Rafael José de Oliveira

Fish ladder of Lajeado Dam: migrations on one-way routes?

Fish ladders are generally conceived to reestablish connectivity among critical habitats for migratory species, thus mitigating the impacts of the blockage of migration routes by dams. If this management tool is to be meaningful for conserving fish species, it must provide a fully permeable connection and assure both upward and downward movements. However, because reservoirs have very different hydrodynamics than the original river, it is expected that, at least in the inner area, they may constitute an additional barrier to this movement, especially for descending fish. Thus, the present study sought to determine if migratory fish and their offspring disperse downstream from the dam after ascending a ladder and spawning in the upper reaches of a basin. To achieve this purpose, we evaluated the limitation imposed by lentic areas to the descent of eggs, larvae and adults of migratory species; we also determined the abundance and composition of larvae present in the plankton near the dam, and compared the intensity of the upward and downward movements of adult fish. Samples of ichthyoplankton were taken upriver, inside the reservoir, in the river downstream from the dam, and in the forebay of the Lajeado Dam on the Tocantins River (Luis Eduardo Magalhaes Hydroelectric Plant), from October, 1999 through September, 2004. The densities of fish ascending and descending the ladder were determined experimentally on eight occasions, from June, 2004 to March, 2005. Due to difficulties in identifying the true fish origin (up or down) in the environments connected by the fish passage system, the evaluation of the distribution of migratory fish in reservoirs was based on the landings of the commercial fishery conducted along the Itaipu Reservoir during the four years preceding (2001 through 2003) the construction of the lateral channel (fish-passage mechanism). Fish eggs and larvae drifting down the Tocantins River did not appear in samples taken in the lower half of the reservoir; those found in water flowing through the spillways, turbines or fish ladder of Lajeado Dam belonged essentially to non-migratory clupeids that spawn in the inner part of the reservoir. In addition, results showed that in a reservoir with no fish-passage mechanism, migrants select habitats that still maintain riverine characteristics, in the upper parts of the impounded area. The downward movements are negligible compared to those upward, in the experiments conducted in the fish ladder. It is concluded, therefore, that the Lajeado fish ladder, and possibly those at other dams, is essentially a one-way route that promotes upstream movements of migrants, without the necessary return of adults or their offspring. Thus, the low permeability of the connections provided by these management tools can drastically increase the level of environmental impact that they were actually intended to reduce.

Movements through a fish ladder: temporal patterns and motivations to move upstream

Fish passages are constructed with the aim of reestablishing connectivity between critical habitats, in order to sustain thosespecies that move over a large area during their lives. The upstream movements of most of the known migratory species aremade for purposes of reproduction (adults) or dispersal (juveniles). The present study was conducted at the ladder con-structed at Lajeado Dam (Luis Eduardo Magalhaes Hydroelectric Power), on the Tocantins River. The objective was to assesswhether there is a temporal pattern in the abundance of fish below the dam and in the ladder, that correlates with their breedi ngseasons. Additionally, it was examined whether reproduction is the predominant motivation of the shoals of fish that ascendthe ladder. Samples were taken monthly from November, 2002 through October, 2003, downriver from the dam with gillnets, andin the resting pools of the fish ladder with cast nets. The analysis of seasonality in the aggregation of the shoals was based onthe temporal variations in abundance and species richness. The possibility of a reproductive motivation for ascending theladder was inferred from the frequency of the stages of gonadal development. However, during the entire study period weobserved a high frequency of individuals with gonads in the pre-vitellogenic stage for all analyzed species, both downriverfrom the dam (97%) and in the fish ladder (98%). These findings suggest that there was no reproductive motivation for theaggregation of the fish downstream and for their entry into the ladder. On the other hand, the dominance of these stagesdownriver suggests that the spawning habitats are distant, and that the upstream movements occur for other reasons such asdispersal and search for more appropriate habitats for feeding and growth. The entrance into the ladder resulted more fromrheophilic behavior, which is more pronounced in migratory species, than from an endogenous motivation linked to reproduc-tive migration.Os mecanismos de transposicao de peixes em barragens visam restabelecer a conectividade entre habitats criticos a manutencaopara as especies que tenham uma ampla area de vida. Os movimentos ascendentes da maioria das especies migradorasconhecidas sao realizados por motivacao reprodutiva (adultos) ou dispersiva (juvenis). Neste contexto, o presente estudo temcomo objetivo avaliar se existe um padrao temporal na abundância de peixes a jusante da barragem e na escada da UHE Lajeado(UHE Luis Eduardo Magalhaes, rio Tocantins) que segue a sazonalidade reprodutiva. Adicionalmente, busca avaliar sereproducao e a motivacao predominante dos cardumes que ascendem a escada. Para isto, as amostragens foram realizadasmensalmente de novembro de 2002 a outubro de 2003 a jusante da barragem, com o uso de redes de espera, e nos tanques dedescanso da escada, com tarrafas. A analise da sazonalidade na agregacao dos cardumes foi baseada nas variacoes temporaisde abundância e riqueza de especies, enquanto a motivacao reprodutiva para a ascensao foi inferida a partir da frequencia dosestadios de maturacao gonadal. Entretanto, durante todo o periodo foi constatada uma elevada frequencia de individuos comgonadas em fase pre-vitelogenica em todas as especies analisadas, tanto a jusante da barragem (97%) como na escada (98%),sugerindo a inexistencia de motivacao reprodutiva para a agregacao dos peixes a jusante e seus ingressos na escada. Por outrolado, o fato destes estadios dominarem as capturas tambem a jusante sugere que os locais de desova estao distantes, e que osdeslocamentos ascendentes ocorrem por outras razoes, como dispersao natural e busca de habitats mais apropriados paraalimentacao e crescimento. Assim, o ingresso na escada decorreu mais do comportamento reofilico, exacerbado nas especiesmigradoras, que de uma motivacao endogena ligada a migracao reprodutiva.

