Large‐scale patterns of fish diversity and assemblage structure in the longest tropical river in Asia

Although the Mekong River is one of the world's 35 biodiversity hot spots, the large‐scale patterns of fish diversity and assemblage structure remain poorly addressed. This study aimed to investigate the fish distribution patterns in the Lower Mekong River (LMR) and to identify their environmental determinants. Daily fish catch data (i.e. from December 2000 to November 2001) at 38 sites distributed along the LMR were related to 15 physicochemical and 19 climatic variables. As a result, four different clusters were defined according to the similarity in assemblage composition and 80 indicator species were identified. While fish species richness was highest in the Mekong delta and lowest in the upper part of the LMR, the diversity index was highest in the middle part of the LMR and lowest in the delta. We found that fish assemblages changed along the environmental gradients and that the main drivers affecting the fish assemblage structure were the seasonal variation of temperature, precipitation, dissolved oxygen, pH and total phosphorus. Specifically, upstream assemblages were characterised by cyprinids and Pangasius catfish, well suited to low temperature, high dissolved oxygen and high pH. Fish assemblages in the delta were dominated by perch‐like fish and clupeids, more tolerant to high temperatures, and high levels of nutrients (nitrates and total phosphorus) and salinity. Overall, the patterns were consistent between seasons. Our study contributes to establishing the first holistic fish community study in the LMR.     

政府渔业补助政策与博弈

渔业补助政策是政府为弥补市场经济缺陷而采取的重要措施，本文应用博弈论对政府与渔民的互动博弈展开研究，并确立了混合策略模型下的政府和渔民各自最佳选择概率，达到纳什均衡，这对于解释当前政府渔业补助政策内涵与指导修订补助政策有参考意义。     

Nutrient digestibility of angling baits for carp, Cyprinus carpio, with implications for groundbait formulation and eutrophication control

Abstract  To evaluate the suitability of angling groundbaits as a fish feed and the potential for nutrient loss, the macronutrient digestibility of four groundbaits was investigated in carp, Cyprinus carpio L., using a sieving method of faeces collection and chromic oxide. Apparent digestibility coefficients (ADCs) of protein and lipids were >80% for all angling baits. ADCs of nitrogen-free extracts and phosphorus (P) differed significantly between the test diets, probably because of divergent feed compositions and ingredient treatments. The generally high digestibility estimates indicated that fish feeding on angling groundbait will benefit from this food source. The differences in nutrient digestibility suggested that type of groundbait and ingredient used will have a major effect on potential eutrophication and fish production caused by groundbaiting. The principle of groundbaits to protect the environment should be to minimise the P-content of the groundaits and maximising P-digestibility and P-retention efficiency.     

略论西北地区渔业发展现状及对策

通过对西北地区渔业现状的分析，从中挖掘出西北地区渔业落后的社会经济原因，并结合当前的社会经济状况和渔业发展形势，总结了西北地区渔业发展的优势所在，以此为基础提出了加强市场宣传和资源开发、引进资金和技术以及政策引导等发展西北渔业的几点建议。     

Designating a greenbelt around the city of Riga, Latvia

Latvian legislation demands that forest protection belts are established around all cities and towns. The main goal of a protection belt is to provide suitable opportunities for recreation to urban dwellers and to minimise any negative impacts caused by urban areas on the surrounding environment. Legislation states the main principles to be adopted, which include the maximum area of protection belts, their integration in territorial development plans and restrictions placed on forest management activities. The largest part of the forest area around Riga is owned by the municipality of Riga, which, as a result, has two competing interests: to satisfy the recreational needs of the inhabitants of Riga, and to maximise the income from its property. In order to compile sufficient background information to solve this problem, the Board of Forests of Riga Municipality initiated the preparation of a proposal for the designation of a new protection belt.The proposal was based on the development and application of a theoretical framework developed during the 1980s. The analysis of the recreational value of the forest (5 classes of attractiveness) was carried out based on categories of forest type, dominant tree species, dominant age, stand density, distance from urban areas and the presence of attractive objects. Information was derived from forest inventory databases, digital forest maps and topographic maps. Additional information was digitised and processed using ArcView GIS 3.2. Local foresters were asked about the recreation factors unique to different locations, such as the number of visitors and the main recreation activities. From a recreational point of view and taking into account legal restrictions and development plans for the Riga region, it was proposed to create three types of zones in the forest: a protection belt, visually sensitive areas and non-restricted areas.     

