我国金枪鱼围网渔业对鲸豚类误捕的影响分析

鲸豚类是中西部太平洋生态系统的顶级捕食者，近年来，金枪鱼围网渔业对鲸豚类的误捕是海洋哺乳动物保护中最令人关注的热点之一。为探讨自由鱼群和人工集鱼装置作业对鲸豚类误捕的影响，提出对鲸豚类保护的建议，笔者根据2016—2019年我国金枪鱼围网渔业在中西部太平洋海域(N 10°～S 13°, E 144°～W 149°)的生产数据，探讨自由鱼群和人工集鱼装置2种作业方式在不同区域、时间段、月份和年份下对鲸豚类误捕的影响。结果显示：中西部太平洋鲸豚类的误捕主要发生在基里巴斯专属经济区；不同时间段下，自由鱼群作业下误捕鲸豚类分布较平均，且差异不显著(P>0.05),人工集鱼装置作业下误捕鲸豚类主要集中在16:00—19:00,差异显著(P<0.05);1、7月和11月的鲸豚类误捕量较高，且自由鱼群和人工集鱼装置作业下不同月份鲸豚类误捕均差异不显著(P>0.05);自由鱼群和人工集鱼装置作业造成的鲸豚类平均死亡率分别为43.04%和33.33%,2种作业方式对鲸豚类死亡率的差异不显著(P>0.05),不同物种误捕死亡率受2种作业方式的影响存在差异性。本研究结果可为中西部太平...     

回声探测浮标在金枪鱼围网渔业中的应用

【背景】回声探测浮标能够为金枪鱼围网渔业远程持续地提供漂流人工集鱼装置（DFADs）的精确地理定位以及金枪鱼集群生物量的估计，有效减少围网船队搜索鱼群所产生的“碳足迹”和船队运营成本，从而提高船队的成功捕获率。除了在商业中的应用外，回声探测浮标有潜力作为观察远洋生物多样性的科学平台，为科学研究提供描述远洋鱼类活动模式的数据来源。【内容】本文介绍了DFADs的定义、类型和结构、生态影响及相关管理措施，以及回声探测浮标的发展沿革、种类和数据结构，并重点从金枪鱼随附鱼群生物量评估、鱼群随附行为和DFADs生态影响评估方面回顾了回声探测浮标在金枪鱼围网渔业中的应用。【总结展望】本文展望了回声探测浮标今后在技术上支持降低非目标物种和目标物种幼鱼死亡率的发展趋势，并从渔业资源可持续管理和海洋生物多样性保护方面讨论了利用浮标观测数据结合渔业数据进行资源评估，以及探究气候变化和人类活动对海洋生态生态系统影响的巨大潜力。     

中国金枪鱼围网船队大眼金枪鱼渔获物的特征变化与人工集鱼装置禁渔期的关系

研究了2012-2015年中国金枪鱼围网船队大眼金枪鱼(Thunnus obesus)渔获物的特征变化与人工集鱼装置(fish aggregation devices,FAD)禁渔期的关系,文章收集了2012-2015年中国大陆金枪鱼围网船队在中西太平洋的渔捞日志数据,对随附鱼群捕捞努力量与小体大眼金枪鱼和大体大眼金枪鱼的船均产量进行分析比较。结果显示:1)从2013年开始,对随附鱼群投网的次数占总投网次数的比例有所降低,均不超过50%;2)K-S检验显示研究期内禁渔期前后的船均随附鱼群网次存在显著差异(P0.05);3)2013-2015年大眼金枪鱼渔获量的平均水平明显低于2012年;4)从2013年开始,禁渔期结束后的第一个月(即11月)的船均产量都发生猛增;5)从捕捞努力量与渔获量的相关性结果看,不论是小体大眼金枪鱼还是全部大眼金枪鱼,2013年和2014年两者都呈现出显著的强正相关关系(P0.05)。这些结果表明2012年以后中国船队对大眼金枪鱼幼鱼的兼捕水平有所下降,延长FAD禁渔期的管理措施对于保护大眼金枪鱼幼鱼在某些年份可能具有一定的效果。     

