Fragmentation of a Neotropical migratory fish population by a century-old dam

Loss of connectivity in impounded rivers is among the impacts imposed by dams, and mitigation measures such as fish passages might not accomplish their purpose of reestablishing an efficient bi-directional gene flow in the fish populations affected. As a consequence, fish populations remain fragmented, and a new interpopulational structure may develop, with increased risk of reduced genetic diversity and stochastic extinction. In order to evaluate the effects of the Gavião Peixoto Dam, which was constructed almost a century ago on the Jacaré-Guaçu River in the Upper Paraná River basin, Brazil, a comparative morphometric study was undertaken on the populations of the Neotropical migratory characid fish Salminus hilarii living up- and downstream of this dam. Population dynamics, spatial segregation, and habitat use by different age classes were monitored for 2 years. We found that segregation caused by the dam and long periods with no efficient connection by fish passages have led to fragmentation and interpopulational structuring of S. hilarii, as revealed by canonical variable analysis of morphometric features. The fish populations occupying the up- and downstream sections have succeeded in performing short-distance reproductive migrations in the main river and tributaries, have found suitable habitats for completing their life cycle, and have been able to maintain distinct small-sized populations so far.     

Hydrological alterations enhance fish invasions: lessons from a Neotropical coastal river

Hydrobiologia - With the aim of assessing whether hydrological alterations differently affect non-native and native fish species in coastal systems, we investigated fish assemblages along the...     

Habitat structural complexity and morphological diversity of fish assemblages in a Neotropical floodplain river

High species richness and evenness in structurally complex habitats has been hypothesized to be associated with niche partitioning. To test this idea, relationships between habitat structural complexity in river littoral-zone habitats and morphological diversity of tropical fishes were examined in the Cinaruco River, Venezuela. Six habitat attributes were quantified in 45 sites spanning a range of structural complexity. Fishes were collected during day and night to estimate species density and relative abundances at each site. Twenty-two morphological variables were measured for each species. Principal components analysis (PCA) of physical habitat data yielded two axes that modeled >80% of variation across sites. The first two axes from PCA of fish morphological variables modeled >70% of variation. Species density during both day and night was negatively associated with flow velocity and positively associated with habitat complexity. Similarity of day and night samples from the same site was significantly greater for sites with high habitat complexity and low flow. In general, mean local assemblage morphological PC scores were not significantly associated with habitat PC scores. Average, maximum, and standard deviation of morphological Euclidean distances of local assemblages revealed positive associations with structural complexity and negative associations with flow. These relationships held even when the positive relationship of species density was statistically removed from assemblage morphological patterns. Findings suggest that both species niche compression and assemblage niche space increase when habitat complexity is greater and flow velocity is lower in this tropical lowland river.Electronic Supplementary Material Supplementary material is available for this article at     

Biocomplexity in a highly migratory pelagic marine fish, Atlantic herring

The existence of biologically differentiated populations has been credited with a major role in conferring sustainability and in buffering overall productivity of anadromous fish population complexes where evidence for spatial structure is uncontroversial. Here, we describe evidence of correlated genetic and life history (spawning season linked to spawning location) differentiation in an abundant and highly migratory pelagic fish, Atlantic herring, Clupea harengus, in the North Sea (NS) and adjacent areas. The existence of genetically and phenotypically diverse stocks in this region despite intense seasonal mixing strongly implicates natal homing in this species. Based on information from genetic markers and otolith morphology, we estimate the proportional contribution by NS, Skagerrak (SKG) and Kattegat and western Baltic (WBS) fish to mixed aggregations targeted by the NS fishery. We use these estimates to identify spatial and temporal differences in life history (migratory behaviour) and habitat use among genetically differentiated migratory populations that mix seasonally. Our study suggests the existence of more complex patterns of intraspecific diversity than was previously recognized. Sustainability may be compromised if such complex patterns are reduced through generalized management (e.g. area closures) that overlooks population differences in spatial use throughout the life cycle.     

Extended jurisdiction and the management of Pacific highly migratory species

Abstract

The Pacific region is the most important producer of tropical tuna in the world. Three subregions account for the production: Pacific Latin America, the Pacific Islands region, and Southeast Asia. Prior to the UN Third Conference on the Law of the Sea, the Tuna Fisheries in the subregions were the preserve of developed distant water fishing nations. The situation has now been entirely reversed, with coastal state jurisdiction and control being realized in all three subregions. It is argued that American opposition to coastal state jurisdiction over tuna resources acted as a goad to the coastal states in Pacific Latin America and the Pacific Islands region in their quest for greater control over tuna resources. There are prospects of cooperation developing among the three Pacific subregional tuna producers. It is argued further that American action may have inadvertently accelerated the progress toward cooperation.     

