Distribution, abundance and conservation status of dugongs and dolphins in the southern and western Arabian Gulf

The marine mammals of Saudi Arabia, Bahrain, Qatar and the United Arab Emirates (UAE) were censussed by three strip-transect aerial surveys. The Arabian Gulf supports a population of ca. 5800 dugongs (Dugong dugon), which is the largest known outside Australia. The most important habitats occur (1) around Murawah Island (UAE), (2) between Qatar and Bahrain and (3) between Qatar and the UAE. Surveys of the UAE were repeated 13 years apart. The two estimates of the dugong population were not significantly different, suggesting a stable population of ca. 3000 between 1986 and 1999. In the region between Kuwait and Oman, the Indian Ocean bottlenose dolphin (Tursiops aduncus) is the most common cetacean (71% of groups and individuals), followed by the Indo-Pacific humpback dolphin (Sousa chinensis; 27%) and finless porpoise (Neophocaena phocaenoides; 2%). The estimates of cetacean abundance in the UAE differed significantly between 1986 and 1999 and indicate a population decline of 71%. At least two die-offs of marine mammals occurred between these surveys. The countries of the southern Gulf are developed and affluent and are well positioned to take a lead in marine conservation in the region. A coordinated series of protected areas could greatly enhance the long-term prospects for marine mammals and other components of biodiversity in the region.     

Impact of upstream changes in rain-fed agriculture on downstream flow in a semi-arid basin

The downstream impacts of increasing water consumption in the upstream rain-fed areas of the Karkheh Basin, Iran are simulated using the semi-distributed SWAT model. Three scenarios are tested at subbasin and basin levels: converting rain-fed areas to irrigation agriculture (S1), improving soil water availability through rainwater harvesting (S2), and a combination of both (S3). The results of these scenarios were compared against the baseline period 1988-2000. The S1 scenario shows a 10% reduction in mean annual flow at the basin level, varying from 8-15% across the subbasins. The reductions in mean monthly flows are in the range of 1-56% at the basin level, with June witnessing the highest flow reduction. Flow reductions are comparatively higher in the upstream parts of the basin, as a result of a relatively higher potential of developing rain-fed areas coupled with comparatively lower amount of available runoff. The impacts of S2 are generally small with reductions of 2-5% and 1-9% in mean annual and mean monthly flows, respectively. The results of S3 are in general similar to those of S1. Although the estimated annual flow reductions remain well within the available water resources development potential, measures needs to be taken to avoid excessive flow reductions in May, June and July. It is recommended that only a limited agricultural area should be converted from rain-fed to irrigated agriculture (about 0.1 million ha), and should practice supplementary irrigation. The supplies should also be augmented through developing additional water storage. Adopting such measures is extremely important for the upper subbasins Gamasiab and Qarasou where comparatively higher flow reductions were estimated.     

Traditional salt-pans hold major concentrations of overwintering shorebirds in Southeast Asia

Shorebirds are declining worldwide due to loss and degradation of critical breeding and wintering habitats. Some human-modified habitats, particularly salt-pans which are used by shorebirds in many regions of the world, may help substitute for natural habitats lost for a wide range of species during migration. We studied the influence of landscape characteristics on species richness, abundance, and diversity of shorebirds at 20 sites covering most of the Inner Gulf of Thailand, a landscape with a long history of salt farming. Sites with salt-pans present held significantly higher species richness, abundance and diversity of shorebirds. Areas with larger proportions given over to aquaculture tended to have lower species richness, abundance and diversity. Generalized additive models indicated that landscapes with a larger proportion of tidal flats in conjunction with salt-pans were the best predictors of sites with higher species richness, abundance and diversity. Landscape configurations with higher richness, abundance and diversity of shorebirds also tended to be less fragmented and contained slightly larger patches. Shorebirds appeared to use ponds with exposed mud in salt-pans as both roosting sites and supplementary feeding grounds during high tide. Traditional salt-pans therefore proved to contribute significantly to maintenance of overwintering shorebird populations in this landscape and should be investigated elsewhere in Asian coastal zones. Collaboration between researchers, salt farmers and planning authorities as to how best to maintain salt-pans as potential shorebird roost sites such as in the Inner Gulf of Thailand is urgently needed in order to maintain habitat for shorebird populations in critical wintering and staging areas of this flyway.     

