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1.
  1. Spatial modelling is an important research tool to improve our knowledge about the distribution of wildlife in the ocean. Using different modelling techniques (MaxEnt and a generalized linear mixed model), a predictive habitat suitability model was developed for one of the most threatened seabirds in the world: the Balearic shearwater, Puffinus mauretanicus.
  2. Models were developed using a 10-year dataset from the Gulf of Cádiz (on the south-western Iberian Peninsula), a key foraging area for Balearic shearwaters during migration and the non-breeding season.
  3. Predictive habitat maps strongly matched the observed distribution patterns, pointing to bathymetric features as the main modelling drivers. The species was concentrated on shallow areas (up to approximately 100 m in depth) of the continental shelf, very close to the mouth of the Guadalquivir River. In contrast with previous studies, Balearic shearwater distribution in the highly dynamic Gulf of Cádiz was not correlated with areas of high chlorophyll a concentration.
  4. This lack of spatial correlation probably arises from the delay between the phytoplankton bloom and the response of the zooplankton and small fish that are preyed upon by Balearic shearwaters, which may result in important displacements of this trophic chain across the Gulf of Cádiz.
  5. The analysis presented contributes to a better understanding of the spatial distribution and ecology of the critically endangered top predator in the Gulf of Cádiz and offers important information to improve management plans.
  相似文献   
2.
采用问卷调查的方式,以钦州市钦南区为例,调查广西北部湾经济开发区荒废土地现状以及当地村民的反应。调查结果表明,在接受调查范围内有55%的村民有荒废土地;针对荒废土地的处理,45%的村民表示将荒废土地转让,33%的村民表示任其自由发展;面对被荒废的土地,28%的村民迫切想改变现状,41%的表示无能为力,31%的持无所谓态度。针对上述情况,分析了原因并提出了一定的措施,以期为当地的土地规划和利用提供参考。  相似文献   
3.
基于北部湾城镇群22个县域单元,利用面板数据模型,实证分析了人口集聚度与经济集聚度时空变化及相互关联情况。结果表明,人口集聚度与经济集聚度存在双向因果关系;南宁市、北海市、防城港市、玉林市及北部湾整体的县域人口集聚度与经济集聚度之间相互呈正效应,而钦州市、崇左市分别相互呈负效应、弱负效应。未来,北部湾城镇群应实施"大县城"战略,大力发展县域经济,加强县域尤其是县城的人口集聚与经济集聚,提高经济发展效率,优化城镇结构,走出一条富有自身特色的新型城镇化道路。  相似文献   
4.
The Atlantic bluefin tuna (Thunnus thynnus) population in the western Atlantic supports substantial commercial and recreational fisheries. Despite quota establishment and management under the auspices of the International Commission for the Conservation of Atlantic Tunas, only small increases in population growth have been estimated. In contrast to other western bluefin tuna fisheries indices, contemporary estimates of catch per unit effort (CPUE) in the southern Gulf of St. Lawrence have increased rapidly and are at record highs. This area is characterized by the Cold Intermediate Layer (CIL) that is defined by waters <3°C and located at depths of 30–40 m in September. We investigated the influence of several in situ environmental variables on the bluefin tuna fishery CPUE using delta‐lognormal modelling and relatively extensive and consistent oceanographic survey data, as well as dockside monitoring and mandatory logbook data associated with the fishery. Although there is considerable spatial and temporal variation of water mass characteristics, the amount of available habitat in the southern Gulf of St. Lawrence (assuming a > 3°C thermal ambit) for bluefin tuna has been increasing. The percentage of the water column occupied by the CIL was a significant environmental variable in the standardization of CPUE estimates. There was also a negative relationship between the spatial extents of the CIL and the fishery. Properties of the CIL account for variation in the bluefin tuna CPUE and may be a factor in determining the amount of available feeding habitat for bluefin tuna in the southern Gulf of St. Lawrence.  相似文献   
5.
Knowledge about vegetation patterns along disturbance gradients is essential for conservation and management of coastal habitats in arid regions. This study focuses on the floristic diversity and the factors controlling the vegetation structure in the Gulf of Gabès (Tunisia). For this purpose, the floristic diversity of 120 relevés belonging to three coastal sites with different disturbance levels (40 relevés per site) was analyzed in relation with 10 environmental and anthropogenic factors. Therophytes constitute 54% of the 237 plants species belonging to 44 families identified in the present study. The species richness and floristic diversity indices exhibited a similar trend and peaked in the slightly disturbed site (H′?=?3.38; S?=?176). The similarity between sites was relatively low and reached its maximum between the little and the highly disturbed sites. Two-way indicator species analysis and detrended correspondence analysis applied on the floristic data resulted in groups mainly determined by disturbance level by explicitly segregating the three sites. Canonical correspondence analysis (CCA) indicated that the spatial pattern of species composition was mainly influenced by anthropogenic variables. Partial CCA revealed that the effect of anthropogenic variables on floristic composition was thrice higher than the effect of environmental variables (57.5% vs. 18.4%, respectively). Overall, this study provides a broad understanding of the floristic diversity and vascular plant richness in the Gulf of Gabès. The obtained results reflected a disturbance–diversity pattern and thus revealed the obvious importance of maintaining the intermediate disturbance for biodiversity conservation and monitoring.  相似文献   
6.
