中西太平洋延绳钓兼捕大青鲨渔获率、性比及叉长分析研究

大青鲨(Prionace glauca)是一种分布广泛的大型中上层远洋性鲨鱼,在以金枪鱼等经济鱼种为目标的延绳钓渔业中渔获率较高。根据中国远洋延绳钓渔船2015—2018年在中西太平洋(Western Central Pacific Ocean,WCPO)海域共51个航次采集的兼捕大青鲨数据,分析了该海域兼捕到的大青鲨渔获率、性别及叉长(Fork length,FL)特征。结果显示,大青鲨兼捕的捕捞努力量渔获量(Catch per unit effort,CPUE)在170°30'E—124°50'W、33°30'N—34°40'S范围内分布较高;2015—2018年间大青鲨兼捕CPUE波动较大,以2017年最高,兼捕CPUE与月份之间无显著性差异(P>0.05);大青鲨的雌、雄个体分布范围基本一致,优势叉长区间均为160~220 cm,各自所占比例为89.26%和85.19%,雌、雄个体的叉长分布存在显著性差异(P<0.05),雌雄比例为1.75。     

大西洋中上层鲨鱼资源状况的初步探讨

据1994—2001年4个航次在金枪鱼延绳钓渔船对热带大洋性中上层鲨鱼资源进行调查，并分析国际大西洋金枪鱼资源保护委员会提供的关于中上层鲨鱼的渔业数据。结果表明：延绳钓渔业共兼捕13种鲨鱼，其中，尖吻鲭鲨和大青鲨是优势种类。尖吻鲭鲨在第1、第2和第4航次的CPUE分别为每千钩0．3502、0．1754和0．0642尾，呈下降趋势。大青鲨在第1～3航次的的CPUE达到每千钩5～7尾，而在第4航次下降为每千钩0．8尾。研究报告了中国金枪鱼船队自1993年开始在大西洋兼捕尖吻鲭鲨和大青鲨的渔获量，并根据捕捞死亡系数和大西洋总渔获量数据，初步探讨了尖吻鲭鲨和大青鲨年平均资源量，影响CPUE的因素和大西洋中上层资源状况。     

东太平洋大青鲨年龄与生长的研究

根据2003年7~11月在东太平洋海域(03°~17°S、96°~146°W)金枪鱼延绳钓生产调查中兼捕获取的89 ind大青鲨样本,通过对大青鲨脊椎骨年轮的观察及其生物学特征数据的记录,研究了大青鲨的年龄与生长。结果表明,大青鲨的最大寿命为17.1龄;von Bertalanffy生长参数L∞=292 cm,K=0.16/yr,t0=-1.6yr;大青鲨的生长拐点年龄为5.3yr,拐点体重为55.8kg,拐点叉长为195 cm。     

东太平洋热带海域大青鲨繁殖生物学特征

人青鲨（Prionace glauca）是一种大型中上层鲨鱼，隶属于真鲨目、真鲨科、人青鲨属．广泛分布在全球热带和温带海域，最大全长可达到300cm，在南海和东海亦有记录。该鱼生活在海洋上层和沿岸海域。大青鲨是金枪鱼延绳钓渔业的重要兼捕对象，占兼捕猫鱼总渔获尾数的50％，是大西洋公海金枪鱼延绳钓兼捕渔获物中的优势鱼种，     

热带中西太平洋金枪鱼延绳钓渔获物组成及其多样性

利用金枪鱼漂流延绳钓作业方式, 于 2018 年 5 月至 2019 年 3 月期间在热带中西太平洋海域(2°03′~11°17′S, 163°14′~173°35′E)进行渔获取样, 分析渔获组成及物种多样性, 并使用广义线性混合模型(GLMM)和圆形统计方法分析渔获水深、月相等时空要素对物种多样性、目标种类和兼捕 CPUE 等影响。结果表明: (1) 3673 尾渔获隶属于 9 目 21 科 30 属 35 种, 其中目标种类大眼金枪鱼(Thunnus obesus)和黄鳍金枪鱼(Thunnus albacores)为优势种, 蓝枪鱼(Makaira nigricans)、长鳍金枪鱼(Thunnus alalunga)、镰状真鲨(Carcharhinus falciformis)、帆蜥鱼(Alepisaurus ferox) 和紫魟(Pteroplatytrygon violacea)为重要种; (2)大眼金枪鱼、黄鳍金枪鱼以及兼捕种类 CPUE 分别为(1.662± 0.89) ind/千钩、(1.39±1.45) ind/千钩、(2.52±1.27) ind/千钩。渔获多样性指数 Shannon-Wiener 指数(H′)、Margalef 指数(D)、Pielou 指数(J)分别为(1.78±0.28)、(2.53±0.60)、(0.79±0.09); (3) GLMM 结果显示, 月相(余弦)对大眼金枪鱼的 CPUE 的具有极其显著的影响(P=0.001, CPUE 在满月较高, 而在新月较低), 而月相(正弦)对黄鳍金枪鱼 CPUE 具有边际显著影响(P=0.067, CPUE 在上弦月较高, 而在下弦月较低), 月相兼捕 CPUE 则没有显著影响, 水深对 CPUE 具有极显著的影响(P＜0.001); (4)月相对多样性指数均不存在显著影响, 但水深对渔获 Shannon-Weiner 指数 (H′)和 Margalef 指数(D)均有显著影响(P＜0.001)。研究结果反映出热带中西太平洋海域物种丰富、群落的复杂程度较高、稳定性较好, 群落对环境变化、渔业活动等具有较好的耐受性。     