Network thinking in riverscape conservation – A graph-based approach

Graph theoretic approaches have received increased interest recently in landscape planning and conservation in the terrestrial realm, because these approaches facilitate the effective modelling of connectivity among habitats. We examined whether basic principles of graph theory can be extended to other ecosystems. Specifically, we demonstrate how a network-based context can be used for enhancing the more effective conservation of riverine systems. We first show how to use graph theoretic techniques to model riverscapes at the segment level. Then we use a real stream network (Zagyva river basin, Hungary) to examine the topological importance of segments in maintaining riverscape connectivity, using betweenness centrality, a commonly used network measure. Using the undirected graph model of this riverscape, we then prioritize segments for conservation purpose. We examine the value of each of the 93 segments present in the Zagyva river basin by considering the conservation value of local fish assemblages, connectivity and the size of the habitat patches. For this purpose we use the ‘integral index of connectivity’, a recently advocated habitat availability index. Based on the results the selection of the most valuable habitat segments can be optimized depending on conservation resources. Because of their inherent advantage in the consideration of connectivity relationships, we suggest that network analyses offer a simple, yet effective tool for searching for key segments (or junctions) in riverscapes for conservation and environmental management. Further, although the joint consideration of aquatic and terrestrial networks is challenging, the extension of network analyses to freshwater systems may facilitate the more effective selection of priority areas for conservation in continental areas.     

Effects of fishing practice changes on pelagic shark longline captures in the Gulf of Gabes,Tunisia

1. In order to increase their catches, longliners targeting sharks in the Gulf of Gabes, Tunisia, have increased the number of hooks per basket and have included new bait types instead of mackerel (Scomber scombrus). This paper reports the effects of these changes on catch composition, catch rates, size distribution, life‐stage captures, and mortality at haulback.
2. Data from 48 and 96 longline sets, carried out during the shark fishing seasons of 2007 and 2008, with two hooks per basket, and 2016 and 2017, with five hooks per basket, respectively, were examined to assess the effect of gear change. Moreover, the effects of bait types were inspected based on 33 fishing sets using whole mackerel, 19 using salema (Sarpa salpa) halves, and 27 using pieces of stingray (Dasyatis spp.), sampled during 2016 and 2017.
3. The species composition indicated that longliners expand the vertical distribution of their hooks to operate from the surface to the bottom. The catches with both longline designs were dominated by sandbar shark (Carcharhinus plumbeus). Despite gear changes, the catch rate of C. plumbeus decreased by 42.21%, suggesting population decline. The size composition indicated a shift towards larger specimens, mainly adult females, which could jeopardize the shark population. Moreover, the mortality of the main species at haulback seems to be affected by the design of the longline.
4. The bait used, mainly pieces of stingray, significantly increased the catch rate of sandbar shark, which suggests a greater attractiveness of the new bait; however, fish size and mortality rates at haulback were unchanged in response to bait variation.
5. The fishery operates in shark nursery grounds, which exposes these fish (principally C. plumbeus) to considerable exploitation pressure. The new fishing practices intensified the pressure and thus the risk of a rapid depletion of populations. To preserve the shark species in the area, the use of new gear and attractive bait should be banned.

     

Discarding practices in a Mediterranean small-scale fishing fleet (Patraikos Gulf, Greece)

Abstract  Discarding practices from 110 fishing operations in a Mediterranean small-scale fishing fleet (Patraikos Gulf, western Greece) from August 2004 to July 2005 were analysed. On average, 1 kg of fish was discarded per fishing operation (10% of the catch). The reasons for discarding were: low commercial value (78% of discards), damage at sea before retrieval of the gear (5%), and bad handling on-board (17%). More than half of discards belonged to Spicara flexuosa (L.), Lepidopus caudatus (Euphrasen), Sardinella aurita Valenciennes and Merluccius merluccius (L.). The bulk of discards of each species were associated with a single fishing method (metier). A Generalized Linear Model (Delta-X – error-model) indicated that, when discards were present, significant differences existed in the discard ratio among different métier groups (groups comprising métiers with similar characteristics). Longlines and trammel nets with small mesh-sizes had the highest discard ratios. Discarding practices for the species Diplodus annularis (L.), S. aurita , Squilla mantis (L.), S. flexuosa and Scorpaena scrofa (L.) did not follow a consistent pattern (these species were either fully discarded or fully retained during a fishing operation). The decision seemed to be dependent on market demands rather than fish size. Significant correlation was found between discarded and catch weight, but the presence of many outliers indicated deviance from a case where discards are high when there is an abundant catch. The findings of the study imply that monitoring and management should be carried out preferably on the métier level. Discards could be reduced by technical measures, controlling effort regulations and by improving working conditions on-board fishing vessels.     

