'Fish in hot water": the challenges facing fish and fisheries research in tropical estuaries

Tropical estuarine areas comprise small systems of a few km, larger estuaries, coastal lakes of hundreds of km 2 and vast shallow coastal waters that are contiguous with estuaries and have similar reduced salinities. Many of the world's great estuaries are in the tropics, e.g. the Amazon, Orinoco, Congo, Zambezi, Niger, Ganges and Mekong. The distribution of tropical and subtropical estuaries approximately follows that of mangroves. Like estuaries everywhere, they are a focus of human activity and are among the most exploited of ecosystems. In few other places do the activities of fishers, industrialists, shippers, farmers, conservationists, sports enthusiasts and biologists overlap to such an extent. Quite apart from the possible eects of all these activities, the fishes of subtropical and tropical estuaries already face one of the most rigorous of aquatic environments; but despite this, species diversity and productivity are high. Only in tropical estuaries are animals from such a wide range of taxa so closely associated, annelid worms, prawns, crocodiles, birds, ' hippos ', dolphins and of course fishes, all may form part of the overall community, often with functional ecological links. Unfortunately, the diculties of working in these often inhospitable environments, has meant that biologists have favoured projects in more appealing areas, such as coral reefs. While it is still true that most estuarine research is conducted in industrialized developed countries, nearly all of which are in cold or temperate regions, there has been a recent upsurge in tropical estuarine fish research. This is being driven by two imperatives, food security and the conservation and maintenance of biodiversity. Both these problems require knowledge of the ecology of tropical estuarine fishes, particularly their relationships with the environment and the extent to which they are dependent on estuaries or adjacent habitats for survival.     

Effects of dynamic landscape elements on fish dispersal: the example of creek chub (Semotilus atromaculatus)

Barriers along a watercourse and interconnections between drainage systems are dynamic landscape elements that are expected to play major roles in the dispersal and genetic structure of fish species. The objective of this study was to assess the role of these elements using creek chub ( Semotilus atromaculatus ) in the Mastigouche Wildlife Reserve (Québec, Canada) as model. Numerous impassable waterfalls and interconnections among drainage systems were inferred with geographic information systems and confirmed de visu . The analysis of 32 populations using seven nuclear microsatellites revealed the presence of three genetically distinct groups. Some groups were found upstream of impassable barriers and in adjacent portions of distinct drainage systems. Admixture among groups was also detected in some populations. Constraining phylogenetic procedures as well as Mantel correlation tests confirmed that the genetic structure is more likely to result from interconnections between the drainage systems than from the permanent network. This study indicates that landscape elements such as interconnections are of major importance for circumventing impassable barriers and colonizing lakes that are otherwise inaccessible. Such an approach could be relevant for determining the origins of fish species (i.e. native vs. introduced) in the context of conservation.     

Extent and role for fish populations of riverine ecotones along the Sinnamary river (French Guiana)

The Sinnamary is a small tropical river (250 km long, watershed of 6500 km²) where a dam is to be impounded in 1994.The extent of naturally periodically flooded areas along the Sinnamary river is estimated by using remote sensing (Landsat TM satellite data) and botanical groupings are described on in situ observations, ground truth and collections. The fish assemblages of these areas are described and their density estimated by rotenone sampling. The role of this ecotone to fish populations is discussed.The extent of the inundated areas appears to be greater than previously estimated by classical mapping.As expected, the fish fauna is mostly composed of fish juveniles and adults of dwarf (< 3 cm) and small (< 15 cm) species. Large predators where not found. Due to these characteristics, fish are abundant but their biomass is low in naturally inundated areas. However, juveniles of some species found only in these zones. Therefore their adult populations will probably be very sensitive to any modification of these land/water ecotones.     

Annual variation in source contributions to a mixed stock: implications for quantifying connectivity

Connectivity among populations of highly migratory species is an area of active research and is often quantified with genetic markers. We determined mitochondrial DNA (mtDNA) sequences in 350 green turtles, Chelonia mydas, in 10 annual samples over a 12-year period from an aggregation of immature green turtles in the southern Bahamas. We found significant temporal structuring in haplotype frequencies among years for all turtles and for recruits. These significant differences were reflected in substantial variation in the relative contributions from different rookeries among years estimated by a Bayesian hierarchical model. Because this foraging aggregation has been the subject of a demographic study for over 30 years, we were able to determine that, among the three potential causes of temporal structuring-differential recruitment, mortality and emigration-recruitment accounts for most of this variation. We found that estimates of connectivity and genetic diversity in sea turtle populations are affected by the level of temporal variation reported here. More studies on the extent of temporal variation in composition of mixed stocks of other migratory species are needed to determine how this affects measures of connectivity.     

