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1.
This study reports on the movements of swordfish tagged within the Pacific Leatherback Conservation Area (PLCA), an expansive region (>500,000 km2) off the U.S. West Coast that has been seasonally restricted to drift‐gillnet fishing since 2001 to reduce leatherback sea turtle (Dermochelys coricea) interactions. Thirteen swordfish were outfitted with satellite‐linked archival tags scheduled for short (2–20 days, n = 11) and longer‐term (150 days, n = 2) data collection. All tags were deployed on basking swordfish using traditional harpoon‐based methods during the fall of 2012–2013, near offshore seamounts (35.6°N/122.9°W to 37.4°N/123.5°W). Depth and temperature data from 11 swordfish (~90 to 150 kg) resulted in <251 days of movement information from the PLCA region. All tagged individuals exhibited surface‐oriented nocturnal movements, spending >99% of the night above the average thermocline depth (37.5 m), with an average night depth of 8.3 ± 1.6 m. Daytime depth distribution was greater and more variable (mean 107.1 ± 21.2 m), with fish primarily displaying three behavioral patterns: (i) basking activity, 16.7% of the day, (ii) a mixed‐layer distribution between 3 m and the thermocline (26.8% of the day), and (iii) prolonged dives below the thermocline, 56.5% of the day. For seven of the tracks, daytime basking rates increased when thermocline depth was <37 m. As fish moved offshore, there was less variability in vertical movements with a reduction in both basking activity and mixed layer occupancy, as well as an increase in average daytime depth. These data are discussed with respect to the potential development of alternative fishery options for the PLCA.  相似文献   
2.
Fish associations with different types of littoral habitats were studied in four canyon‐shaped reservoirs in the Czech Republic in years 2010 and 2011 by gillnets. Two to three habitats per reservoir–beaches (former meadows), stump fields (former forest) and rubble slopes–were defined and sampled along the longitudinal axis of reservoirs. Effects of reservoir, habitat and locality (position along longitudinal axis) on fish biomass, abundance and species structure were tested for juvenile and adult fish separately. Hierarchical analysis of variance revealed that habitats differed significantly in fish biomass and abundance. Redundancy analysis showed that analysed environmental variables had significant influence on fish community structure. Most variability in community structure was explained by reservoir and then by combination of habitat and slope steepness. Locality position had the smallest influence on community structure. For both adult and juvenile fish total abundance and biomass, the most inhabited habitat was beaches; rubble slopes were the least inhabited. Habitat associations differed among species. Among adults, bream Abramis brama, white bream Blicca bjoerkna and roach Rutilus rutilus were associated with beaches and stump fields, whereas perch Perca fluviatilis, ruffe Gymnocephalus cernuus, asp Aspius aspius and pike Esox lucius were associated with rubble slopes. Bream, white bream, bleak Alburnus alburnus, roach, ruffe and pikeperch Sander lucioperca were associated with beaches among juveniles, whereas the only juvenile associated with rubble slopes was perch. We showed that most common species are associated with distinct habitats and also that utilisation of various littoral habitats differs in general.  相似文献   
3.
为研究南海马鲛流刺网网目对康氏马鲛Scomberomorus commersoni的选择性,于2015年3月在南海北部用网目尺寸分别为80、100、120、138、142、160 mm的刺网进行了共同捕捞试验,基于SELECT(Share Each LEngth's Catch Total)模型的基本架构下,用Normal和Bi-normal选择性概率模型拟合试验数据,并就刺网对康氏马鲛的渔获方式、选择性曲线形状和SELECT模型应用展开了探讨。结果表明:试验共捕获康氏马鲛172尾,康氏马鲛的渔获方式以刺挂为主;Normal和Bi-normal的估计分隔模型均比等分隔模型拟合效果好,其中Bi-normal的估计分隔模型拟合效果最好,两个选择性峰值点对应的相对叉长分别为R_a=4.4399和R_b=6.7278;6组网目尺寸的刺网对康氏马鲛的相对作业强度(pi)大小依次为138 mm142 mm160 mm100 mm80 mm120 mm。本研究结果可为制定南海马鲛流刺网最小网目尺寸提供参考。  相似文献   
4.
