Search

Balanced ecosystems benefit meso and top predators, which help to maintain the quality of the habitat. Thus, the presence of sharks can be considered an indicator of environmental health. Baited remote underwater stereo-videos (BRUVs) were used to assess the relative abundance of sharks in the Alcatrazes Archipelago, Southwestern Atlantic, after an important no-take zone expansion from 12 to 675 km2 with the creation of the Wildlife Refuge and enhanced enforcement, comparing our findings with previous BRUV surveys. This study observed sharks in 16 (10.7%) of the 150 stereo-BRUV deployments and recorded seven species (Squalus cf. albicaudus, Carcharias taurus, Carcharhinus plumbeus, Carcharhinus falciformis, Rhizoprionodon porosus, Sphyrna lewini, and Sphyrna zygaena). These data, combined with the perception of frequent and experienced divers (management staff and diving operators) about the increase in shark sightings, suggest a recent positive effect of the no-take zone for these predators and a healthier ecosystem. Results also show that long-term monitoring and effective enforcement of the Alcatrazes Wildlife Refuge are crucial to maintain and enhance the positive effects in the area. [ABSTRACT FROM AUTHOR]

Marine plastic litter, originating from land-based sources, enters the marine environment by passing through coastal ecosystems such as lagoons and estuaries. As early life history stages (ELHS) of many commercially important fish species rely on these transitional areas as nursery grounds, we hypothesized that they encounter a spatial gradient of habitat quality and pollution from inner to outer parts of their vital environment. With sizes < 5 mm, anthropogenic particles (AP), among them microplastic (MP) fibers and fragments, entail a high bioavailability for ELHS of fish, potentially facilitating AP uptake at early developmental stages which may have implications for their survival and growth. This study provides a contextualization baseline between feeding preferences and uptake of AP by the white seabream Diplodus sargus (Linnaeus, 1758) in an estuarine nursery ground on the southern coast of Portugal. Juvenile fish showed a generalized, omnivorous feeding mode with differences in trophic resource utilization between individuals collected at distinct seagrass meadows in the lagoon. A total of 23.13% of the fish (n = 147) were detected with AP in the gastrointestinal tract, and the mean number of AP per AP-feeding individual was 1.64 ± 1.04, with anthropogenic fibers (n = 47) occurring more frequently than fragments (n = 9). Knowledge of the underlying factors for MP ingestion will be greatly enhanced by considering environmental conditions along with species-stage and life-stage specific feeding modes and prey preferences which shape the uptake probability of anthropogenic fibers and fragments. [ABSTRACT FROM AUTHOR]

The objective of this study was to use larval density data to investigate the temporal reproductive pattern and use of different biotopes of the Paraná River as areas of reproduction and the initial development of the migratory fish Salminus brasiliensis. During 15 reproductive periods (October to March) between 2001 and 2019, three biotopes (channel, tributary, and lake) of the upper Paraná River floodplain were sampled using conical-cylindrical plankton nets equipped with a flowmeter. The highest larvae densities were recorded between October and January, with a predominance of the pre-flexion and flexion stages captured mainly in the Paraná River channel. Larvae in the yolk-sac stage were most common in the tributaries. Temperature, pH, and rainfall were the main variables that influenced larval density. Our results showed that the reproduction of S. brasiliensis may have failed during a few reproductive periods and that the species uses different biotopes of the Paraná River for spawning and development, i.e., the tributaries and the river channels and lakes, respectively. Thus, providing conditions enabling a smooth migration to the tributaries for spawning as well as ensuring safe development in the river channels and lakes during their reproductive periods could help conserve this vulnerable species. Moreover, actions aimed at recovering the stocks of the species depend on the conservation of different floodplain environments and the maintenance of their original characteristics and on policies aimed to conserve the species, such as the prohibition of fishing. [ABSTRACT FROM AUTHOR]

