Nelson Ferreira Fontoura

Fish and aquatic habitat conservation in South America: a continental overview with emphasis on neotropical systems.

Fish conservation in South America is a pressing issue. The biodiversity of fishes, just as with all other groups of plants and animals, is far from fully known. Continuing habitat loss may result in biodiversity losses before full species diversity is known. In this review, the main river basins of South America (Magdalena, Orinoco, Amazon and Paraná-La Plata system), together with key aquatic habitats (mangrove-fringed estuaries of the tropical humid, tropical semi-arid and subtropical regions) are analysed in terms of their characteristics and main concerns. Habitat loss was the main concern identified for all South American ecosystems. It may be caused by damming of rivers, deforestation, water pollution, mining, poor agricultural practice or inadequate management practice. Habitat loss has a direct consequence, which is a decrease in the availability of living resources, a serious social and economic issue, especially for South American nations which are all developing countries. The introduction of exotic species and overfishing were also identified as widespread across the continent and its main freshwater, coastal and marine ecosystems. Finally, suggestions are made to find ways to overcome these problems. The main suggestion is a change of paradigm and a new design for conservation actions, starting with integrated research and aiming at the co-ordinated and harmonized management of the main transboundary waters of the continent. The actions would be focused on habitat conservation and social rescue of the less well-off populations of indigenous and non-indigenous peoples. Energy and freshwater demands will also have to be rescaled in order to control habitat loss.

Estimating size at first maturity (L50) from Gonadossomatic Index (GSI) data

Correct estimates of size at first maturity (L50) are useful for fish stock management and different methods have been proposed. In this study we propose the use of a modified logistic to estimate L50, including a variable asymptote (A). We also test the use of the Gonadossomatic Index (GSI) as a flag to establish the reproductive status of each female fish. The method is demonstrated using GSI data for four Neotropical fish species: Characiformes: Astyanax fasciatus (n = 473) and Oligosarcus robustus (n = 297); Siluriformes: Loricariichthys anus (n = 427) and Trachelyopterus lucenai (n = 195). The results were stable enough to propose this method be used for other fish species with different life histories and with a relatively unconstrained sampling programs. Nevertheless, a wide scale test program is desirable to identify any possible bias in this approach.

Seasonal changes in the gonadossomatic index, allometric condition factor and sex ratio of an auchenipterid catfish from eastern Amazonia

The aim of the present study was to evaluate the seasonal pattern of the gonadosomatic index (GSI), condition factor (K), and sex ratio in the catfish Auchenipterichthys longimanus (Siluriformes: Auchenipteridae) as an approach to identify its reproductive period. A total of 589 A. longimanus specimens (251 males and 338 females) were captured in the rivers of the Caxiuana National Forest, in the Brazilian state of Para, between July, 2008 and July, 2009. Among the male specimens, 171 were classified as adults and 80 as juveniles, while there were 249 adults and 89 juvenile females. Using a sinusoidal equation, analysis of the GSI revealed a reproductive asynchrony between the genders, with males attaining their highest GSI values in January, while females peaked in March. For males, the sinusoidal regression for GSI values was significant only when used the complete data set (P=0.001), wears no trend was identified for bimonthly means (P=0.136). For females, by contrast, significant values were obtained for both the complete data set (P=0.012) and bimonthly GSI means (P=0.026). For the condition factor, the sinusoidal equation returned significant seasonal variation in both raw data (P=0.02) and with mean values (P=0.00) for males, but only with raw data for females (P=0.04), which appears to reflect variation in the energy budget between genders. With regard to the sex ratio, more reproductive females were captured than males in January and March, 2009, which suggests a pattern of segregation related to the reproductive process. These parameters are fundamental to the assessment, protection, and management of natural fish stocks, as well as providing guidelines for the development of conservation strategies.

Can weight/length relationship predict size at first maturity? A case study with two species of Characidae

A weight/length relationship was established for Astyanax jacuhiensis (Cope, 1894) (n = 370) and Cheirodon ibicuhiensis Eigenmann, 1915 (n = 701), from samples taken monthly in Fortaleza Lagoon, Cidreira, Rio Grande do Sul, from December 1991 through November 1992. Both species showed a polyphasic allometric growth pattern, each stanza described by an independent power equation controlled by a switch function. For C. ibicuhiensis, this change in the growth pattern occurred at 2.948 cm standard length (SL), close to published sizes for the attainment of female maturity. The change in the growth pattern of A. jacuhiensis (SL = 3.481 cm) was below the predicted size at first maturity, and merits further investigation. Although not conclusive, our data suggest that a complex growth pattern is frequent in nature, and perhaps is not usually identified because trends are obscured by natural variability. Despite the increased complexity resulting from the application of a more-complex equation, the identification of a change in the growth pattern could indicate important aspects of fish biology, including the attainment of sexual maturity.