马绍尔群岛海域大青鲨栖息地综合指数

通过2006年10月—2007年6月在马绍尔群岛海域利用金枪鱼延绳钓调查所取得的43个站点的大青鲨兼捕数据,以及测得的温度、盐度、溶解氧浓度等环境数据,应用分位数回归的方法分析各水层(40～280 m,每40 m为一层)中各环境因子与大青鲨渔获率的关系,建立 “栖息地综合指数(integrated habitat index,IHI)模型”,用来预测其空间分布,并利用另外的18个站点的数据对模型进行验证。结果表明,(1) 模型的预测能力良好;(2) 不同的水层影响大青鲨分布的环境因子不同;(3) 大青鲨较适宜的栖息水层为80～120 m;(4) 大青鲨IHI较高的海域有两个,分别为9°N~12°N,172°E~176°E与3°N~6°N,166°E~169°E。建议对大青鲨IHI较高的两海域采取规定延绳钓的作业深度为120 m以深等管理措施。     

中东太平洋金枪鱼延绳钓渔获量及其分布

根据2000年9月至2002年8月两年的中东太平洋金枪鱼延绳钓探捕调查结果,对延绳钓渔获量及其分布特征进行了初步分析。结果显示,延绳钓渔获物以金枪鱼为主,大眼金枪鱼(Thun-nusobesus)等3种金枪鱼的渔获量占总渔获量75·9%。“海欣”船延绳钓作业的平均日产量为(994·8±19·9)kg/d,上钩率为(12·5±0·3)ind/103钩。主要目标鱼种大眼金枪鱼和黄鳍金枪鱼(Thunnusalbacares)的平均日产量分别为(466·9±13·9)kg/d和(190·6±7·2)kg/d。探捕期间日产量的月间差异显著(P<0·001),6~8月为渔发汛期,日产量较高;2~5月为相对淡季,日产量较低。探捕区南部的平均日产量最高,与中、北部比较差异显著(P<0·001);东部平均日产量与西部比较差异不显著(P>0·05)。     

北太平洋金枪鱼延绳钓钓钩垂直分布及浸泡时间对渔获物的影响

根据中国金枪鱼延绳钓渔业观察员于2018年9—12月在北太平洋公海(150°W—164°W,30°N—37°N)采集的金枪鱼延绳钓渔获数据,分析了钓钩的垂直分布及浸泡时间与渔获物之间的关系。结果表明,11种主要渔获物钓获深度差异很大,鲣(Katsuwonus pelamis)的平均钓获深度最浅,大青鲨(Prionace glauca)最深;除大青鲨和帆蜥鱼(Alepisaurus ferox)外,其他兼捕鱼类的钓钩深度分布与大眼金枪鱼(Thunnus obesus,目标鱼种)之间差异显著;随着浸泡时间的增加,总渔获率呈先增加后下降的趋势,10～14 h内渔获率较高,且在第10小时达到峰值[1.44尾·(千钩·h)~(-1)];浸泡时间在10～16 h内大眼金枪鱼的渔获率较高,且在第11小时达到峰值[0.45尾·(千钩·h)~(-1)]。研究结果可为渔业生产和CPUE的标椎化提供参考,为制定有效减少兼捕鱼种的管理措施提供科学依据。     

