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.     

2008年南海北部拖网渔获组成及其多样性分析

采用分层随机抽样的方法,调查了2008年南海北部海域拖网渔获物组成,利用Shanon-weiner群落多样性指数(H’)、Pileou均匀度(J’)指数、相对多度(RD)等分析其多样性;根据渔获物季度组成,分析了主要种类的季节更替规律。研究表明,拖网渔获组成多样性指数介于3.36~5.36,均匀度指数介于0.54~0.74,优势度指数介于0.08~0.89,季节更替率介于22.83%~32.50%。另外,经济种类的优质鱼类与低质鱼类的产量比例为21∶100,与20世纪80年代相比,优质鱼类与经济鱼类的比率呈下降趋势,优质鱼类个体日趋小型化。     

调水调沙前后黄河口渔业资源结构变化

黄河口调水调沙是以人工调控的方式将淤积的泥沙送入大海,增加河床和水库主槽行洪能力的过程。根据2011―2013年调水调沙前(6月)、后(7月)在黄河口海域的渔业资源调查数据,利用相对优势度指数、方差分析以及多元统计分析等方法,研究了该海域夏季渔业资源密度、种类组成、优势种及其年际变化,并探讨调水调沙对黄河口渔业资源结构的影响。结果表明,本次调查共鉴定渔业资源生物92种,其中鱼类52种;黄河口主要优势种为矛尾虾虎鱼(Chaemrichthys stigmatias)、枪乌贼(Loligo spp.)和葛氏长臂虾(Palaemon gravieri)等,各年份优势种有所变动;夏季渔业资源量有明显年际波动,在2011—2013年呈先增加后减少的趋势,各年间差异显著;黄河口渔业资源结构在调水调沙前后有明显变化,调水调沙后渔业资源平均密度增大,且近河口区资源密度较小;CLUSTER聚类分析表明黄河口渔业资源结构年际变化最为明显,其次是调水调沙前后的变化,而断面间的差异性最低。结论认为,黄河调水调沙引起的径流量、营养盐变化可能是引起调水调沙前后渔业资源种类组成、资源量变化的重要原因。     

黄渤海区拖网渔业现状与分析

2010年6—7月和2012年6—8月,利用随机抽样调查方法对黄渤海区的拖网渔业进行了实地调查和现场测量。依据调查资料及有关拖网捕捞分类统计资料,对黄渤海区的拖网渔业进行了研究。结果表明:截止至2012年6月底,三省一市共有拖网渔船12 358艘,其中单拖渔船6 926艘,双拖渔船5 432艘。渔船功率44.1 kW以下的渔船占36.86%,44.1～109.5 kW占30.34%,110.3～219.8 kW占19.41%,220.5～441kW占12.59%,441 kW以上占0.80%。2003—2011年期间,除2007年外,拖网渔船总量呈下降趋势,渔船总功率呈上升趋势。拖网渔业捕捞产量1999年最高,达271.11万t,此后逐年下降,2011年为201.92万t。拖网是黄渤海区的主要作业方式,当前该海区拖网捕捞强度较大,渔船装备落后。因此,应对三省一市拖网渔业的捕捞强度加以控制,在鼓励拖网渔船改造升级的同时,适当压减拖网渔船的总数量,逐步发展外海拖网渔业。     

莱州湾污染及其对渔业资源的影响

根据1998年4、7、10月对莱州湾污染调查结果，讨论了入海污染物对莱州湾的污染影响、分布特征及其入海通量。结果表明，莱州湾主要污染物分布在西部和西南部，污染物入海通量估算结果，小清河是莱州湾污染的主要污染源之一，对渔业资源影响关系表明，环境因子对幼虾对虾相对数量变化均有一定的影响。1990－1998年COD与幼对虾相对数量相关相对较明显（γ＝－0．565．8），无机磷和无机氮与幼对虾数量相关性不明显，但从不同时间段看，1990－1993年只有无机氮与幼对虾数量相关性明显，呈正相关关系，而1994－1998年COD、无机磷与幼对虾相对数量却呈显著负相关（γ=-0．86333，γ=-0.7928)。说明近年来COD、无机磷对莱州湾幼对虾相对数量的变动构成一定的负面影响。由于陆源性污染对海域环境影响加剧，使得渔业资源，结构，组成和数量 发生了很大的变化，河口污染的加剧，不仅破坏了渔业资源，更重要的是破坏了产卵场。鱼卵的种类和数量在小清河附近海域的分布范围也缩小，仔稚鱼分布数量，已由小清河附近海域北移至黄河口至刁口一带，仔稚鱼有回避该区污染的现象，在莱州湾中，小清河为主要污染物之一，其对渔业资源的破坏，即有代表性，又有普遍性，从中说明了渤海污染对渔业资源的危害。     