Although many shark species display predictable and seasonal aggregations related to breeding activities, few studies have reported direct evidence of reproductive interactions of large sharks. In this context, the present study reports the first evidence of mating scars in female tiger sharks Galeocerdo cuvier at the Fernando de Noronha Archipelago (FEN), an oceanic remote insular system in the South Atlantic Ocean. Results from the records of seven wounded females suggest that mating activity may occur between February and August. These females measured between 267 and 372 cm in total length, which is aligned with previous studies reporting size at sexual maturity for Atlantic tiger sharks. Although some females exhibited healed wounds, three of them had fresh, open wounds. One of the females also had a swollen and red cloaca. We also report the first presumably gravid female tiger shark for the region. Although sporadic, the observations herein reported indicate the importance of FEN for tiger shark reproduction in western equatorial Atlantic waters. This finding is especially relevant as FEN has been identified as an important genetic hotspot for tiger sharks, with the largest global genetic diversity for the species. [ABSTRACT FROM AUTHOR]

The bentfin devil ray (Mobula thurstoni) is a migratory elasmobranch species with a wide distribution range. Despite the recent increase in mobulid research, critical habitats and home ranges are still being identified for these threatened species. In the present study, photo and video records opportunistically gathered by SCUBA diving effort were used to identify individuals and habitat usage by M. thurstoni in a marine protected area in the western equatorial Atlantic Ocean, Fernando de Noronha Archipelago (FNA). The bentfin devil ray was identified in five distinct records, in different years and sites around the archipelago. All the males showed developed claspers, suggesting mature individuals using the area. The UNESCO heritage site of FNA is considered an area of high biological importance, containing essential habitats for several species of fish, turtles and marine mammals. However, habitat usage by devil ray species is poorly reported in the region; therefore, the present study presents the first report of M. thurstoni at FNA, which adds the fifth mobulid ray species recorded in the region. Additionally, these results correspond to the second record of living specimens of M. thurstoni in Brazilian jurisdictional waters, highlighting new information on the species' distribution and the home range of mobulids in Brazil. [ABSTRACT FROM AUTHOR]

Cookiecutter sharks are pelagic ectoparasites that feed on pieces of flesh from large marine animals. Knowledge on these sharks is still rather scant, with the few existing works successfully using bites found on prey to reveal ecological patterns. This study aims to identify cookiecutter shark bite patterns on pelagic fishes in aggregated schools to gain an understanding of the ecology of these sharks. Data were collected by accompanying landings and onboard in tuna fishing vessels in the western equatorial Atlantic Ocean off Brazil. A total of 138 bite wounds were found on the bigeye tuna (Thunnus obesus), common dolphinfish (Coryphaena hippurus), skipjack tuna (Katsuwonus pelamis), and yellowfin tuna (Thunnus albacares). The most bitten species were the bigeye and yellowfin tuna, together accounting for 85% of all bites. Our findings offer novel insights into ectoparasitic ecology between cookiecutter sharks and pelagic fishes, identifying three major patterns: (i) preference of the sharks for the ventral surface of pelagic fishes; (ii) plasticity in biting tactics, with both bottom-up and lateral attacks; and (iii) habitat-dependent bite incidence (larger sharks commonly bite the skipjack tuna in epipelagic zones, whereas smaller sharks predominantly bite the bigeye tuna in mesopelagic zones). These results contribute to narrowing the gaps in knowledge on the ecology of the elusive, dwarf cookiecutter sharks. Further studies are needed for a better understanding of how shark-pelagic fish interactions are affected by the fishing of aggregated schools. [ABSTRACT FROM AUTHOR]

Scalloped hammerhead shark, Sphyrna lewini, is considered a generalist predator, showing individual specializations and different trophic levels. This species inhabits both oceanic islands and coastal nursery areas in the eastern tropical Pacific (ETP) Ocean. Existing trophic ecology studies on S. lewini have been focused on stomach contents. This study provides new insights into its foraging preferences, habitat use, and trophic position, using stable isotope analysis (SIA) of muscle tissue. Stable isotope signatures of δ13C and δ15N were determined in S. lewini muscles (n = 29) from the Ecuadorian Pacific in 2013. Trophic position (TP), isotopic niches, and overlap of S. lewini were estimated by sex, age, and maturity stages to infer their dietary habits throughout life stages. SIA revealed complex movement patterns related to sex and age classes of S. lewini, highlighting high degrees of dietary plasticity and habitat use, with a stronger relation to coastal regions than previously reported. This study provides crucial information regarding essential areas and the related migration behavior of S. lewini, with important implications for their conservation and management in the ETP. [ABSTRACT FROM AUTHOR]

