Diversity and status of sea turtle species in the Gulf of Guinea islands

In West Africa, the Gulf of Guinea islands are important nesting places for four sea turtle species. The Green turtle (Chelonia mydas), the Hawksbill (Eretmochelys imbricata), the Olive Ridley (Lepidochelys olivacea) and the Leatherback (Dermochelys coriacea) turtles nest on Bioko's southern beaches. The Green, Hawksbill and Leatherback turtles breed on Príncipe and São Tomé. The Leatherback turtle nests, at least, on Annobón. The Leatherback turtle is reported on the four islands for the first time, and the Olive Ridley turtle for Bioko. Bioko is probably the most important island in terms of number of species and nesting individuals; the Green turtle being the most abundant species. However, the nesting places are at present restricted to barely 20 km along the coastline. On Príncipe and São Tomé, the most common species is the Hawksbill turtle. Sea turtle nesting populations are being severely depleted on the four islands. The main causes of cverexploitation are the meat and egg trade on Bioko and the Hawksbill shell-craft trade on São Tomé and Príncipe.     

Bats of the Gulf of Guinea islands: faunal composition and origins

The present study compares the bat faunas of the islands of the Gulf of Guinea. Species composition. endemism and hypothetical origins are discussed. All families present in the mainland region are found in Bioko, a typical landbridge island. Foliage gleaning guild species (Nycteridae) show limited colonization abilities. This is also true of the family Rhinolophidae, but not for the closely related family Hipposideridae. The majority of the oceanic island species are African bats which show a widespread distribution and, therefore, have a high ecological plasticity. The continental relatives of the two endemic species Myonycteris brachycephala and Chaerephon tomensis are restricted to relatively small forested areas. Bioko's bat fauna is the result of the recent isolation from a formerly land-connected community. The oceanic bat faunas originated from the establishment of incomers from other areas. Nevertheless, extinction appears in both vicariant and dispersal processes, as an important factor in modelling the current bat communities of the Gulf of Guinea islands.     

Distribution of the Simulium damnosum complex on Bioko island, Equatorial Guinea, and the potential for onchocerciasis elimination by vector eradication

Onchocerciasis is endemic on the island of Bioko, Equatorial Guinea, where it is transmitted by the 'Bioko form' of the Simulium damnosum complex, a cytospecies unique to the island. To determine the distribution of vector breeding, three dry season and two wet season expeditions were made in 1989, 1996 and 1997, and 226 of the island's 247 rivers (91.5%) were visited. Of these 226 rivers, 130 (58%) were flowing during the dry season, forty-five (20%) supported aquatic stages of Simuliidae of any species and twenty-five (11%) contained larvae or pupae of the S. damnosum complex. The twenty-one rivers not prospected were in the mountainous south of the island, where an additional seventeen rivers were reached but not satisfactorily prospected. Of these thirty-eight rivers, twenty-nine were considered highly likely to support vector breeding, bringing the total number of rivers which could harbour the vector during the dry season to fifty-four (21.9% of the island's total). Breeding was believed to be limited to river stretches below 1000 m altitude, and during the dry season the total length of those stretches which could support breeding on Bioko was estimated to be 1020 km. A combination of factors, including low river discharges during the dry season, the relatively low water temperature on Bioko, the suitability of limited stretches of most rivers as vector breeding sites and the close proximity of many rivers within a small geographical area, render the vector vulnerable to eradication by aerial treatment of rivers with insecticide. The isolation of the Bioko form of the S. damnosum complex suggests that reinvasion following treatment would be unlikely, and eradication of the vector might be achieved by a dry season larviciding programme in one or two years.     

