Does reintroduction stabilize the population of the critically endangered gharial (Gavialis gangeticus,Gavialidae) in Chitwan National Park,Nepal?

• 1 Despite conservation programmes (India 1975, Nepal 1978) gharial populations (Gavialis gangeticus) have declined over their entire distribution range. Information about the current status and main threats is needed to implement effective conservation measures.
• 2 This study presents a survey (2003/2004) of the largest Nepalese gharial population in the Chitwan National Park that has benefited from regular re‐introduction of young gharials since 1981.
• 3 Population size estimates fluctuate between 34 (2003) and 38 (2004). The reintroduction programme, although of limited success, has helped to maintain the gharial population.
• 4 Gharials bask preferentially in large sand banks, and these sites must be protected.
• 5 The main threats are from a dam that causes fish depletion and flushes gharials from the protected area, sand mining and grazing that destroy basking sites, fishing that causes food shortage, drift nets that kill gharial, and water pollution.
• 6 Improvement in the survival of reintroduced gharials is needed. Strict protection of preferred basking sites and prohibition of fishing in the main settling zones are the principal conservation measures while in the long term, education and participatory management by local people are also necessary. Copyright © 2010 John Wiley & Sons, Ltd.

     

Differential response to disturbance factors for the population of sympatric crocodilians (Gavialis gangeticus and Crocodylus palustris) in Katarniaghat Wildlife Sanctuary,India

相似文献   

Basking site and water depth selection by gharial Gavialis gangeticus Gmelin 1789 (Crocodylia,Reptilia) in National Chambal Sanctuary,India and its implication for river conservation

• 1. The species diversity of inland waters is among the most threatened of all ecosystems and in many parts of the world it is in continuing and accelerating decline. Such decline could be restrained by acknowledging the scope of target species, so that all relevant stages in their life cycle are considered.
• 2. The gharial Gavialis gangeticus is a prominent riverine species of the Indus, Ganges, Brahmaputra and Mahanadi river systems that is becoming increasingly rare due to reduction in water flow and available nesting beaches, modification of river morphology and increased mortality in fishing nets. Despite these threats, scientific information on habitat selection by gharial is still inadequate, which hinders conservation measures.
• 3. This paper presents the population status, basking site selection and water depth preferences of different size‐classes of gharial based on a study conducted in the National Chambal Sanctuary, India.
• 4. Between 1992 and 2007 a 40% decline in the gharial population was observed in the National Chambal Sanctuary. The decline was prominent in the recruitment class (<120 cm), which primarily comes from the nests laid in the wild, and also in sub‐adults (>180 to 270 cm) comprising both wild and reintroduced gharial.
• 5. Along the Chambal River, gharial preferred sandy parts of the river banks and sand bars for basking and showed less preference for rocky river banks and rocky outcrops. Clay river banks were least preferred.
• 6. Juvenile gharials <120 cm and 120–180 cm preferred water depths 1–3 m and 2–3 m, respectively. Gharial >180 cm (including sub‐adults and adults) preferred water depths >4 m.
• 7. Increasing demands for sand for development activities, and water abstraction for irrigation and energy generation coupled with mortality in fishing nets, are likely to affect gharial and other aquatic species, and steps need to be taken to maintain the minimum river flow necessary to sustain ecosystem processes.

Copyright © 2009 John Wiley & Sons, Ltd.     

Gharial (Gavialis gangeticus) populations and human influences on habitat on the River Chambal,India

相似文献   

Movement ecology of imperilled fish in a novel ecosystem: River‐reservoir movements by razorback sucker and translocations to aid conservation

