Jerry Penha

Spatial pattern of a fish assemblage in a seasonal tropical wetland: effects of habitat, herbaceous plant biomass, water depth, and distance from species sources

The influence of habitat, biomass of herbaceous vegetation, depth and distance from permanent water bodies on the structure of fish assemblages of a seasonal floodplain was evaluated using data collected along 22 transects in an area of 25 km 2 in the floodplain of Cuiaba River, Pantanal, Brazil. Each transect was sampled for fish using throw traps and gillnets during the flood period of 2006. Multivariate multiple regression analysis and multivariate analysis of covariance indicated that depth was the only variable that affected the structure of the fish assemblage, both for quantitative data (abundance) and qualitative data (presence-absence). Species such as Neofundulus parvipinnis and Laetacara dorsigera were more abundant in shallower sites (below 25 cm), while Serrasalmus maculatus and Metynnis mola were found mostly in the deepest areas (over 55 cm). However, species such as Hoplias malabaricus and Hoplerythrinus unitaeniatus occurred at all sampled depths. Although the distribution of most species was restricted to a few sites, there was a positive relationship between species richness and depth of the water body. Surprisingly, the replacement of native vegetation by exotic pasture did not affect the fish assemblage in the area, at the probability level considered. A influencia do habitat, biomassa de vegetacao herbacea, da profundidade e da distância de corpos d’agua permanentes sobre a estrutura da assembleia de peixes da planicie sazonalmente inundada foi avaliada com dados coletados em 22 transectos em uma area de 25 km² na planicie de inundacao do rio Cuiaba, Pantanal. Cada transecto foi amostrado para peixes usando “throw trap” e rede de espera no periodo de cheia de 2006. Analises de regressao multipla multivariada e analises de covariância multivariada indicaram que a profundidade foi a unica das variaveis consideradas no estudo que afetou a estrutura da assembleia de peixes, tanto para os dados quantitativos (abundância) quanto para os dados qualitativos (presenca-ausencia). Especies como Neofundulus parvipinnis e Laetacara dorsigera foram mais abundantes em locais mais rasos (abaixo de 25 cm), enquanto as especies Serrasalmus maculatus e Metynnis mola foram encontradas principalmente nos locais mais profundos (acima de 55 cm). Entretanto especies como Hoplias malabaricus e Hoplerythrinus unitaeniatus ocorreram em todas as profundidades amostradas. Apesar de grande parte das especies apresentarem distribuicao restrita a poucos locais, houve uma relacao positiva entre a riqueza de especies e a profundidade do corpo d’agua. Surpreendentemente, no nivel de probabilidade considerado, a substituicao da vegetacao nativa por pastagens exoticas nao afetou a assembleia de peixes na area estudada.

Fishing resources in the rio Cuiabá basin, Pantanal do Mato Grosso, Brazil

The rio Cuiaba is one of the most important tributaries of the upper rio Paraguay basin that form the Pantanal wetlands. The fishing resources of the rio Cuiaba basin were studied based on landing data obtained from the Fish Market of the city of Cuiaba, State of Mato grosso, Brazil. A description is given of the composition and origin of the 2000 and 2001 catch. The rio Cuiaba is the main source of fish for Cuiaba, although some fish sold locally comes from the rio Paraguay. The 2000-2001 catch consisted mainly of migratory species. The main landed species were the pimelodids pintado -Pseudoplatystoma corruscans, cachara -Pseudoplatystoma fasciatum, and jau -Paulicea luetkeni, and the characiforms pacu -Piaractus mesopotamicus, piraputanga -Brycon microlepis, piavucu -Leporinus macrocephalus, and dourado -Salminus brasiliensis. Large catfishes (Pimelodidae) represented 70% of the landed fish, among which pintado was the most abundant. The data indicate that current catches are smaller than those recorded in the early 1980s and fish are caught far off the urban zone. Moreover, although the number and composition of species caught were similar to those of the 80s, the distribution of species abundance has changed. Currently, fisheries catch more carnivorous species than fish from lower trophic levels. These findings cannot be credited solely to overfishing, but appear to result from a complex interaction of factors, i.e., environmental degradation, changes in market preferences, and restrictive legal fishing regulations.