基于张网渔业休渔前后的黄茅海河口渔业资源群落比较

根据2015年休渔前后(春季和夏季)利用张网在黄茅海河口获得的渔业资源调查资料,应用数量生物量比较曲线和生物量谱方法分析了其渔业资源群落状况。结果显示,调查共捕获渔获56种,其中鱼类47种,隶属于12目27科38属;甲壳类9种,隶属于2目5科7属。休渔前(春季)渔获种类大于休渔后(夏季), 春季优势种为凤鲚(Coilia mystus)、红狼牙虎鱼(Odontamblyopus rubicundus)和脊尾白虾(Exopalaemon carinicauda);夏季优势种为凤鲚、康氏小公鱼(Anchoviella commersonii)和红狼牙虎鱼。春季渔业资源群落的数量优势度曲线与生物量优势度曲线相交,群落处于中度干扰状态;夏季其数量优势度曲线高于生物量优势度曲线,群落处于严重干扰状态。春夏两季数量生物量比较曲线(ABC曲线)中生物量和丰度的相对关系统计量W分别为-0.015和-0.046。从渔业资源群落的生物量谱来看,春季标准化生物量谱线性回归的斜率大于-1,生物量随着个体体质量的增加而增加;夏季其线性回归的斜率小于-1,生物量随着个体体质量的增加而减少。捕捞能够影响生物量谱,生物量谱斜率下降反映了休渔在过度捕捞下并没有达到预期效果。建议加大管理力度,增加捕捞限制条件。     

Incidental capture and mortality of sea turtles in the industrial double‐rig‐bottom trawl fishery in south‐eastern Brazil

1. Incidental capture by fisheries is one of the principal threats to sea turtles. This study analysed spatial and temporal patterns of sea turtle bycatch, and estimated the direct initial mortality rate of these animals, in the industrial double‐rig‐bottom trawl fishery in south‐eastern Brazil. This is also the first attempt to relate bycatch/at‐sea mortality in bottom trawling to stranded turtles found along the adjacent coast.
2. The fishery was monitored from October 2015 to April 2018 through data collected voluntarily by the captains of eight industrial double‐rig trawlers. Two hundred and one sea turtles were captured during 9362 tows (43,657.52 trawling hours), resulting in a catch per unit effort (CPUE) of 0.0025 ± 0.0032 turtles h^?1 with a standard net of 30.5 m headrope, with no significant difference between the estimated CPUEs for licensed shrimp and demersal fish trawlers.
3. Caretta caretta (52.24%) and Lepidochelys olivacea (38.81%) were the most frequently captured species. According to Generalized Linear Models, C. caretta bycatch was significantly higher during winter, at lower latitudes (?24° to ?23°) and higher longitudes (?42° to ?40°), while the L. olivacea bycatch was significantly higher at higher latitudes (?23° to ?21°). The direct initial mortality rate of sea turtles in the shrimp trawlers was 7.65 ± 3.85%. However, none of the dead individuals subsequently released with plastic tags (n = 10) were found stranded on the coast. Mortality was not significantly related to the depth or duration of the trawling.
4. The results of this study suggest the need for improvements to the current management of the bottom trawl fishery in Brazil, moving from a species‐based to a spatial and seasonal‐based approach. There is also a need to develop turtle excluder devices adapted to local fishing conditions.