西班牙金枪鱼船队试用生物可降解集鱼装置

正西班牙金枪鱼远洋围网捕捞船队将在印度洋进行的此项试验将至少部署100个此类生物可降解集鱼装置,以评估它们在实际使用条件下的耐久性以及所用制造材料的无毒性。该装置的应用旨在尽可能地减少对生态系统的影响。除了像竹子、黄麻和其它天然纤维等材料之外,新型集鱼装置包含了由棉花、亚麻等天然纤维制成的材质以及多种类型的生物可降解塑料,其目的是为了实现集鱼装置在耐久性     

青干金枪鱼野生幼鱼陆基驯养技术

由于金枪鱼营养价值高,口感好,市场价值高,导致过度捕捞现象严重,野生金枪鱼资源量急剧下降。为解决这一问题,人工养殖金枪鱼的试验已经在各个国家开展。目前为止,金枪鱼养殖取得了一定的成功,但商品鱼供应依然以海洋捕捞为主。对金枪鱼的研究主要集中在捕获方式、鱼肉保存、运输、加工、资源评估、提取物应用等方面,主要为野生金枪鱼捕捞提供技术支撑,对于金枪鱼的陆基驯化养殖研究较少。     

MSS—2型脉冲电赶鱼机（一）

集鱼方法的研究，是目前国内外水库渔业技术发展的一个主要动向。我国各地水库集鱼方法除采用“网赶”外，各地还陆续进行了白板赶鱼、气幕赶鱼、声响配合网具赶鱼等试验研究，都取得了一定的效果。所有这些，对水库渔业的发展都起了积极的作用。但以上方法尚有不足之处，因此研制适应于库形和底貌复杂的水库捕捞集鱼装置仍是十分重要的。     

中西太平洋金枪鱼围网人工集鱼装置 (FADs)的集鱼特性

为了解鱼类在人工集鱼装置(FADs)周围的集群特性,基于2021年我国金枪鱼围网船在中西太平洋的回声探测浮标数据,对FADs投放后鱼类首次到达FADs的时间以及聚集的动态过程进行了探究。利用U检验和H检验分析了鱼类首次到达FADs时间的差异性,利用广义加性混合模型(GAMMs)分析了金枪鱼类聚集生物量随FADs海上漂流时间和漂流速度的变化情况,结果显示：(1)鱼类首次到达FADs的时间为(8.9±9.0) d,其中金枪鱼类为(3.8±4.2) d,非金枪鱼类为(16.0±8.9) d;(2)金枪鱼类在不同水下长度FADs下的首次到达时间存在显著差异,而非金枪鱼类无显著差异;(3)金枪鱼类在FADs周围的聚集生物量随FADs海上漂流时间呈现动态变化,约在其投放后第25天到达峰值,随后逐渐下降;(4)金枪鱼聚集生物量随着FADs漂流速度的增加而逐渐降低;(5)随机效应表明,水下长度为80 m的FADs下金枪鱼类聚集生物量一般最高,其次是60 m,90 m最低。研究表明,FADs投放后金枪鱼类往往先于非金枪鱼类到达,其首次到达时间与FADs的水下长度有关;具有较浅水下长度和缓慢漂流速度的FA...     

四种方形鱼礁对黑鲪和大陇六线鱼的集鱼效果

为了解不同构型的人工鱼礁对鱼苗的聚集效果,利用室内装置,在静水和流水条件下,研究了大窗箱型、大小窗箱型、"卍"字型和双层增殖型四种方形人工鱼礁及其不同组合对于大泷六线鱼(Hexagrammos otakii)和黒鲪(Sebastes schlegelii)的聚集行为的影响。实验结果表明,在静水条件下,大小窗箱型对黑鲪的诱集指数最高,为0.74,双层增殖型对大泷六线鱼的诱集指数达0.8;而在流水条件下,大小窗箱型和双层增殖型诱集指数均大于0.6。在实验的四种礁型中,上述两种礁型的诱鱼效果较好。     

50年间，全球金枪鱼和鲐鱼种群减少50％

一项研究显示,过去50年间由于大肆捕捞,金枪鱼和鲐鱼种群在全球范围内减少了60％,研究结果发表在Proceedings of the National Academy of Sciences（PNAS）。研究结果显示,受捕捞影响最大的是大西洋和澳大利亚金枪鱼资源,其资源量下降了80％。同时过度捕捞也影响到鲐鱼的资源,而鲐鱼的个体相对较小,寿命较短。     