Dinâmica populacional de quatro espécies de grandes bagres na bacia do rio Cuiabá, Pantanal norte, Brasil (Siluriformes, Pimelodidae)

The length structure of the stocks of four species of large Pimelodidae catfishes was used to study the dynamics of their populations in the Cuiaba river basin, north Pantanal. The estimative of the growth parameters, recruitment and mortality rates for the species were obtained. Among the species studied the Barbado presented the fastest growth than the others. The Pintado, Cachara and Jau exhibited similar growth rate. For the Barbado and the Pintado we observed two annual picks of recruitment, however the Cachara and the Jau presented a single annual pick. The analysis of the mortality indicates that the fishing is a source of mortality more important for the Barbado than for the other species.

Variação temporal e espacial na composição de guildas alimentares da ictiofauna em lagoas marginais do Rio Cuiabá, Pantanal Norte

O presente trabalho teve como objetivo avaliar a variacao espacial e temporal das guildas alimentares das comunidades de peixes em 10 lagoas marginais do Rio Cuiaba no Pantanal. As lagoas foram amostradas em tres periodos do ciclo hidrologico (inicio e final da seca e inicio da enchente de 2005). As guildas alimentares foram determinadas atraves da analise do conteudo estomacal das especies mais abundantes da comunidade. Foram analisadas 37 especies pertencentes a oito guildas alimentares (insetivora, herbivora, onivora, zooplanctivora, planctivora, detritivora, bentivora e iliofaga), as quais variaram espacial e temporalmente. Observamos uma mudanca na composicao das guildas troficas entre os periodos e locais analisados, porem o numero de guildas nao variou espaco-temporalmente. Nossos resultados sugerem que as mudancas espaciais e temporais na composicao das guildas podem estar relacionadas com diversos fatores, como as alteracoes na composicao da comunidade onde novas especies podem compor as diferentes guildas; a exploracao de recursos mais abundantes em determinadas epocas do ano favorecendo a presenca de algumas guildas somente em alguns periodos.

A dimensão espacial e temporal da diversidade de peixes da zona litoral vegetada de lagoas marginais da planície de inundação do rio Cuiabá, Pantanal, Brasil

The present work has evaluated the spatial and temporal distribution of fish species richness of the vegetated littoral zone of 15 marginal lagoons in the floodplain of the Cuiaba River, Pantanal. The lagoons were sampled in three periods along of the dry season (June, September and December of 2005), through nine sieve throws distributed systematically at a minimum distance of five meters from each other. We caught 12,784 individuals belonging to seven orders, 21 families and 98 species of fish. Most of the captured species were rare and presented restricted geographical distribution. Drought intensification did not affect the spatial species distribution and the loss of species as dry season proceeded was proportional in the different orders. The total abundance of individuals as well as the richness varied with time. Rarefaction curves indicated that the reduction in richness was an artifact of the reduction in the abundance of individuals. When we compared the estimated richness under a same abundance level we did not find difference among the richness of species in the beginning and at the end of the dry season. Richness estimators indicated that to distribute the samples in the time was an appropriate strategy to reduce the problem of the false absences and to improve the efficiency of the sampling. Thus, our results suggest that for the design of reserves in the Pantanal, areas with a large number of lagoons of different forms and sizes would conserve the regional fish diversity, as the distribution of most small size species is restricted to a few lagoons.

Stability and generalization in seed dispersal networks: a case study of frugivorous fish in Neotropical wetlands

When species within guilds perform similar ecological roles, functional redundancy can buffer ecosystems against species loss. Using data on the frequency of interactions between fish and fruit, we assessed whether co-occurring frugivores provide redundant seed dispersal services in three species-rich Neotropical wetlands. Our study revealed that frugivorous fishes have generalized diets; however, large-bodied fishes had greater seed dispersal breadth than small species, in some cases, providing seed dispersal services not achieved by smaller fish species. As overfishing disproportionately affects big fishes, the extirpation of these species could cause larger secondary extinctions of plant species than the loss of small specialist frugivores. To evaluate the consequences of frugivore specialization for network stability, we extracted data from 39 published seed dispersal networks of frugivorous birds, mammals and fish (our networks) across ecosystems. Our analysis of interaction frequencies revealed low frugivore specialization and lower nestedness than analyses based on binary data (presence–absence of interactions). In that case, ecosystems may be resilient to loss of any given frugivore. However, robustness to frugivore extinction declines with specialization, such that networks composed primarily of specialist frugivores are highly susceptible to the loss of generalists. In contrast with analyses of binary data, recently developed algorithms capable of modelling interaction strengths provide opportunities to enhance our understanding of complex ecological networks by accounting for heterogeneity of frugivore–fruit interactions.

