Colonization,diversity, and seasonality of fishes at pelagic fish aggregating devices

The pelagic zone of the ocean can be a challenging environment in which to conduct research and as a result we lack the robust baseline abundance and diversity data, compared to what is available in more accessible coastal habitats, to be able to track changes or stressors to the biota in this environment. Many large-scale fisheries target pelagic fish, and much of the information available on these species is based on fisheries-dependent data that may be biased towards hotspots and commercially valuable fishes. Here, a long-term video and visual fish survey was conducted on two subsurface moored fish aggregating devices (FADs) in the pelagic waters of the central Bahamas to determine the feasibility of using moored pelagic FADs as tools for collecting fish abundance and diversity data. A wide range of species was documented, including large migratory fish that are the focus of commercial and recreational fisheries, and smaller often overlooked species on which little abundance or seasonality information exists. We found that FADs colonize quickly and reach a peak stable (albeit seasonally cyclical) abundance and diversity within the first several months after deployment. Species richness was higher in video surveys, but abundance was higher in visual surveys, except for sharks. Our results highlight the need to tailor survey methods to fit the context and study objective, and provide further evidence for the importance of fisheries-independent data in monitoring pelagic species.     

人工集鱼装置对热带金枪鱼类行为模式的影响

金枪鱼类会聚集在漂浮物周围,人类依据该行为特性研制出人工集鱼装置(fish aggregation devices,FADs)诱集金枪鱼,从而使金枪鱼围网的产量和捕捞效率大幅提高.但目前科学界仍不确定FADs为何能够吸引金枪鱼以及其广泛使用是否会对金枪鱼资源和大洋中上层生态系统产生潜在影响.针对这些问题,国外学者展开了大量以FADs周围金枪鱼为研究对象的个体行为学试验.本文归纳并整理了过去30多年中较可靠和经典的相关试验,从金枪鱼的趋向性行为、集群行为、随附行为、摄食行为和垂直移动行为5个方面分别阐述了漂流FADs和锚泊FADs下金枪鱼的行为模式,并对国内今后开展相关研究的重点方向和注意事项进行了展望.     

人工集鱼装置对热带金枪鱼类摄食模式的影响研究进展

热带金枪鱼类具有聚集在漂浮物体周围的行为特性,形成的集群表现稳定,可捕性较高。以此特性,金枪鱼围网渔业研制并投放了大量的人工集鱼装置(Fish Aggregation Device,FAD)用于聚集并捕捞金枪鱼。然而,大规模出现的FAD会使某些海域海面漂浮物的密度迅速增加,从而在一定程度上人为地改变了金枪鱼的表层栖息环境,对金枪鱼种群具有一系列可能的潜在负面影响,摄食模式的改变就是其中之一。归纳并综合了近年来国内外关于FAD对金枪鱼类摄食模式影响的相关研究,从摄食行为、日摄食量、饵料种类与组成以及生态位宽度4个方面对比了随附于FAD的金枪鱼和自由状态下同类的不同,发现大多情况下FAD的存在会使金枪鱼的摄食模式发生一定的改变。最后,归纳了过往实验存在的不足,对今后研究的发展方向进行了展望。     

The Contribution of Nearshore Fish Aggregating Devices (FADs) to Food Security and Livelihoods in Solomon Islands

Fish aggregating devices, or FADs, are used widely in developing countries to concentrate pelagic fish, making them easier to catch. Nearshore FADs anchored close to the coast allow access for rural communities, but despite their popularity among policy makers, there is a dearth of empirical analysis of their contributions to the supply of fish and to fisheries management. In this paper we demonstrate that nearshore FADs increased the supply of fish to four communities in Solomon Islands. Estimated total annual fish catch ranged from 4300 to 12 000 kg across the study villages, with nearshore FADs contributing up to 45% of the catch. While it is clear that FADs increased the supply of fish, FAD catch rates were not consistently higher than other fishing grounds. Villages with limited access to diverse or productive fishing grounds seemingly utilized FADs to better effect. Villagers believed FADs increased household income and nutrition, as well as providing a source of fish for community events. FADs were also perceived to increase intra-household conflict and reduce fishers'' participation in community activities. FADs need to be placed within a broader rural development context and treated as another component in the diversified livelihoods of rural people; as with other livelihood options they bring trade-offs and risks.     

