Long-term effects of hydropower installations and associated river regulation on River Shannon eel populations: mitigation and management

The Shannon, Ireland’s largest river, is used for hydroelectricity generation since 1929. Subsequently, the Electricity Supply Board assumed responsibility for management of its eel stocks, due to the impact of the hydro-dam on recruitment to the commercial fishery. In order to negate a decline in juvenile recruitment resulting from the installation of hydroelectric facilities, management was focused on stocking lakes with elvers and fingerling eels. These were trapped at the hydropower facilities and in estuarine tributaries during their up-stream migrations. Due to the decline of natural recruitment in more recent times, attempts have also been made to develop an estuarine glass eel fishery. Stock levels are then monitored through annual surveys of the population trends of juvenile (glass eel, elver), growing phase (yellow eel) and downstream migrating pre-spawners (silver eels). Survey results and fishery management programmes are reviewed in this article. In addition to the long-term effects the hydroelectric facilities have had on the stock levels, there is also an annual effect on the migratory patterns of downstream migratory silver eels. In the lower reaches of the river system flow rates are regulated by the hydroelectric stations. We review previous work that had highlighted the importance of flow in determining the timing of the silver eels migrations, and assess the relationship between flow and migration in more detail through the use of hydroacoustic and telemetric studies. Current research on seaward migrating silver eel populations, suggests that spawner escapement rates can most effectively be increased by trapping migrating eels at fishing weirs located up-stream of the power station and transporting them towards the estuary. Guest editors: R. L. Welcomme & G. Marmulla Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries     

Low seed availability may limit recruitment in grazed Atriplex vesicaria and contribute to its local extinction

Poor recruitment in Atriplex vesicaria Hewd exBenth (bladder saltbush) under sheep grazing in the chenopodshrublands of southern Australia contributes to a decline in the shrub'spopulation growth rate. This may lead to local extinction of the species overlarge areas around watering points. This study investigated whether low seedavailability may contribute to poor recruitment. It examined the incidence offlowering and seed bank size at sites distributed across a large grazedpaddock,and examined the longevity of seed in the soil. Grazing by sheep reduced theincidence of flowering and input to the seed bank. The proportion of shrubswithflowers increased with distance from water, showing the characteristicpiosphereresponse. Shrubs on grazed sites closer to water experienced extended periodswhen they failed to flower or flowered poorly. The seed bank was negligible atthree of the sites within 1650 m of water for all three years ofsampling. In contrast, the seed bank at the most distant site sampled (2800m from water) was small in 1990 (37 ± 5.1seeds/m²) but in 1991 and 1992 seed numberswere substantial (626 ± 315.2 seeds/m²and 318 ± 169.0, respectively). Soil seed was short-lived inthis study, with only 34% and 17% of the original seed remainingas viable ungerminated seed after 12 months for the under-canopy andexposed treatments respectively. Whilst recruitment may also be limited byaltered soil conditions due to grazing and trampling and the availability ofsafe sites, the results of this study suggest that low seed availability may bean important factor contributing to poor recruitment and may limit the abilityof the population to recover from the loss of established plants. Management ofgrazing must take into account the need for A. vesicariapopulations to flower and set seed on a regular basis.     

Representations of specific acoustic patterns in the auditory cortex and hippocampus

Previous behavioural studies have shown that repeated presentation of a randomly chosen acoustic pattern leads to the unsupervised learning of some of its specific acoustic features. The objective of our study was to determine the neural substrate for the representation of freshly learnt acoustic patterns. Subjects first performed a behavioural task that resulted in the incidental learning of three different noise-like acoustic patterns. During subsequent high-resolution functional magnetic resonance imaging scanning, subjects were then exposed again to these three learnt patterns and to others that had not been learned. Multi-voxel pattern analysis was used to test if the learnt acoustic patterns could be ‘decoded’ from the patterns of activity in the auditory cortex and medial temporal lobe. We found that activity in planum temporale and the hippocampus reliably distinguished between the learnt acoustic patterns. Our results demonstrate that these structures are involved in the neural representation of specific acoustic patterns after they have been learnt.     

Faunal changes and geographic crypticism indicate the occurrence of a biogeographic transition zone along the southern East Pacific Rise

Aim Deep‐sea hydrothermal vents have now been reported along all active mid‐ocean ridges and back‐arc basins, but the boundaries of biogeographic entities remain questionable owing to methodological issues. Here we examine biogeographic patterns of the vent fauna along the East Pacific Rise (EPR) and determine the relative roles of regional and local factors on the distribution of biodiversity associated with mussel beds along a poorly explored zone, the southern EPR (SEPR). Location East Pacific Rise. Methods A species list of macrobenthic invertebrates along the EPR was compiled from the literature and supplemented with data recovered during the French research cruise BIOSPEEDO carried out in 2004 along the SEPR. Biogeographic patterns were assessed by combining the identification of morphological species with a molecular barcoding approach. A multivariate regression tree (MRT) analysis was performed to identify any geographic breaks, and an empirical distribution of species richness was compared with predictions provided by a mid‐domain effect model. Macrofaunal community structure associated with mussel beds along the SEPR was analysed in relation to environmental factors using cluster and canonical redundancy analyses. Results Sequencing of the cytochrome c oxidase subunit I gene revealed the occurrence of several cryptic species complexes along the EPR, with the equator separating the southern and northern clades. Furthermore, during the BIOSPEEDO cruise at least 10 still unnamed species were collected between 7°25′ S and 21°33′ S. The shift in community structure identified by MRT analysis was located south of 17°34′ S or south of 13°59′ S, depending on the data used, suggesting that the southern part of the SEPR (17°25′–21°33′ S) constitutes a biogeographic transition zone in the vent fauna along the EPR. At a regional scale, latitude combined with the type of venting was significantly correlated with the community structure associated with mussel beds. Main conclusions Together, the molecular data, in situ observations, and the distribution of species suggest that the high diversity of vent fauna species presently observed between 17°25′ S and 21°33′ S is probably a result of the overlap of several distinct biogeographic provinces. We argue that this area thus constitutes a biogeographic vent fauna transition zone along the EPR.     

