This study applies surveys of business and household expenditure to draw inferences about the size of regional multipliers to assess the cascading economic impacts of the data-limited Indonesian tropical tuna fishery. The average business-level production multiplier was estimated at around 1.3 across survey respondents, while household-level consumption effects were considerably higher, with the total economic effect roughly three times larger than the production value. A statistical analysis using generalized additive models suggests that there is considerable difference in production multipliers across regions, driven by the individual characteristics of operators, such as revenue/profit, size of the boat, type of gear, and the class of the port where the business is located. This research has the potential to provide a practical management tool to measure flow-on economic impacts of a fishery when information necessary for more formal economic analysis is unavailable, such as for data-limited fisheries or small regional studies.

Islands offer unique model systems for studying fisheries development in relation to the growing global seafood trade. This study examines how export-driven fisheries in India's oceanic islands (Andaman and Nicobar Islands and Lakshadweep Islands) differ significantly as a result of their varied history, culture, available infrastructure and market access. Despite being geographically closer to export centres on the Indian mainland, processing and transport infrastructure in the Lakshadweep Islands are limited. This only allows for the trade of non-perishable commodities like dried tuna that are caught using traditional pole-and-line fishing techniques, restricting reef exploitation to local preference-based consumption and opportunistic export. The Andaman Islands, on the other hand, with multiple daily flight connections and large private and government processing facilities, are better connected to export markets. The relatively recent and multicultural fisheries of these islands supply marine commodity chains for reef fishery goods such as dried shark fins, frozen snapper fillets and chilled groupers. The Nicobar Islands are furthest away from mainland export centres and are mostly populated by indigenous communities – fishing here is mostly for subsistence and local sale. Revised estimates of travel times to export market centres are counterintuitive in terms of geographical distances and are significantly different from travel times to local markets.

This study adopted the scaling approach to examine the impacts of inventories on tuna auction prices in Japan using the Rotterdam inverse demand system. The inclusion of two inventory variables in the model only increases the number of parameters by two. Results indicate that frozen tunas are more likely to be close substitutes, fresh and frozen tunas of the same species are also likely to be substitutes, and inventory had significant impacts on auction prices.

Seamounts are expected to attract pelagic top predators due to the higher abundance of possible prey aggregating around these structures. The importance of seamounts on benthic fauna and bottom fish is vastly documented, while little is known about their role as possible hotspots of pelagic biodiversity. This aspect is poorly investigated in the Mediterranean Sea, a basin considered a hotspot of endemism and biodiversity where, in addition, seamounts are widely present, with 227 structures. Our study focuses on the determination of the attraction effect of seamounts on some pelagic species in a Mediterranean sub-basin: the Tyrrhenian Sea. Here, seamounts are thought to be attraction structures for pelagic top predators. Cetaceans and sea turtles were found to be the most attracted taxa among the top predators taken into consideration with peak of presence around 5–10 miles from the seamounts.

Uncertainty about reporting rates of tags returned by fishermen has often prevented tagging data from being used in stock assessments. In this study we conduct a meta-analysis to estimate tag reporting rates of commercial tuna fleets by comparing their tag return data with those of the USA longline pelagic observer program. The longline fleets of Venezuela and the USA are estimated to report about 0.8% of tags caught, compared with less than 0.1% for Canadian, Spanish and Japanese longline fleets. For some fleets with sparse return data or for those that do not overlap often with the observer fleet, reporting rate estimates are sensitive to changes in the spatio-temporal resolution over which comparisons are made. Regardless of these sensitivities, the estimated reporting rates are low and there are likely to be large differences in reporting rate between different combinations of flag and gear.

The bigeye cigarfish (Cubiceps pauciradiatus) is a small pelagic nomeid of the tropical world ocean, often recovered in the stomach contents of top predators such as tunas, billfishes and marine mammals. In the Indian Ocean, a few studies have investigated the biology and the ecology of this species that is one of the most abundant fish of the intermediate trophic levels. In this paper, we investigated the spatial distribution of C. pauciradiatus in the Indian Ocean using pelagic trawl catches carried out between 20°N and 45°S, and the importance of bigeye cigarfish in the diet of 9 piscivorous fishes sampled by different fishing gears in the western part of the Indian Ocean. The highest densities were observed along the eastern coast of Africa and in the Arabian Sea (87 000 individuals per square nautical mile) during the South-West Monsoon and in the eastern part of the Seychelles archipelago (62 200 ind. square nmi) during the North-East Monsoon. Small sized bigeye cigarfish (20–80 mm SL) was a regular and abundant prey (20 to 200 ind. per stomach) for schooling predators exploited by purse seine fishery such as large yellowfin and bigeye tunas chasing prey near the sea surface. Large sized bigeye cigarfish (61–150 mm SL) occurred in small numbers (3 to 20 ind. per stomach) in the stomach contents of swordfish and of large yellowfin and bigeye tunas caught by longline sets at great depths. Large concentrations of bigeye cigarfish occurred in zones of high productivity, and that species constituted seasonally a strong link in the transfer of energy from low to high trophic levels in this part of the Indian Ocean.