  1. This study evaluated the circle hook use as a tool for shark management in the pelagic longline fishery in the Gulf of Gabès.
  2. The usual J‐hook No. 2 with 10° offset, which has been traditionally used by the fishery, was compared to the 18/0 non‐offset circle hook in an alternating fashion along the main line. In total, 22 experimental longline sets were deployed through the shark fishing seasons of 2016 and 2017 to examine the effects of hook types on the catch composition, the catch rates, the hooking location, and the status at haulback.
  3. The catch composition differed significantly among hook types. Moreover, an overall increase in catch rates for the main species, the sandbar shark Carcharhinus plumbeus, and the shortfin mako shark Isurus oxyrinchus, was observed when using circle hooks.
  4. There was no size‐selective effect of circle hooks for the common species. The circle hooks were not effective at reducing at‐haulback mortality of sandbar shark. Conversely, shortfin mako and smooth‐hound shark Mustelus mustelus showed significantly lower relative mortality at haulback with circle hooks than with J‐hooks. Furthermore, circle hooks were more frequently hooked externally than the J‐hooks for the three shark species.
  5. Results demonstrated that the use of 18/0 non‐offset circle hooks in the pelagic shark longline fishery can reduce mortality at haulback for some species without any benefit for the dominant species, the sandbar shark.
  6. Overall, it is difficult to promote the adoption of the use of circle hooks as a management measure in this specialized fishery. Management measures focusing on fishing effort controls, fishing closures in critical habitats, and size limits could have significant benefits for the conservation of shark species and may help to improve the sustainability of the shark fishery in the Gulf of Gabès.
  相似文献   
7.
  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.
  相似文献   
8.
基于GEE的广西北部湾沿海水产养殖池塘遥感提取   总被引:1,自引:1,他引:0  
沿海水产养殖池塘带来经济效益的同时,也会引起诸多环境问题,了解其空间分布对于海岸带的科学管理和渔业可持续发展具有重要意义。广西北部湾海岸带地形错综复杂,养殖池塘沿岸线散乱分布,导致传统遥感识别方法难以实现高精度提取。针对此问题,该研究提出一种基于Google Earth Engine(GEE)平台和全年Sentinel-1和Sentinel-2时序遥感数据的水产养殖池塘识别方法,结合多阈值分割和面向对象分类提取2019年广西北部湾海岸带的水产养殖池塘。结果表明:1)广西北部湾海岸带养殖池塘面积总计199.3 km2,遍布整个沿岸地区;识别结果总体精度达到0.921,Kappa系数为0.842;2)选取4个典型区域,对比该研究方法提取结果与Google高清影像目视解译结果,在规模化集聚型养殖区域中,识别结果占目视解译的面积比例达到90%以上,在排布密集的小型池塘区域面积占比也能达到80%以上;3)以时序遥感数据作为分类特征值,能够有效排除废弃池塘、水稻田和季节性水域。该方法在大范围复杂环境中仍具有良好性能,显著提高了水产养殖池塘遥感识别的精度,能够为海岸带生态环境的智能监控、养殖区域空间优化提供技术支持。  相似文献   
9.
To investigate their diel vertical migration (DVM), 599 sablefish (Anoplopoma fimbria) were implanted with electronic archival tags in the Gulf of Alaska, Aleutian Islands, and the eastern Bering Sea. Of these tags, 98 were recovered with usable depth data (7,852,773 recordings representing 81,233 days) that we used to identify DVM and to classify DVM into one of two types: normal DVM (rise from the bottom during nighttime) and reverse DVM (rise from the bottom during daytime). The results of our study highlight three important attributes of DVM for sablefish. First, all tagged sablefish carried out DVM, although the occurrence was intermittent (26% of the days with usable data) and most commonly for short durations (10 days or less). Second, bottom depth for normal DVM was about 78 m shallower than for reverse DVM. Third, normal DVM occurred most often in fall and least often in spring, whereas this high/low pattern was shifted about 3 months later for reverse DVM; reverse DVM occurred most often in winter and least often in summer. Normal DVM likely occurred to increase foraging opportunity (e.g., nightly shift to match depth of prey). Reverse DVM more commonly occurred during winter and may represent an increase in foraging by sablefish during the daytime to compensate for decreased pelagic resources. The default foraging strategy for sablefish may be benthic because of the uncertainty of vertically migrating to a location where the occurrence of prey is not guaranteed; sablefish may invoke DVM when the non‐DVM foraging benefit is reduced.  相似文献   
10.
中外农业保险模式及其对北部湾经济区农业保险的启示   总被引:1,自引:1,他引:0  
李燕 《安徽农业科学》2011,39(27):17030-17032,17035
概述了国内外农业保险模式,并对中外农业保险模式进行了比较,在此基础上,提出了国内外农业保险模式对北部湾经济区农业保险模式构建的经验启示:北部湾经济区发展农业保险应根据经济发展的实际情况;北部湾经济区农业保险应定性为政策性保险;政府应对农业保险给予全面支持;加快完善农业保险相关的法律体系。  相似文献   
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