Temporal variability of pelagic fish assemblages around fish aggregation devices: biological and physical influences

Pelagic fishes were counted around four fish aggregation devices (FADs) moored between 3 and 10 km offshore on the continental shelf off Sydney, Australia. Visual counts were made at FADs on 81 days periodically from April 1999 to April 2002. Surface water temperature and current speed were also measured at the FADs. Assemblages of fishes at FADs followed a seasonal pattern, however, biological and physical variables influenced seasonal structure greatly. Abundances at FADs were greatest in spring due to the appearance of large schools (100s to 1000s) of juvenile Trachurus sp. In contrast, diversity was far greater in summer and autumn, principally due to the appearance of schools (10s to 100s) of juvenile Coryphaena hippurus (Coryphaenidae), and other warm water species from January to May when water temperatures were >20° C. Short‐term variability differed among species; C. hippurus fluctuated greatly among counts separated by 2–3 days, while Seriola lalandi (Carangidae) and Alutera monoceros (Monacanthidae) abundances were more stable, indicating greater residence times at FADs for these two species. Marked differences in fish assemblages occurred between times when predators were present and absent, with few small fishes being observed when piscivorous predators occurred at FADs, regardless of season. Furthermore, abundances of C. hippurus and A. monoceros were correlated with current speed, with greatest abundances observed when currents were strong and weak, respectively. The results indicated that much of the temporal variability in fish assemblages at moored FADs could be explained by biological and physical factors.     

FAD: Fish Aggregating Device or Fish Attracting Device? A new analysis of yellowfin tuna movements around floating objects

Tropical tuna are known to associate with floating objects. Because fish are easier to detect and to catch when around these objects, fishermen have extensively deployed a large number of artificial floating objects in the tropical oceans. Although such objects are referred to as Fish Aggregating Devices (FADs), there is yet no strong evidence that fish do show an aggregative behaviour around them. The high probability of finding tuna around FADs may be the result of an aggregation process (high density of fish because fish stay for a long time around FADs) as well as an attraction process (high flow of fish through FADs). We analysed the movements of 14 yellowfin tuna, Thunnus albacares, in relation to FADs moored in the Indian and Pacific Oceans (corresponding to all the published tracking data) to determine whether the observed movement patterns resulted from an aggregation or an attraction process. Tuna appeared to be attracted by FADs. In general, they did not stay for long close to the FADs reached, and so did not aggregate there. Some FADs may nevertheless act as Fish Aggregating Devices. The possible reasons why tuna associate with floating objects are discussed in the light of these results.     

An interdisciplinary evaluation of fishery production systems off the state of Pará in North Brazil

The performance of 20 fishery production systems off the state of Pará in the northern region of Brazil was compared using the 'RAPFISH' methodology, with 57 identified attributes distributed among five evaluation fields: economics, sociology, ecology, technology and politics. The results indicated the existence of three large groups of fishery sectors: (i) industrial (red snapper with traps, the Laulao catfish, shrimp trawl) and semi-industrial (lobster) fisheries; (ii) large-scale artisanal fisheries (acoupa weakfish, red snapper with lines, king mackerel, Spanish mackerel, coco sea catfish); and (iii) small-scale artisanal fisheries (shellfish, crab, estuarine longline, fish traps, etc.). While the industrial and large-scale artisanal systems demonstrated greater sustainability from an economic and social standpoint, small-scale fisheries appeared to be more ecologically sustainable. Based on the results, a reduction in industrial fishing efforts is recommended, along with the establishment of licensing quotas for fishing vessels, as well as an increased investment in research on proper guidance and management of the semi-industrial and large-scale artisanal fisheries sectors. For small-scale artisanal fisheries, economic incentives are suggested for the aggregate value of the products and to assist fishers in the development of an appropriate social organization. Finally, it is believed that a greater stakeholder involvement in the decision-making process would improve management actions for all modalities.     