Trophic guilds of fishes in sandbank habitats of a Neotropical river

The objective of this study was to characterize the trophic structure of the community of fishes exploiting riverine sandbank habitats. Collections were carried out during the period of October 1999 to December 2003, on six sand banks in the upper and middle portions of the Tocantins River drainage basin in central Brazil. The availability of food resources was evaluated based on the volume of the items present in the stomachs of all species. A total of 2,127 stomachs of fish belonging to 50 species were analyzed. Nine main trophic guilds grouped the local ichthyofauna according to diet. Aquatic-origin items were the preferred source for 55.5% of the groups analyzed, whereas terrestrial-origin items composed 44.4%. Items of undetermined origin (detritus and sediment), although present in 89% of the guilds, were the predominant food in only one trophic group. Terrestrial insects and fish were the food sources with the largest biomass available in the environment. Sandbank environments are homogeneous, with little shelter and food available; as a rule, the species that occupy these environments are generalists.

Fish, Lajeado Reservoir, rio Tocantins drainage, State of Tocantins, Brazil

The Lajeado HR is the fourth hydroelectric power plant constructed in the rio Tocantins. The implementation of hydroelectric plants in the rio Tocantins basin is of high environmental concern because they may result in severe damage to the ichthyofauna. A species list of the area of influence of the Lajeado HR is provided, in the hope that it will contribute to the knowledge of this potentially threatened ichthyofauna. A few comments on the ichthyofauna of the rio Tocantins drainage are also provided.

Triagem das hemoglobinas S e C e a influência das condições sociais na sua distribuição: um estudo em quatro comunidades quilombolas do Estado do Tocantins

Neste trabalho foi realizada a triagem das hemoglobinas S e C e o estudo do perfil social de quatro comunidades quilombolas. O estudo foi desenvolvido nas comunidades quilombolas de Malhadinha, Corrego Fundo, Curralinho do Pontal e Manoel Joao, municipio de Brejinho de Nazare (TO). O perfil das hemoglobinas foi obtido com a triagem de 167 amostras de sangue, utilizando o teste de eletroforese em pH alcalino (pH 8,6). Para confirmar o diagnostico, as amostras alteradas foram submetidas a eletroforese em pH acido (pH 6,2). Foram identificadas 11 amostras (6,6%) com hemoglobinas variantes: oito (4,8%) com traco falciforme e tres com hemoglobina C (1,8%). Os dados sociais foram obtidos atraves de entrevista realizada com representantes de 48 familias, levantando informacoes sobre a renda familiar, idade, sexo e atividade ocupacional de cada individuo. O estudo mostrou que essas comunidades sao formadas predominantemente por adultos e idosos, com renda mensal maior que um salario minimo, para 50% das familias entrevistadas. Apesar do percentual das hemoglobinas S e C encontradas nas comunidades estarem dentro do observado para varias regioes do Brasil, a ausencia de informacao sobre a doenca e os aspectos sociais podem aumentar o numero de individuos com doenca falciforme no municipio ou areas vizinhas.

Feeding ecology of Pterodoras granulosus (Siluriformes, Doradidae) in the Lajeado Reservoir, Tocantins, Brazil

The diet and feeding habits of armado catfish, Pterodoras granulosus (Valenciennes, 1821), were studied in the Lajeado Reservoir, Tocantins, Brazil, and the mouth of its tributaries. Stomach contents of 327 specimens were analyzed by the percentage composition and volumetric methods. The feeding of armado on a wide variety of foods, including both animal and plant items, leads to its classification as a euriphagic species with herbivorous tendency. However, it should be noted that armado showed a strong ontogenetic diet shift, with the gradual replacement of detritus and sediment by plant items, especially terrestrial ones. The environmental use pattern of P. granulosus corroborates the ontogenetic shift observed in its diet. Small fish predominated mainly in the benthic region and detritus and sediment represented an important resource, whereas large fish fed mainly on terrestrial plants, as they explore open water sites and the surface of the water column.