珠江口水域秋季刺网的渔获组成及多样性分析   总被引:4,自引:0,他引:4  
2014年9月使用3种不同结构(单片、双重、三重)和不同网目尺寸(40 mm、50 mm、60 mm)的刺网在珠江口水域进行了海上捕鱼试验,并从多样性和相异性两方面探讨了珠江口水域刺网渔业资源群落结构的差异。试验结果显示,3种刺网的渔获种类数、尾数和质量都随着网目尺寸的增大而减少;相对重要性指数(IRI)大于1 000的优势种有所差异,但深水金线鱼(Nemipterus bathybius)是共同优势种。针对珠江口渔获个体大小悬殊的特点,分别以个体数和生物量为基础计算了该水域的多样性指数,t检验结果显示这两者之间存在显著差异。采用欧氏距离法(Euclidian distance)计算,结果显示不同网目刺网渔业资源群落结构的差异性较高,而同一网目刺网差异性较低。从提高渔业资源群落结构的多样性和恢复其生态稳定性来看,控制网目尺寸是当前最主要和最有效的措施。  相似文献   
5.
南海北部马鲛流刺网渔获组成初步分析   总被引:3,自引:0,他引:3  
为了明确南海北部马鲛(Scomberomorus)流刺网的渔获组成、主要种类的生物学特征、幼鱼比例等情况,2012年4月2113~24日在海南岛东北部渔场进行了调查研究,并对主要渔获种类的刺挂部位作了初步探讨。结果表明,马鲛流刺网的主要渔获种类为康氏马鲛(S.commersoni)、白b鲔(S.guttatus)和乌鲳(Formioniger),其相对重要性指数(IRI)分别为10969.80、5502.49和1937.34;优势体长(叉长)组分别为701~800mm、501~600mm和231~250mm。建议尽快制定主要渔获种类的最佳开捕长度,进行渔具选择性试验,制定并出台最小网目尺寸等相关管理措施,以促进马鲛刺网渔业的可持续发展。  相似文献   
6.
ABSTRACT:   The effects of the different catching methods (gillnet, longline, harpoon) on sensory, chemical (pH, total volatile base nitrogen, K -value) and microbiological (total viable count [TVC]) changes in pike perch Sander lucioperca stored in ice were investigated. The same soaking time was used for both gillnet and longline fishing. The catching method had considerable influence on the freshness quality of pike perch. The acceptable shelf life was 15 days for pike perch caught by gillnet, and 22 days for longline and harpoon. The initial concentrations of inosine monophosphate (2.4 μmol/g) in pike perch caught by gillnet were significantly lower ( P  < 0.05) than longline (4.1 μmol/g), and especially by harpoon (16.7 μmol/g). However, the initial K -values for fish caught by harpoon were significantly ( P  < 0.05) lower (24.36%) than fish caught by longline and gillnet (57.69%, 64.41%, respectively). The average K , Ki, G and H -values at rejection day in terms of sensory assessment were approximately 90, 98, 156 and 40%, respectively, for all catching methods during ice storage. However, TVC reached 7.0 log cfu/g after approximately 11 days of storage for fish caught by gillnet, 19 days for fish caught by longline and 8 days for fish caught by harpoon. The result of this study suggests that the best catching method for preserving the freshness of pike perch is longline, based on the data obtained from the sensory and microbiological analysis.  相似文献   
7.
SUMMARY: Flume-tank experiments were performed to examine the depth response of a new type of depth-controlled gillnet. Variations of net depth were investigated as the warp was paid out and wound up for different changes of warp length, main sinker weights, and winch speeds. In most experiments, when the warp finished paying out, the net continued to descend and then ascended slightly to an equilibrium depth (overshoot phenomenon). The overshoot distance was nearly constant when the warp was wound up and increased linearly with increasing winch speed when the warp was paid out. An increase in winch speed reduced net settling time, which converged on a constant value for both paying out and winding up.  相似文献   
8.