     

Spatial distribution and abundance of the by‐catch coastal elasmobranch Raja undulata: Managing a fishery after moratorium

The undulate ray Raja undulata Lacepède is a coastal species common along the north‐eastern Atlantic Ocean and Mediterranean Sea and is highly accessible to coastal fisheries. Between 2009 and 2015, the species was under a European Union (EU) fisheries moratorium that hampered the collection of data to assess its stock status in Portuguese waters. After that period, a small experimental EU fishing quota was set for Portugal enabling collection of fishery data under a fishermen self‐sampling scenario. Based on the data collected, R. undulata abundance was estimated along the Portuguese continental coast through the application of a N‐mixture model and incorporating environmental factors. The results support the species coastal and patchy nature across the study area with higher abundances estimated in areas associated with shallow sandy bottoms as the Southwest region. The present work constitutes an important step for the management of this fishery resource, in particular concerns about its abundance trends over time and its spatial distribution and habitat requirements.     

大亚湾潮间带生物种类组成、数量分布及生物多样性研究

分析了广东省大亚湾潮间带生物的种类组成、数量分布和生物多样性等特点。结果表明,该海域潮间带调查采获的潮间带生物标本共70科150种,以软体动物和甲壳类出现的种类最多,二者占了总种类数的80%,其中部分属经济价值较高的种类。潮间带生物全年平均生物量为1954.26g·m-2,平均栖息密度为1003.77ind·m-2。全年各类群生物中,平均生物量及栖息密度都以软体动物居首位。其Shannon-Weaner多样性指数(J)属中等水平,分布范围在1.419~3.562,平均为2.663。     

Projections of the impacts of gear‐modification on the recovery of fish catches and ecosystem function in an impoverished fishery

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长江口、杭州湾附近渔业水域生态环境质量评价研究

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莱州湾“伏休”结束前三疣梭子蟹的资源状况及其分布特征

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东海、黄海秋季渔业生物群落结构及其平均营养级变化特征初步分析

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海州湾双斑蟳栖息分布特征与环境因子的关系

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Effect of environmental factors and prey species on daytime and nighttime vertical distribution of juvenile walleye pollock in and around Funka Bay

We examined factors affecting the vertical distribution of juvenile walleye pollock during “the second critical period” (i.e. the transition period of prey size) in and around Funka Bay, Hokkaido, Japan. During the day, small juveniles (<30 mm) were distributed mainly in shallow, warm, and low-salinity water within the bay, whereas larger ones (≥30 mm) occurred in deeper, cold and saline water. During the night, the large juveniles migrated to shallower depths. Outside the bay, small- and large-sized juveniles were distributed in water masses of similar physical properties during the daytime, whereas during the nighttime, most of the juveniles moved to shallower depth, and some juveniles dived to deeper water mass. Dietary analysis revealed that large juveniles fed on large copepods (≥0.5 mm in body width) more than small juveniles did. The composition of zooplankton in our survey area showed that large-sized copepods often occurred in deeper saline water. From these results, there is a possibility that juvenile pollock inside and outside Funka Bay occupied different water masses preferable for each feeding advantage.     

Annual variation of potential predation impacts on larval and juvenile marbled sole <Emphasis Type="Italic">Pseudopleuronectes yokohamae</Emphasis> by sand shrimp <Emphasis Type="Italic">Crangon uritai</Emphasis> in Hakodate Bay,Hokkaido

An investigation was conducted to evaluate the annual variation in potential predation impact (PPI) on larval and juvenile Pseudopleuronectes yokohamae by Crangon uritai in Hakodate Bay using predator-prey size relationships. Laboratory experiments were designed to estimate the favorable prey size of C. uritai through back-calculation of body length (BL) of P. yokohamae from sagittal otolith diameter observed in the stomachs of C. uritai. The most favorable prey-predator size ratio (BL of P. yokohamae-total length (TL) of C. uritai) class was 0.15–0.19, and ranged from 0.12–0.31. There was a significant positive correlation between the BL increase of P. yokohamae and the bottom water temperature in the field, such that BLs stagnated during the cold year of 1999 from April to June, and increased during the warm year of 2002. In contrast, no significant correlation was found between the TL increase of C. uritai and the bottom water temperature. Moreover, there were no significant differences in the mean TL of C. uritai between months (April–June) or years (1998–2002). Variation of PPI depended on the relationships between the growth rates of P. yokohamae and bottom water temperature. Therefore, the warm year of 2002 resulted in higher potential predation impact (PPI≥20), and it was at least 20 days shorter than that of the cold year of 1999. These results suggest that increased bottom water temperature in the nursery area was one of the most important factors for cumulative predation loss.     