Community structure of fishes attracted to shallow water fish aggregation devices off South Carolina,U.S.A.

Synopsis Twenty-two fish aggregation devices were deployed in 14 m of water off South Carolina. Species composition and abundance were determined by diver visual census on eight occasions from May through November, 1985. A total of 21 families and 36 species of fishes was observed at 121 stations. Pelagic fishes dominated the fauna with a 99.3% relative abundance, and Decapterus punctatus accounted for 97.6% of the individuals. Caranx crysos, Diplectrum formosum, Decapterus punctatus, Centropristis striata and Monacanthus hispidus were the most frequent species. Total fish abundance, number of species and abundance of four of the six most common species were significantly affected by season. Hurricane activity may have caused a significant drop in pelagic fish abundance at the FADs in July. No significant correlations among species abundances were found after removal of season and FAD type effects. Spatial zonation and seasonal occurrence patterns suggest some competition among pelagic fishes. Several factors that regulate FAD faunal abundance and composition are hypothesized, including: juvenile fish availability, availability of shelter, availability of adequate food resources, interspecific and intraspecific competition, severe sea conditions, and sporadic intrusions of large predatory fishes. It is hypothesized that the abundances of benthic and pelagic FAD fishes are correlated and that there is a direct or indirect energetic link between shallow water pelagic and benthic fish assemblages near FADs.     

Energy Consumption in the Danish Fishery: Identification of Key Factors

Previous studies based on life-cycle assessment (LCA) in Denmark and Sweden have shown that the fishery is the environmental "hot spot" in the life cycle of certain fish products. Within the fishery, fuel consumption is one of the most important factors addressed by LCA. The present study reveals that there are great differences in fuel consumption between fisheries targeting groundfish or shellfish and those targeting pelagic fish or industrial fish. Here, I show that fuel consumption per kilogram of caught fish varies considerably as a function of fishing gear and vessel size, even considering the same target species. I argue that these differences need to be addressed in the search for a fuel-efficient fishery. Improvements in fuel efficiency may be consistent with other objectives, such as reduced impacts on seafloor habitats and reduced discard.     

Run timing of pelagic fishes in Gulf of St Lawrence: area and species effects

Run timings of four ubiquitous pelagic fishes in the Gulf of St Lawrence were compared for area and year effects. Run timing of alewife, Alosa pseudoharengus (Wilson), smelt, Osmerus mordax (Mitchill), and Atlantic salmon, Salmo salar L., was estimated at index rivers, and time of arrival of herring, Clupea harengus L., on spawning grounds was estimated from gillnet fisheries located around the Gulf, 1978–87. Time of pelagic fish migrations had strong species and area effects, but weak year effects. The species had their own unique migration times and durations, and could be divided into two groups: herring and smelt, which arrived in all areas of the Gulf at the same time; and alewife and salmon, which had significant area effects. Environmental data were not correlated with run timing. There was little annual variation in run timing among early-run species; only alewife had significant year effects. There was annual variation in the timing of late-run species, but it was not correlated with proximate environmental factors. Because run timing is an easily defined stock characteristic, observations over large areas and many years might be useful for understanding the impact of large-scale environmental changes on natural populations.     

Interactions of pelagic cnidarians and ctenophores with fish: a review

Medusae, siphonophores and ctenophores (here grouped as `pelagic coelenterates') interact with fish in several ways. Some interactions are detrimental to fish populations, such as predation by gelatinous species on pelagic eggs and larvae of fish, the potential competition for prey among pelagic coelenterates and fish larvae and zooplanktivorous fish species, and pelagic coelenterates serving as intermediate hosts for fish parasites. Other interactions are positive for fish, such as predation by fish on gelatinous species and commensal associations among fish and pelagic coelenterates. The interactions range from beneficial for the gelatinous species (food, parasite removal), to negative (predation on them). We review existing information and present new data on these topics. Although such interactions have been documented frequently, the significance to either fish or pelagic coelenterate populations is poorly understood. The effects of pelagic coelenterates on fish populations are of particular interest because of the great importance of fisheries to the global economy. As fishing pressures mount, it becomes increasingly important to understand how they may influence the balance between pelagic coelenterates and fish.     