Statistical distribution models for migratory fish in Jacuí basin, South Brazil

The aim of the present study was to identify the distribution patterns of migratory fishes in the Jacui river basin (Rio Grande do Sul, South Brazil), proposing a statistical model of presumed distribution based on geomorphologic environmental data. Through maps of occurrence probability, we hope to contribute to decisions regarding basin environmental management. The analyzed species were: Salminus brasiliensis (dourado), Leporinus obtusidens (piava), Prochilodus lineatus (grumata) and Pimelodus pintado (pintado). Samples were made through interviews with fishermen and local inhabitants, covering the main channel and tributaries of the rivers Jacui, Taquari-Antas, Vacacai, Vacacai-Mirim, Pardo, Pardinho, Sinos, and Cai. The sampling program resulted in 204 interviews, being 187 considered as valid in 155 different sampling points. The probability of migratory fish occurrence was adjusted through the LOGIT routine of the Idrisi Andes Software: P = e (b0 + b1 . altitude + b2 . basin area) . (1 + e (b0 + b1 . altitude + b2 . basin area) ) -1 , where P is the occurrence probability of the species (0-1) and b 0 , b 1 and b 2 are the equation parameters. Model accuracy, for estimating presence, ranged from 82% to 93%. Pimelodus pintado was cited to occur in 121 points among the 155 sampled (78.06%), Prochilodus lineatus in 72 (46.45%), L. obtusidens in 62 (40.00%) and S. brasiliensis in 58 (37.42%). Equation parameters were estimated (± standard error) as follow: S. brasiliensis: b 0 = -2.8762 ± 0.2597; b 1 = 1.3028 ± 0.0332; b 2 = 1.1487 ± 0.0301; L. obtusidens: b 0 = -0.8364 ± 0.2213; b 1 = -1.5564 ± 0.0462; b 2 = 0.9947 ± 0.0206; Prochilodus lineatus: b 0 = 0; b 1 = -1.3067 ± 0.0544; b 2 = 0.8128 ± 0.0177; Pimelodus pintado: b 0 = -0.9487 ± 0.3688; b 1 = -0.8269 ± 0.0496; b 2 = 0.9255 ± 0.0304. O objetivo do presente estudo foi identificar o padrao de distribuicao de peixes migradores da bacia hidrografica do rio Jacui (Rio Grande do Sul, Sul do Brasil), propondo um modelo matematico de distribuicao presumida baseado em parâmetros ambientais geomorfologicos. Atraves de mapas de probabilidade de ocorrencia, espera-se contribuir para a tomada de decisoes relacionadas ao gerenciamento desta bacia hidrografica. As especies analisadas foram: Salminus brasiliensis (dourado), Leporinus obtusidens (piava), Prochilodus lineatus (grumata) e Pimelodus pintado (pintado). As amostras foram obtidas a partir de entrevistas com pescadores e moradores locais, percorrendo-se a calha principal dos rios Jacui, Taquari-Antas, Vacacai, Vacacai-Mirim, Pardo, Pardinho, Sinos e Cai. O programa de amostragens resultou em 204 entrevistas, sendo 187 consideradas como validas em 155 pontos diferenciados. A probabilidade de ocorrencia de peixes migradores foi ajustada utilizando-se a rotina LOGIT do software Idrisi Andes: P = e (b0 + b1 . altitude + b2 . area de bacia) . (1 + e (b0 + b1 . altitude + b2 . area de bacia) ) -1 ; onde P e a probabilidade de ocorrencia da especie (0-1) e b 0 , b 1 e b 2 sao os parâmetros da equacao. Pimelodus pintado foi citado como presente em 121 pontos dentre os 155 amostrados (78.06%), Prochilodus lineatus em 72 (46.45%), L. obtusidens em 62 (40.00%), e S. brasiliensis em 58 pontos (37.42%). A precisao do modelo, para a presenca estimada, ficou entre 82% e 93%. Os parâmetros estimados da equacao sao descritos a seguir: S. brasiliensis: b 0 = -2.8762 ± 0.2597; b 1 = -1.3028 ± 0.0332; b 2 = 1.1487 ± 0.0301; L. obtusidens: b 0 = -0.8364 ± 0.2213; b 1 = -1.5564 ± 0.0462; b 2 = 0.9947 ± 0.0206; Prochilodus lineatus: b 0 = 0; b 1 = -1.3067 ± 0.0544; b 2 = 0.8128 ± 0.0177; Pimelodus pintado: b 0 = -0.9487 ± 0.3688; b 1 = -0.8269 ± 0.0496; b 2 = 0.9255 ± 0.0304.

Food-web structure in a subtropical coastal lake: how phylogenetic constraints may affect species linkages

To describe a food-web structure is a main goal in any attempt to understand ecosystem functioning. In the present study, we analysed the isotopic composition (δ13C and δ15N) of primary producers and consumers in the large subtropical Mangueira Lake in southern Brazil. On the basis of the δ13C and δ15N values and analysis of stomach contents of several fish species, we provide a description of the food-web structure and trophic positions of the dominant fish species. Analysis of nitrogen isotope ratios indicated the existence of two consumer trophic levels. Isotopic signatures of primary consumers were compatible with those of producers, indicating a food web sustained by autochthonous carbon. Nevertheless, when food items were classified in larger groups by relative size and source, the combined analysis of isotopic signature and feeding preferences revealed a phylogenetically structured arrangement for the fish species of Mangueira Lake. This indicates that the main feeding niches are shared by taxonomically related species.