Automated acoustic receivers are now widely used by biologists to study the behavior of fish. However, currently available acoustic receivers require physical recovery of the units to download stored data. Such operation is often difficult in remote study areas like in the open ocean. We present a new satellite-linked acoustic receiver (Vemco VR3-Argos) that allows downloading data through a satellite uplink (Argos). The VR3-Argos can last up to one year, sending GPS positions and tag data at regular time intervals. We illustrate the advantages of this new technology with tagging data from 121 fish of seven species (yellowfin tuna, bigeye tuna, skipjack tuna, wahoo, dolphinfish, silky shark and oceanic triggerfish) caught and released around drifting fish aggregating devices (FADs) in the Western Indian Ocean, far from any land. In opposition with the classic acoustic receivers (Vemco VR2), the use of VR3-Argos allowed to collect data for several weeks after leaving the drifting FADs. Maximum residence times of 3 days for bigeye tuna, 7 days for skipjack, 8 days for wahoo, 10 days for silky shark and 15 days for yellowfin tuna, dolphinfish and oceanic triggerfish could be recorded. VR2 and VR3-Argos are equivalent in terms of quality of residence times data, however depth data obtained through satellites are aggregated in 8 classes for compression purposes, which leads to a loss of precision available with raw data. Future directions of this technology are discussed.

Multibeam omnidirectional sonars are tools currently used by fishers, but also allow the monitoring of pelagic fish schools surrounding a platform. Multibeam processing methods now offer improved capacities for raw data storage. The Simrad SP90 sonar was used for the detection of fish schools associated with drifting fish aggregating devices (FADs), and digital systems developed for the acquisition and processing of volume backscattering echoes and position data. Data sampling methods were defined based on two modes: one for periods searching for FADs and associated schools, and one for school monitoring in drifting mode. Validation of the detection of several FAD-associated schooling species was made by simultaneous visual observations or/and cross-checking with echosounder recordings. The characteristics of schooling behaviour in the targeted fish species are fundamental for the correct interpretation of acoustic data. Sonar detection threshold is the result of a compromise between fish number, size, species and the nearest neighbour distance (NND) of individuals per dynamic structure (school or shoal). Tuna schooling dynamics mean that NND can sometimes be too large to allow the presence of these fish to be detected, despite their number. Sonar data should be analysed and interpreted in a holistic manner, in combination with behaviour pattern and dynamics of all species around the drifting FADs. An autonomous sonar buoy prototype equipped with 360° scanning sonar coupled to video cameras will increase our understanding of tuna behaviour around drifting or anchored objects. A similar methodology can be applied to different kinds of platforms, either anchored or in permanent positions. This would improve the monitoring of fish schools around artificial reefs, open sea aquaculture farms, and across estuaries, channels or straits; applications which are undoubtedly essential for progressive fisheries management.

From April 2003 to April 2004 monthly sea surveys were conducted around 2 fish aggregating devices (FADs) moored at 2000 and 2500 m depth in Martinique (Lesser Antilles). The use of a dual frequency splitbeam echosounder combined with an underwater camera and fishing methods allowed assessment of average space and time distribution of pelagic fish aggregated beneath the FADs, as well as identification of their overall size and species composition. At daytime, 4 fish aggregations were identified at each FAD, representing 4 distinct types: i) an aggregation of small juvenile tuna (mean fork length, FL: 30 cm) observed very close to the surface in 25% of daytime periods; ii) a small surface aggregation dominated by carangids, Caranx crysos, present in 65% of daytime periods; iii) a large sub-surface aggregation observed during all daytime periods: this aggregation appeared to be primarily comprised of 58 cm FL blackfin tuna (Thunnus atlanticus), mixed with yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas of the same size; and iv) sub-surface scattered large predators (mainly blue marlin, Makaira nigricans) present in 10% of daytime periods. A smaller sub-surface aggregation comprised of medium tuna mixed with “extranatants” (fishes which remain within 10 to 50 m of a FAD) was observed in 75% of night-time periods, whereas unidentified scattered fishes were detected from 70 to 400 m depth. The low daytime vulnerability of medium sub-surface tunas to applied line techniques leads us to assume that their feeding motivation was low during daytime. These tunas could preferentially feed on mesopelagic organisms during night-time and transition periods around Martinican moored FADs. Local fishermen mainly targeted the large scattered predators using very small tunas as living bait. The sub-surface tuna aggregation hence appeared to be currently unexploited by local fisheries, though it represented the large majority of the pelagic biomass around the moored FADs.