1. Reservoirs and associated river fragments are novel ecosystems not experienced by fishes in their evolutionary history, yet they are now commonplace across the globe. Understanding how fishes use these novel habitats is vital to conservation efforts in contemporary riverscapes.
2. Movement patterns of the endangered razorback sucker (Xyrauchen texanus) synthesized from tagging efforts in the upper Colorado River basin, USA, illustrate the applications of tagging technology and data sharing by multiple agencies to better understand the spatial ecology of large river fishes.
3. Tagging studies between 2014 and 2018 in Lake Powell and its two main tributary rivers, the Colorado (unfragmented) and San Juan (waterfall‐fragmented), were used to quantify movement of razorback sucker within this river–reservoir habitat complex. In addition, facilitated translocations of fish upstream of a waterfall barrier in the San Juan River were assessed in 2016–2017.
4. Extensive movement of fish occurred within and across river and reservoir habitats. Of 722 fish captured in the Colorado River arm of Lake Powell, 36% of re‐encounters occurred upstream in the Colorado or Green rivers, or fish dispersed through the reservoir and were detected in the San Juan River arm. Fourteen fish moved more than 600 km. In the San Juan arm of the reservoir, 29% and 20% of fish in 2017 and 2018, respectively, had moved ~30–40 km upstream below the waterfall in the San Juan River within a year. In 2016–2017, 303 fish were translocated upstream of the waterfall into the San Juan River, but 80% were re‐encountered downstream of the waterfall within a year.
5. Long‐distance movements by razorback sucker were common within and among rivers and reservoirs illustrating how large river fish, in general, might maintain population connectivity in highly altered ecosystems.

     

Quantifying the extent of river fragmentation by hydropower dams in the Sarapiquí River Basin,Costa Rica

• 1. Costa Rica has recently experienced a rapid proliferation of dams for hydropower on rivers draining its northern Caribbean slope. In the Sarapiquí River Basin, eight hydropower plants were built between 1990 and 1999 and more projects are either under construction or proposed. The majority of these dams are small (<15 m tall) and operate as water diversion projects.
• 2. While the potential environmental effects of individual projects are evaluated prior to dam construction, there is a need for consideration of the basin‐scale ecological consequences of hydropower development. This study was a first attempt to quantify the extent of river fragmentation by dams in the Sarapiquí River Basin.
• 3. Using simple spatial analyses, the length of river upstream from dams and the length of de‐watered reaches downstream from dams was measured. Results indicated that there are currently 306.8 km of river (9.4% of the network) upstream from eight existing dams in the Sarapiquí River Basin and 30.6 km of rivers (0.9% of the network) with significantly reduced flow downstream from dams. Rivers upstream from dams primarily drain two life zones: Premontane Rain Forest (107.9 km) and Lower Montane Rain Forest (168.2 km).
• 4. Simple spatial analyses can be used as a predictive or planning tool for considering the effects of future dams in a basin‐scale context. In the Sarapiquí River Basin, we recommend that future dam projects be constructed on already dammed rivers to minimize additional river fragmentation and to protect remaining riverine connectivity.

Copyright © 2007 John Wiley & Sons, Ltd.     

Ecology of southern European pearl mussels (Margaritifera margaritifera): first record of two new populations on the rivers Terva and Beça (Portugal)

相似文献   

Smalltooth sawfish (Pristis pectinata Latham, 1794) in the Casamance River,Senegal: A historical perspective

相似文献   

Riverine spawning,long distance larval drift,and floodplain recruitment of a pelagophilic fish: A case study of golden perch (Macquaria ambigua) in the arid Darling River,Australia

1. Pelagic spawning riverine fish (pelagophils) spawn in free‐flowing river habitats with downstream drift of eggs and larvae but the spatial scale is often unknown, and this constitutes a major ecological knowledge gap.
2. In the arid Darling River in south‐eastern Australia, the present objectives were: (i) to determine the potential downstream dispersal distance of young golden perch (Macquaria ambigua); and (ii) to evaluate whether provision of environmental water enhanced dispersal of young fish from Menindee Lakes to the lower Darling River (LDR) while also cueing further spawning in downstream lotic reaches.
3. Golden perch spawned in unregulated lotic tributaries on a flood pulse and larvae drifted or dispersed >1,600 km downstream and entered large ephemeral productive floodplain lake nursery habitats as fully scaled fingerlings.
4. Planned releases of environmental water cued golden perch spawning in the LDR and enabled juvenile fish to disperse downstream from the Menindee Lakes nursery into receiving populations in the LDR, Great Darling Anabranch, and southern Murray River, with some fish potentially completing an active migration of >2,100 km by age 1 year.
5. The Darling River case study highlights the need for a system‐scale approach to the conservation management of pelagophilic fish, along with multi‐year perennial flow strategies to improve ecosystem integrity in large rivers globally.