Fish ecology and management of the Sepik-Ramu,New Guinea,a large contemporary tropical river basin

Synopsis The ichthyofauna of the Sepik-Ramu basin is composed of diadromous species and the freshwater derivatives of marine families. Fish species diversity, ichthyomass and fish catches are low even by Australasian standards. Three major factors have produced the depauperate ichthyofauna and restricted fishery within the basin: First, the zoogeographic origins of the ichthyofauna. Australasian freshwater fishes, being mainly derived from marine families, generally exhibit ecological characteristics that have evolved for life in estuaries, not rivers. This has led to peculiarities in river fish ecology and explains the probable low fish production from rivers in this region in general. Several important riverine trophic resources are not exploited by the Australasian freshwater ichthyofauna. The modes of reproduction amongst the Australasian freshwater ichthyofauna have limited the colonisation and exploitation of floodplain habitats. Second, Sepik-Ramu lowland habitats, especially floodplains, are very young. This has resulted in low fish species diversity in lowlands, whilst diversity at higher altitudes is equable, in comparison to river systems in southern New Guinea/ northern Australia. Third, the Sepik-Ramu lacks an estuary in sharp contrast to river systems in southern New Guinea or northern Australia. Most of the 18 families of Australasian fishes missing from the Sepik-Ramu are probably absent because of this factor alone. In particular, the Sepik-Ramu has not been colonised by any family of fishes having pelagic eggs, resulting in the loss from the fauna of the few Australasian fish taxa with high reproductive rates. Consequently, the general problems with river fish ecology in Australasia are exacerbated within the Sepik-Ramu by the particular development and morphology of the basin. Fish species diversity in the Sepik-Ramu is low, even in comparison with those taxa representative of marine families resident in rivers in nearby zoogeographic regions (S.E. Asia) whose ichthyofaunas are otherwise dominated by freshwater dispersant groups. The Sepik-Ramu ichthyofauna is considered noteworthy for what is absent, not what is present. Ichthyomass and fish production can be increased by fish species introductions whilst, in theory, biodiversity of the native fish fauna can be maintained. The directions in which ecological evaluations of proposed introductions might proceed in practice for the Sepik-Ramu are discussed but are constrained by the lack of knowledge on species interactions from other areas.     

Species composition and dynamics of larval and juvenile fishes in the surf zone of Mauritius

The importance of the surf zone as a nursery ground for larval and juvenile fishes has been widely recognized, however the zone has yet to be studied in Mauritius. Recently, the coastal area of the island has been increasingly affected by human activities, especially by tourism. We collected fish samples with a hand pulled seine net during the period of August 2001 to March 2003 to clarify the fish fauna and the dynamics of fishes in the surf zone. Two sampling sites adjacent to river mouth areas and one sampling site adjacent to a mangrove area were selected for comparison of fish fauna in relation to environmental conditions. A total of 9,429 fish larvae and juveniles, representing at least 112 species from 48 families were collected. The abundant species were hardyhead silverside, Atherinomorus lacunosus, bluespot mullet, Valamugil seheli, and Ambassis spp., each contributing 16.2, 12.4, and 11.8% of the total number of individuals, respectively. Estuarine species dominated in the surf zone adjacent to the river mouth areas. Species composition and diversity changed seasonally. The number of fish increased during the rainy season. Species diversity increased at the turn of the seasons from the dry season to the rainy season. We conclude that species composition in each site was affected by environmental factors, such as the scale of the flux from the rivers, which is related to the precipitation. The results indicated that freshwater from the river is a trigger to aggregate larvae and juveniles in the surf zone.     

Mismatch between fishway operation and timing of fish movements: a risk for cascading effects in partial migration systems

Habitat fragmentation is a growing problem worldwide. Particularly in river systems, numerous dams and weirs hamper the movement of a wide variety of species. With the aim to preserve connectivity for fish, many barriers in river systems are equipped with fishways (also called fish passages or fish ladders). However, few fishways provide full connectivity. Here we hypothesized that restricted seasonal opening times of fishways can importantly reduce their effectiveness by interfering with the timing of fish migration, for both spring‐ and autumn‐spawning species. We empirically tested our hypothesis, and discuss the possible eco‐evolutionary consequences of affected migration timing. We analyzed movements of two salmonid fishes, spring‐spawning European grayling (Thymallus thymallus) and autumn‐spawning brown trout (Salmo trutta), in Norway's two largest river systems. We compared their timing of upstream passage through four fishways collected over 28 years with the timing of fish movements in unfragmented river sections as monitored by radiotelemetry. Confirming our hypothesis, late opening of fishways delayed the migration of European grayling in spring, and early closure of fishways blocked migration for brown trout on their way to spawning locations during late autumn. We show in a theoretical framework how restricted opening times of fishways can induce shifts from migratory to resident behavior in potamodromous partial migration systems, and propose that this can induce density‐dependent effects among fish accumulating in lower regions of rivers. Hence, fragmentation may not only directly affect the migratory individuals in the population, but may also have effects that cascade downstream and alter circumstances for resident fish. Fishway functionality is inadequate if there is a mismatch between natural fish movements and fishway opening times in the same river system, with ecological and possibly evolutionary consequences for fish populations.     

