西藏雅鲁藏布江中游下段沙地高山松林研究

在有种源的情况下,该区高山松不仅可以在粉粒(0.01～0.05mm)含量40％以上的阶地上生长更新,而且可以在细砂为主的阶地覆沙地和山坡覆沙地上生长,并可在沙丘移动较慢的地段天然更新。繁茂枝叶可阻挡沙丘前移,形成高7m以下的沙丘。因此高山松不仅可作为先锋固沙树种,且具有强的阻沙固沙能力。阶地高山松幼林高生长主要受自身生物节律所控制,山坡覆沙地高山松高生长已受环境因子(4月份平均气温)制约。     

九甸峡泄洪洞突扩跌坎体型的水力学试验

通过水力学模型试验,对偏心铰弧门突扩跌坎体型的水流流态、空腔特性及其对掺气量、侧墙压力分布和水下噪声等的影响进行了观测,对突扩跌坎体型水力及空化特性进行了研究,确定突扩宽度Δb=0.8m,并以突体高度低于4mm作为施工不平整度的控制标准。     

东海区拖网网囊网目选择性研究

通过东海区拖网网囊网目对带鱼和小黄鱼的选择性试验,对拖网最适网囊网目尺寸进行了分析研究。结果表明：1．网囊网目45mm,小黄鱼和带鱼的逃逸率均较低,渔获中兼捕大量当年生经济幼鱼;2．网囊网目54mm,小黄鱼的50％选择体长尚小于其优势体长组范围,带鱼的50％,选择体长已部分进入其优势体长组范围;3．网囊网目65mm,选择体长范围与选择鱼种的优势体长组范围基本一致。综合分析认为：目前东海区最理想的拖网网囊网目不小于60mm。     

Size selection by diamond- and square-mesh codends in multi-species Mediterranean demersal trawl fisheries

Mediterranean demersal trawl fisheries traditionally operate using small diamond-shape meshes in the codend, which tend to retain almost all animals. We investigated the effect of mesh configuration on the size selectivity of nine species (the scaldfish Arnoglossus laterna, the broad-tail shortfin squid Illex coindettii, the European hake Merluccius merluccius, the red mullet Mullus barbatus, the Norway lobster Nephrops norvegicus, the common pandora Pagellus erythrinus, the deepwater rose shrimp Parapenaeus longirostris, the Mediterranean horse mackerel Trachurus mediterraneus and the poor-cod Trisopterus minutus capelanus) commonly captured in the Mediterranean demersal trawls. Two codends having meshes with the same opening (ca. 38 mm) but different mesh configuration (DM38: diamond-mesh and SM38: square-mesh configuration) were fished daily and alternately on the same trawl. They demonstrated a substantial improvement in selectivity with square-mesh. Selectivity was measured using the covered codend technique, the cover being supported by circular hoops.The results were analysed taking into account the between-haul variation in selectivity. Two other important external variables were identified: the trawling depth and the codend catch, which for some species influenced between-haul variation, but there was no evidence of a coherent effect on selectivity parameters.The selectivity of 40 mm diamond-mesh codend has been reported to be rather poor because a large proportion of the codend catch is immature and smaller than the minimum landing size (MLS) or first maturity size. With the exception of the flatfish (A. laterna), the effect of a change of mesh configuration from diamond- to square-mesh on size selectivity positively affected the retention length at 50% (L₅₀). However, square-meshes were found to be unsuitable for flat and/or deep-bodied fish as these escape more readily from diamond-meshes.The Council Regulation (EC) No. 1967/2006, concerning management measures for the sustainable exploitation of fishery resources in the Mediterranean, establishes the MLS of marine organisms. However, the increase in L₅₀ with square-mesh would not avoid some of the existing contradictions in allowing the use of codend mesh which leads to lower L₅₀ than the MLS.     

底拖网调查数据的Delta-模型分析及其在黄海小黄鱼和银鲳资源评估中的应用

底拖网调查(扫海面积法)的数据处理方法主要有两大类,即基于调查设计的方法(design-based method)和基于模型的方法(model-based method),其中基于调查设计的方法在我国的应用较为常见,而基于模型的方法则较少应用.介绍了渔业资源底拖网调查数据的Δ-分布模型分析方法,并采用此方法对2000年秋季黄海小黄鱼和银鲳的资源量进行了评估.结果显示,调查海区小黄鱼资源的平均分布密度为66.3 kg·km-2,95%置信区间为(23.4,109.2) kg·km-2;总资源量均值为14 626.9 t,95%置信区间为(5 168.4,24 085.5) t.银鲳资源密度均值为19.0 kg·km-2,95%置信区间为(3.5,34.5) kg·km-2;总资源量均值为4 194.3 t,95%置信区间为(773.2,7 615.4) t.传统的基于调查设计的方法得到的置信区间范围则较宽,且下限出现负值.上述结果表明Δ-分布模型法的评估结果具有较高的精度,是一种值得推广的渔业资源底拖网调查数据分析与资源评估方法.     