     

Residential movements of top predators in Chile’s most isolated marine protected area: Implications for the conservation of the Galapagos shark,Carcharhinus galapagensis,and the yellowtail amberjack,Seriola lalandi

1. Marine protected areas (MPAs) are becoming a widely used tool for the conservation of biodiversity and for fishery management; however, most of these areas are designed without prior knowledge of the basic ecological aspects of the species that they are trying to protect.
2. This study investigated the movement of two top predators: the Galapagos shark, Carcharhinus galapagensis, and the yellowtail amberjack, Seriola lalandi, in and around the Motu Motiro Hiva Marine Park (MMHMP) using MiniPAT satellite tags to determine the effectiveness of this MPA for the protection of these species.
3. The Galapagos sharks (n = 4) spent most of their tag deployment periods inside the MMHMP. However, high intraspecific variability was observed in their movement dynamics. Daily individual maximum movements ranged from 17 to 58 km and the maximum distance from Salas y Gómez Island, the only emergent island within the MMHMP, ranged from 31 to 139 km.
4. The maximum linear distance travelled for a female juvenile Galapagos shark (152 cm total length) was 236 km, which is greater than the maximum distance previously documented for juveniles of this species (<50 km).
5. For the yellowtail amberjack (n = 1), 91% of the satellite geolocations were within the MMHMP, with a maximum daily distance travelled of 6 km. The maximum distance travelled between points was 111 km and the maximum distance from Salas y Gómez Island was 62 km.
6. All archival tagged fish spent most of their time at depths of <50 m and never left the epipelagic zone. Daytime versus night-time differences were pronounced in all individuals but showed high interindividual variability.
7. This study provides a baseline on the movement of these two top predators in the MMHMP and provides valuable insights for the creation of MPAs in the region and elsewhere.

     

Population assessment and potential functional roles of native mussels in the Upper Mississippi River

• 1. Despite a heightened global concern for native mussels, fundamental research on mussel ecology in large rivers is lacking. These gaps in knowledge about where mussels occur, and why, are limiting habitat restoration activities.
• 2. Large‐scale systematic surveys for native mussels in three reaches of the Upper Mississippi River documented mussel communities composed of 16–23 species and ranging from 2.9–4.5 live mussels m^?2 that were actively recruiting new cohorts into their populations (87–100% of the species were found as juveniles ?5 years old). Estimates of mean tissue biomass and production in these reaches ranged from 2.1–3.1 g C m^?2 and 0.4–0.6 g C m^?2 year^?1, respectively.
• 3. Mussels filtered a significant amount of water (range, 0.05–0.07 m³ m^?2 d^?1) over a 480 km reach of the Upper Mississippi River – amounting to a filtration rate of 53.1 million m³ day^?1. The filtration rate of mussels as a percentage of river discharge ranged from 0.5–1.4% at high flows (5% exceedance), from 1.5–4.4% at moderate flows (50% exceedance) and from 4.4–12.2% during low flows (95% exceedance).
• 4. Collectively, these data suggest that native mussels play an integral role in this ecosystem by sequestering suspended materials that can be used by other benthic organisms. Published in 2011 by John Wiley and Sons, Ltd.