崇明岛内河夏季鱼类群落组成及分布特征

崇明岛为世界最大的河口冲积沙岛,岛内河网水系发达。2018年6月,选择崇明岛内主要代表性河道包括北横引河、南横引河和竖河（庙港、堡镇港、八滧港）,设置16个固定站点,对内河鱼类开展了拖网调查,分析了崇明岛内河夏季鱼类群落组成及分布特征。调查期间共采集到鱼类4417尾,分属6目9科30种,主要为鲤形目鲤科鱼类;其中,淡水鱼类27种,洄游鱼类2种,近海鱼类1种。从空间分布来看,北横引河记录鱼类20种,南横引河记录鱼类17种,竖河记录鱼类18种,不同河道鱼类种类组成及优势种特征存在明显差异,其共有优势种为鲫Carassius auratus、似鳊Pseudobrama simoni和翘嘴红鲌Erythroculter ilishaeformis,部分种类只在特定的河段有记录。北横引河各站点平均物种数、丰度和生物量均高于南横引河和竖河,但3类河道间不存在显著差异（P>0.05）;主要优势种鲫、翘嘴红鲌和似鳊平均体长均以北横引河为最大,且在南横引河与北横引河中的个体体长均存在极显著差异（P<0.01）。聚类和排序分析结果表明,北横引河和南横引河鱼类组成差异较大,而竖河介于两者之间。相似性分析的结果也表明,南、北横引河鱼类群落结构差异极显著（R=0.524,P=0.008）,且这两组间鱼类种类组成的平均相异性最高,为43.92%,造成两组间差异的主要物种有10种（贡献率均大于5%）。综合来看,崇明岛内河鱼类群落组成与分布特征不同于一般的内陆河流,而具有河口型岛屿的特点。未来需要在长期监测基础上,综合多种因素,对崇明岛内河鱼类组成、分布、变化趋势及内在机理开展系统研究。     

Parasitofauna study of the brown trout, Salmo trutta (Pisces, Teleostei) from Corsica (Mediterranean island) rivers

Corsica is a Mediterranean island characterised by a great number of rivers. Salmonides are the main fishes which populate these rivers. Very appreciated by fishermen, Salmonides are represented by three species in the insular hydrographical network, among which an autochthonous species, the brown trout (Salmo trutta). In the present work, we have analysed the parasitofauna of this species. According to our knowledge, this research has never been carried out in Corsica. In a first step, we drew up an inventory of the parasites found in this freshwater fish. In a second step, we studied the differences which appeared in the composition of parasite communities of this species.     

Phylogeography and speciation in the <Emphasis Type="Italic">Pseudocrenilabrus philander</Emphasis> species complex in Zambian Rivers

Haplochromine cichlids form the most species-rich lineage of cichlid fishes that both colonized almost all river systems in Africa and radiated to species flocks in several East African lakes. The enormous diversity of lakes is contrasted by a relatively poor albeit biogeographically clearly structured species diversity in rivers. The present study analyzed the genetic structure and phylogeographic history of species and populations of the genus Pseudocrenilabrus in Zambian rivers that span two major African drainage systems, the Congo- and the Zambezi-system. The mtDNA phylogeny identifies four major lineages, three of which occur in the Congo-system and one in the Zambezi system. Two of the Congo-clades (Lake Mweru and Lunzua River) comprise distinct albeit yet undescribed species, while the fish of the third Congo-drainage clade (Chambeshi River and Bangweulu swamps), together with the fish of the Zambezi clade (Zambezi and Kafue River) are assigned to Pseudocrenilabrus philander. Concerning the intraspecific genetic diversity observed in the sampled rivers, most populations are highly uniform in comparison to lacustrine haplochromines, suggesting severe founder effects and/or bottlenecking during their history. Two bursts of diversification are reflected in the structure of the linearized tree. The first locates at about 3.9% mean sequence divergence and points to an almost simultaneous colonization of the sampled river systems. Subsequent regional diversification (with about 1% mean sequence divergence) occurred contemporaneously within the Kafue River and the Zambezi River. The clear-cut genetic biogeographic structure points to the dominance of geographic speciation in this lineage of riverine cichlid fishes, contrasting the importance of in situ diversification observed in lake cichlids.     