对应分析在福建拖网捕捞影响因素分析中的应用

采用随机抽样调查的方法在福建省选择29个拖网作业单位(样品)、11个作业因素(变量),用对应分析法对其影响因素进行分析,以判断福建拖网捕捞效率的主要影响因素以及了解作业单位(作业船)之间和作业单位与变量之间的关系。结果表明,当前影响福建拖网作业的主导因素是网具结构,其次是渔船的主机功率和作业天数。据此,建议从适当增大网口网目尺寸和网口周长、增加船舶主机功率和延长作业天数等方面入手,提高拖网作业单位捕捞效率。本文还通过分析平面变量与样品聚点图,将福建拖网作业分成4个类群,通过分析各类群与各作业生产因素的亲疏关系,进一步了解各类群的特点,可对生产单位和管理者调整拖网作业、优化生产资源配置等提供理论参考。     

Reducing seabird bycatch in longline, trawl and gillnet fisheries

With an increasing number of seabird species, particularly albatross and petrels, becoming threatened, a reduction of fishery impacts on these species is essential for their future survival. Here, mitigation methods to reduce and avoid seabird bycatch are assessed in terms of their ability to reduce bycatch rates and their economic viability for longline, trawl and gillnet fisheries worldwide. Factors influencing the appropriateness and effectiveness of a mitigation device include the fishery, vessel, location, seabird assemblage present and season of year. As yet, there is no single magic solution to reduce or eliminate seabird bycatch across all fisheries: a combination of measures is required, and even within a fishery there is likely to be refinement of techniques by individual vessels in order to maximize their effectiveness at reducing seabird bycatch. In longline demersal and pelagic fisheries, a minimum requirement of line weighting that achieves hook sink rates minimizing seabird bycatch rates should be tailored with a combination of strategic offal and discard management, bird‐scaring lines (BSLs) and night‐setting, particulary in Southern Hemisphere fisheries. Urgent investigation is needed into more effective measures at reducing seabird interactions with trawl nets and gill nets. In trawl fisheries, a combination of offal and discard management, the banning of net monitoring cables, paired BSLs, and a reduction in the time the net is on or near the surface are likely to be the most effective in reducing seabird interactions with the warp cables and net. Few seabird bycatch reduction methods have been developed for gillnet fisheries, although increasing the visibility of the net has been shown to reduce seabird bycatch. Further studies are required to determine the efficacy of this technique and its influence on target species catch rates.     

塞拉里昂海域双支架虾拖网作业中试验小网设计的研究

本文应用动力相似原理,研究设计了塞拉里昂渔场双支架虾拖网的试验小网,用来判断渔场资源和中心渔场。通过对试验小网的研究设计和实际应用发现,使用试验小网判断渔场的资源情况,具有快速性、方便灵活性和实用性等特点。     

拖网作业参数对南极磷虾捕捞效率的影响

为了解南极磷虾(Euphausia superba Dana)拖网作业中捕捞效果及影响因素,根据 2017 年 12 月 2018 年 6月随“龙腾”轮在南极海域生产时收集的作业参数、网具深度和声学数据等信息,利用声学方法获取磷虾集群质量中心深度与期望入网渔获量,结合网位变化和渔捞统计情况量化捕捞效率;利用广义可加模型(GAM)分析不同拖速和曳纲长度下,网位与磷虾集群质量中心的偏离程度,研究其对网具捕捞效率的影响。结果表明:(1)磷虾集群质量中心水深为(37.29±9.72) m,拖网稳定拖曳期间网位深度为(30.72±10.41) m,网位调整幅度为(11.52±7.09) m。网位与磷虾集群质量中心深度偏离(6.33±3.58) m。(2)网次渔获量为(16.25±6.77) t,拖曳过程中网口始终对准磷虾集群质量中心进入网口的磷虾总量为(27.06±10.19) t,捕捞效率为(63±19)%。(3)网位与磷虾集群质量中心深度差值对捕捞效率影响极显著(P<0.001),两者吻合较好时捕捞效率高;拖速与捕捞效率呈显著相关关系(P<0.05),拖速增大网位上升,捕捞效率越低;曳纲长度增加网位下降,但曳纲长度变化与捕捞效率相关性不明显(P=0.087)。研究结果将有助于南极磷虾拖网作业中有效利用磷虾行为特征,改善网具性能,提高拖网捕捞效率。