根据2014年11月~2015年8月在雷州湾开展的4个航次的流刺网调查数据,分析了游泳生物多样性指数的相关性、相对资源丰度及其影响因子。共鉴定游泳动物113种,隶属于5纲16目49科86属;其中鱼类(82种)和软甲纲(27种)分别占出现总种类数的72.5%和23.9%。种类的丰度排序结果显示,重要性居前10位的种类中,近底层鱼类和中上层鱼类各2种,甲壳类6种。该海域群落多样性水平总体较高,由湾内向湾口海域呈递增趋势;分类多样性指数(Δ)与Shannon-Wiener多样性指数(H')、Pielou均匀度指数(J')均显著相关(Pearson test,P0.01),能更全面地反映游泳生物群落特征。基于RAD的建模分析表明,Mandelbrot模型拟合优度最佳(AIC=485),初步推断该群落总体处于生态竞争占优势的动态平衡。基于广义线性模型的单位捕捞努力量渔获质量(BPUE)、单位捕捞努力量渔获尾数(NPUE)与环境因子分析表明:1)水体溶解氧(DO)极显著影响BPUE(P0.01),而溶解氧、水温及季节变动与水温交互作用显著影响NPUE(P0.05)。2)流刺网的网具长度、站位的地理位置差异对BPUE、NPUE的影响均不显著(P0.05)。调查海域湾内、湾中和湾口的渔业资源群落结构的季节、空间差异较小,仅NPUE的分布存在显著季节波动(P0.05)。  相似文献   
9.
  1. Gillnets are commonly used in tropical multi‐species fisheries and there is a need to investigate the comparative efficiency and impacts of this gear on fish populations and diversity. The efficiency and the impact of gillnets of distinct mesh sizes were compared in the Lower Tocantins River (Brazilian Amazon).
  2. Fish sampling was conducted in 12 floodplain lakes using gillnets of distinct mesh sizes and 345 fish landings were recorded. Indicators of gillnet efficiency were: (1) catch per unit of effort (CPUE) of total fish sampled; (2) CPUE of fish caught by fishers; (3) CPUE of commercial fish sampled; and (4) proportion of biomass of commercial fish sampled. Indicators of impact were: (1) the number of non‐commercial fish (by‐catch); (2) the proportion of fish above the length at first maturity; (3) mean fish size (length); (4) total number of fish species and of rare fish species caught.
  3. Gillnets of 8 cm mesh size showed a higher CPUE in fish samples and fish landings. This mesh size also showed reduced impacts (lower numbers of non‐commercial fish caught and higher proportion of adult fish).
  4. Gillnets of 6 cm mesh size caught a smaller proportion of adult fish, smaller fish, more species and more rare species. Therefore, intensive use of these gillnets could increase the risk of regional species extinctions and impair the provision of ecosystem services by target fish.
  5. Gillnets of 8 cm mesh size could improve fish catches while minimizing adverse effects of gillnet fishing. The practical management recommendation would be to replace the more damaging small mesh gillnets by gillnets with intermediate mesh size. This recommendation could simultaneously protect small‐sized rare species and larger fish, being broadly applicable to other small‐scale and multi‐species fisheries that use gillnets intensively in tropical countries with high fish diversity.
Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
10.
Abstract Standardised fishing methods using gillnets (EN 14575), electric fishing (EN 14011) and hydroacoustics (WI 00230244 CEN enquiry) to estimate species composition, abundance, biomass and size distribution were compared in 14 alpine lakes >50 ha. More fish species were detected using benthic gillnets (mean = 72.7%) than electric fishing (mean = 59.5%) and pelagic gillnets (mean = 29.6%). For all but two lakes, additional information from a local fisheries manager was required to obtain a complete list of species. Biomass data generated by standardised gillnetting and hydroacoustic surveys were not fully comparable, but a positive correlation was found. Gill netting and hydroacoustics both indicated a nearly fishless habitat below 75 m, which confirmed the maximum required fishing depth according to the European Standard EN 14757. Size distributions obtained from gillnet and hydroacoustic surveys differed statistically for large fish (>40 cm). Each standardised method reflected typical shortcomings. The European standard (EN 14757) should be amended for pelagic fish habitat in deep alpine lakes to include sampling effort corresponding to water volume, and additional gillnets with larger mesh sizes (e.g. 70 mm). Furthermore, the electric fishing standard (EN 14011) should be extended to incorporate requirements of lake fish sampling.  相似文献   
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