Pampean Lakes Research Articles

Biology of growth of Hoplias aff. malabaricus (Bloch, 1794) in a shallow pampean lake (Argentina)

The trahira Hoplias aff. malabaricus is a top predator in pampean shallow lakes and is highly appreciated by recreational anglers and artisanal fishermen. Trahira growth from Yalca shallow lake was determined by lepidological analysis and age validated by marginal increment. When growth was fitted to the von Bertalanffy model, annual classes exhibited a bimodal pattern as a result of the presence of spring and summer annual cohorts associated with a three month spawning season, each period in turn showing different growth patterns. The trahira population-age structure at Yalca shallow lake showed a truncated profile with very low numbers of large adults and few individuals older than three to four years, thus producing an unbalanced length-structure population. Growth parameters and growth performance were similar to the corresponding parameters estimated for other shallow pampean lakes of the region, but strongly diverged from the data for those populations inhabiting subtropical and tropical environments. Such differences could be accounted for by dissimilarity in metabolic rates associated with thermal differences accompanying seasonal variability among latitudes as well as by the development of adaptive physiologic and demographic responses to cope with the high thermal amplitude and hydrologic instability observed in pampean lakes.

Vulnerability of pejerrey Odontesthes bonariensis populations to climate change in pampean lakes of Argentina

The vulnerability of the pejerrey Odontesthes bonariensis population in Lake Chasicó was assessed under different climate change conditions. During the sampling period, the water temperature was adequate for fish reproduction and to sustain an adequate sex ratio. Climate-driven higher temperatures, however, may severely distort population structure and cause drastic reduction or local extinction of stocks. Lake Chasicó can be classified as eutrophic with clear waters and cyanobacteria that regularly cause fish mortality were identified as Nodularia spumigena and Oscillatoria sp. Global warming may strengthen the effects of eutrophication (e.g. toxic blooms or anoxia). Since many Cyanophyta species tolerate higher temperatures better than other algae, toxic blooms could increase. Furthermore, cyanobacteria have low nutritional value and could decouple the low-diversity food web. Lake Chasicó has currently the salinity optimum (c. 20) for the development of the early life-history stages of O. bonariensis. Climate change, however, is likely to amplify the intensity of droughts or inundations. Floods can endanger O. bonariensis development due to its sub-optimal growth at low salinity and droughts could increase lake salinity and also temperature and nutrient concentration. In order to reduce some of the effects of climate change on the O. bonariensis population in Lake Chasicó, integrated basin management based on an eco-hydrological approach is proposed.

Extensive cage culture of pejerrey (Odontesthes bonariensis) in a shallow pampean lake in Argentina

AbstractPejerreyisanimportantzooplanktivorousnative¢shof theArgentinean inland waters. It has been tradi-tionally propagated for stocking purposes by rela-tively costly semi-intensive and intensive methods.Inthis study, we evaluated the implementationof anextensiveculturemethodbyusing£oatingcagesinashallow pampean lake. Four cages were installed inthe Lacombe Lake and stocked with juveniles(16.24 1.69mmlength)at50¢shm 3 density forgrowing until the size of 150mm, which is consid-ered as a suitable size for stocking. Throughout theexperiment, thetemperaturerangedbetween10 and26 1C and the zooplankton biomass ranged between12 and 3269 mgdwL 1 . The growth patterns in thelengthwere similar inthefourcages anddirectly re-latedtothelakethermalconditionsandzooplanktonavailability. The average ¢nal length after 315 dayswas 154.4 8.8mm. The survival rates ranged be-tween 53.5% and 64.7% during the ¢rst 110 daysand 11.1^25.7% at termination. Growth rate for the¢rst2monthswasthehighestdocumentedforpejer-reyculture.This simple technique oiers the possibi-lity to produce juvenile pejerrey at a low cost andprovidesthealternativeofreinforcingthenaturalpo-pulationswith¢shalreadyadaptedtothenaturalen-vironmentalconditions.Keywords: Odontesthes bonariensis,cageculture,pampean lakes, ¢shgrowth, zooplanktivorous ¢shIntroductionThe pejerrey (Odontesthes bonariensis) is consideredas one of the most important commercial and sport¢sh species inhabiting the inland waters of Argenti-na (Bonetto & Castello1985; Grosman1995; Reartes1995; Somoza, Miranda, Berasain, Colautti, RemesLenicov & Strˇssmann 2008). Because of the highqualityof its £esh and sport ¢shing attractiveness, ithasbeenintroducedwitharelativelygoodsuccesstoother South American, European and Asian coun-tries (Loubens & Osorio1992;Toda,Tonami,Yasuda S Strˇssmann & Yasuda 2005).The inter-est in this species stimulated the ¢rst culture at-tempts for stocking at the beginning of the pastcentury. Since then, the techniques of pejerrey pro-ductionhaveimprovedprogressivelyanditispossibleat present to complete the production cycle in tanks(Miranda,Berasain,Velasco,ShirojoSRinguelet, Iriart & Escalante 1980). Because pam-pean lakesareusuallyeutrophic, zooplanktonrepre-sents an important and abundant community(Escalante 2001; Claps, Gabellone & Ben|¤tez 2004).This feature represents a unique opportunity fordeveloping pejerrey culture based on natural zoo-plankton as the source of food.The use of cages is awell-developedtechnologythathasbeenmostlyused