几种不同类型人工鱼礁的稳定性和集鱼效果比较

根据唐山祥云湾海洋牧场海域具体特点,设计并投放了钢筋混凝土构件礁(A_1、A_2、A_3、A_4)、岩石礁(B_1、B_2)和船礁(C_1)等三种不同性质的鱼礁。通过对鱼礁抗滑移、抗倾覆参数及集鱼效果进行比较,筛选出适宜的人工鱼礁礁型。结果显示:上述几种礁体抗倾覆系数、抗滑移系数均大于1,保证了礁体在海水中的稳定性。几种礁体对渔获量的影响差别较小,从集鱼效果上看,最好的是A_2型的钢筋混凝土构件礁。     

Just a FAD? Ecosystem impacts of tuna purse‐seine fishing associated with fish aggregating devices in the western Pacific Warm Pool Province

The western and central Pacific Ocean supports the world's largest tuna fisheries. Since the 1990s, the purse‐seine fishery has increasingly fished in association with fish aggregating devices (FADs), which has increased catches of juvenile bigeye and yellowfin tunas and vulnerable bycatch species (e.g., sharks). This has raised concerns regarding the sustainability of these species’ populations and the supporting ecosystem, but may provide improved food security of Pacific Island nations through utilisation of FAD‐associated byproduct species (e.g., wahoo). An ecosystem model of the western Pacific Warm Pool Province was used to explore the potential ecological impacts of varying FAD fishing effort (±50% or 100%) over 30 years. The ecosystem has undergone a significant change in structure since 1980 from heavy exploitation of top predators (e.g., tunas) and “fishing up the food web” of high‐trophic‐level non‐target species. The ecosystem appeared resistant to simulated fishing perturbations, with only modest changes (<10%) in the biomass of most groups, although some less productive shark bycatch species decreased by up to 43%, which had a subsequent positive effect on several byproduct species, the prey of sharks. Reduction of FAD effort by at least 50% was predicted to increase the biomass of tuna species and sharks and return the ecosystem structure to a pre‐industrial‐fishing state within 10 years. Spatial disaggregation of the model and integration of economic information are recommended to better capture ecological and economic changes that may result from fishing and/or climate impacts and to develop appropriate management measures in response.     

Do drifting and anchored Fish Aggregating Devices (FADs) similarly influence tuna feeding habits? A case study from the western Indian Ocean

Anchored and drifting Fish Aggregating Devices (FADs) are intensively used in tropical tuna fisheries. In both small-scale and industrial fisheries, skipjack (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) are the main targets. The increasing development of this fishing practice by industrial purse seiners has raised the question of the impact of FADs on tuna communities, as they might act as an ecological trap. This study investigated the feeding habits of skipjack and yellowfin tuna associated with anchored and drifting FADs in the western Indian Ocean. The diet of 352 tunas was analysed taking into account the type of FAD, ontogenetic variations, and the resources richness of the area. Poor-food and rich-food areas were defined according to the abundance of stomatopod Natosquilla investigatoris, the main prey of tunas, on the fishing sites. Diet composition was expressed through functional groups of prey. Significant dietary differences were found between both FAD types, as well as an effect of individual size. Around anchored FADs tuna preyed on diverse assemblages of coastal fish and crustacean larvae and juveniles, whereas a low diversity of epipelagic prey dominated the tuna diet associated with drifting FAD. Compared to anchored FADs, the frequency of empty stomachs was significantly higher and the stomach content mass significantly lower among skipjack and small yellowfin tunas caught around drifting FADs. This was magnified in poor-food areas, where drifting FADs often evolved, suggesting that these FADs could negatively impact the growth of skipjack and small yellowfin tuna. Larger yellowfin tuna exhibited differences in their dietary habits between anchored and drifting FADs, and between poor-food and rich-food areas. However, drifting FADs did not impact them as strongly as juveniles of yellowfin or skipjack tunas. Our study gives new highlights on possible detrimental effects of FAD on tunas, and this has to be considered in future sustainable management strategies of tuna fisheries.     

Is it good or bad to fish with FADs? What are the real impacts of the use of drifting FADs on pelagic marine ecosystems?