Putting all the pieces together: integrating current knowledge of the biology,ecology, fisheries status,stock structure and management of yellowfin tuna (<Emphasis Type="Italic">Thunnus albacares</Emphasis>)

Yellowfin tuna (Thunnus albacares; YFT) is an apex marine predator inhabiting tropical and sub-tropical pelagic waters. It supports the second largest tuna fishery in the world. Here, we review the available literature on YFT to provide a detailed overview of the current knowledge of its biology, ecology, fisheries status, stock structure and management, at global scale. YFT are characterized by several peculiar anatomical and physiological traits that allow them to survive in the oligotrophic waters of the pelagic realm. They are opportunistic feeders, which allows fast growth and high reproductive outputs. Globally, YFT fisheries have expanded over the last century, progressively moving from coastal areas into the majority of sub-tropical and tropical waters. This expansion has led to a rapid increase in global commercial landings, which are predominantly harvested by industrial longline and purse seine fleets. For management purposes, YFT is divided into four stocks, each of which is currently managed by a separate tuna Regional Fisheries Management Organization. Our current understanding of YFT stock structure is, however, still uncertain, with conflicting evidence arising from genetic and tagging studies. There is, moreover, little information about their complex life-history traits or the interactions of YFT populations with spatio-temporally variable oceanographic conditions currently considered in stock assessments. What information is available, is often conflicting at the global scale. Finally, we suggest future research directions to manage this valuable resource with more biological realism and more sustainable procedures.     

A general theory on fish aggregation to floating objects: An alternative to the meeting point hypothesis

An immense variety of fish may, on occasions, aggregate around or beassociated with floating structures such as drifting algae, jelliedzooplankton, whales, floats or anchored fish aggregating devices (ineffect, there are over 333 fish species belonging to 96 familiesrecorded in the literature).Several hypotheses have been advanced to explain this behaviour ofpelagic fish, although the most widely accepted theory is that fish usefloating materials, to some extent, to protect themselves frompredators. However, we think that aggregation under floats may be theresult of behaviour that has evolved to safeguard the survival of eggs,larvae and juvenile stages, during dispersion to other areas. Naturalfloating structures (e.g., algae, branches of trees) drift in seacurrents that originate in places where the floating objects arefrequently found (e.g., river estuaries, coastal areas). These same seacurrents also introduce some of the planktonic production generated inthese areas into the oligotrophic pelagic environment. Fish associatedwith drifting floating structures probably feed on invertebratesassociated with the structures. However, they may also benefit from theaccumulated plankton in the converging waters. Adult fish of somemigratory species (tuna, dolphinfish, etc.) have also developed similarassociative behaviour around drifting objects for other reasons (e.g.,resting places, presence of bait fish, geographical references andschool recomposition). In this context, the meeting point hypothesis isonly applicable to one specific case, the tuna and tuna-like species.Aggregative and associative behaviour, under and around floatingdevices, may be the result of convergent behaviors that result fromdifferent motivations. However, generally this behaviour can beexplained by the fact that drifting floating objects represent a meansof reaching relatively rich areas, where larvae and juvenile fish havean increased chance of survival.     