This study provides information about the diet across geographic areas and throughout ontogeny and sex of two coastal and commercial batoid species in Peru (Chilean eagle ray Myliobatis chilensis and Pacific guitarfish Pseudobatos planiceps). Data was collected in the central coast (13°30′S to 14°30′S; Pisco district, Lima) and in the northern coast (13°12′S to 13°49′S; San Jose district, Lambayeque) off Peru during the second semester of the years 2015 and 2016 (i.e., winter and spring) in an El Niño event. A total of 357 stomach contents were analyzed in northern and central Peru with different oceanographic and ecological conditions. In the central coast, M. chilensis showed a high trophic position (tertiary consumer) due to its high consumption of Peruvian anchoveta (Engraulis ringens), while P. planiceps had a lower trophic position (secondary consumer) and a less specialized diet of benthic invertebrates (i.e., crustaceans and mollusks) and pelagic fish (e.g., E. ringens). In the northern coast, both species preyed mainly upon benthic invertebrates and to a lesser degree on fish; therefore, their trophic position was lower. Dietary variation was influenced by species, geographic location, and ontogeny. The diet variability between geographic locations shows insights of these batoids' trophic plasticity and opportunistic feeding behavior in response to differences in the local prey availability, an effect that may be amplified during the El Niño–Southern Oscillation (ENSO). The spatial variation in this species diet may indicate that they play different ecological roles in distinct environments. This study contributes to the scarce literature about batoids' ecology in the southeast Pacific Ocean and presents novel information on habitat-specific diet composition. [ABSTRACT FROM AUTHOR]

Large sharks generally occupy the highest trophic levels and are important links in the structuring of trophic networks. However, the decline of these predators has been observed worldwide, with population reduction rates reaching over 90% for some species. Through these declines, it is believed that the effect of the loss of predators could result in the disturbances in ecosystems. Based on this, the present study aimed to test the role of elasmobranchs in a coastal ecosystem in southern Brazil. Also, we tested if the changes in fishing effort cause changes in trophic structure. For this, a trophodynamic model was performed, based on reliable data on biomass and species feeding in the region. The mass balance modeling software Ecopath with Ecosim (EwE) was used to assess the trophic position of sharks and rays, and to understand what their interactions are with other groups in the ecosystem. Among the parameters of the model, the Paraná coast showed to be an immature system, with high connectivity and medium complexity. The trophic levels of the coast varied from 1 to 4.4, with level > 4 composed of sharks, and rays belonging to the third trophic level. Sharks were strong impacted by fishing. According to changes in fishing effort simulations, we observed changes of intermediate levels due to the decline of large sharks. However, no cascade effects were observed from the simulations. The high diversity of the system, feeding overlap, and the redundancy between mesopredator and other teleosts can decrease the chances of a cascade effect occurring. [ABSTRACT FROM AUTHOR]

Our study sought to analyze patterns and overlap in prey items consumed by elasmobranch species in southern Brazil through a complex network analysis. We hypothesized that species with the same habitat use would show greater trophic niche overlap and lower diet specialization than species with different habitat use. We conducted a literature survey of the species recorded in southern Brazil and analyzed publications with quantitative data on the diet of each species. We found records of 103 species in the region, of which 58 had their diets analyzed and had quantitative data to contribute to this analysis. The results suggest nested diet patterns in this community. Nestedness may arise for different reasons, and suggests that species might be balancing their high feeding niche overlap through compensatory mechanisms. There are no prior records of such a pattern in elasmobranch communities, which brings to light important information about their feeding niche. Data on prey consumption and temporal and spatial patterns of elasmobranch feeding may yield further insight into how these species are interacting in the environment and assist the investigation of the processes that shaped the current community's trophic structure. [ABSTRACT FROM AUTHOR]

Billfishes are considered important fishery resources and the identification of aggregation sites is imperative for proper management. Here we present evidence of a seasonal aggregation site for juvenile istiophorid billfishes in southern Brazil. We discuss the results as they relate with the need for management at a local scale and participatory monitoring with artisanal fishing communities as a way to ensure access to data on the occurrence and population status in the long term. [ABSTRACT FROM AUTHOR]

