tilapias, can be added tothis list of threats most of which now exist through-out the country. Deforestation has perhaps the mostwidespread and far-reaching impacts on aquatic lifewithin the Orinoco basin. Deforestation in the An-dean piedmont results in erosion and siltation ofstreams and rivers, greater solar radiation and streamdesiccation, and alteration of instream habitats andfood webs. Deforestation has the same effects inthe llanos and Amazonian/Guayana Shield regions;however, siltation is usually not as extensive in theseregions.

Dams have multiple impacts on rivers andaquatic life, including alteration of natural hydro-logic regimes and nutrient cycles, reduction of sedi-ment transport, and blockage of fish migrations. Al-teration of river hydrological regimes in Venezuelahas serious consequences for fishes, most of whichare adapted for seasonal spawning in response to sea-sonal flood pulses (Winemiller, 1989). Dams tend toreduce flows in downstream reaches during normalhigh-flow periods, and often increase flow duringthe annual dry period that normally has low flows.Seasonal, or periodic, spawning fishes depend onannual floods for spawning cues and creation of sea-sonal wetlands in floodplains that function as nurs-ery areas. Dams also trap sediments and nutrients,especially in whitewater ecosystems. These riversnormally show high primary and secondary produc-tivity in low-velocity habitats within channels andfloodplains. Lentic habitats of whitewater rivers gen-erally support dense growth of emergent and floatingaquatic macrophytes, that in turn support high den-sities of aquatic invertebrates and fishes, especiallyjuveniles.

As discussed above, overfishing is a serious prob-lem throughout Venezuela. Most of the major com-mercial and sportfish stocks already have been fullyor overexploited throughout their ranges. Only pop-ulations in remote regions of the Guayana Shieldand Amazonas have escaped heavy exploitation bycommercial and subsistence fishers. Large piscivo-rous catfishes and pavones tend to be the first speciesto show signs of overharvesting (i.e., reduced av-erage size and stock abundance). The coporo andother species that mature in 1-2 years and producelarge numbers of eggs seem to withstand harvest-ing better, but even these populations have been re-

duced in areas where gillnets stretched across theriver channel can catch virtually every migratingindividual. Fish populations in the western llanosseem to be relatively resilient to fishing pressure,probably because these populations normally expe-rience explosive growth and catastrophic decline inconcert with habitat changes and ecological dynam-ics derived from the annual flood pulse (Winemiller1996a, b). Fish populations in unproductive black-water rivers appear to be more sensitive toexploitation (e.g., pavon discussed above).

Pollution in Venezuela derives from severalsources, most of which have severe negative im-pacts on fish stocks. In the Guayana Shield, largemining operations for bauxite, iron, and gold causesiltation and introduce toxic chemicals and elementsinto rivers. In regions exploited by gold miners,mercury contamination poses a particularly acutethreat to fishes and other aquatic organisms (Nicoand Taphorn, 1994). Organic waste from sewageand agriculture results in severe aquatic hypoxiain several rivers and streams in Venezuela. Sugarcane processing plants in the western llanos re-lease large amounts of liquid organic waste intostreams that provide critical dry-season habitat fora great diversity of fishes (Winemiller et al., 1996).Normally, adult fishes from these dry-season refu-gia move into seasonally flooded marshes to spawnduring the rainy season. Thus, induction of se-vere hypoxia during the dry season has the poten-tial to completely extirpate entire populations fromwatersheds.

Future trends and potential for habitats,fishes, and fisheries

More than half of the population in southernVenezuela lives in poverty, and this region is there-fore a high development priority for the country.The decline of opportunities in the large north-ern cities has led to massive migrations to theGuayana region of people seeking new economicopportunities. Three zones potentially threatened byrapid development in the future merit special notice.First, aquatic environments in the scarcely populateddelta will likely be degraded by the development ofinfrastructures (dredging, channeling of wetlands,road construction, drainage networks, and peat min-ing), and burning and clearcutting of forests to cre-ate agricultural land and rangeland. Second, theOrinoco oil belt, which spans the states of Guarico,

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007


Anzoategui, Monagas, and Delta Amacuro, containshuge reserves of extra-heavy oil and bitumen. Thebelt may be soon subject to large scale exploitation,especially given the increasing worldwide demandfor oil. Extractive activities pose the risk of oil spills,salinization of soils, and hydrological alterations. Fi-nally, plans for building a hydroelectric dam in thesouth-eastern Caura River, a pristine region of highbiodiversity, or to divert the Caura’s waters to theCaronı River, have been under study for a long time.Additionally, dredging is planned to improve navi-gation along both the Orinoco, which accepts ocean-going vessels, and the Apure rivers. In addition toencouraging development in unaltered sectors, suchplans may degrade aquatic and floodplain habitats,release pollutants stored in the sediments, modifyerosion and siltation patterns, affect groundwaterflow, and promote saltwater intrusion in the delta.Use of low-draft vessels may reduce the need fordredging.