金枪鱼延绳钓渔获性能研究进展

金枪鱼延绳钓渔获性能主要按目标鱼种和兼捕物种渔获效率进行评价。对其研究有助于改进延绳钓渔具渔法, 提高目标鱼种捕捞效率和减少兼捕。本文以时间顺序为主对国内外关于金枪鱼延绳钓渔获性能研究的文献进行梳理, 从钓具选择性、钓钩深度、饵料选择性、环境因素以及钓具浸泡时长等方面概括了金枪鱼延绳钓渔获性能的研究进展, 并提出存在的不足和建议, 为金枪鱼延绳钓渔获性能的研究提供参考。前人研究取得的成果有: (1)不同鱼种最佳作业深度和钓具浸泡时长不同; (2)较大尺寸的圆形钩能减少兼捕; (3)拟饵也具有选择性, 鱼类饵料和蓝色染色饵料有利于减少兼捕; (4)具体水层的环境因素对延绳钓渔获性能影响较大。建议今后金枪鱼延绳钓渔获性能研究应: (1)确定钓钩最佳沉降速度和深度; (2)分水层建立不同物种渔获性能预测模型; (3)针对不同的目标鱼种探索最佳尺寸和钩形; (4)研究不同气味和颜色的饵料或拟饵对物种选择性的影响; (5)考虑诱饵、钓钩类型和尺寸和钓具浸泡时长对渔获率、死亡率、兼捕率和兼捕物种释放后存活率的潜在协同效应。     

中东太平洋金枪鱼延绳钓渔获物组成分析

根据2000年9月至2002年8月两年的中东太平洋金枪鱼延绳钓探捕调查结果，对延绳钓渔获物组成进行了初步分析。结果显示，延绳钓的主要渔获种类有肥壮金枪鱼(Thunnus obesus)和黄鳍金怆鱼(Thunnus albacares)等15种大洋性鱼类，渔获物中金枪鱼类分别占重量和尾数的76．41％和76．91％，旗鱼类占11．05％和7．83％．鲨鱼类占10．80％和12．08％，其他鱼类占1．73％和3．18％。相对重要性指标(IRI)表明，延绳钓渔业以肥壮金枪鱼和黄鳍金枪鱼为目标鱼种，其他大型中上层经济鱼类为兼捕对象。各渔获种类的渔获重量组成比例月间变化和海域变化明显。     

Standardized catch and survival rates,and effect of a ban on shark retention,Palau pelagic longline fishery

1. Pelagic longline fisheries affect both market and vulnerable bycatch species and can have broad effects on community structure and processes.
2. Observer data from the Palau longline fishery were analysed to identify opportunities to mitigate vulnerable species bycatch, determine temporal trends in local abundance, and assess changes following a ban on shark retention and wire leaders. Catch and haulback condition data for bigeye and yellowfin tunas, blue and silky sharks and pelagic stingrays were fitted to standardized catch and survival rate models.
3. The fishery caught silky and blue sharks, olive ridley sea turtles and other species of conservation concern.
4. Changing from shallow sets to deep daytime sets might reduce shark and sea turtle catch rates but increase turtle haulback mortality rates, maintain economically viable tuna catch rates, but increase catch rates of pelagic stingrays, a lower conservation concern than main caught species of sharks and turtles.
5. Focusing fishing effort during the middle of the calendar year would maximize yellowfin tuna and minimize silky shark standardized catch rates, but maximize blue shark catch rates.
6. A large decline in shark fishing mortality rate very likely occurred following a ban on shark retention and wire leaders. This was due to large reductions in the nominal shark catch rate and shark retention, partially offset by decreases in the shark haulback survival rate and pre‐catch survival rate. Significantly higher blue shark and lower pelagic stingray nominal catch rates occurred on wire vs. monofilament leaders. Significantly higher blue shark and lower yellowfin tuna nominal catch rates occurred on sets using shallow ‘shark lines’. It is a research priority to compare the probability of shark pre‐catch survival after escaping from monofilament leaders with an ingested hook and trailing line to the survival probability when captured on wire leaders.

Copyright © 2015 John Wiley & Sons, Ltd.     

基于最小势能原理的延绳钓渔具作业状态数值模拟

基于有限元理论及最小势能原理,以2008年9月到2009年1月海上实测的188枚钓钩的深度、24个站点不同深度的三维海流数据、渔具参数和作业参数为基础,建立并验证了延绳钓三维最小势能模型。结果表明:(1)建立的延绳钓最小势能模型可以计算得出任何三维分层海流作用下延绳钓的三维形状和钓钩的深度,大部分钓钩的实测深度与数学模型数值深度之间的差别不大,其平均差值为12.03 m,差值范围为0.02～40.36 m(方差S2=100.30,标准差S=10.01,n=188),通过成对双样本均值分析,实测深度与数值深度无显著性差异(P>0.05);(2)延绳钓渔具的干线在海水中稳定后并不是呈平滑的悬链线,而是波浪形的曲线;(3)圆柱体轴线与流向垂直时的阻力系数(CN90)取值对于数值模拟的结果有一定的影响,CN90值的选取与研究对象的雷诺数有关。延绳钓最小势能数值模型能够有效模拟并预测延绳钓在不同深度的三维海流作用下的形状、钓钩深度并达到可视化。     