The effects of light availability in shallow, turbid waters: a mesocosm study

Seasonal patterns of water transparency in turbid Pampean lakes suggest that the amount of seston is strongly influenced by incident solar radiation. However, the unequivocal identification of light as the major forcing variable is precluded due its co-variation with several potentially confounding variable. In order to specifically investigate the role of light, we performed a mesocosm (3000 L) experiment aimed at investigating the effects of different degrees of light availability on planktonic community structure and metabolism. The experimental setup successfully mimicked the light limiting conditions prevailing in Pampean turbid lakes. We used neutral density filters to create four light treatments, approximately covering the natural annual range of incident irradiance. Our results are consistent with field patterns and light-limitation theory: (i) light attenuation and (ii) primary production increased with light availability. In contrast, the abundance of most grazers displayed negative relationships with light availability. The decreases in the density of grazers could have resulted from changes in the nutritional value of the food. This possibility is also supported by (iii) decreases in seston P-content and (iv) increases in community respiration with increasing light availability.

Assessment of condition in pejerrey Odontesthes bonariensis (Atheriniformes: Atherinopsidae) populations: which index works best?

The pejerrey Odontesthes bonariensis is the most important target species in temperate freshwater fisheries of Argentina, and assessment of condition has been a regular practice and common diagnostic tool. Most pejerrey fishery studies have used Fulton's (K) index, without testing whether underlying assumptions or requirements were met. We analyzed and contrasted the applicability of K, Kn and Wr indices to assess condition status in several pejerrey populations inhabiting Pampean lakes. Our results showed that whereas Wr and Kn displayed significant condition changes across length at some study lakes, Kn portrayed a small range of variation. We also noted that pejerrey maximum length and size structure strongly varied among populations probably due to the characteristics of trophic niche changes through lifespan, depending on lake limnological characteristics and zooplankton availability. We conclude that the K index should be disregarded in those cases where populations show allometric growth and size ranges strongly vary. In turn, the Kn index appears to be only appropriate for regular within population assessment, being difficult to apply when comparisons between populations are needed and when they exhibit different weight-length relationship slopes. Finally, the Wr index should be strongly preferred if the objective is to perform comparisons between pejerrey populations, particularly when population structure is not well known, stocking has been used for population recovery, lakes are strongly supported by limnological changes, data are limited to only one or few samplings and metaphoetesis is suspected in pejerrey populations.