Hotspots identification can be used to establish protected or priority areas for conservation at different geographic scales. We aimed to determine if San Andres, Providencia and Santa Catalina Archipelago could be considered as a hotspot of elasmobranch diversity within the Greater Caribbean. For that, we updated the elasmobranch species richness and analyze its distribution pattern, evaluated the assembly structure and composition and estimated the occurrence probability of the more abundant species of the Archipelago. A total of 46 species, 33 of sharks and 13 of batoids were recorded, with 8 categorized as threatened by IUCN. Quadrants of San Andres and Providencia islands presented the highest richness with 16 species. Oceanic environments differed significantly in composition and abundance from the other four large areas evaluated. Northern banks were the most favorable environments for large-sized pelagic sharks while San Andres and Providencia Islands were for batoids; this difference could be due to the pelagic and benthic habits, respectively, and their relation with availability of substrate, food and sheltered areas. Our study confirmed that the Archipelago has at least 21% of the total richness of the northwestern Atlantic region, 43% of that of the Greater Caribbean and 49% of that registered in the Colombian Caribbean Coast, suggesting that the Archipelago is a potential richness hotspot in the Caribbean region. This high elasmobranch diversity could be due, among others, to its status as a Biosphere Reserve, to its high diversity of habitats and more recently to the establishment of the shark fishing ban. [ABSTRACT FROM AUTHOR]

Along the Pacific coast of Baja California Sur (PCBCS), the banded guitarfish (Zapteryx exasperata), shovelnose guitarfish (Pseudobatos productus) and bat ray (Myliobatis californica) are highly abundant. Their ecological roles as predators in demersal communities can be key in this ecosystem. To better understand their trophic relationship in the PCBCS, stable isotopes analysis of carbon (ẟ13C) and nitrogen (ẟ15N) were used. Muscle samples (n = 265) were collected from shovelnose guitarfish (n = 94), banded guitarfish (n = 87) and bat ray (n = 84). We observed high variability in stable isotopes values, ẟ13C and ẟ15N of shovelnose guitarfish ranged from −18.53 to −12.85‰ and 15.93‰ to 20.37‰, respectively; banded guitarfish from −18.12‰ to −13.57‰ and 14.41‰ to 19.26‰, respectively; and bat ray from −17.73‰ to −13.98‰ and 13.97‰ to 18.46, respectively. Statistically significant interspecific differences were found (p < 0.05) for ẟ13C and ẟ15N values, as bat ray showed a lower mean ẟ15N value and less negative mean ẟ13C value. Mature male (MM) bat ray) showed significantly higher ẟ15N values and shovelnose guitarfish (MM) significantly lower ẟ13C values compared to other cohorts. Isotopic niche analysis using Bayesian ellipses (SEAc) indicated shovelnose guitarfish occupies the widest isotopic niche compared with bat ray and banded guitarfish. Based on SEAc, the banded guitarfish overlapped 0.46 with the shovelnose guitarfish, while the bat ray overlapped 0.38 and 0.39 with banded and shovelnose guitarfish, respectively. Reported data suggest there is a relative overlap among all species, with probably greater amount of partitioning between the bat ray and the other two species. [ABSTRACT FROM AUTHOR]

Understanding the ecological role of a species in an ecosystem and the dynamics of the communities depends largely on knowledge of the trophic relationships. We evaluated the feeding habits and the trophic ecology of the endemic Colombian stingray Potamotrygon magdalenae, integrating stomach content and isotopic analyses (13C and 15N). The samples were collected in the middle Magdalena River basin, Colombia, during artisanal fishing operations in the dry and rainy seasons. The stomach content analysis indicated that P. magdalenae fed on a high number of occasional items, such as seeds, Planariidae, Teleostei and Nematoda, with Diptera being the dominant food component at the population level. There were no significant differences in diet between males and females. In contrast, isotopic analysis showed that Coleoptera was the most important food source assimilated by the species, followed by Ephemeroptera; Chironomidae and Trichoptera made the lowest contributions. No significant differences in δ13C and δ15N were observed between the sexes or hydrological seasons. Estimates of the isotopic niche indicated that P. magdalenae has a narrower trophic niche than the teleost fishes present in the study area. The trophic level was identified as intermediate, suggesting that Potamotrygon magdalenae plays a role as a mesopredator in the food web in the study area. [ABSTRACT FROM AUTHOR]