Elasmobranch captures in the Fijian pelagic longline fishery

1. Pelagic longline fisheries for relatively fecund tuna and tuna‐like species can have large adverse effects on incidentally caught species with low‐fecundity, including elasmobranchs.
2. Analyses of observer programme data from the Fiji longline fishery from 2011 to 2014 were conducted to characterize the shark and ray catch composition and identify factors that significantly explained standardized catch rates. Catch data were fitted to generalized linear models to identify potentially significant explanatory variables.
3. With a nominal catch rate of 0.610 elasmobranchs per 1000 hooks, a total of 27 species of elasmobranchs were captured, 48% of which are categorized as Threatened under the IUCN Red List. Sharks and rays made up 2.4% and 1.4%, respectively, of total fish catch. Blue sharks and pelagic stingrays accounted for 51% and 99% of caught sharks and rays, respectively.
4. There was near elimination of ‘shark lines’, branchlines set at or near the sea surface via attachment directly to floats, after 2011.
5. Of caught elasmobranchs, 35% were finned, 11% had the entire carcass retained, and the remainder was released alive or discarded dead. Finning of elasmobranchs listed in CITES Appendix II was not observed in 2014.
6. There were significantly higher standardized shark and ray catch rates on narrower J‐shaped hooks than on wider circle hooks. Based on findings from previous studies on single factor effects of hook width and shape, the smaller minimum width of the J‐shaped hooks may have caused the higher shark and ray catch rates. For sharks, the effect of hook width may have exceeded the effect of hook shape, where small increases in shark catch rates have been observed on circle vs J‐shaped hooks.
7. Shark and ray standardized catch rates were lowest in the latter half of the year. Focusing effort during the second half of the year could reduce elasmobranch catch rates.

Copyright © 2016 John Wiley & Sons, Ltd.     

Identification and evaluation of shark bycatch in Georgia’s commercial shrimp trawl fishery with implications for management

Abstract Many US states have recreational and commercial fisheries that occur in nursery areas occupied by subadult sharks and can potentially affect their survival. Georgia is one of few US states without a directed commercial shark fishery, but the state has a large, nearshore penaeid shrimp trawl fishery in which small sharks occur as bycatch. During our 1995–1998 investigation of bycatch in fishery‐dependent sampling events, 34% of 127 trawls contained sharks. This bycatch totalled 217 individuals from six species, with Atlantic sharpnose shark, Rhizoprionodon terraenovae (Richardson), the most common and finetooth shark, Carcharhinus isodon (Müller & Henle) and spinner shark, Carcharhinus brevipinna (Müller & Henle), the least common. The highest catch rates for sharks occurred during June and July and coincided with the peak months of the pupping season for many species. Trawl tow speed and tow time did not significantly influence catch rates for shark species. Gear configurations [net type, turtle excluder device (TED), bycatch reduction device] affected catch rates for shark species. Results of this study indicate gear restrictions, a delayed season opening, or reduced bar spacing on TEDs may reduce shark bycatch in this fishery.     

Distribution,body length,and abundance of blue shark and shortfin mako offshore of northeastern Japan,as determined from observed pelagic longline data, 2000–2014

Longline surveys have been conducted in the Northwest Pacific Ocean from 2000 to 2014 using chartered commercial longline vessels. Each year, two cruises were conducted offshore of northeastern Japan from mid‐April to mid‐June. For each longline set during the surveys, onboard scientists collected detailed biological information about the species caught, such as the size and sex, and recorded the catch numbers for all species. Blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) have eurythermal distributions, but the application of a generalized additive model (GAM) showed that the sea surface temperatures (SSTs) at catch sites positive for shortfin mako were warmer than those for blue shark. On the basis of the GAM, the probabilities of occurrence of both sharks differed by size category: small sharks had a narrower SST range than that of large sharks. Most catches of both sharks were juveniles, and the nominal catch rate of blue shark was more than 10 times that of shortfin mako. The standardized catch per unit effort (CPUE) for both species was calculated using a generalized linear model (GLM) with negative binomial errors, or a delta‐lognormal GLM. The standardized CPUE for blue shark in the second quarter of the year peaked in the mid‐2000s and then decreased, but it has been increasing since 2012. The CPUE for shortfin mako in the second quarter generally increased, with fluctuations.     