The use of fish aggregating devices (FADs) by purse seine fisheries has come under increasing criticism for its potential deleterious impacts on tuna stocks, for high levels of by‐catch and threats to the biodiversity of tropical pelagic ecosystems. Here, we review the current state of scientific knowledge of this fishing technique and current management strategies. Our intent is to encourage objective discussion of the topic and highlight areas worthy of future research. We show that catching juvenile tuna around FADs does not necessarily result in overfishing of stocks, although more selective fishing techniques would likely help obtain higher yield. Levels of non‐tuna by‐catch are comparable to or less than in other commercial tuna fisheries and are primarily comprised of species that are not considered threatened. Accordingly, to minimize impacts on ecosystem balance, there is merit in considering that all species captured in purse seine fisheries (excluding vulnerable species such as turtles and sharks) should be retained, but the consequences of such a measure should be carefully examined before implementation. The take of vulnerable species could be further reduced by introduction of additional mitigation measures, but their potential benefits would be limited without parallel efforts with other gears. Finally, there is no unequivocal empirical evidence that FADs represent an ‘ecological trap’ that inherently disrupts tuna biology although further research should focus on this issue. We encourage RFMOs to expand and improve their FAD management plans. Under appropriate management regimes, FAD fishing could be an ecologically and economically sensible fishing method.     

Fish aggregating devices in the eastern tropical Pacific marine corridor,according to the Colombian Fisheries Observer Program

1. Fish aggregating devices (FADs) are floating objects that facilitate the aggregation of fish; those that aggregate pelagic species such as tunas are of particular interest for artisanal and industrial fisheries.
2. Due to the increasing use of these devices worldwide, bodies responsible for the administration and management of fishery resources have proposed control and surveillance activities focused on the use of such devices. To achieve this, it is essential to have access to quality information, which is usually obtained through on-board observer programmes such as the Colombian Fisheries Observer Program.
3. Based on the historical records of this programme, and for the first time, the spatial–temporal distribution of the FADs in the eastern tropical sector of the Eastern Pacific Ocean is presented, analysing 166 records of tuna fishing operations carried out between 2009 and 2015. Of the 2,328 sets identified in the records, 957 corresponded to sets on FADs, of which 80.56% were effective and caught 12,246 tons of tuna.
4. The number of sets of FADs increased over time, representing approximately 86.9% of the sets recorded in 2015, compared to 4.8% of this type of set recorded in 2009, with the Eastern Tropical Pacific Marine Corridor being the area of greatest concentration of sets.
5. Considering that the Eastern Tropical Pacific Marine Corridor was designed to promote the conservation and sustainable use of biological diversity in the Eastern Tropical Pacific, this study highlights the need to include as a research priority, the potential effect that aggregation devices may have on the biological connectivity processes present in the corridor, as well as on the dynamics of large pelagic fish populations of commercial interest.
6. In terms of management of FADs, it is recommended that a precautionary approach be adopted and that regulations related to the maximum number of FADs per vessel be adjusted according to their Inter-American Tropical Tuna Commission class, in addition to assigning a maximum number of sets per vessel.

     

How much do fish aggregating devices (FADs) modify the floating object environment in the ocean?

Natural floating objects (e.g., logs) have always been a component of the habitat of tropical tunas. However, the introduction of fish aggregating devices (FADs) modifies this environment. To assess the changes due to the deployment of FADs, we compared the spatial distribution of natural and artificial floating objects (FADs), using data from observers onboard tuna purse seine vessels in the Indian Ocean from December 2006 to December 2008. Although natural objects occur more commonly in waters south of 7°S and FADs are more common in waters north of 7°S, all types of floating objects can be found everywhere. Using different spatial scales (quadrats of size 1° × 1°, 2° × 2°, 5° × 5°, and 10° × 10°), we computed the proportion of FADs observed in quadrats without natural objects. The scale of 2° × 2° quadrats represented a threshold: distributions of the two types of objects were different at scales smaller than this threshold. The strongest change that has occurred since the introduction of FADs (besides the increased catches) has been the dramatic increase in the total number of floating objects. Since the introduction of FADs, the number of objects has at least doubled everywhere (except in the Mozambique Channel and Chagos) and in some areas (e.g., Somalia area) the multiplication factor has reached as high as 20 or 40. Our study sets the ranges of values of key parameters of the floating object environment, which are crucial in the design of future experimental studies aimed at investigating the impacts of FADs on the ecology of tunas.     