     

Preliminary study of the endangered populations of pearl mussel Margaritifera margaritifera (L.) in the River Tera (north‐west Spain): habitat analysis and management considerations

• 1. During 2001 and 2002, 12 tributaries of the River Duero basin, north‐west Spain, were sampled. Pearl mussels Margaritifera margaritifera (L.) were located in two of them. Isolated individuals were found in the River Tera, a tributary of the River Esla; and only a few colonies with more than 20 mussels were found in the River Negro.
• 2. All of the specimens found were adults (mean length 95 mm), with juveniles being absent in the river bed. The River Negro plots showed a low median mussel density (0.11 m^?2), and that of greatest size consisted of 164 ageing individuals.
• 3. Mussels were mainly located in permanent rivers and in shallow stretches with little flow of water, with heterogeneous substrates and heavily shaded by the riparian woods. The whole basin has well‐conserved rivers with cold oligotrophic water and poor mineralization due to the insolubility of the rocks.
• 4. This relic population has a severely restricted distribution because of a series of large reservoirs in a hydropower complex of the rivers Duero and Esla (caused by the construction of the Ricobayo Dam in 1947) and their negative impact on the rheophilous fish. The mussels of the River Tera have been isolated from the rest of the Duero basin since 1969 (Cernadilla Dam), whereas in the River Negro they have been isolated since 1995 (Agavanzal Dam).

Copyright © 2004 John Wiley & Sons, Ltd.     

Priority habitats for the conservation of large river fish in the Ganges river basin

• 1. Three classes of habitat used by groups of fish species classified as conservation and management priorities were developed for the Gerua River (also known as the Girwa River, Karnali River) in the Ganges river basin. This river is large (mean annual discharge ca 1500 m³ s^?1, up to 900 m wide), surrounded by protected lands of India and Nepal, and upstream of major diversions and river alterations.
• 2. Fish and habitat sampling was conducted at 45 sites from 2000 to 2003. Data were analysed for 2172 fish of 14 species. Species and life stages found occupying a statistically distinct subset of the river habitats were grouped to identify classes of river habitat for conservation.
• 3. Most species and life‐stage groups specialized on specific habitat conditions revealed by multivariate analyses of variance and a principal component analysis. The most numerous and diverse group (six species, 15 life stages) was associated with deep depositional habitats with sandy substrate. Two species covering three life stages were primarily oriented to erosional habitat marked by fast current velocity with pebble and cobble substrate. A third group of three species of adults and juveniles were intermediate in habitat use.
• 4. River conservation for fish faunas should maintain both erosional and depositional channel habitats with depths, substrates, and current velocity inclusive of the ranges reported. The erosional and depositional nature of the key habitats requires that rivers be maintained with flows capable of channel‐forming functions.

Copyright © 2006 John Wiley & Sons, Ltd.     

Dams in the Amazon: The importance of maintaining free-flowing tributaries for fish reproduction

1. Free-flowing tributaries are important for the maintenance of fish diversity in dammed systems. In relation to the reproduction of fish species, the role of a free-flowing tributary was evaluated and compared with that of a dammed tributary downstream of large dams in the Madeira River, one of the main tributaries of the Amazon River.
2. Two hypotheses were tested: (i) the densities of the ichthyoplankton differ between the dammed and the free-flowing tributaries; and (ii) the free-flowing tributary contributes a greater diversity of fish larvae species to the assemblage structure of the main stem than the dammed tributary.
3. Fish eggs and larvae were sampled at five sites: one in each tributary (Jamari – dammed – and Machado – free-flowing) and three in the main stem (Madeira River), upstream and downstream from the mouth of each tributary.
4. Fitted Bayesian models showed that the densities both of eggs and larvae were more than twice as high in the free-flowing tributary than in the dammed tributary. The results also indicated that the free-flowing tributary makes a major contribution to the fish assemblage structure of the Madeira River, whereas the dammed tributary does not have a significant influence on the main stem assemblage structure.
5. The results demonstrate the importance of conservation and maintenance not only of the Machado River but also of other free-flowing tributaries in dammed basins, especially those basins with high biodiversity, such as the Amazon. Moreover, this study helps inform the decision-making process regarding the location of new dams, which is critical in fish diversity conservation.