Reproductive characteristics and the weight-length relationship in Anableps anableps (Linnaeus, 1758) (Cyprinodontiformes: Anablepidae) from the Amazon Estuary

The present study analyzed the length-weight relationship and some aspects of the reproductive biology of Anableps anableps from the mouth of the Maracana River, in the Brazilian state of Para. The specimens were collected using two 30 m-long gillnets with 15 and 20 mm mesh size, as well as a 1 m-diameter hand net with a 10 mm mesh. A total of 865 specimens were collected, from which an adult sex ratio of 2.12 females per male was recorded (χ² = 13.07; p<0.05). Females presented positively allometric growth, whereas males were negatively allometric. In the additional analyses, the gonads of 371 female specimens were observed microscopically. Gonadal development was classified in three stages: immature (5.0%), maturing (12.0%), and mature (83.0%). Embryonic development was classified in five phases, according to the size of the embryo and the vitelline sac. Mean fecundity was 12 eggs/embryos per female (range: 1-37 eggs/embryos). A significant relationship was recorded between the standard length of females and ovaries weight (R² = 0.257; p < 0.001), and the number of embryos carried (R² = 0.573; p < 0.001). Mean body length of females at initial sexual maturation (L50) was estimated at 11.7 cm. The species reproduced throughout the year.

Dial behavioral responses of Metamysidopsis elongata atlantica (Crustacea, Mysida) to gradients of salinity and temperature

Metamysidopsis atlantica elongata (Bascescu, 1968) is a common mysid in the surf zone of sandy beaches from the state of Rio Grande do Sul, Brazil, where it is frequently recorded forming dense aggregations. Trough laboratory trials, behavioral responses to salinity (10, 20, 25, 28, 30, 40 e 45), temperature (10, 15, 20, 30±1oC) and light (yes/no) were tested using adult males, adult females and juveniles. Although there was no response to temperature, the species showed clear response to salinity and light. In the presence of light, organisms remained in the bottom of the aquaria, but moved to surface when bottom salinities were increased. In the absence of light, adults moved to the surface. However, juveniles moved down to or remained on the bottom, maybe as a response to avoid adult predation.

The freshwater artisanal fishery of Patos Lagoon.

In this study data relative to the fishery in the freshwater area of the Patos Lagoon are analysed, and the dynamics, fishing gears used and catches evaluated. The results reveal the existence of two fishery strategies: forbidden mesh size gillnets (FMG; <35 mm; square measure) and allowed mesh size gillnets (AMG; ≥35 mm; square measure). In total, 31 species were caught (AMG = 27 and FMG = 24), but selectivity due to mesh size was significant (P < 0·001). The FMG may be very harmful since it captures individuals of most species below size at first maturity, including the target species, the armoured catfish Loricariichthys anus (61% of the total catch). In addition, this gear is used throughout the year, including the closed season (CS; November to January), when the target species is reproducing. Target species for the AMG are larger in size, comprising mainly the mullet Mugil liza, the marine catfish Genidens barbus and the whitemouth croaker Micropogonias furnieri. AMS gillnets were not used during the CS. The use of FMG reveals the need for effective fishery law enforcement and the need for additional studies to assess the status of populations of the exploited species.

Aspects of fish conservation in the upper Patos Lagoon basin

The Patos Lagoon basin is a large (201 626 km(2) ) and complex drainage system in southern Brazil. The lagoon is 250 km long and 60 km wide, covering an area of 10 360 km(2) . The exchange of water with the Atlantic Ocean occurs through a 0·8 km wide and 15 m deep inlet, fixed by 4 km long jetties, at the southernmost part of the Patos Lagoon. The estuarine area is restricted to its southern portion (10%), although the upper limit of saline waters migrates seasonally and year to year, influenced by the wind regime and river discharge. The known number of recorded limnetic fish species is 200, but this number is expected to increase. A higher endemism is observed in fish species occurring in upper tributaries. The basin suffers from the direct impact of almost 7 million inhabitants, concentrated in small to large cities, most with untreated domestic effluents. There are at least 16 non-native species recorded in natural habitats of the Patos Lagoon basin, about half of these being from other South American river basins. Concerning the fishery, although sport and commercial fisheries are widespread throughout the Patos Lagoon basin, the lagoon itself and the estuarine area are the main fishing areas. Landing statistics are not available on a regular basis or for the whole basin. The fishery in the northern Patos Lagoon captures 31 different species, nine of which are responsible for most of the commercial catches, but only three species are actually sustaining the artisanal fishery: the viola Loricariichthys anus: 455 kg per 10 000 m(2) gillnet per day, the mullet Mugil liza: 123 kg per 10 000 m(2) gillnet per day and the marine catfish Genidens barbus: 50 kg per 10 000 m(2) gillnet per day. A decline of the fish stocks can be attributed to inadequate fishery surveillance, which leads to overfishing and mortality of juveniles, or to decreasing water quality because of urban and industrial activities and power production. Global climatic changes also represent a major threat to the Patos system by changing the frequency of El Niño-La Niña-Southern Oscillation (ENSO).