The feeding behaviour of small tuna on the mesopelagic fish Vinciguerria nimbaria was studied in an equatorial area of the Atlantic Ocean (10–20° W, 0–5° N). Acoustic data (from a scientific cruise) and tuna stomach content data (from the tuna purse-seine fishery) were combined. V. nimbaria formed loose schools that occurred in clusters during daytime, and large aggregations during the night. The characteristics of the schools and clusters were analysed. The average length, size and packing density of the day-school were estimated at 48.5 m, 24400 individuals, and 5.8 fish m–3, respectively. The average length of clusters was close to 10 km. The packing density of night-school was estimated at 1.6 fish m–3. The preying of tuna on V. nimbaria was modelled as a stochastic process based on two Poisson processes. Daily rations of tuna were estimated at 3.5% and 7% of the body weight. Taking into account the swimming performance of the prey and the predator, we showed that tuna were able to feed on day-schools in a very short time, whereas feeding during the night by filtering was not competitive. Furthermore, a cluster is able to feed a single tuna school during 2 months, proving the sustainability of the biomass of small tuna in the area by V. nimbaria.

A total of 361 skipjack tuna (Katsuwonus pelamis) between 41.5 and 71.5 cm fork length and 333 yellowfin tuna (Thunnus albacares) between 48 and 150 cm fork length were collected in the western Indian ocean, between latitude 5° N to 10° S and longitude 45° to 65° E from February 1989 to November 1990. Yellowfin populations have one major reproductive season during the north monsoon while in skipjack the reproduction is almost continuous all year round with two peaks in activity during north and south monsoons. The gonadosomatic indexes (GSI) are correlated with the three climatic situations: the north monsoon, the south monsoon and two inter-monsoon seasons. The steroid hormone variations (oestradiol, oestrone and testosterone) are well correlated with the GSI in females. In males, maximum levels coincided with the two main reproduction periods in skipjack while the maximum values of testosterone and 11-ketotestosterone levels were only found during the north monsoon. Even if both species are continuous spawners, these results indicate the existence of different reproductive traits, especially when considering steroidogenesis and vitellogenesis. These findings suggest that over our fishing zone, the reproductive activity is significantly modulated by climatic changes.

Each summer the presence of large concentrations of bait fish in the area of the central Azores Islands gives rise to mixed-species feeding aggregations usually at dawn and dusk. The encircling of prey initiated by common dolphins (Delphinus delphis), often mixed with spotted dolphins (Stenella frontalis), results in the formation of a compact ‘ball’ of several thousands prey fish close to the surface. Other dolphins, in particular the bottlenose (Tursiops truncatus), also eat the prey fish, whose high concentration makes them easy to capture. Large tunas (Thunnus thynnus, Thunnus albacares) sometimes participate in the phenomenon. Seabirds (mainly cory’s sheawaters, Calonectris diomedea borealis) are always present throughout the few minutes during which the entire collective food hunt takes place. A model of the phenomenon, based on 15 observations, is proposed. It comprises 4 stages: a preparation phase, an intensification phase, a mature phase, and a dispersion phase. These observations allow a better understanding of the tuna-dolphin aggregation process. They show that it is the tunas that generate and beneficiate from the aggregation with dolphins, rather than the contrary.

This article describes tracking experiments conducted on eleven yellowfin tuna using ultrasonic transmitters in French Polynesia between 1985 and 1997. Nine fish were caught near Fish Aggregating Devices (FADs) while the other two were tracked in coastal areas without FADs. The fish showed different patterns of horizontal movements: tight associations with FADs lasting several days, foraging movements confirmed by simultaneous acoustic observations of prey-sized fauna, movements parallel to the shore, and traveling between FADs. This intra- and inter-individual variety of behaviour might depend on the local environment (prey), and on individual biological differences. The influence of FADs, coastlines, and prey on tuna movements is discussed. The lack of information about the surrounding environment, the internal state of the fish and the recent history of the fish usually prevent scientists from adequately interpreting the observed movements. Ideas for future research to studying tuna behaviour near FADs are discussed.

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.