Density distribution and size sorting in fish schools: an individual-based model

In fish schools the density varies per location and often individualsare sorted according to familiarity and/or body size. High densityis considered advantageous for protection against predatorsand this sorting is believed to be advantageous not only toavoid predators but also for finding food. In this paper, welist a number of mechanisms and we study, with the help of anindividual-based model of schooling agents, which spatial patternsmay result from them. In our model, schooling is regulated bythe following rules: avoiding those that are close by, aligningto those at intermediate distances, and moving towards othersfurther off. Regarding kinship/familiarity, we study patternsthat come about when agents actively choose to be close to relatedagents (i.e., ‘active sorting’). Regarding bodysize, we study what happens when agents merely differ in sizebut behave according to the usual schooling rules (‘sizedifference model’), when agents choose to be close tothose of similar size, and when small agents avoid larger ones(‘risk avoidance’). Several spatial configurationsresult: during ‘active sorting’ familiar agentsgroup together anywhere in the shoal, but agents of differentsize group concentrically, whereby the small agents occupy thecenter and the large ones the periphery (‘size differencemodel’ and ‘active sorting’). If small agentsavoid the risk of being close to large ones, however, smallagents end up at the periphery and large ones occupy the center(‘risk avoidance’). Spatial configurations are alsoinfluenced by the composition of the group, namely the percentageof agents of each type. Furthermore, schools are usually oblongand their density is always greatest near the front. We explainthe way in which these patterns emerge and indicate how resultsof our model may guide the study of spatial patterns in realanimals.     

Partitioning the diversity of riverine fish: the roles of habitat types and non-native species

1. Quantifying how biological diversity is distributed in the landscape is one of the central themes of conservation ecology. For this purpose, landscape classifications are being intensively used in conservation planning and biodiversity management, although there is still little information about their efficacy. 2. I used data from 158 running water sites in Hungary to examine the contribution of six a priori established habitat types to regional level diversity of fish assemblages. Three community measures [species richness, diversity (Shannon, Simpson indices), assemblage composition] were examined at two assemblage levels (entire assemblage, the native assemblage). The relative role of non‐native species was quantified to examine their contribution to patterns in diversity in this strongly human influenced landscape. 3. Additive diversity partitioning revealed the primary importance of beta diversity (i.e. among‐site factors) to patterns in species richness. Landscape‐scale patterns in species richness were best explained by between‐habitat type (beta₂: 41.2%), followed by within‐habitat type (beta₁: 37.7%) and finally within‐site (alpha: 21.1%) diversity. Diversity indices showed patterns different from species richness, indicating the importance of relative abundance distributions on the results. Exclusion of non‐natives from the analysis gave similar results to the entire‐assemblage level analysis. 4. Canonical analysis of principal coordinates, complemented with indicator species analysis justified the separation of fish assemblages among the habitat types, although classification error was high. Multivariate dispersion, a measure of compositional beta diversity, showed significant differences among the habitat types. Contrary to species diversity (i.e. richness, diversity indices), patterns in compositional diversity were strongly influenced by the exclusion of non‐natives from the analyses. 5. This study is the first to quantify how running water habitat types contribute to fish diversity at the landscape scale and how non‐native species influence this pattern. These results on riverine fish assemblages support the hypothesis that environmental variability (i.e. the diversity of habitat types) is an indication of biodiversity and can be used in large‐scale conservation designs. The study emphasises the joint application of additive diversity partitioning and multivariate statistics when exploring the contribution of landscape components to the overall biodiversity of the landscape mosaic.     