Optical characteristics of shallow lakes from the Pampa and Patagonia regions of Argentina

Sixteen Argentinean shallow lakes from the Pampa plains and the Patagonian steppe were characterized using optical properties and water-quality parameters. In this set of lakes a wide range in water transparency descriptors was observed [broadband vertical attenuation coefficient ( kd PAR) varied from 0.40 to 47 m −1, Secchi disk depth ( Sd) from 0.07 to 12.00 m, and nephelometric turbidity ( t n) from 0.50 to 103.70 NTU (±10.00)]. Among Pampean lakes, highly turbid lakes presented significant higher kd PAR values (>13 m −1) than clear-vegetated ones (<10 m −1), though all Patagonian lakes showed significant lower light attenuation ( kd PAR<2.5 m −1). Our estimations of light scattering were supported by the significant relationship found between t n and Effler and Auer's scattering coefficient estimate ( b est). Allowing for lakes with t n<80 NTU, we obtained a significant linear regression with a slope close to the unity. However, when values of t n were higher than 80 NTU, no clear relationship was observed between t n and b est. Although we found significant relationships between kd, Sd and t n over the whole range of underwater light scenarios, we noticed some disparities between Sd, t n and light attenuation in lakes with certain optical characteristics. Considering the whole data set, including clear and turbid lakes, as much as 92% of the variation observed in kd PAR could be explained by a regression model including absorption of chromophoric dissolved organic matter (CDOM) and t n. Our results showed that a suitable and practical method to estimate light attenuation could be the use of empirical models based on absorption coefficients and t n measured with bench top instruments. The direct measurement of paired values of Sd and t n, in addition with main absorbing components are a useful and precise way of describing underwater light availability and optical regimes. The latter, combined with occasional in situ measurements of kd would permit the development of highly accurate lake-specific models of light attenuation.

Effects of fish manipulation on the plankton community in small hypertrophic lakes from the Pampa Plain (Argentina)

Trophic cascade hypotheses predict that fish will affect the structure and biomass of pelagic plankton communities. In order to investigate trophic cascade effects from fish down to phytoplankton, whole-lake studies were performed in five hypertrophic (mean total phosphorus (TP) concentrations higher than 1000 mg m −3) shallow lakes located in the Pampa Plain. The main climatic characteristic of this region is the alternation between periods of drought and flood, with corresponding changes of lake depth and conductivity of lake water. All lakes were studied from April to December 2000. Samples were taken of their physical and chemical characteristics and biotic communities, focusing on the zooplankton community. Fish were manipulated in four lakes (Capurro, Longinotti, Vedia 1, Vedia 2), while the fifth (Lake Vedia 3) was left undisturbed as a reference system. High abundance of planktivorous minnows ( Jenynsia multidentata and Cheirodon interruptus) dominated the fish community in the reference lake. In the manipulated lakes, fish stocks were largely reduced in late autumn (May). During winter, Capurro, Longinotti and Vedia 1 were stocked with a visual planktivore, the pampean silverside ( Odontesthes bonariensis, Atherinidae). Fish stocking was 24, 33 and 19 kg ha −1, respectively. In contrast, no fish were stocked in Lake Vedia 2. Following fish removal, large Daphnia appeared in these lakes and grazed intensively on the phytoplankton. In contrast, no Daphnia were found in the reference lake (Vedia 3). The stocking of O. bonariensis in lakes Capurro, Longinotti and Vedia 1 led to a decrease in the percentage of large cladocerans and a rise in the phytoplankton biomass:TP ratio. Moreover, the lakes mentioned were stocked with different quantities of silversides over different periods of time. These differences were reflected temporarily in the plankton dynamics, affecting mainly larger sized zooplankton. Nevertheless, the presence of Daphnia was short lived in the lake where fish had been removed and no O. bonariensis were stocked. Competition for resources and recruitment of remaining fish probably caused a collapse in the zooplankton biomass. Our results support the idea that fish predation on zooplankton and its effect on phytoplankton is very intense in small pampean lakes. Fish removal was short lived, however. This could be because in small pampean lakes fish recolonization is favored, and minnows are highly prolific. Moreover, if manipulation of the trophic structure of lakes is undertaken in the pampean region, high nutrient loading from the watershed, climate and hydrology should also be taken into account.