Industrial fisheries have reversed the carbon sequestration by tuna carcasses into emissions

To limit climate warming to 2°C above preindustrial levels, most economic sectors will need a rapid transformation toward a net zero emission of CO₂. Tuna fisheries is a key food production sector that burns fossil fuel to operate but also reduces the deadfall of large-bodied fish so the capacity of this natural carbon pump to deep sea. Yet, the carbon balance of tuna populations, so the net difference between CO₂ emission due to industrial exploitation and CO₂ sequestration by fish deadfall after natural mortality, is still unknown. Here, by considering the dynamics of two main contrasting tuna species (Katsuwonus pelamis and Thunnus obesus) across the Pacific since the 1980s, we show that most tuna populations became CO₂ sources instead of remaining natural sinks. Without considering the supply chain, the main factors associated with this shift are exploitation rate, transshipment intensity, fuel consumption, and climate change. Our study urges for a better global ocean stewardship, by curbing subsidies and limiting transshipment in remote international waters, to quickly rebuild most pelagic fish stocks above their target management reference points and reactivate a neglected carbon pump toward the deep sea as an additional Nature Climate Solution in our portfolio. Even if this potential carbon sequestration by surface unit may appear low compared to that of coastal ecosystems or tropical forests, the ocean covers a vast area and the sinking biomass of dead vertebrates can sequester carbon for around 1000 years in the deep sea. We also highlight the multiple co-benefits and trade-offs from engaging the industrial fisheries sector with carbon neutrality.     

Molecular resolution of marine turtle stock composition in fishery bycatch: a case study in the Mediterranean

Based on an extensive sampling regime from both nesting populations and bycatch, frequency analyses of mitochondrial (mt) DNA control region haplotypes in the Mediterranean were used to assess the genetic structure and stock composition of the loggerhead sea turtle, Caretta caretta, in different marine fisheries. The analyses show the following. (i) In drifting longline fisheries working in Mediterranean pelagic habitats 53–55% of turtles caught originated from the Mediterranean stock; (ii) In bottom-trawl fisheries all turtle bycatch is derived from this regional stock; (iii) This regional stock contribution to fishery bycatch suggests that the population size of the Mediterranean loggerhead nesting population is significantly larger than previously thought. This is consistent with a recent holistic estimate based on the discovery of a large rookery in Libya. (iv) Present impact of fishery-related mortality on the Mediterranean nesting population is probably incompatible with its long-term conservation. Sea turtle conservation regulations are urgently needed for the Mediterranean fisheries. (v) The significant divergence of mtDNA haplotype frequencies of the Turkish loggerhead colonies define this nesting population as a particularly important management unit. Large immature and adult stages from this management unit seem to be harvested predominantly by Egyptian fisheries. (vi) Combined with other data, our findings suggest that all the nesting populations in the Mediterranean should be considered as management units sharing immature pelagic habitats throughout the Mediterranean (and possibly the eastern Atlantic), with distinct and more localized benthic feeding habitats in the eastern basin used by large immatures and adults. (vii) Between the strict oceanic pelagic and the benthic stages, immature turtles appear to live through an intermediate neritic stage, in which they switch between pelagic and benthic foods.     

Small marine pelagic fish and the threat of fishing; are they endangered?

Evidence of the collapse and recovery of major marine fisheries for pelagic fish species is reviewed, distinguishing the influence of fishing compared with natural (environmental) effects. In one only of the best documented cases (Icelandic spring-spawning herring) has the stock failed to reappear, after 20 years. Several others, e.g. California sardine, have persisted at 1/000th or possibly less of their peak size for some years before beginning to recover. Fishing has been the main cause of collapse in most but not all cases, due initially to the escalation of catchability as stock size decreases–a phenomenon characteristic of fisheries for pelagic species due to their shoaling habit, ease of detection and vulnerability to modern fishing methods. It is concluded that although the threat of fishing to the continuity of the species is remote, excessive depletion (although avoidable by firm and timely management) is potentially able to cause temporary disappearance of local stock and disruption of the ecosystem.     