Effects of seasonality and fish movement on tropical river food webs

Tropical rivers and their associated floodplain habitats are dynamic habitat mosaics to which fishes are challenged to respond in an adaptive manner. Migratory fishes create linkages among food webs that are partitioned along a nested hierarchy of spatial scales. Such linkages are examined across a hierarchy of spatio-temporal scales, ranging from small streams to entire drainage basins, for rivers in South America and Africa. Migratory herbivorous fishes originating from eutrophic, productive ecosystems may subsidize resident predators of oligotrophic river ecosystems, which may result in cascading direct and indirect Effects on other species in local food webs. Successful management of many of the most important stocks of tropical river fishes requires conceptual models of how fish movement influences food web structure and dynamics.     

Changes in the distribution of native fishes in response to introduced species and other anthropogenic effects

Aim Globally, one of the major threats to the integrity of native faunas is the loss of biodiversity that can result from the introduction of exotics. Here we document recent changes in the distribution of five common fish species that are linked to introductions in Chile. Location Chile from 28° S to 54° S. Methods We assess the extent of changes in distribution of galaxiid species by comparing their historical and current distributions based on the results of the most extensive survey of freshwater fishes in Chile to date, a range that encompasses the full latitudinal and elevational range of the Galaxiidae in Chile. We test for relationships of the distributions and abundances of native fishes with the incidence of introduced species. Results The latitudinal range of Galaxias maculatus has declined by 26%, and most of this reduction has occurred in the northern part of its range. Aplochiton taeniatus and Brachygalaxias bullocki have experienced reductions (8–17% loss) in total drainage area occupied, and they have disappeared from, or are now extremely difficult to find, in latitudes 36° to 41° S, coincidently with areas of urban growth and intense economic activities. The distribution of Galaxias platei has, instead, increased considerably. In northern basins, G. maculatus has apparently been replaced by an introduced poeciliid Gambusia sp. High‐elevation systems remain dominated by native Galaxias platei, whereas systems at intermediate elevations, especially rivers, are now dominated by introduced salmonids. Within drainages, native galaxiids remain abundant where exotic salmonid abundance is low. Main conclusions We suggest that negative interactions between introduced and native fish are responsible for some of the range reductions among Galaxiidae in Chile. The severity of the impacts varies with latitude and altitude and is probably related to temperature. The effects of Gambusia are restricted to warmer systems. Native fish also appear to have found temperature refugia from salmonids; impacts are low in the warmer northern and coastal systems, as well as in high‐altitude relatively cold systems. Native fish also appear less vulnerable to salmonids in lakes than in rivers. This study identifies watersheds critical for the conservation of biodiversity within the Galaxiidae.     

Fish, climate and the Gulf Stream: the influence of abiotic factors on the recruitment success of cyprinid fishes in lowland rivers