Reproductive biology of Rhaphiodon vulpinus (Ostariophysi: Cynodontidae) in the Tocantins River Basin, Brazil

In order to evaluate aspects of the reproductive biology of Rhaphiodon vulpinus in the Upper and Middle Tocantins River, samples were taken monthly from October, 1999 through September, 2001, by means of gill nets. Males, which were more abundant than females (c2 146.87: df=1: p<0.05), matured at a smaller size. The reproductive period of the species extended essentially from November through January, with a peak of activity in November. Fecundity, with an estimated mean value of 98,185 oocytes, varied from 38,177 to 215,841 oocytes, and it did not correlate with the length of the individual female analyzed (r=0.4663: p=0.206). Relative fecundity was 130.6 oocytes/g total weight. Mature oocytes had a mean diameter of 0.98 mm, corresponding to a volume of 0.50 mm3.

Efeitos alelopáticos de extratos vegetais de Hancornia speciosa, Gomes na germinação de Lactuca sativa L.

Hancornia speciosa Gomes (Apocynaceae) e uma fruteira, conhecida como mangabeira, com ampla distribuicao no Brasil e muito utilizada na medicina popular, por suas propriedades anti-inflamatorias, anti-hipertensivas, antidiabeticas e antimicrobianas. Entretanto, nenhum estudo foi realizado com objetivo de avaliar o potencial alelopatico dessa especie. Nesse sentido, esse estudo objetivou investigar a atividade alelopatica de H. speciosa , a partir do extrato aquoso de folhas secas sobre a germinacao de sementes de Lactuca sativa L. O experimento foi conduzido no municipio de Porto Nacional, Tocantins, Brasil, no periodo de agosto/2015 a julho/2016. Folhas de mangabeira coletadas em tres areas de Cerrado foram trituradas, ate obter-se um po que posteriormente foi diluido em agua destilada, resultando no extrato aquoso com concentracoes de 10%, 7,5%, 5,0%, e 2,5% m/v, sendo a agua destilada utilizada como testemunha. Utilizou-se o delineamento inteiramente casualizado, apos a analise do delineamento, nos efeitos dose, local e interacao dose versus local, os graus de liberdade de dose foram desdobrados em polinomios ortogonais. Pode-se verificar que o extrato aquoso de folhas de H. speciosa apresentou efeito alelopatico negativo sobre as sementes de L. sativa , pois retardou a germinabilidade e aumentou o tempo medio de germinacao, enquanto que o indice de sincronia nao foi fortemente influenciado.

Crescimento inicial de Parkia platycephala (Benth.) e Enterolobium timbouva (Mart.) sob condições de campo numa área de Cerrado

Este trabalho teve como objetivo analisar o crescimento inicial de Parkia platycephala e de Enterolobium timbouva (Mimosaceae), especies arboreas nativas de Cerrado, em uma area de Cerrado sentido restrito, no municipio de Porto Nacional, Tocantins. Foram analisados 20 individuos, com leituras realizadas a cada 30 dias, de fevereiro de 2008 a fevereiro de 2010, observando-se as seguintes variaveis: numero de folhas, altura da planta e diâmetro do caule. Entre agosto de 2008 e fevereiro de 2010, estudou-se tambem a dinâmica foliar, para a qual foram selecionados, aleatoriamente, cinco individuos de cada especie, nos quais foram escolhidos tres ramos e todas as suas folhas foram marcadas. Para cada folha marcada, foram anotados os periodos de natalidade e de abscisao. Avaliou-se, ainda, a herbivoria foliar, por meio de uma escala de quatro classes com intervalos de 25% entre elas. De acordo com os dados analisados, pode-se verificar que P. platycephala e E. timbouva apresentaram maior producao de folhas, bem como maior crescimento em altura, no periodo chuvoso. Em relacao ao diâmetro, P. platycephala apresentou resultados superiores aqueles observados em E. timbouva. A taxa de crescimento relativo apresentou aumentos mais pronunciados durante o periodo chuvoso, em ambas as especies. No que se refere a herbivoria, tambem foi verificado um aumento em sua intensidade, no periodo chuvoso, nas duas especies. Como elas foram expostas a condicoes ambientais semelhantes, a maior taxa de crescimento relativo, observada em P. platycephala, pode ser atribuida as suas caracteristicas fisiologicas e anatomicas, que, dentre outros fatores, contribuiram para menor predacao por herbivoros.