Main diseases of pejerrey (Odontesthes bonariensis) in central Argentina

Argentina's central region includes an important area covered by shallow pampean lakes and dams. In these environments, fishing of pejerrey Odontesthes bonariensis Valenciennes, 1835 (Pisces, Atherinopsidae), the most important fresh-water fish of the country, is a relevant social activity and also a considerable economic resource. The main diseases found in this species were studied from 1992 to 2003 in the provinces of Córdoba, La Rioja and Santa Fe (30º and 35º S, 61º and 67º W). Most cases were registered in high temperature months. Lernaea sp and Aeromonas hydrophila were the etiological agents most frequently found. The trophic characteristics of the aquatic environments enhanced disease processes and caused massive death of O. bonariensis, due to complex hydrochemical interactions.

Silica dynamics in a pampean lake (Lake Chascomús, Argentina)

Silica dynamics in a pampean lake, Lake Chascomús (Chaco-Pampa plain, Argentina) is described. Pampean lakes are shallow alkaline ecosystems, with circulation pattern corresponding to polymictic lakes, due to the nearly continuous vertical mixing that promotes a high concentration of suspended particulate matter and low transparency. A silica budget was calculated in Lake Chascomús in 1999–2000 using a one-box model that constitutes the first one for a shallow pampean lake. In general terms, the dissolved silica in Lake Chascomús contributed by streams and groundwater, the latter responsible for 70% of the incoming dissolved silica, was able to support the diatom production development. However, in the algal bloom period (spring and summer), the winter input contributed by the streams and groundwater was insufficient, and therefore, an extra source of dissolved silica was necessary. Dissolution of silicate mineral phases, or silica desorption from metallic oxides might provide the dissolved silica needed for the seasonal increase in diatom abundance.

Assessment of Social and Economic Factors For Management of Summer Pejerrey Recreational Fisheries in Pampean Lakes (Argentina)

ABSTRACT This study illustrates the importance of assessing social and economic variables for management of recreational pejerrey fisheries in Pampean lakes. We conclude that summer pejerrey anglers differed by lakes in their motivations, preferences, and economic valuation of their fisheries and that most of the differences were attributed to travel distance, facilities, and quality of the fishery. We surveyed four fisheries located in different geographical areas, assessing preference and motivation by interviewing boat anglers at access points and then applying the contingent value method to assess economic values under current and different management conditions, (greater catch or larger size). Results indicated that anglers considered factors other than catching fish to be important, and a continuum of preferences and motivations was observed on a regional basis. Economic analysis yielding expenditures for study lakes averaged US$ 126,000. Consumer surplus for current conditions averaged 30% greater than actual trip costs. Under the preferred management option for the better fishing (greater catch or larger size, depending on the lake), average consumer surplus increased 65% over current expenditures, to US $208,000 per lake. The combination of socio-economic information representing non-market goods with traditional biological and fishery data will provide more comprehensive management criteria to achieve sustainable pejerrey fisheries in Pampean lakes.

Structural Indices for Stock Assessment of and Management Recommendations for Pejerrey Odonthestes bonariensis in Argentina

Stock assessments based on catch per unit effort (CPUE), relative weight (Wr), and proportional stock density (PSD) were conducted on 18 populations of pejerrey in pampean lakes ofeastern Argentina. The CPUE ofgill nets ranged from 2.9 to 435.2 kg/net-night and was correlated with zooplankton biomass (r = 0.68; P < 0.01). The average Wr (the ratio of empirical weight to a “standard” weight for a fish of the same size, expressed as a whole number) of designated size-groups ranged from 68 to 119. Low Wr was apparent in all size-groups in two lakes with high inorganic turbidity and in one hypertrophic lake with a chlorophyll-a concentration higher than 400 μg/L. Among all the lakes, the PSD (the proportion of fish of “quality” size in a stock, expressed as a percentage) ranged from 0 to 90 and was not related to Wr of any size-group. The indices of CPUE and PSD provided useful criteria to define five types of pejerrey populations and propose minimum size or slot length limit regulations for harvest management. These evaluations and recommendations represent major challenges and opportunities for the development of fishery management plans in Argentina.