1. Climatic effects are increasingly being recognised as an important factor causing inter‐annual variability in organism abundances in aquatic and terrestrial ecosystems. This study investigated the relationships between water temperature (cumulative degree‐days >12 °C), river discharge (cumulative discharge‐days above basal discharge rate), the position of the North Wall of the Gulf Stream (NWGS), and the 0+ growth (September mean length) and recruitment success (year‐class strength, YCS) of three species of cyprinid fishes in two contrasting English lowland rivers, using a 21‐year dataset. 2. Contrary to the majority of studies on 0+ fishes, growth in the Yorkshire Ouse was most significantly correlated with river discharge, with water temperature of less importance. By contrast, temperature was more influential than discharge in the River Trent, possibly because of its regulated hydrological regime, although none of the relationships were statistically significant for this river. 3. Year‐class strength of roach (Rutilus rutilus) was positively correlated with the position of the NWGS, and there was evidence of synchrony in recruitment success between rivers, but the relationships were poorer for chub (Leuciscus cephalus) and dace (Leuciscus leuciscus). The strongest relationships between YCS and discharge during specific time periods were for when the fish were in their early (especially larval) developmental stages, although none of the relationships were statistically significant because of inter‐annual variations in river discharge relative to the timing of fish hatching. 4. Fishes are key predators in the majority of aquatic ecosystems and, as such, fluctuations in their abundances can have implications for ecosystem functioning as a whole. This study has demonstrated an underlying influence of broad‐scale climatic effects on the recruitment of riverine fishes, in spite of local variations in biotic and abiotic conditions. The relative importance of various abiotic factors on the recruitment success of riverine cyprinid populations varies spatially and temporally. For example, river discharge is likely to be of relatively greater importance in poorly‐structured rivers or those that are prone to large and rapid fluctuations in flow, while temporal variations occur because of inter‐annual differences in river discharge relative to the timing of fish hatching. Biotic factors may also be important determinants of fish recruitment success, especially in rivers with stable and predictable flow regimes.     

Habitat preference of the Preuss's guenon<Emphasis Type="Italic">(Cercopithecus preussi), on Bioko island,Equatorial Guinea</Emphasis>

The Press's guenon (Cercopithecus preussi) is considered to be one of the most threatened African primates. There is little information on the ecology and status of this primate on Bioko island, where it is found in the form of an endemic subspecies. The Press's, guenon shows preference for theSchefflera forest and the mountain habitat on Bioko island. As on the mainland they also have semitterrestrial habits and are found usually at the understorey of the forest. Competitive exclusion between this guenon and other guenon species could be an explanation of these ecological preferences. Habitat use and vertical stratification of the activity in the forest canopy seem to reduce competition with other sympatric primate species that inhabit on the island. Habitat destruction, and isolation in a reduced habitat, show to be the major threats for the survival of this primate on Bioko island.     

Ecological variation in invasive brown trout (Salmo trutta) within a remote coastal river catchment in northern Patagonia complicates estimates of invasion impact

Salmonids were first introduced into the Chilean fresh waters in the 1880s, and c. 140 years later, they are ubiquitous across Chilean rivers, especially in the southern pristine fresh waters. This study examined the brown trout (Salmo trutta) and native taxa ecology in two adjacent but contrasting rivers of Chilean Patagonia. During spring 2016 and spring–fall 2017 we examined the variation in benthic macroinvertebrate and fish community composition and characterized fish size structure, stomach contents, and stable isotopes (δ¹³C and δ¹⁵N) to understand population structure, fish diet, and trophic interactions between S. trutta and native taxa. The native Galaxias maculatus (puye) dominated the fish community (74% of abundance). S. trutta was less abundant (16% of survey catch) but dominated the fish community (over 53%) in terms of biomass. S. trutta showed distinct diets (stomach content analysis) in the two rivers, and individuals from the larger river were notably more piscivorous, consuming native fish with a relatively small body size (<100-mm total length). Native fishes were isotopically distinct from S. trutta, which showed a wider isotopic niche in the smaller river, indicating that their trophic role was more variable than in the larger river (piscivorous). This study provides data from the unstudied pristine coastal rivers in Patagonia and reveals that interactions between native and introduced species can vary at very local spatial scales.     

Freshwater fish biodiversity in the River Ganga (India): changing pattern, threats and conservation perspectives

The river Ganges is the largest river in India and the fifth longest in the world. Although, many studies on fish ecology and systematic have been conducted largely to improve fisheries but fish diversity and their distribution pattern from conservation point of view have never been adequately addressed in the Ganges. In this connection, current distribution and abundance of freshwater fishes of river Ganges was studied and assessed from April 2007 to March 2009. We documented and described 143 freshwater fish species in the all stretches of the river which is higher than what was reported earlier. Some species were observed with shift in their distribution ranges. First time, a total of 10 exotic fishes, including Pterygoplichthys anisitsi, which has never been reported from India found in the Ganges. Alterations of the hydrological pattern due to various types of hydro projects was seems to be the largest threat to fishes of Ganges. Indiscriminate and illegal fishing, pollution, water abstraction, siltation and invasion of exotic species are also threatening the fish diversity in the Ganges and as many as 29 species are listed under threatened category. The study advocates a need to identify critical fish habitats in the Ganga basin to declare them as conservation reserves to mitigate the loss of fish diversity from this mighty large river.     