In spite of recent successful efforts to modernizefishery legislation, the lack of institutional will to en-force the law bodes for a bleak future of Venezuela’sinland fisheries. Near major fishing centers such asSan Fernando de Apure, Cabruta, and Barrancas,attempts to implement the fishery law have been in-effective. As a result, fishers operate out of season,use nets with illegal mesh sizes, and capture fishbelow the legal size limits. The gradual but con-tinual decline in harvests seen in the last decadeswill likely worsen under these conditions. There is,however, some reason for hope because many sec-tors of the Orinoco basin are only lightly exploitedor unexploited. Furthermore, fishes adapted to theannual pulse of the wet and dry seasons typical ofthe entire Orinoco drainage can recover lost habi-tat and recover from low population sizes quickly ifgiven the opportunity. Timely enforcement of fish-ery regulations can help prevent stock collapsesand other, possibly irreversible, changes in thefishery.

Fish culture in Venezuela is still underdevelopeddespite decades of research and promotion, partlybecause of the absence of strong research centerswith steady funding. Commercial ventures in culti-vation of cachama and red tilapia are hindered bythe unavailability of high quality fingerlings and ab-sence of extension programs to provide advice andguidance on fish culture. Extensive cultivation ofthese species by small scale producers could effec-tively promote fish culture while lessening risk tothe environment.

ReferencesArrington, D. A., Winemiller, K. O., 2003. Diel changeover in

sandbank fish assemblages in a Neotropical floodplain river.Journal of Fish Biology 63, 442–459.

Arrington, D. A., Winemiller, K. O., Layman, C. A., 2005. Com-munity assembly at the patch scale in a species rich tropicalriver. Oecologia 144, 157–167.

Barbarino Duque, A., Winemiller, K. O., 2003. Dietary segrega-tion among large catfishes of the Apure and Arauca rivers,Venezuela. Journal of Fish Biology 63, 410–427.

Barbarino Duque, A., Taphorn, D. C., Winemiller, K. O., 1998.Ecology of the coporo, Prochilodus mariae (Characiformes,Prochilodontidae), and status of annual migrations in westernVenezuela. Environmental Biology of Fishes 53, 33–46.

Chernoff, B., Machado-Allison, A., Saul, W. G., 1991. Mor-phology, variation and biogeography of Leporinus brunneus(Pisces: Characiformes: Anostomidae). Ichthyological Ex-ploration of Freshwaters 1, 295–306.

Ginelly, G., 1990. Cachama culture in Venezuela. AquacultureMagazine May/June, 52–65.

Hoeinghaus, D. J., Layman, C. A., Arrington, D. A., Winemiller,K. O., 2003. Movement of Cichla spp. (Cichlidae) in aVenezuelan floodplain river. Neotropical Ichthyology 1, 121–126.

Hoeinghaus, D. J., Winemiller, K. O. Taphorn, D. C., 2004.Compositional change in fish assemblages along the Andeanpiedmont–Llanos floodplain gradient of the Rıo Portuguesa,Venezuela. Neotropical Ichthyology 2, 85–92.

Jepsen, D. B., Winemiller, K. O., 2002. Structure of tropical riverfood webs revealed by stable isotope ratios. Oikos 96, 46–55.

Lasso, C., Machado-Allison, A., Perez, H., 1991. Considera-ciones zoogeograficas de los peces de la Gran Sabana (AltoCaronı) Venezuela, y sus relaciones con las cuencas vecinas(Considerations on the zoogeography of fishes of the Gran Sa-bana (Upper Caronı) Venezuela, and their relationships withneighbouring basins. In Spanish). Memorias de la Sociedadde Ciencias Naturales La Salle 133–134, 109–129.

Lasso, C. A., Lew, D., Taphorn, D., DoNascimiento, C., Lasso-Alcala, O., Provenzano, F., Machado-Allison, A., 2004a. Bio-diversidad ictiologica continental de Venezuela. Parte I. Listade especies y distribucion por cuencas (Continental ichthy-ological biodiversity of Venezuela. Part I. Species list anddistribution by basin. In Spanish). Memoria de la FundacionLa Salle de Ciencias Naturales 159–160, 105–195.