Despite its worldwide distribution and vulnerable status, knowledge on the biology and ecology of the smooth hammerhead Sphyrna zygaena in the temperate NE Atlantic is very scarce. Here, we reveal intra-annual fluctuations in S. zygaena abundance in the Portuguese southwestern coast, using sightings data collected on board whale watching boats over five years (2010-14; excluding winter months). Moreover, we investigated how shark abundance is related to local environmental conditions. We describe the first smooth hammerhead “hotspot” in the NE Atlantic, and we show a recurrent pattern of occurrence during the warmer summer and autumn months (from July to October) near Sagres and Martinhal Bay and islands. Intra-annual variations in abundance were significantly associated with sea surface temperature and negatively related with upwelling index and chlorophyll a, suggesting horizontal movements linked to the seasonal changes. Hence, hammerheads moved inshore during the warmer periods (with low primary productivity), due to either direct influence of temperature in their movements or indirect influence in prey distribution. This hammerhead “hotspot” may constitute a nursery ground for S. zygaena, nevertheless, our data does not allow us to prove or refute such claim. Future telemetry-based studies should be conducted to fully understand hammerhead movements and habitat preferences, and to evaluate this “hotspot” as a critical habitat for this predator. [ABSTRACT FROM AUTHOR]

Most of the world’s fish fauna is suffering from different types of human impacts and new conservation tools are required. The fish diet analysis is a tool that has been used to evaluate degradation processes of aquatic environments, however, few long-term studies are performed by several reasons (e.g., lack of funding, opportunity). Our aim was to test whether the fish gut content from biological collections can be used for comparisons with current data and, consequently, be used as a tool for long-term environmental impact studies. We compared the gut content of fish preserved for fifteen years in a biological collection with recently sampled fish, considering the factors size of the specimen, preservation time and preservation form. We did not find differences in the gut content percentage of preservation between fish size classes and preservation time. However, we found differences between preservation form, in which the fish fixed in formalin kept the digestive content preserved while the fish preserved directly in alcohol did not. Thus, we encourage the use of fish gut content from biological collections fixed in formalin for long-term ecological studies. Our findings may help elucidate some long-term effects of human impacts on fish fauna. [ABSTRACT FROM AUTHOR]

Life history strategies of batoid fishes have evolved within dynamic marine ecosystems. Adaptations in reproductive and developmental biology are paramount to the survival of species, and therefore knowledge of growth rates to maturity is fundamental for identifying constraints on the conservation of populations. The butterfly rays (Myliobatiformes: Gymnuridae) are highly derived batoids with generally low reproductive potentials for which age and growth information remains unknown. In this study we applied high-resolution X-ray computed tomography (HRXCT) to vertebral centra from a stingray for the first time to estimate age, and used a multimodel approach to investigate growth of spiny butterfly ray, Gymnura altavela. Estimated ages of the oldest male and female were 11 and 18 yrs. at disk widths (WD) 1355 mm and 2150 mm, respectively. Disk width-at-age data were analyzed using three growth models (von Bertalanffy, logistic, Gompertz), and the most parsimonious and empirically supported model was the logistic function with sex treated as a fixed effect on asymptotic disk width ( WD ) and k parameters. Model parameter estimates were (males) WD = 1285.46 ± 67.27 mm, k = 0.60 ± 0.10, and (females) WD = 2173.51 ± 129.78 mm, k = 0.27 ± 0.04. Results indicated sexually dimorphic growth patterns, with males growing faster and reaching asymptotic size at earlier ages than females. These age and growth results are the first reported for the genus, and suggest that G. altavela grows at a similar rate as some teleosts and batoids, and relatively fast among chondrichthyans. [ABSTRACT FROM AUTHOR]