Animal ecology meets GPS-based radiotelemetry: a perfect storm of opportunities and challenges

Global positioning system (GPS) telemetry technology allows us to monitor and to map the details of animal movement, securing vast quantities of such data even for highly cryptic organisms. We envision an exciting synergy between animal ecology and GPS-based radiotelemetry, as for other examples of new technologies stimulating rapid conceptual advances, where research opportunities have been paralleled by technical and analytical challenges. Animal positions provide the elemental unit of movement paths and show where individuals interact with the ecosystems around them. We discuss how knowing where animals go can help scientists in their search for a mechanistic understanding of key concepts of animal ecology, including resource use, home range and dispersal, and population dynamics. It is probable that in the not-so-distant future, intense sampling of movements coupled with detailed information on habitat features at a variety of scales will allow us to represent an animal''s cognitive map of its environment, and the intimate relationship between behaviour and fitness. An extended use of these data over long periods of time and over large spatial scales can provide robust inferences for complex, multi-factorial phenomena, such as meta-analyses of the effects of climate change on animal behaviour and distribution.     

Proteomics in uveal melanoma research: opportunities and challenges in biomarker discovery

Uveal melanoma (UM) is the most frequent primary intraocular tumor in adult humans. Despite the significant advances in diagnosis and treatment of UM in the last decades, the prognosis of UM sufferers is still poor. Metastatic liver disease is the leading cause of death in UM and can develop after a long disease-free interval, suggesting the presence of occult micrometastasis. Proteomics technology has opened new opportunities for elucidating the molecular mechanism of complex diseases, such as cancer. This article will review the recent developments in biomarker discovery for UM research by proteomics. In the last few years, the first UM proteomics-based analyses have been launched, yielding promising results. An update on recent developments on this field is presented.     

Freshwater fishes of the Burdekin River, Australia: biogeography, history and spatial variation in community structure

Spatial variation in freshwater fish community structure in a large, structurally monotonous sub-tropical Australian river over 1989–1992 is described. The number of species collected (25) over the period of study, was low, given the large size of the river's catchment. The low diversity of fishes present in the river was suggested to be due to a combination of factors including the imposition of an ancient downstream barrier to fish movement (the Burdekin Falls), substantial volcanic activity during the late Tertiary, past climatic stress and little variation in habitat structure over the range of sites examined. Notwithstanding the low species richness, the Burdekin River's freshwater fish fauna is distinctive, containing elements of the fauna of both eastern and northern Australia, and this was suggested to reflect aspects of ancient landscape evolution. Spatial variation in fish community structure was most strongly influenced by the presence of the Burdekin Falls (the present site of a very large reservoir) and secondarily by minor differences in habitat structure of main channel and tributary streams.     

Effects of longitudinal variations in stream habitat structure on fish abundance: an analysis based on subunit-scale habitat classification

SUMMARY 1. Stream reaches contain assortments of various habitat types that can be defined at different spatial scales, such as channel unit (e.g. pools, riffles) and subunit (patches within channel units). We described longitudinal (upstream–downstream) patterns of stream habitat structure by considering subunits as structural elements, and examined their effects on the abundance of masu salmon ( Oncorhynchus masou ) and rosyface dace ( Leuciscus ezoe ) in a third-order tributary of the Teshio River in northern Hokkaido, Japan.
2. Nine subunit types were determined on the basis of water depth, current velocity and substrate, using 0.5 × 0.5 m grids. Although both masu salmon and rosyface dace used pools as a major habitat, the former preferred a subunit type occurring at pool heads (PH subunit) while the latter preferred a slow-current edge type (SE-2 subunit).
3. Along the course of the stream, slow-edge subunits (SE-1, 2 and 3) increased in frequency downstream while fast-edge subunits (FE-1 and 2) decreased, suggesting a downstream development of slow-current edges. Regression analyses indicated that longitudinal variation in masu salmon abundance was explained by the area of PH, rather than pools. Masu salmon density increased with the area of PH. Rosyface dace abundance was explained by a combination of water depth and the area of SE-2, both effects being positive.
4. Longitudinal variations in the abundance of both species were related to the abundance of their preferred habitat at the subunit scale, rather than channel-unit scale. The results emphasise the importance of fine-scale patchiness when examining stream fish habitats.     