     

Averting co-extinction: Successful mussel translocation rescues an endangered population of the European bitterling,Rhodeus amarus

1. Local extinctions break species interactions and have cascading effects throughout ecosystems; parasites are often severely affected. The European bitterling, Rhodeus amarus, is a cyprinid fish that parasitizes unionid mussels by laying eggs into the mussel gill cavity, where embryos develop and emerge as active juveniles; this relationship is obligatory for the bitterling.
2. This article describes a field experiment aimed at averting the secondary extinction of the European bitterling after a complete die-off of a freshwater mussel community, as a result of habitat destruction.
3. Approximately 5,000 unionid mussels were reintroduced within the short time frame in which the remnant bitterling population was still present at the site. Mussel survival was high, and bitterling resumed reproduction, with vigorous courtship observed within 24 hours of mussel release. Recruitment was successful, as evidenced by increased occupancy, densities, and relative frequencies in the fish assemblage. The frequency of sub-adults and young-of-the-year changed from 0% before mussel reintroduction to 80% a year later, and 50% 2 years later, when young-of-the-year contributed to about half of the young fish. No bitterling were observed at two control sites where mussels were not reintroduced.
4. This study exemplifies how the timely restitution of affiliate species can avert co-extinction. It also shows how the conservation of the bitterling within its historical distribution range can serve mussel conservation, including species that although not legally protected, are important keystone species and ecosystem engineers, shaping the structure and function of a broad range of freshwater habitats.

     

Population crash in Lesotho's endemic Maloti minnow Pseudobarbus quathlambae following invasion by translocated smallmouth yellowfish Labeobarbus aeneus

相似文献   

Difference in light perception capability and spectral response between juveniles and sub-adults of the whiteleg shrimp <Emphasis Type="Italic">Litopenaeus vannamei</Emphasis> as determined by electroretinogram

In this study, we determined light perception capability in juveniles and sub-adults of L. vannamei by means of electroretinogram (ERG) measurements. Eyes were assumed to be dark-adapted when the response magnitude had stabilized after 70–80 min under dark conditions. ERG responses elicited by mono-wavelength (336–694 nm) stimuli of equal intensity were determined in individual dark-adapted specimens. Relative spectral response curves determined from the amplitudes of on and off relative responses were found to be significantly different in juveniles and sub-adults. Both maximum on relative spectral response magnitudes were observed at 544 nm, but the on relative spectral response magnitudes of sub-adults to 518 nm were higher than for juveniles, and the on relative spectral response magnitudes of sub-adults to 568 nm were lower than for juveniles. The on and off relative spectral response curves of juveniles were steeper than those of sub-adults, while the on relative spectral response magnitude of juveniles was lower than that of sub-adults from 336 to 544 nm. The off relative spectral response magnitude of juveniles was higher than that of sub-adults from 518 to 597 nm.     

Population abundance and habitat preference of the Yangtze finless porpoise in the highest density section of the Yangtze River

1. Habitat loss and degradation together represent one of the five major factors contributing to the rapid decline of the Yangtze finless porpoise in the Yangtze River. Protecting key habitat patches and maintaining migration corridors between habitat patches are major conservation objectives to ensure the in situ viability of the Yangtze finless porpoise. Baseline information essential for addressing these two objectives includes that pertaining to distribution and habitat preference.
2. To investigate the distribution and habitat preferences of the Yangtze finless porpoise, five transect surveys were conducted in the Anqing section of the Yangtze River, which has the highest porpoise density among all sections of the river. Porpoise abundance estimates were calculated, and preferences for different habitat types were evaluated.
3. The calculated porpoise abundance in the Anqing section was 181 (95% CI 125–239) animals on average. The inter‐annual and inter‐seasonal differences in porpoise abundance estimates were not significant. The natural river banks and sandbar shores were the most preferred habitats, representing 46.3 and 29.8% of the porpoise observations, respectively. In contrast, 8.1% of the porpoises were observed in habitats along reinforced river banks, which account for 38.7% of the total coastline. In subsections with natural habitat patches, porpoises were observed in almost every survey, while porpoise occurrence became highly stochastic in subsections with long reinforced river banks. These results indicate a significant tendency of the Yangtze finless porpoise to prefer natural habitats with natural river bank or sandbars but to keep away from reinforced river‐bank habitats.
4. According to porpoise density in different subsections, free migration may be impeded or only one migration corridor remains in some subsections.
5. Although protecting finless porpoise habitats has become a primary conservation objective, this study highlights the need to protect frequently used habitat patches and migration corridors, particularly those near natural river banks and sandbars, and to restore ecological environments along reinforced river banks.