大型水母迁移规律和灾害监测预警技术研究进展

20世纪80年代以来,全球大型水母灾害发生频率与成灾种类不断增加,已严重影响了近海海洋渔业、沿海工业、滨海旅游业和海洋生态系统,已引起了各国政府高度重视,并且越来越多海洋工作者投身水母迁移等科学研究和监测预警工作中。回顾近年来国内外学者对水母漂移聚集和溯源等迁移规律的研究进展以及水母灾害监测预警工作现状。水母研究为预测预警工作服务,应侧重于开展系统的水母海上和室内试验,建立业务化立体监测体系;加强水母漂移聚集机理研究,建立更完善的水母预警模式。     

The biology and ecology of the ocean sunfish <Emphasis Type="Italic">Mola mola</Emphasis>: a review of current knowledge and future research perspectives

Relatively little is known about the biology and ecology of the world’s largest (heaviest) bony fish, the ocean sunfish Mola mola, despite its worldwide occurrence in temperate and tropical seas. Studies are now emerging that require many common perceptions about sunfish behaviour and ecology to be re-examined. Indeed, the long-held view that ocean sunfish are an inactive, passively drifting species seems to be entirely misplaced. Technological advances in marine telemetry are revealing distinct behavioural patterns and protracted seasonal movements. Extensive forays by ocean sunfish into the deep ocean have been documented and broad-scale surveys, together with molecular and laboratory based techniques, are addressing the connectivity and trophic role of these animals. These emerging molecular and movement studies suggest that local distinct populations may be prone to depletion through bycatch in commercial fisheries. Rising interest in ocean sunfish, highlighted by the increase in recent publications, warrants a thorough review of the biology and ecology of this species. Here we review the taxonomy, morphology, geography, diet, locomotion, vision, movements, foraging ecology, reproduction and species interactions of M. mola. We present a summary of current conservation issues and suggest methods for addressing fundamental gaps in our knowledge.     

The biological control of snail intermediate hosts of schistosomiasis by fish

Summary The use of molluscivorous fish for biological control of snail intermediate hosts of schistosomiasis is a regularly reappearing theme in the literature on schistosomiasis control. The effectiveness of this control method has not yet been demonstrated, and conclusive field evidence is lacking. In this article the literature on snail control by fish is critically reviewed. Special attention is paid to the cichlid fish Astatoreochromis alluaudi that has been used in well-documented field trials in Kenya and Cameroon. After some small initial success, after a longer period the fish appeared to be ineffective in snail control. Moreover, the fish reproduces at a pace too slow to be of use in large-scale biocontrol trials. Laboratory observations on foraging behaviour and anatomy of the fish give essential cues to explain the failure of the fish in snail control. An observed reduction in the fishes' pharyngeal jaw apparatus, used to crush snails shells, results in a lower profitability of snails. As predicted by a simple foraging model, the prey preference of the fish shifts towards other more profitable prey items, such as benthic and pelagic macrofauna. Although eradication of snails by fish will not be feasible in most cases, the role of natural predators of snails cannot be neglected, and may still be of importance in integrated control efforts.     

Consequences of fishing moratoria on catch and bycatch: the case of tropical tuna purse-seiners and whale and whale shark associated sets

Time–area regulations have been introduced to manage stocks of tropical tuna, given the increased use of drifting fish aggregation devices (FADs). However, the consequences in terms of changes in fishing strategies and effort reallocation may not always be as expected. For instance, in the eastern Pacific Ocean, previous studies have highlighted that the increase use of FAD-fishing following the demand for tuna caught without dolphin mortality has raised concerns about the bycatch and the capture of juvenile tuna. In the tropical eastern Atlantic and western Indian Oceans, this study aimed to (1) assess, using before–after analysis, the consequences of previous time–area regulations on FAD sets on the fishing effort allocated to megafauna associated sets, and (2) evaluate through Monte Carlo simulations the potential effect of new regulations banning whale or/and whale shark associated sets. Firstly, we showed that previous time–area regulations, which were mainly implemented during seasons with few whale and whale shark associated sets, generally had thus little effect on the number of megafauna associated sets. Secondly, some simulations, particularly when both whale and whale shark associated sets were banned, predicted consequences of changes in fishing strategy. Indeed, these types of ban could lead to an increase in the number of FAD and free school sets but no change in the tuna catch, as well as a slight decrease in bycatch. These results indicate that an ecosystem approach to fisheries, by taking into account megafauna associated sets and bycatch, should thus be adopted when implementing management or conservation measures.