Lasso, C. A., Mojica, J. I., Usma, J. S., Maldonado-O., J. A.,DoNascimiento, C., Taphorn, D. C., Provenzano, F., Lasso-Alcala, O. M., Galvis, G. Vasquez, L., Lugo, M., Machado-Allison, A., Royero, R., Suarez, C., Ortega-Lara, A., 2004b.Peces de la cuenca del rıo Orinoco. Parte I: lista de especiesy distribucion por subcuencas (Fishes of the Orinoco Riverbasin. Part I: Species list and distribution by sub-basin. InSpanish). Biota Colombiana 5, 95–158.

Lewis, W. M. Jr., Hamilton, S. K., Saunders, J. F. III, 1995. Riversof Northern South America. In: C. Cushings, K. Cummins, G.W. Minshall (Eds.), River and Stream Ecosystems, pp. 219–256. University of California Press, Berkeley, California.

Lewis, W. M. Jr., Hamilton, S. K., Lasi, M. A., Rodrıguez,M. A., Saunders, J. F. III, 2000. Ecological determinism onthe Orinoco floodplain. BioScience 50, 681–692.

Dow

nloa

ded

By:

[Can

adia

n R

esea

rch

Kno

wle

dge

Net

wor

k] A

t: 16

:43

15 J

une

2007


Lewis, W. M. Jr., Hamilton, S. K., Rodrıguez, M. A., Saunders,J. F. III, Lasi, M., 2001. Foodweb analysis of the Orinocofloodplain based on production estimates and stable isotopedata. Journal of the North American Benthological Society20, 241–254.

Lilyestrom, C., 1983. Aspectos de la biologıa del coporo(Prochilodus mariae) (Aspects of the biology of the coporo(Prochilodus mariae). In Spanish). Revista UNELLEZ deCiencia y Tecnologıa 1, 5–11.

Lilyestrom, C., Taphorn, D., 1983. Aspectos sobre la biologıa yconservacion de la palambra (Brycon whitei) Myers y Weitz-man 1960 (Aspects of the biology and conservation of thepalambra (Brycon whitei) Myers y Weitzman 1960. In Span-ish). Revista UNELLEZ de Ciencia y Tecnologıa 1, 53–59.

Lundberg, J. G., Lewis, W. M. Jr., Saunders, J. F. III, Mago-Leccia,F., 1987. A major food web component in the Orinoco Riverchannel: Evidence from planktivorous electric fishes. Science237, 81–83.

Machado-Allison, A., 1993. Los peces de los Llanos de Venezuela(The fishes of the Llanos of Venezuela. In Spanish). Universi-dad Central de Venezuela, Caracas, Venezuela.

Machado-Allison, A., Fink, W., 1996. Los peces caribes deVenezuela (The piranhas of Venezuela. In Spanish). Univer-sidad Central de Venezuela, Caracas, Venezuela.

Nico, L. G., Taphorn, D. C., 1994. Mercury in fish from gold-mining regions in the upper Cuyunı River systems, Venezuela.Fresenius Environmental Bulletin 3, 287–292.

Novoa, D. (Ed.), 1982. Los recursos pesqueros del Rıo Orinocoy su explotacion (The fishery resources of the Orinoco Riverand their exploitation. In Spanish). Corporacion Venezolanade Guayana. Caracas, Venezuela.

Novoa, D., 1989. The multispecies fisheries of the Orinoco River,development, present status, and management strategies. Can.Spec. Publ. Fish. Aquat. Sci. 106, 422–428.

Novoa, D., 2002. Los recursos pesqueros del eje fluvial Orinoco-Apure: Presente y futuro (The fishery resources of theOrinoco-Apure fluvial axis: present and future. In Spanish).INAPESCA, Caracas, Venezuela.

Perez, A., Taphorn, D. C., 1993. Relaciones zoogeograficas entrelas ictiofaunas de las cuencas del Rıo Magdalena y Lago deMaracaibo (Zoogeographic relationships between the ichthy-ofaunas of the Magdalena River and Lake Maracaibo basins.In Spanish). BioLlania 9, 95–106.

Rodrıguez, J. P., Rojas-Suarez, F., 1999. Libro rojo de la faunavenezolana (Redbook of Venezuelan fauna. In Spanish).Provita, Caracas, Venezuela.