凤县休闲农业发展现状及存在问题与对策

近年来,凤县转型发展休闲农业取得了巨大成功,对其发展历程进行深入研究,可以进一步促进凤县休闲农业规范快速发展,同时为我国休闲农业发展提供范例参考。详细阐述了凤县休闲农业发展的现状,对凤县发展休闲农业的优势进行了分析,就存在的问题重点从加强政府引导、理顺管理体制、制定规划标准及加大扶持力度4个方面阐明了凤县休闲农业发展的新举措,以期为凤县在休闲农业发展中获取更大的竞争优势提供参考。     

Association between porpoise presence and fish choruses: implications for feeding strategies and ecosystem-based conservation of the East Asian finless porpoise

The associations between feeding activities and environmental variables inform animal feeding tactics that maximize energetic gains by minimizing energy costs while maximizing feeding success. Relevant studies in aquatic animals, particularly marine mammals, are scarce due to difficulties in the observation of feeding behaviors in aquatic environments. This data scarcity concurrently hinders ecosystem-based fishery management in the context of small toothed-cetacean conservation. In the present study, a passive acoustic monitoring station was deployed in an East Asian finless porpoise habitat in Laizhou Bay to investigate potential relationships between East Asian finless porpoises and their prey. The data revealed that porpoises were acoustically present nearly every day during the survey period. Porpoise detection rates differed between spring and autumn in concert with activities of fish choruses. During spring, fish choruses were present throughout the afternoon, and this was the time when porpoise vocalizations were the most frequently detected. During autumn, when fish choruses were absent, porpoise detection rates decreased, and diurnal patterns were not detected. The close association between fish choruses and finless porpoise activities implies an “eavesdropping” feeding strategy to maximize energetic gains, similar to other toothed cetaceans that are known to engage similar feeding strategies. Underwater noise pollution, particularly those masking fish choruses, could interrupt finless porpoises’ feeding success. Fisheries competing soniferous fishes with finless porpoise could impact finless porpoise viability through ecosystem disruption, in addition to fishing gear entanglement.     

渔场鱼量模型的建立

微分方程的平衡点可分为稳定和不稳定两种。当轻轻扰动平衡点时，系统状态就会剧烈变化。若新的状态决不会回到原平衡点，此点就是不稳定的；相反，如果一个系统在稳定平衡点附近受到干扰，它总是企图回到平衡点，那么此点就是稳定的。用这一数学工具可以解决诸如渔场鱼量等一系列实际问题。     

基于大型渔业平台的深远海渔业发展现状与思考

基于渔业产业现状,分析国内外在大型渔业平台、深海网箱和养殖工船方面的发展现状,提出“游弋式”养殖工船及深远海渔业的基本概念。受限于投资成本、技术发展水平等客观因素,中国深远海养殖发展速度缓慢,但近年来取得了一定的发展成效。笔者针对现阶段渔业粗放型生产方式的现状,从国家战略、渔业改革和产业需求等角度分析深远海渔业发展的必要性,认为发展以养殖工船为代表的深远海大型渔业平台是实现渔业强国之路的有效途径之一,走出一条符合中国国情的深远海渔业平台的开发之路势在必行。     

基于 DEA 和 Malmquist 指数的广东省渔业效率研究

【目的】分析掌握广东渔业的产出效率,为发展可持续的低耗高产渔业提供数据参考。【方法】基于数据包络分析（DEA）及 Malmquist 指数,对 2011—2022 年期间广东渔业综合技术效率和全要素生产率指数及其分解进行测算和分析,并与全国平均值进行对比。【结果】广东渔业综合技术效率每年均高于全国平均水平,但2011—2014 年、2018—2019 年和 2021 年广东渔业规模报酬呈现递减。通过对广东水产养殖和水产品捕捞的综合技术效率分别进行测算,发现 2011—2022 年期间广东水产养殖的综合技术效率较高,除 2013 年和 2014 年外,均为DEA 有效。将 DEA 无效年份的广东水产养殖和水产品捕捞在生产前沿面上的投影调整为 DEA 有效,结果显示,2013 年和 2014 年广东水产养殖投入的冗余率分别为 5.98% 和 10.46%,而 2011—2014 年、2018—2019 年和 2021年广东水产品捕捞投入的冗余率在 39.73%~74.27% 之间,说明水产品捕捞的过度投入以及由此引发的捕捞综合技术效率低下是造成 2011—2014 年、2018—2019 年和 2021 年广东渔业规模报酬递减的主要原因。广东渔业的技术进步和全要素生产率上升幅度与全国平均水平相差较远,全要素生产率和技术进步指数均比全国平均增幅低 4.7%,说明广东省在渔业技术进步方面有较大提升空间。【结论】建议广东加大渔业科技的投入力度,加强渔业技术创新,以促进渔业技术进步和提高全要素生产率;加快渔业产业结构调整,合理布局养殖和捕捞规模,以解决广东渔业规模报酬递减的问题;加强渔业资源保护和增殖放流,利用自然生产力增加可捕捞渔业资源;加强水产良种创制及养殖新模式和新技术的开发,进一步拓展水产养殖空间和提高水产养殖的产出效率。