Catch rate and at‐vessel mortality of circle hooks versus J‐hooks in pelagic longline fisheries: A global meta‐analysis

We conducted a meta‐analysis of literature reporting on the use of circle hooks and J‐hooks in pelagic longline fisheries. Our study included more data than previous meta‐analyses of the effects of hook type, due to both a larger number of relevant studies available in recent years and a more general modelling approach. Data from 42 empirical studies were analysed using a random effects model to compare the effects of circle hooks and J‐hooks on catch rate (43 species) and at‐vessel mortality (31 species) of target and bycatch species. Catch rates with circle hooks were greater for 11 species, including four tuna species, six shark species and one Istiophorid billfish. Catch rates on circle hooks were lower for seven species, including two Istiophorid billfishes and two species of sea turtle. At‐vessel mortality was significantly lower with circle hooks in 12 species, including three tuna species, three Istiophorid billfishes, swordfish (Xiphias gladius) and three shark species. No species had significantly greater at‐vessel mortality when captured with a circle hook rather than a J‐hook. While our general approach increased model variability compared to more detailed studies, results were consistent with trends identified in previous studies that compared the catch rates and at‐vessel mortality (between hook types) for a number of species. Our results suggest that circle hooks can be a promising tool to reduce mortality of some bycatch species in pelagic longline fisheries, although the effects depend on the species and the metric (catch rate or at‐vessel mortality), emphasizing the need for fishery‐specific data in conservation and management decisions.     

The effectiveness of Shark-Management-Alert-in-Real-Time (SMART) drumlines as a tool for catching white sharks,Carcharodon carcharias,off coastal New South Wales,Australia

White (Carcharodon carcharias L.), bull (Carcharhinus leucas, Müller & Henle) and tiger (Galeocerdo cuvier, Péron & Lesueur) sharks are the primary species responsible for unprovoked shark bites. Historically, management practices were based on culling “target” shark species (i.e. white, bull and tiger sharks), which resulted in high levels of bycatch and mortality. Shark-Management-Alert-in-Real-Time (SMART) drumlines were trialled in New South Wales, Australia, aiming to optimise the capture of target shark species while minimising bycatch and mortality. Target shark species accounted for 70% of the total catch, with white sharks contributing 298 of the 350 sharks that were caught. Four animals died, and bycatch consisted of 13 species including two threatened species. Generalised linear mixed models (GLMMs) revealed a significant spatial, temporal, environmental and gear influence on white shark catch rates. SMART drumlines are a useful tool for catching target shark species with low bycatch and mortality relative to historical bather protection methods.     

Hawaii longline tuna fishery temporal trends in standardized catch rates and length distributions and effects on pelagic and seamount ecosystems

1. Declines in absolute abundance and altered size distributions from size‐selective removals of market species of pelagic apex predators in tuna fisheries alters evolutionary characteristics of populations and ecosystem processes and stability. Pelagic fishing at seamounts, where hyperstability of pelagic predators may occur, can exacerbate declining abundance and have high bycatch of species groups that are highly vulnerable to overexploitation.
2. Generalized additive mixed Poisson regression models (GAMMs) were fitted to Hawaii longline tuna fishery observer data to determine temporal trends in standardized catch rates, an index for local, relative abundance. Temporal trends in expectile length distributions were determined through geoadditive expectile GAMMs.
3. Significant declining trends in relative abundance in this fishery were observed for tunas, sharks and billfish. A decline in seabird standardized catch rate occurred concurrently with the uptake of seabird bycatch mitigation technology. Changed spatial distribution of fishing effort and increased use of wider circle hooks likely contributed to a declining sea turtle standardized catch rate.
4. Tuna and billfish mean lengths significantly increased over the time series due to entire distributions of length classes having shifted towards larger fish. Larger tunas comprised a larger proportion of the catch due to fewer small tunas being caught, and to a lesser extent because mean lengths of larger size classes increased. Conversely, billfish largest length classes experienced the largest increases in average lengths. Changes in spatial and seasonal distributions of fishing effort, increased use of wider circle hooks, and possibly increasing purse seine selective removals of juvenile tunas, may have contributed to increased selectivity for larger fish.
5. Significant differences in standardized catch rates and length distributions at a shallow seamount vs. the open ocean confirms the aggregating effect of seamounts on pelagic predators, including juvenile market species of pelagic fish and species groups relatively vulnerable to overexploitation.
6. Wider circle hooks significantly improved valuable tuna standardized catch rates, but also increased unwanted shark and reduced valuable billfish standardized catch rates.

Copyright © 2012 John Wiley & Sons, Ltd.