Elevated river discharge enhances the immigration of juvenile catadromous and amphidromous fishes into temperate coastal rivers

Anthropogenic alterations to river flow regimes threaten freshwater biodiversity globally, with potentially disproportionate impacts on species that rely on flow cues to trigger critical life history processes, such as migration for diadromous fishes. This study investigates the influence of river discharge on the abundance of juvenile fish moving into rivers by four temperate catadromous or amphidromous species (common galaxias Galaxias maculatus, spotted galaxias Galaxias truttaceus, climbing galaxias Galaxias brevipinnis and the threatened Australian grayling Prototroctes maraena). Fyke netting or fishway trapping was used to catch juvenile fish moving from estuaries into freshwater in five coastal waterways in south-eastern Australia during the spring migratory period. There was a positive relationship between the probability of high catch rates and mean discharge in September. We also found a positive relationship between discharge and the number of recruits captured 22–30 days later in a flow stressed system. In addition, day-of-year had a strong influence on catch rates, with the peak abundance of juveniles for three species most likely to occur midway through the sampling period (spotted galaxias in October, climbing galaxias in late October and Australian grayling in late October and early November). Our study shows that higher magnitudes of river discharge were associated with increased catches of juvenile catadromous and amphidromous fishes. With a limited supply of environmental water, environmental flows used to enhance immigration of these fishes may be best targeted to maintain small amounts of immigration into freshwater populations in waterways or years when discharges are low and stable. When there are natural, large discharge volumes, relatively large numbers of juvenile fish can be expected to enter coastal waterways and during these times environmental flows may not be required to promote immigration.     

Ecology of fishes in a high-latitude,turbid river with implications for the impacts of hydrokinetic devices

Hydrokinetic devices generate electricity by capturing kinetic energy from flowing water as it moves across or through a rotor, without impounding or diverting the water source. The Tanana River in Alaska, a turbid glacial system, has been selected as a pilot location to evaluate the effects of such a device on fish communities that are highly valued by subsistence, sport, and commercial users. The basic ecology and habitat use of fishes in turbid glacial systems are poorly understood; therefore it is necessary to study the species composition of the fish community and the spatial and temporal patterns of mainstem river use by these fishes to evaluate impacts of a hydrokinetic device. In this document, we provide an overview of existing knowledge of fish ecology in the Tanana River and impacts of hydrokinetic devices on fishes in other river systems. Seventeen fish species are known to inhabit the Tanana River and several may utilize the deepest and fastest section of the channel, the probable deployment location for the hydrokinetic device, as a seasonal migration corridor. Previous studies in clearwater river systems indicate that mortality and injury rates from turbine passage are low. However, the results from these studies may not apply to the Tanana River because of its distinctive physical properties. To rectify this shortcoming, a conceptual framework for a comprehensive fish ecology study is recommended to determine the impacts of hydrokinetic devices on fishes in turbid, glacial rivers.     

Biodiversity in the Gulf of Guinea: an overview

Patterns of species-richness and endemism in the Gulf of Guinea reflect the region's biogeographic history. Bioko is a continental-shelf island that was recently connected to the African mainland, whereas Príncipe, São Tomé and Annobón are truly oceanic and have never been connected with each other or with the mainland. As a result, Bioko supports a much more diverse flora and fauna but with relatively low levels of endemism at the species level, whereas the oceanic islands are relatively depauperate because of their isolation but rich in endemic taxa. Species endemism is 0–3% on Bioko for angiosperms, bats, birds, reptiles and amphibians, compared with much higher values on Principe for these same taxa of 8% (plants) to 100% (amphibians), on São Tomé between 14% (plants) and 100% (amphibians), and on Annobón 0% (bats) to 71% (reptiles). On a global scale, for their size both Príncipe and São Tomé support unusually high numbers of single-island endemic species of birds, reptiles and amphibia. For its tiny size, Annobón is also notable for its endemic birds and reptiles. Among terrestrial molluscs the rates of endemism are in general higher than for plants and vertebrates, from ca 50% on Bioko to ca 80% on the oceanic islands. In contrast and as might be expected, only Bioko supports a rich freshwater fish fauna and it contains many endemic taxa, whereas the oceanic islands support only a few salt-tolerant species. The Gulf of Guinea islands are also important for their marine organisms, amongst which coral reef fish and marginellid molluscs show high levels of endemism, though they are not especially species-rich. The Gulf of Guinea islands are of great interest to conservationists and evolutionary biologists. Each island, of greatly differing size and degree of isolation, has acquired its unique sub-set of plants and animals separately from the neighbouring mainland, followed by adaptive radiations in situ. For this reason the conservation value of the archipelago as a whole is greater than the sum of the biodiversity contained in its individual islands. Conservation initiatives in the Gulf of Guinea should therefore ensure that representative terrestrial, freshwater and marine habitats and groups of organisms are targeted in a co-ordinated manner among the islands.     