Uncertainty in estimating fish trophic positions and food web structure in highly polluted river basins

Environmental Biology of Fishes - Tributaries greatly influence the supply of organic matter to large rivers. In this study, we used carbon (?13C) and nitrogen (?15N) stable isotopes to...     

Genetic structure of island and mainland populations of a Neotropical bumble bee species

As a consequence of founder effects, small population size and demographic constraints, island populations are often characterized by low genetic diversity and high inbreeding. The effects of inbreeding are more pronounced in haplo-diploid insects like bees than in similar diploid species, because their method of sex determination requires heterozygosity at a sex locus. Inbreeding leads to homozygosity at the sex locus and the production of non-viable diploid males. This means that island populations of bees are particularly prone to extinction. Here we determine the levels of diversity and isolation between islands and mainland populations of the bumble bee Bombus morio in southeast Brazil. We analyzed 659 individuals from 24 populations, sequencing two mitochondrial genes (COI and Cytb) and genotyping all individuals at 14 microsatellite loci. Surprisingly, genetic diversity was high and genetic isolation was low in all populations except Teodoro Sampaio (mainland) and Ilha da Vitória (island). Genetic diversity is not significantly correlated with island area, but is lower in populations that are more distant from the mainland. Except perhaps for Ilha da Vitória, we suggest that the island populations are unlikely to go extinct due to genetic factors. Finally, based on its genetic distance from all other populations, we identify a putative new subspecies in the Teodoro Sampaio region.     

Seasonal response of fish assemblages to habitat fragmentation caused by an impoundment in a Neotropical river

Changes in fish assemblages between the zones above and below Funil dam in Southeastern Brazil were investigated to evaluate the possible impacts of this impoundment in two contrasting seasons: summer/wet and winter/dry. We expect differences in fish assemblage structure and in environmental conditions between seasons and between the reservoir and the zone downriver of the dam. A total of 3,579 individuals comprising 38 species, including six non-natives, were collected. As expected, the comparatively high habitat complexity and water flow regime of the downriver zone favored a richer and more abundant fish assemblage compared with the reservoir, especially in the wet season. In this period, water covers part of the riparian vegetation, increasing habitat availability and nutrient input. Additionally, the dam prevents upriver migration of rheophilics fish species such as the Characiformes Prochilodus lineatus and Leporinus copelandii, and the Siluriformes Pimelodus fur and Pimelodus maculatus, thus increasing shoals below the dam. Although the reservoir represents a simplified ecosystem highly influenced by non-native top predator species (e.g. the Perciformes Cichla kelberi and Plagioscion squamosissimus), seasonal processes (e.g. water level fluctuations and flood pulses) seem to play a role in structuring of the fish assemblage. Environmental variables, mainly turbidity, temperature, and conductivity were significantly associated to spatial-temporal patterns of fish assemblage. In this freshwater tropical reservoir, the spatial scale, rather than the seasonal changes in environmental variables, was the dominant factor structuring fish assemblage in the reservoir and in the zone downriver of the dam.     

Metacommunity of a host metapopulation: explaining patterns and structures of a fish parasite metacommunity in a Neotropical floodplain basin

Host-parasite metacommunities are influenced by a myriad of factors, although little is known about which processes affect this relationship at different scales. Here, we tested how local habitat characteristics and host traits explained the parasite metacommunity of a migratory fish in a large Brazilian river floodplain. The parasite metacommunity structure showed a Clementsian pattern, which indicates a more deterministic assembly pattern, in accordance with partial Redundancy Analysis results. Results indicated that species filtering is the predominant mechanism driving community assembly. Patterns were clearer in the dry season of the floodplain. Environmental determinism seems to explain ectoparasite metacommunities in the dry season, in contrast with endoparasites that were more correlated to host traits. Overall, our results indicated that ectoparasitism is an interaction marked by opportunity, whereas endoparasitism is likely related to host features. Thus, we argue that metacommunity structuring of parasites depends on the infection strategy. Our results show that floodplain dynamics are central not only for free-living animal organizations but also for symbiotic interactions. Here, we highlight the importance of understanding the factors influencing the distribution of parasites to predict their transmission, as well as the importance of floodplain dynamics and its hydrological regime on the maintenance of ecological interactions.

     

Reef fish diversity components as indicators of cumulative effects in a highly impacted fringe reef

The main goal of our research was to determine which indicators describing cumulative stress might better explain the differences observed in diversity components of reef fish assemblages off Havana City, Cuba. A total of 35,078 individuals of 119 species were counted in 480 stationary point censuses. Counts were distributed among three zones with different levels of pollution and four habitats with different wave stress. Four indexes of diversity components (S, H′, J′ and PIE) were calculated and correlative analyses performed to explore the best indicators of cumulative effects explaining observed variation. High correlation was found between all diversity components and two indexes of cumulative effects (ICE) built after distinct criteria. In the first case, pollution and wave action were combined following an interactive model. In the second case, an empirical ICE was obtained by totaling the abundance indicators of three groups of organisms, namely sponges, sabellid polychaetes and filamentous algae.     