Variability in the feeding ecology of young fishes over short and long time scales in estuaries is likely to affect population dynamics. We studied 14 years of early stage Striped Bass feeding ecology in the Hudson River Estuary over a 25-year time span, including years in which invasive zebra mussels markedly altered energy flow within the estuary. We predicted that feeding success would be low and that diet composition would be altered during years of high zebra mussel impact, particularly in upriver locations where mussels occur. Feeding success in the short term was indicated by volume of gut contents and in the long term by dry mass at length, i.e. condition; these measures were positively intercorrelated and varied significantly year to year. We tested for associations between condition and multiple biotic and abiotic environmental variables. There was a strong negative effect of zebra mussel grazing rate on condition in upriver locations and a weak positive effect in downriver locations. In upriver locations, condition was 33% higher when local salinity was high and zebra mussel grazing rates were low, whereas in downriver locations, condition was 35% higher when zebra mussel grazing rates and copepod abundance were high and local dissolved oxygen was low. Copepods, amphipods, mysids, and Leptodora constituted the highest prey-specific index of relative importance throughout the estuary. There was no evident effect of the zebra mussel invasion on diet composition. This long-term study corroborates the inferences of earlier studies that zebra mussels reduced early-stage striped bass growth rate. [ABSTRACT FROM AUTHOR]

The present study describes the life history of Gymnotus refugio, a species classified as Endangered in the last published list of threatened species of the Brazilian fauna. The study was conducted at a conservation unity that protect one of the last remaining semideciduous forests in the region. The reproductive period was estimated as occurring from the end of winter to the last summer months. Gymnotus refugio exibited fractional spawning, the lowest relative fecundity registered among the Gymnotifomes species studied at the present, and male parental care behavior. The analyses showed a seasonal pattern on the species diet, associating different food categories to winter, autumn, and spring. According to food items analysis and estimated intestinal quotient, G. refugio was classified as invertivorous, feeding mainly on autochthonous insects. The results obtained herein suggest that the position of G. refugio as an Endangered species might be influenced by its territoriality, habitat specificity, parental care behavior, and low fecundity, reinforcing the importance of swampy forest environment conservation as the only means of the species maintenance. [ABSTRACT FROM AUTHOR]

Trophic ecology is essential to understand ecosystem functioning and structure and assist biological conservation. Here we investigate, for the first time, the feeding ecology of Aphanius farsicus, a cyprinodontid fish endemic of a single landlocked river basin in central Iran. We sampled monthly a population of this fish species during a year and examined differences in food across seasons, sexes and sizes. Similarly to other cyprinodonts, A. farsicus showed sexual dimorphism and more abundance of females. Size structure and individual condition varied across seasons, with larger fish in spring and better condition in summer and less in winter. We found no empty guts, suggesting that these fish feed all year round due to the warm climate of its native distribution. Farsi toothcarp diet was based on detritus, algae (particularly diatoms, green algae, and cyanobacteria), and small invertebrates. Seasonal variation in diet was more important than variation due to fish size and the Farsi toothcarp consumed more green algae in spring and early summer and more diatoms and insects the rest of the year. Herbivory was considerable, similarly to a few other cyprinodonts, and increased with fish size, particularly because of higher consumption of green algae. As with species composition in diet, season was more important than size in the variation of number, biovolume, mean size, and diversity of prey captured, with higher number, richness and size of prey captured in summer. The ontogenetic diet shift was less marked in this cyprinodont than in many other Aphanius species, probably due to its reduced size and the resource availability of its habitat, but was also shown by size-dependent feeding selectivity for a few invertebrates. [ABSTRACT FROM AUTHOR]

The reproductive tactics of Deuterodon stigmaturus were investigated in this study, testing whether the species presents a seasonal or opportunistic life-history strategy in a high latitude Atlantic Forest stream in Brazil. The relation between the development of anal-fin spinelets (sexually dimorphic structures in characids) and the reproductive period of D. stigmaturus was also investigated. The species displayed a seasonal life-history strategy, with the reproductive period occurring between austral spring and summer. The reproductive period was related to increase in temperature and photoperiod, corroborating several studies that suggest positive relation between seasonal reproduction and abiotic predictability. The data indicated total spawning occurring in January, coinciding with the month of greatest rainfall (historical and in the study year). However, the observation of postovulatory follicles in previous months suggests small spawning before January. The development of spinelets on the anal-fin was the only sexual dimorphic trait between males and females. Contrasting with several other studies, seasonal development of anal-fin spinelets was observed in adult males, following the reproductive period and regressing afterwards. Thus, some characid species probably retain this structure throughout the year and others do not, which may be related to life-history strategy differences. [ABSTRACT FROM AUTHOR]