Can drifting objects drive the movements of a vulnerable pelagic shark?

1. Juvenile silky sharks (Carcharhinus falciformis) regularly associate with floating objects yet the reasons driving this behaviour remain uncertain. Understanding the proportion of time that silky sharks spend associated with floating objects is essential for assessing the impacts of the extensive use of fish aggregating devices (FADs) in the tropical tuna purse-seine fisheries, including increased probability of incidental capture and the potential of an ecological trap.
2. Previous studies provided insight into the amount of time that silky sharks spent at an individual FAD but were unable to assess neither the time spent between two associations nor the proportion of time spent associated/unassociated.
3. The percentage of time that juvenile silky sharks spend unassociated with floating objects was estimated through the analysis of horizontal movements of 26 silky sharks monitored with pop-up archival tags. Under the assumption that a high association rate with drifting FADs would align the trajectories of tracked sharks with ocean surface currents, a novel methodology is proposed, based on the comparison of shark trajectories with simulated trajectories of passively drifting particles derived using a Lagrangian model.
4. Results revealed that silky shark trajectories were divergent from surface currents, and thus unassociated with FADs, for at least 30% of their time. The potential of the methodology and the results are discussed in the context of increasing FAD densities in the Indian Ocean.

     

Comparison of the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (T. obesus) tuna associated with drifting FADs in the equatorial central Pacific Ocean

We evaluated the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye tuna (T. obesus) associated with drifting fish aggregating devices (FADs) in the equatorial central Pacific Ocean. A total of 30 skipjack [34.5–65.0 cm in fork length (FL)], 43 yellowfin (31.6–93.5 cm FL) and 32 bigeye tuna (33.5–85.5 cm FL) were tagged with coded transmitters and released near two drifting FADs. At one of the two FADs, we successfully monitored the behavior of all three species simultaneously. Several individuals remained around the same FAD for 10 or more days. Occasional excursions from the FAD were observed for all three species, some of which occurred concurrently for multiple individuals. The detection rate was higher during the daytime than the nighttime for all the species, and the detection rate for bigeye tuna was higher than for yellowfin or skipjack tuna. The swimming depth was deeper during the daytime than nighttime for all species. The fish usually remained shallower than 100 m, but occasionally dived to around 150 m or deeper, most often for bigeye and yellowfin tuna during the daytime. The swimming depth for skipjack tuna was shallower than that for bigeye and yellowfin tuna, although the difference was not large, and is probably not sufficient to allow the selective harvest of skipjack and yellowfin tuna by the purse seine fishery. From the detection rate of the signals, bigeye tuna is considered to be more vulnerable to the FAD sets than yellowfin and skipjack tuna.     

Modeling tuna behaviour near floating objects: from individuals to aggregations

A fuzzy logic model of tuna behaviour near Fish Aggregating Devices (FADs) was developed to reproduce individual differences in horizontal movements observed from ultrasonic telemetry experiments. In this model, the behaviour of an individual is based on its surrounding environment (FADs and prey) and on its internal state (stomach fullness), which depends on its recent past actions. Internal sensors are used to determine the motivation of the fish, combined with external sensors, this determines its movements. Sensory information and motivation are modeled using fuzzy sets. A FAD attracts an individual when it is located within the FAD’s range of influence. The time spent near a FAD depends on the feeding motivation of the fish and on its surrounding environment. If the fish is not hungry, it stays near the FAD. Otherwise, the fish has to forage in order to eat, and might therefore leave the FAD if no prey is available in its vicinity. By varying the environmental conditions near FADs, the model reproduces the different horizontal movement patterns observed for tunas. The model is then extended to allow multiple individuals to co-exist, each individual modeled through the above behavioural model, without any direct or indirect interactions between them. This way, we study the effects of individual behaviour on tuna aggregation near FADs. We find that the model predicts the temporal dynamics of aggregation around FADs exhibited by tunas. By examining the effects of several FAD network models on the aggregation, we also estimate optimal spatial arrangements of FADs.