Patterns and drivers of fish extirpations in rivers of the American Southwest and Southeast

Effective conservation of freshwater biodiversity requires spatially explicit investigations of how dams and hydroclimatic alterations among climate regions may interact to drive species to extinction. We investigated how dams and hydroclimatic alterations interact with species ecological and life history traits to influence past extirpation probabilities of native freshwater fishes in the Upper and Lower Colorado River (CR), Alabama‐Coosa‐Tallapoosa (ACT), and Apalachicola‐Chattahoochee‐Flint (ACF) basins. Using long‐term discharge data for continuously gaged streams and rivers, we quantified streamflow anomalies (i.e., departure “expected” streamflow) at the sub‐basin scale over the past half‐century. Next, we related extirpation probabilities of native fishes in both regions to streamflow anomalies, river basin characteristics, species traits, and non‐native species richness using binomial logistic regression. Sub‐basin extirpations in the Southwest (n = 95 Upper CR, n = 130 Lower CR) were highest in lowland mainstem rivers impacted by large dams and in desert springs. Dampened flow seasonality, increased longevity (i.e., delayed reproduction), and decreased fish egg sizes (i.e., lower parental care) were related to elevated fish extirpation probability in the Southwest. Sub‐basin extirpations in the Southeast (ACT n = 46, ACF n = 22) were most prevalent in upland rivers, with flow dependency, greater age and length at maturity, isolation by dams, and greater distance upstream. Our results confirm that dams are an overriding driver of native fish species losses, irrespective of basin‐wide differences in native or non‐native species richness. Dams and hydrologic alterations interact with species traits to influence community disassembly, and very high extirpation risks in the Southeast are due to interactions between high dam density and species restricted ranges. Given global surges in dam building and retrofitting, increased extirpation risks should be expected unless management strategies that balance flow regulation with ecological outcomes are widely implemented.     

River‐lake migration of fishes in the Dongting Lake area of the Yangtze floodplain

Over the past few decades, fish resources have declined severely owing to the river–lake disconnection within the Yangtze River floodplain. Studies on fish migrations between rivers and floodplain waters are imperative for fish resources restoration and lake management. However, few studies have as yet documented the migration rhythms of river–lake migratory fishes. Monthly investigations of the fish assemblage structure were conducted in three regions of the Dongting Lake, which is connected to the Yangtze River. Main results were: (i) Fish catches varied greatly, depending on the water level and area of the lake; (ii) Ten river–lake migratoty species were caught during the study, 80% of these during July–October when the water level was high. Species richness and relative abundance both decreased with increasing distance from the river, and the timing of peak abundance occurred later in the year; (iii) Abundance of grass carp (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix) peaked in July and August and were mainly composed of 0 + fishes. The results revealed that the key time for migration into the lake is July–August. Combining the results from previous studies, a comprehensive view is given of migration patterns of four domestic Chinese carps; (iv) Brass gudgeon (Coreius heterodon), appeared to migrate into the Dongting Lake as two separate shoals, differentiated by body size. They also appeared to remain close to the lake mouth area. Based on the above results, two recommendations can be made for river–lake migratory fish conservation in the Yangtze floodplain: prolonging the current fishing ban period of April–June to April–September; and opening sluice gates for as long as possible during April–September in order to maximize the opportunities for fish migration.