Environmental management of a highly impacted,urbanized tropical estuary: rehabilitation and restoration

The principles of the dynamics and interrelationships within the dominant subtropical and tropical Caribbean seagrass community have been studied previously before, during, and after impact. From these and scores of observations of damage and recovery patterns inThalassia ecosystems, a sense of management recovery strategy has emerged. Artificial restoring ofThalassia testudinum seeds into areas cut off from stock (fruit, seeds) appeared feasible on a large scale after the Turkey Point (Biscayne Bay, Miami, Florida) restoration and test sampling throughout North Biscayne Bay. Two large-scale seeding attempts were made; after 11 months they compared favorably with Turkey Point specimens with regard to growth parameters, despite the turbidity and other persistent pollution. Thus, the possible areas in whichThalassia seed restoration can be used has increased to include estuaries of multiple impact still in various stages of recovery after physical and sewage pollution. This technique should be especially useful to “developing” nations where important nearshore fisheries nurseries based onThalassia ecosystems have been heavily damaged and now lie barren. Man's impact on the estuary where seed restoration was attempted includes the following activities: 50% of the bay bottom directly dredged or filled (leaving much unconsolidated sediment); 50 million gallons of domestic waste dumped directly into a low flushing part of the bay for 20 years; seven major causeways transecting the bay, restricting circulation and flushing; two artificial inlets made into navigational channels; freshwater sheet flow drastically changed due to channelization by flood-control canals; urban runoff from a million people entering the bay. Most of the impacts have now abated; however, their long-term effects remain.     

Genetic diversity and structure of Populus nigra populations in two highly fragmented river ecosystems from Turkey

Tree Genetics & Genomes - This study aimed to further clarify the mechanisms of salt-alkali tolerance in Fraxinus velutina Torr. Shoots obtained from Fraxinus velutina Torr (also known as...     

Toxicity and effects of a glyphosate-based herbicide on the Neotropical fish Prochilodus lineatus

The toxicity of Roundup, a glyphosate-based herbicide widely used in agriculture, was determined for the Neotropical fish Prochilodus lineatus. The 96 h-LC(50) of Roundup was 13.69 mg L(-1), indicating that this fish is more sensitive to Roundup than rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). These differences should be considered when establishing criteria for water quality and animal well-being in the Neotropical region. Short-term (6, 24 and 96 h) toxicity tests were then performed to evaluate the effects of sub-lethal concentrations of the herbicide (7.5 and 10 mg L(-1)) to P. lineatus. Roundup did not interfere with the maintenance of the ionic balance and there was no significant alteration in plasma cortisol levels in Roundup-exposed fish. However an increase in plasma glucose was noted in fish exposed to 10 mg L(-1) of the herbicide, indicating a typical stress response. Catalase liver activity also showed an increase in fish exposed to 10 mg L(-1) of the herbicide, suggesting the activation of antioxidant defenses after Roundup exposure. In addition, Roundup induced several liver histological alterations that might impair normal organ functioning. Therefore, short-term exposure to Roundup at subletal concentrations induced biochemical, physiological and histological alterations in P. lineatus.     

Distribution of fish and the biotopic structure of the basin of the small salmon river (the Nachilova River,Western Kamchatka)

For one of the small Western Kamchatka rivers, according to the combination of several characteristics (watershed, channel slope, water abundance of the flow, pattern of bottom sediments), the classification of channel processes was performed, and on its basis, six biotopes successively replacing each other from the effluents to the mouth were separated. It was shown that against the background of relatively stable conditions of the summer-autumn period, an independent population of Salmonoidei, an assembly, is formed within each biotope. This is manifested in specific features of species composition, size and age structure, and the density of populating biotopes. The stability of the distribution of fish population is supported by constant species composition in particular biotopes over three years and by a comparatively high level of residence of the dominant salmon species.     

Occurrence of Monogenea in Italian freshwater fish (Po river basin)

Sixteen Monogenean species were found on the skin and gills of 10 different fish species collected from north Italian water bodies. Cleidodiscus pricei from Ictalurus melas; Dactylogyrus alatus from Alburnus alburnus; D. anchoratus, D. formosus and D. vastator from Carassius carassius; D. difformis from Scardinius erythrophthalmus; D. rutili from Rutilus aula; D. tincae and Gyrodactylus gasterostei from Tinca tinca; D. ergensi from Leuciscus cephalus and Telestes muticellus; D. vistulae and Paradiplozoon rutili from Leuciscus cephalus; D. extensus and G. katharineri from Cyprinus carpio; G. lucii and Tetraonchus monenteron from Esox lucius. All species are new records for Italy with the exception of D. difformis, D. ergensi, D. vistulae and T. monenteron.