High beta diversity of fishes in vegetated littoral zones of floodplain lakes in the Cuiabá River Basin, northern Pantanal, Brazil

This study evaluated whether the alpha and beta diversity of fishes in vegetated littoral zones of floodplain lakes in the Pantanal are randomly distributed on three different spatial scales: within the lake, among lakes, and between regions. Three alternative hypotheses were contrasted: (1) that regional diversity is generated at local scale, depending on the internal environmental heterogeneity of lakes, (2) that the diversity of fishes in floodplain lakes is produced at intermediate spatial scales, depending on structural differences and on the landscape matrix between lakes, and (3) that the diversity of fishes in the littoral zone is generated at regional scale, due to regional differences in land-use pattern and the presence of a geographical barrier represented by the river. Our results indicate that the regional diversity of fishes in the vegetated littoral zone of lakes in the northern Pantanal is a consequence of high diversity at the local level (α) and the wide differences in species composition among lakes and between regions. This suggests that we need to maintain environmental heterogeneity, represented by the structural differences among the lakes and their landscape matrix as well as regional differences in the flood pattern, if we hope to preserve the diversity of fishes in the region. Besides, it is necessary to establish new conservation units at the different Pantanal subregions, which should incorporate a set of lakes with different landscape features such as size, shape, and distance from and degree of connection to rivers.

The efficacy of clove oil as an anaesthetic and in euthanasia procedure for small-sized tropical fishes

Clove oil is used as a fish anesthetic because it is a natural and inexpensive product with low toxicity risks. The goal of the present study was to determine the appropriate concentration of clove oil for small-sized tropical fish to be used in mark-recapture studies or when individuals are to be sacrificed. We applied three different clove oil concentrations (D1=0.05 mL, D2=0.10 mL and D3=0.20 mL per 500 mL of water) on three small-sized fish species. We found a negative relationship between induction time and treatment for two species (Hyphessobrycon sp.1 and Hemigrammus sp.), while concentration was unrelated to recovery time. Fish body length was positively related to induction time in the D2 treatment for Hemigrammus sp., and negatively for Hyphessobrycon sp.1 in the D1 treatment, but was unrelated to recovery time for three species and treatments. Mortality rates varied across treatments, but higher rates were observed with higher clove oil concentrations. We conclude that 0.05 mL of clove oil per 500 mL of water is the most efficient dose for studies where fish will be released back to their natural habitats, while 0.20 mL of clove oil is recommended for studies that require fish euthanization for further laboratory analyses.

Persistence and stability of cichlid assemblages in neotropical floodplain lagoons

In this study, we evaluated how cichlid assemblages are affected by seasonal and interannual variations in water volume in the floodplain lagoons of the Cuiabá River in the Pantanal wetland. Eleven lagoons were sampled in the early dry season and the early rainy season over a three-year period. Analysis of similarity (ANOSIM) showed that the species compositions and relative abundances were distinct between the seasons, which indicates that neither persistence nor stability was maintained on a seasonal basis. However, the interannual comparisons show the opposite tendency, indicating strong stability and persistence on an annual basis. These results indicate that the cichlid assemblages in these lagoons have two equilibrium points, one in the early dry season and the other in the early rainy season, and that the assemblages alternate between these points through the hydrologic cycle. In addition to the effect of the water level variation, the abundance distribution is also affected by conductivity and pH, which also influence the total abundance of the species in the assemblage.

Interchange between flooding and drying, and spatial connectivity control the fish metacommunity structure in lakes of the Pantanal wetland

We evaluated if the homogenizing effect of flooding and the environmental differentiation during the dry period, as reflected in fish communities, are related to the type of connection between floodplain lakes and rivers. In order to do this, we sampled fish in the early dry and the early flood hydroperiods. We estimated the fish assemblage structure, as fish species richness, abundance, biomass, and beta diversity. We found that biomass varied among connectivity levels and hydroperiods, while richness varied among hydroperiods and density was influenced by an interaction between connectivity and hydroperiod. Species composition varied as a function of both connection type and hydroperiod, but the interaction between these factors was not observed. The fish assemblage in isolated lakes differed from those in temporarily and permanently connected lakes. Beta diversity increased from the early dry to the early flood period and was higher in temporarily connected lakes than in permanently connected lakes. These results indicated that the spatio-temporal variations in local fish communities of floodplain lakes can be attributed to differences in connectivity. Consequently, they strengthen the hypothesis that dispersal plays a fundamental role in shaping the pattern of fish species diversity in floodplain lakes.