Rodrıguez, M. A., Lewis, W. M. Jr., 1990. Diversity and speciescomposition of fish communities of Orinoco floodplain lakes.National Geographic Research 6, 319–328.

Rodrıguez, M. A., Lewis, W. M. Jr., 1994. Regulation and stabilityin fish assemblages of neotropical floodplain lakes. Oecologia99, 166–180.

Rodrıguez, M. A., Lewis, W. M. Jr., 1997. Structure of fish as-semblages along environmental gradients in floodplain lakesof the Orinoco River. Ecological Monographs 67, 109–128.

Rodrıguez, M. A., Richardson, S. E., Lewis, W. M. Jr., 1990.Cryptic behavior and aspects of the ecology of a nocturnaldriftwood catfish, Entomocorus gameroi (Auchenipteridae).Biotropica 22, 435–438.

Saldana, J., Venables, B., 1983. Energy compartmentalization ina migratory fish, Prochilodus mariae (Prochilodontidae), ofthe Orinoco River. Copeia 1983, 617–623.

Saunders, J. F. III, Lewis, W. M. Jr., 1988. Transport of phos-phorus, nitrogen, and carbon by the Apure River, Venezuela.Biogeochemistry 5, 323–342.

Taphorn, D. C., Royero, R., Machado-Allison, A., Mago-Leccia,F., 1997. Lista actualizada de los peces de agua dulce deVenezuela (Updated checklist of the freshwater fishes ofVenezuela. In Spanish). In E. La Marca (Ed.), VertebradosActuales y Fosiles de Venezuela, pp. 55–100. Serie CatalogoZoologico de Venezuela, Vol. 1. Museo de Ciencia y Tec-nologıa de Merida, Venezuela.

Turner, T. F., McPhee, M. V., Campbell, P., Winemiller, K. O.,2004. Phylogeography and intraspecific genetic variation ofprochilodontid fishes endemic to rivers of northern SouthAmerica. Journal of Fish Biology 64, 186–201.

Valbo-Jørgensen, J., Lasso, C. A., Blanco-Belmonte, L. 2000.Fish biomass and density in macrophyte habitats in flood-plain lakes of the Orinoco basin, Venezuela. Memoriasde la Fundacion La Salle de Ciencias Naturales 60, 35–49

Vispo, C., Daza, F., Ferrer, A., 2003. The fishery of the lowerCaura Basin, Bolıvar state, Venezuela: A description andconsideration of its management. Scientia Guaianæ 12, 247–272.

Weibezhan, F.H., Alvarez, H., Lewis, W.M. Jr., (Eds.), 1990. TheOrinoco River as an ecosystem. Impresos Rubel, Caracas,Venezuela.

Willis, S. C., Winemiller, K. O., Lopez-Fernandez, H., 2005.Habitat structural complexity and morphological diversity offish assemblages in a Neotropical floodplain river. Oecologia142, 284–295.

Winemiller, K. O., 1989. Patterns of variation in life historyamong South American fishes in seasonal environments. Oe-cologia 81, 225–241.

Winemiller, K. O., 1991. Ecomorphological diversification inlowland freshwater fish assemblages from five biotic regions.Ecological Monographs 61, 343–365.

Winemiller, K. O., 1996a. Dynamic diversity: Fish communitiesof tropical rivers. In: M. L. Cody, J. A. Smallwood (Eds.),Long-term studies of vertebrate communities, pp. 99–134.Academic Press, Orlando, Florida.

Winemiller, K. O., 1996b. Factors driving spatial and temporalvariation in aquatic floodplain food webs. In: G.A. Polis, K.O.Winemiller (Eds.), Food webs: Integration of patterns anddynamics, pp. 298–312. Chapman and Hall, New York.

Winemiller, K. O., 2001. Ecology of peacock cichlids (Cichlaspp.) in Venezuela. Journal of Aquariculture and Aquatic Sci-ences 9, 93–112.

Winemiller, K. O., Marrero, C., Taphorn, D. C., 1996. Perturba-ciones causadas por el hombre a las poblaciones de peces delos Llanos y del piedemonte andino de Venezuela (Man-madedisturbances to fish populations of the Llanos and the An-dean foothills of Venezuela. In Spanish). BioLlania 12, 13–48.

Winemiller, K. O., Jepsen, D. B., 1998. Effects of seasonality andfish movement on tropical river food webs. Journal of FishBiology 53 (Supplement A), 267–296.

aquatic ecosystem health &...

Documents