     

Damming insights: Variable impacts and implications of river regulation on platypus populations

1. River regulation has extensively changed the ecology and hydrology of rivers worldwide, particularly downstream of dams, affecting the viability of freshwater species. The platypus (Ornithorhynchus anatinus) is a semiaquatic monotreme, endemic to eastern Australia, with a distribution overlapping Australia’s most regulated rivers.
2. Dams and changes to flow regimes have affected critical platypus habitat, yet our understanding of the impacts of these threatening processes on platypus ecology remains poor. Over a period of 3 years (2016–2018), platypuses were surveyed across three regions (Upper Murray, Snowy, and Border river regions), above and below large dams, and in adjacent unregulated rivers, comparing captures, demographics, abundances, and densities. We hypothesized that platypus captures and abundances would be lower downstream of dams, owing to altered flow regimes that have secondary impacts on the demographics of these populations.
3. In the Upper Murray Rivers region, captures were significantly lower in the Mitta Mitta River below Dartmouth Dam, compared with captures upstream of the dam and the unregulated Ovens River, probably reflecting significant alteration to the seasonality and temperature of flows caused by the dam. Conversely, there were no significant differences in captures or abundance and density estimates above and below the dams in the Snowy or Border river regions, where the extent of regulation was less severe, probably as a result of restoration efforts in recent years on some rivers.
4. Low proportions of juveniles on the Snowy River and Mitta Mitta River downstream of the dams, compared with upstream, raises concerns of other impacts of altered flow regimes to platypus breeding success and juvenile survival, given the sensitivity of juveniles to unseasonably high flows.
5. The results highlighted the potential impact of river regulation, with direct implications for the management of regulated rivers, providing opportunities to mitigate impacts through improved management of the seasonality and temperature of flows, to the benefit of platypuses and other freshwater species.

     

Río de la Plata voyagers: Deciphering the migration ecology of a vulnerable marine catfish (Genidens barbus) in a large subtropical river (lower Uruguay River)

1. Genidens barbus is a vulnerable marine migrant catfish with low fecundity, a complex life cycle (i.e. mouth breeding), and is the target of industrial and artisanal fisheries of several countries. This species regularly migrates from marine to freshwater environments of the south-western Atlantic.
2. The aim of this work was to delve deeper into the migration ecology of G. barbus, characterizing both its timing and potential environmental drivers. Furthermore, aspects of the population structure and reproduction of migrants in the lower Uruguay River were studied and the presence of juveniles in the adjacent estuarine recruitment area was evaluated.
3. Data from 11 years (2008–2018) of records of adult G. barbus captured by artisanal fisheries were used alongside relevant environmental variables that were recorded monthly. Reproductive biology (i.e. sex ratio, gonadosomatic index, fecundity, and oocyte size) was analysed for a period of 3 years (2016–2018). The juvenile abundance in the Río de la Plata estuary was evaluated seasonally.
4. A total of 935 adult individuals of G. barbus were captured, representing a total biomass of 3,123 kg. The migration timing was from early spring to early summer. The abundance of migrants strongly increased with river discharge, suggesting that this variable regulates the upriver migration. Furthermore, pre- and post-spawn females and males displaying mouth breeding were recorded during the study period, confirming G. barbus reproduction in the lower Uruguay River.
5. The results obtained suggest that G. barbus ascend to spawn in the freshwater environments upstream from the mouth of the Uruguay River. Then, adult males incubate and carry the embryos downstream, releasing juveniles in the Río de la Plata estuary.
6. This relevant information will help with the implementation of effective management polices (e.g. fishing restrictions during the reproductive period) for the presently unregulated fishery of this vulnerable species in the lower Uruguay River.