Drug discovery and development for ageing: opportunities and challenges

The prevention and treatment of late-life dysfunction are the goals of most geriatricians and should be the primary target for discovery and development of new medicines for elderly people. However, the development of new medicines for elderly people will face a number of challenges that are not seen for other patient populations. The burdens of multiple chronic diseases, low physiological reserve and polypharmacy must result in new clinical trials in frail older people with a high expectation of safety and efficacy. The etiology of functional limitations in elderly people is complex and often ascribed to conditions that escape the traditional definition of disease. While our society urgently needs new treatments that can reduce the burden of physical decline among older persons, guidelines on how these treatments should be developed and tested are currently lacking, in part because a consensus has not yet been achieved regarding the identifiable target diseases. New potential indications included sarcopaenia, anorexia of ageing, frailty, mobility disability and reduced functional capacity secondary to hospitalization. The challenges to conducting clinical trials in the elderly should not offset the great opportunity for the development of new medicines to prevent or reverse age-associated changes in body composition and poor functional capacity in the elderly.     

Conservation of freshwater fish resources of India: new approaches, assessment and challenges

The freshwater resources of India are currently experiencing an alarming decline in fish biodiversity due to several factors and as a result, a sizeable portion of fresh water fishes have been categorized as threatened. This emphasizes an immediate need for initiating research and actions for alternative management techniques to protect these aquatic systems. One such option that has potential to protect freshwater ecosystem from numerous threats is the creation of freshwater aquatic sanctuary (FAS) within protected area network. Though similar conservation practices are well established in the terrestrial and marine ecosystem, however, the work on freshwater systems has been very slow and negligible. In the present communication we conceptualized the need and approach for developing FAS within the protected area network based on our observations in the water bodies of the selected wildlife sanctuaries in Northern India as well as success stories of some other countries. In this study we assessed the fish diversity in the selected protected areas of Northern India. The assessment indicated that these sanctuaries harbor 28.26–31.13% of freshwater fishes, which are threatened in other areas. Apart from Indian Major Carps, Tor putitora, Chitala chitala, Pangasius pangasius, Clupisoma gerua, Ailia coila, Aorichthys aor, Wallago attu, Rhinomugil corsula, Ompok pabda, Ombok pabo etc. were the important species encountered in the protected waters. The various issues related to FAS including objectives, approach, potential tools, implementation and management are discussed towards saving endangered fish germplasm resources. Approaches, tools and modus operandi proposed in this communication could be utilized by other developing countries in the region.     

Marine ecosystem regime shifts: challenges and opportunities for ecosystem-based management

Regime shifts have been observed in marine ecosystems around the globe. These phenomena can result in dramatic changes in the provision of ecosystem services to coastal communities. Accounting for regime shifts in management clearly requires integrative, ecosystem-based management (EBM) approaches. EBM has emerged as an accepted paradigm for ocean management worldwide, yet, despite the rapid and intense development of EBM theory, implementation has languished, and many implemented or proposed EBM schemes largely ignore the special characteristics of regime shifts. Here, we first explore key aspects of regime shifts that are of critical importance to EBM, and then suggest how regime shifts can be better incorporated into EBM using the concept of integrated ecosystem assessment (IEA). An IEA uses approaches that determine the likelihood that ecological or socio-economic properties of systems will move beyond or return to acceptable bounds as defined by resource managers and policy makers. We suggest an approach for implementing IEAs for cases of regime shifts where the objectives are either avoiding an undesired state or returning to a desired condition. We discuss the suitability and short-comings of methods summarizing the status of ecosystem components, screening and prioritizing potential risks, and evaluating alternative management strategies. IEAs are evolving as an EBM approach that can address regime shifts; however, advances in statistical, analytical and simulation modelling are needed before IEAs can robustly inform tactical management in systems characterized by regime shifts.     

Spatial and Temporal variations of mangrove fish assemblages in Martinique (French West Indies)

A study of the mangrove fish fauna in a bay of Martinique Island (French West Indies) was carried out at different seasons during two consecutive years. fishes were sampled with specific hoop-nets in the coastal areas at 8 stations.A total of 87 species was collected in the bay. Most individuals were represented by small-size specimens and juveniles. The overall species richness varied according to the stations and the sampling periods. The biomass and number of individuals were variable according to the location but remained stable in time. A factor correspondence analysis and a hierarchical clustering with median links were used to follow the evolution of the stations in space and time. Two types of stations were differentiated: the stations characterized by the mangrove and those under the influence of seagrass beds. A seasonal cycle, opposing the dry periods to the others, was observed.Thus, it seems that the use of the mangrove habitat by the fishes is optimized through a complete reorganization of communities in terms of species composition whereas the overall number and biomass remain stable. This model remains valid even for the most constraining biota of the mangrove ecosystem inhabited by a small number of well adapted species.