沿浦湾秋茄种植前后大型底栖动物生态位和功能群变化

基于沿浦湾2014年10月(秋季)和2016年10月(秋季)的潮间带大型底栖动物调查资料,运用生态位宽度、生态位重叠、功能群分类和冗余分析(RDA)等指标与方法,分析秋茄(Kandelia candel)种植前、后大型底栖动物的生态位、功能群变化。研究结果表明,秋茄种植后广生态位种和中生态位种物种数占比与种植前相比较均有所增加,窄生态位种物种数占比减少。种植前生态位重叠值最大的种对为大青弹涂鱼(Scartelaosgigas)和细螯虾(Leptochela gracilis)(0.94),种植后则分别为豆形拳蟹(Pyrhila pisum)和微黄镰玉螺(Lunatica gilva)(0.99)、堇拟沼螺(Assiminea violacea)和光滑河篮蛤(Potamocorbula laevis)(0.99)。种植后高、中潮带功能群多样性较种植前上升,而低潮带功能群多样性下降;种植后浮游生物食者(Pl)、植食者(Ph)和杂食者(Om)的密度较种植前均增加,而肉食者(Ca)的密度略有减少。秋茄种植前3个潮带之间无显著性差异(P0.05);秋茄种植后高潮带与低潮带,以及中潮带与低潮带均有显著性差异(P0.05)。冗余分析(RDA)得出,对大型底栖动物群落具有较大影响的因子由种植前的铅、镉和石油类变为种植后的锌、镉和砷。总之,苍南沿浦湾秋茄林种植对大型底栖动物生态位和功能群总体上具有积极的改善作用。     

长江安庆江段鱼类调查及物种多样性初步研究

为了解禁捕初期长江下游鱼类群落结构特征,实验于2021年春季、夏季、秋季和冬季对长江下游鱼类群落进行4次调查。结果显示,实验共采集鉴定鱼类84种,分属10目18科63属,其中47.62%为鲤科鱼类。以物种数和多样性指数分析群落多样性特征,结果表明长江下游鱼类多样性水平较高,但鱼类种类较历史记录偏少。单因素方差结果显示,鱼类种类数、种群数量和重量空间差异显著,季节差异不明显。群落优势种为光泽黄颡鱼、鳊、鲢、短颌鲚、贝氏䱗等9种。4种摄食功能群中,肉食性(47.62%)和杂食性(40.47%)鱼类物种比例较高;洄游习性方面,淡水定居性鱼类占绝对优势(76.19%);3种栖息水层类型中,底层鱼类物种数比例较高(46.43%)。大型经济鱼类占总量比例低,但个体相对较大,因而相对重要性指数(IRI)更高。长江下游鱼类多样性指数为3.28,水域鱼类多样性水平较高。长江下游鱼类个体小型化、低龄化现象依然存在,长江十年禁渔实施后,禁渔效果初步显现,鱼类物种数、多样性指数和单位捕捞努力量渔获量均有所增加。建议进一步加强禁捕期科研监测,加大监管力度,保障长江下游鱼类资源得以有效恢复,巩固禁捕成效。本研究可掌握禁捕初期长江下游鱼类群落基本特征及变动趋势,为长江下游禁渔效果评估和长江水生生物完整性指数评价提供支撑。     

Size influences the spatial distribution and fish‐aggregating device use of five Mediterranean fish species

Abstract Fish‐aggregating devices are floating objects used worldwide to improve pelagic fishery yield. Fish‐aggregating devices use the natural attraction exerted by floating objects on juveniles and adults of both pelagic and demersal fish. In this study, it was hypothesised that fish change their degree and type of interaction with moored floating objects depending on size. This is because fishes in early life stage remain close to floating objects, using them as a shelter, but as they grow they move further away from floating objects spending their time swimming to seek food. To test this hypothesis, the spatial distribution and habitat use of five Mediterranean fish species were quantified. The results enabled the hypothesis to be accepted for all species, except Balistes carolinensis Gmelin. For this species, a shelter from predator model was applicable, but for the other species, the generalised meeting point model was more adaptable.