Feeding ecology of fish assemblage in a costal river of the Atlantic Rain Forest in Southern Brazil was investigated. Monthly samples using different fishing techniques were completed on a section of the river characterized as a freshwater environment, and an adjacent tide-influenced estuarine section. Species were grouped into three major Feeding Mode Functional Groups: Zoobenthivore, Omnivore and Detritivore. The river section with the greatest occurrence was the site where the most abundant species are likely to feed most intensively. Freshwater strangler species ( Cyphocharax santacatarinae - detritivorous, Rhamdia quelen and Oligosarcus hepsetus - zoobenthivorous) presented higher stomach repletion in the freshwater environment while marine migrants ( Genidens genidens and Etropus crossotus - zoobenthivorous) and estuarine residents ( Bairdiella ronchus - zoobenthivorous) presented higher repletion in the tide-influenced estuarine stretch. Use of food resources was influenced by spatial and temporal variations linked to environmental characteristics such as salinity, habitat heterogeneity, life history evolution, feeding specialization and resource partitioning. Hypotheses concerning potential keystone species, ecosystem engineers or strong interactors were also discussed. [ABSTRACT FROM AUTHOR]

Longitudinal size segregation and reproductive aspects of Mimagoniates microlepis were studied along the catchment of the Piraquara River, a tributary of the Iguaçu River. Monthly fish sampling were completed at four sites along a longitudinal gradient. In addition, we summarized and compared key species-ecological traits of three different populations of this species. Data from the two additional populations were obtained from the literature. Our findings concerning population structure and reproduction of this species demonstrate that ontogenetic migration occurs within this population. During flash floods small individuals (C1) are carried to downstream habitats (P1). As they grow, we assume that their swimming capacity tends to increase and they are able to explore upstream habitats. This ontogenetic migration dynamic is a common and underexplored pattern for small stream fish in the Neotropics, and it helps to ensure, as a consequence, the long term persistence of the population along the entire hydrographic basin. Therefore, the alteration of only one portion of the river can compromise the entire migration process and consequently the entire population. In addition, the present study is the only source of ecological information for this population from before the recent construction of the Piraquara II dam. This reinforces the urgent need for conservation strategies for this population of M. microlepis and other similar populations or species. [ABSTRACT FROM AUTHOR]

The feeding ecology and trophic level of the banded guitarfish, Zapteryx exasperata, from the Gulf of California, were assessed using stable isotope analysis (SIA) of carbon and nitrogen in muscle samples, and stomach contents analysis (SCA). Males and females showed similar diet preferences with a high diet overlap (Cλ = 0.99) and similar values of δC and δN (ANOVA, F = 0.0 p = 0.94 for δC; F = 0.1 p = 0.78 for δN). The main prey groups found were demersal fishes dominated by the daisy midshipman, Porichthys margaritatus, (>90%IRI), however, pelagic fishes were also found ( Engraulis mordax 2%IRI). An ontogenetic diet shift was found, indicated by the importance of crustaceans in the juvenile diet and the significant isotopic differences between juveniles and adults (δC, ANOVA, F = 13.3 p = 0.0004 and δN, ANOVA, F = 4.7 p = 0.03). An overall trend of increase in δN values with increasing body length ( F = 8.15 p = 0.005) was observed. The mean trophic level estimated in this work by the two methods was ~4.1, indicating that this species is a top predator in the Gulf of California. Zapteryx exasperata is a specialist feeder ( Bi = 0.11, H' = 2.32), consuming mainly benthic fishes in coastal areas of the Gulf of California. The importance of this species in the benthic ecosystem equilibrium as a top predator is an important point to keep in mind when developing future management plans of the batoid fishery in the Gulf of California. [ABSTRACT FROM AUTHOR]