Phylogeny, traits, environment, and space in cerrado plant communities at Emas National Park (Brazil)

Soil, drought, and fire are abiotic factors that may act as environmental filters in the cerrado, the Brazilian savanna. We used a framework to analyze environmental filtering in geographic and phylogenetic context, sampling woody species in one of the largest cerrado reserves. In 100 quadrats, we measured 10 functional traits on each woody individual. We also measured several soil variables, altitude and slope as a rough surrogate of water availability, interval between fires, and time since last fire. Almost all environmental variables were spatially auto-correlated. We found an overall trait clustering, but not an overall phylogenetic clustering. Nevertheless, we found a phylogenetic signal for some traits. Linking phylogeny, traits, environment, and space, we were able to detect a major dichotomy between two geomorphological units. The flat tableland was positively related with altitude, fire frequency, and nutrient-richer soil. Environmental filtering caused by water availability and fire lead to trait clustering, with smaller shrubs and trees that presented thicker barks, denser woods, sclerophyllous leaves, highlighted by the prevalance of Myrtaceae. The other geomorphological unit, hilly terrain, was positively related with slope, low fire frequency, and nutrient-poorer soil. Environmental filtering was caused especially by nutrient-poor soil that lead to trait clustering, assembling taller trees, with thinner barks, lighter woods, and compound, large, tender, nutrient-richer leaves, distributed across many lineages, including Fabaceae. Hence, the high environmental variability in space with different environmental filters assembled different combination of plant traits and lineages, increasing the overall diversity in cerrado.     

Richness, Abundance, and Complementarity of Fruit-feeding Butterfly Species in Relict Sacred Forests and Forest Reserves of Ghana

Sacred forest groves in Ghana are centuries old protected areas that were once part of continuous forest cover but now mostly exist as relict forest patches embedded in an agropastoral landscape. We conducted a year-long survey of the fruit-feeding butterfly fauna of four sacred groves and two forest reserves in the moist semi-deciduous forest zone of Ghana to characterize resident species diversity and complementarity among communities. Joint analysis of frugivorous butterfly diversity at these six forest fragments, which ranged in size from 6 to 5000 ha, was used to evaluate the conservation potential of these ancient indigenous reserves. A total of 6836 individuals were trapped across all sites, representing 79 species and five subfamilies. Community diversity was characterized in terms of, (a) number of species accumulated versus sampling effort, (b) rarefied species richness, (c) nonparametric richness estimates, (d) species evenness, (e) Simpson’s Index of Diversity, and (f) complementarity of communities. Diversity of the fruit-feeding butterfly communities, quantified in terms of both species evenness and rarefied species richness, was higher at the larger forest reserves than at the small sacred forest groves. Additionally, although all sites had species trapped only at that site, the 5000-ha forest reserve harbored a resident community that was clearly distinctive from and more diverse than the other communities including the other forest reserve. Hence, our findings add to the burgeoning body of data that indicates large reserves are the foundation of successful conservation programs. Nonetheless, we found these small forest patches contribute to biodiversity conservation in at least three ways and these are identified and discussed. We also identify a number of species that appear more or less vulnerable to dynamics of forest fragmentation based on changes in their relative abundance across sites and we interpret these data in the context of potential indicator species and theoretical predictions of at-risk species.     

Environmental niche patterns of native and non-native fishes within an invaded African river system

To test ecological niche theory, this study investigated the spatial patterns and the environmental niches of native and non-native fishes within the invaded Great Fish River system, South Africa. For the native fishes, there were contrasting environmental niche breadths that varied from being small to being large and overlapped for most species, except minnows that were restricted to headwater tributaries. In addition, there was high niche overlap in habitat association among fishes with similar distribution. It was therefore inferred that habitat filtering-driven spatial organisation was important in explaining native species distribution patterns. In comparison, most non-native fishes were found to have broad environmental niches and these fishes showed high tolerance to environmental conditions, which generally supported the niche opportunity hypothesis. The proliferation of multiple non-native fishes in the mainstem section suggest that they form a functional assemblage that is probably facilitated by the anthropogenic modification of flow regimes through inter-basin water transfer. Based on the distribution patterns observed in the study, it was inferred that there was a likelihood of negative interactions between native and non-native fishes. Such effects are likely to be exacerbated by altered flow regime that was likely to have negative implications for native ichthyofauna.