Experiment Study on Soil Properties of Shennv Stream Landslide in Wu Gorge

Accurate obtainting soil parameters of landslide is the key links for landslide stability evaluation and project management . This article takes Shennv Stream landslide in Chongqing Wushan County as an example, implementing unconsolidated and undrained shear test and mineral composition analysis by X ray diffraction for soil in different elevations of landslide ,conducting sensitivity test for various soil parameters of reservoir landslide change with different water level.Study shows that : Mineral composition of soil mainly contains Calcite, Quartz and clay mineral. Hydrophilic minerals in clay mineral have great effect on stability of landslide. Shear strength decreases by influence of water content on cohesion. Cohesion decreases sharply in a quadratic function relation with water content increasing .When water content comes to 18.21% ,change of cohesion tends to be stable.But the internal friction angle of landslide soil decreases linearly in small amplitude with an increase of water content. Research results may provide some important references for rationally choosing strength parameters of soil in similar landslide.     

基于GIS的广西北部湾经济区生态系统间接利用价值评估研究

针对目前生态系统间接利用价值评估中缺乏空间表达、对数据要求高、评估效率低等不足,构建了基于GIS的广西北部湾经济区生态系统间接利用价值评估方法.2005 ～ 2010年北部湾经济区间接利用价值呈现上升趋势;按研究区域间接利用价值统计,价值最高的是南宁市辖区,价值最低是北海市辖区;按单位面积间接利用价值统计,上思县价值最高,北海市辖区最低;间接价值较高区域主要分布在较高植被覆盖度的区域,如南宁市辖区、钦州市辖区、灵山县、上思县和防城港市辖区.     

Predicting the occurrence of Atlantic bluefin tuna (Thunnus thynnus) larvae in the northern Gulf of Mexico: building a classification model from archival data

Although bluefin tuna are found throughout the Atlantic Ocean, spawning in the western Atlantic has been recorded predominantly in the Gulf of Mexico (GOM) in spring. Larval bluefin tuna abundances from the northern GOM are formulated into an index used to tune the adult stock assessment, and the variability of this index is currently high. This study investigated whether some of the variability in larval bluefin tuna abundances was related to environmental conditions, by defining associations between larval bluefin tuna catch locations, and a suite of environmental variables. We hypothesized that certain habitat types, as defined by environmental variables, would be more likely to contain bluefin tuna larvae. Favorable habitat for bluefin tuna larvae was defined using a classification tree approach. Habitat within the Loop Current was generally less favorable, as were warm‐core rings, and cooler waters on the continental shelf. The location and size of favorable habitat was highly variable among years, which was reflected in the locations of larval bluefin tuna catches. The model successfully placed bluefin tuna larvae in favorable habitat with nearly 90% accuracy, but many negative stations were also located within theoretically favorable habitat. The probability of collecting larval bluefin tuna in favorable habitat was nearly twice the probability of collecting bluefin tuna larvae across all habitats (35.5 versus 21.0%). This model is a useful addition to knowledge of larval bluefin tuna distributions; however, the incorporation of variables describing finer‐scale features, such as thermal fronts, may significantly improve the model’s predictive power.     

The influence of pelagic habitat selection and interspecific competition on productivity of juvenile walleye pollock (Theragra chalcogramma) and capelin (Mallotus villosus) in the Gulf of Alaska

Here we investigate processes affecting productivity of capelin and walleye pollock in the Gulf of Alaska. We examine pelagic habitat selection by comparing the distribution of juvenile fish and their prey with oceanographic properties and we evaluate the potential for interspecific competition by comparing diets and measures of foraging. The primary field study was conducted in Barnabus Trough, Kodiak Island, Alaska, during September 2005. The distribution of fish was assessed acoustically and trawls were used to collect individual fish for stomach content analyses. Physical and biological data were collected with conductivity–temperature–depth probes and zooplankton tows. Age‐0 pollock were distributed in cool waters offshore of a mid‐trough front, coincident with the distribution of euphausiids, their preferred prey. In contrast, capelin and their prey (copepods) were distributed throughout the trough. We observed that sympatric capelin (occurring with pollock) often had reduced foraging success compared to allopatric capelin (occurring alone). Results of a bioenergetic model also suggest that the exclusion of capelin from foraging on euphausiids can have negative consequences for capelin growth.