This paper compares the species composition of free swimming schools and schools associated with fish aggregating devices (or FADs) observed by scientists in the eastern equatorial Atlantic during the early eighties and late nineties. This comparison shows that in free swimming schools, big changes in the species composition have occurred. The main change is a rarefaction of mixed species free schools (skipjack and small yellowfin or bigeye). This change is probably a real biological one, and possibly a consequence of the large numbers of FADs seeded in the area since 1990. Nowadays, most small tuna living in the equatorial area appear to be concentrated under these drifting FADs instead of in free schools. Further study is recommended in order to evaluate the validity and interpretation of this result and to examine its implications.

The behaviour and spatial distribution of tuna, aggregated beneath fish aggregating devices (FADs), have been studied through ultrasonic tagging experiments but, surprisingly, very few studies on FADs have used underwater acoustic devices. We present techniques, and their limits, incorporating a scientific echo sounder connected to a split-beam transducer to observe and characterise tuna aggregations around FADs, and propose a general approach for future studies. Experiments were conducted in French Polynesia between December 1995 and February 1997. Two methods, echo-counting and echo integration, were used. Echo-counting is possible when individual fish are sufficiently scattered so that each target can be discerned. On the other hand, echo integration can be used with both scattered and aggregated fish schools. The knowledge of tuna target strength is useful for separating targets for echo-counting, and essential for obtaining absolute estimates of densities by echo integration. Sonar performances and settings should be considered when choosing the most suitable method to determine fish density or assessing spatial structure of a tuna aggregation. These techniques allow one to study an entire tuna aggregation, its behaviour in space and time at very fine time–space scales (about a nautical mile and over a few hours), and open up a new scientific field to study the spatial structure and behaviour of tuna aggregations around anchored or drifting FADs.

The diurnal vertical behaviour of yellowfin tuna observed from sonic tagging experiments in the western Indian Ocean (Comoros archipelago) is compared with the vertical profiles of temperature and dissolved oxygen concentration. Two different behavioural situations: off-FAD and FAD-associated yellowfin tuna, are characterized by the relationships between swimming depth and vertical structure of temperature and dissolved oxygen concentration (i.e.depth and thickness of the mixed layer, of the thermocline layer and of the oxycline) observed in the tracking area. Gradients of both paramelers are shown to be the key factors which determine the vertical swimming behaviour. From an analysis carried out on the whole oceanographic data set of the Western Indian Ocean, oxyeline is found to match with the depth of the 4.2-4.3 ml.1−1 dissolved oxygen concentration.

Vertical distributions of yellowfin tuna, for both off-FAD and FAD-associated situations, are modelled by using normal-derived distributions. These models indicate the probability of the presence of yellowfin tuna, related to the vertical profiles of temperature and dissolved oxygen concentration. A single mode distribution is fitted to describe the FAD-associated situation, and a bi-modal one for the off-FAD situation. Positions of the modes are determined by the relationship between the vertical swimming behaviour and the position of either maximum gradient of temperature or dissolved oxygen concentration. An iterative calculation of normal distribution standard error is conducted to adjust the shape of the eurve to cover the entire layer in which yellowfin tuna is considered to be present. Both models were applied in a remote area, east of the Seychelles, where purse seine catches are important. The predicted vertical distribution seems to be realistic and matches the observations given by echosound pictures of tuna schools obtained in the same area by purse seiners.

Il est bien connu des pêcheurs que les monts sous-marins, nombreux dans l'Atlantique tropical est, concentrent parfois de fortes biomasses de thons. Cette association thons et monts sous-marins n'a paradoxalement fait l'objet d'aucun programme de recherches. Le présent article fait un bilan des captures de thons réalisées par les flottilles thonières internationales sur les monts sous-marins connus dans l'Atlantique tropical est durant les années récentes (période 1980 à 1987). La prise annuelle de thons sur certains monts sous-marins peut atteindre plusieurs milliers de tonnes. Les statistiques de pêche thonière montrent que certains monts sous-marins sont riches en thons, alors que d'autres semblent pauvres en permanence, bien qu'ils soient situés dans des zones prospectées par les pêcheurs. Les particularités biologiques de ce type de pêche sont analysées : les captures sont en général plurispécifiques; albacores (Thunnus albacares), listaos (Katsuwonus pelamis) et patudos (Parathunnus obesus) sont pêchés en proportions voisines avec des individus de tailles relativement petites en comparaison des zones voisines. Des hypothèses sont développées sur les causes et sur la dynamique de l'agrégation des thons autour de ces hauts-fonds en utilisant les statistiques de pêche journalières et les résultats de marquages classiques et par marques émettrices réalisés sur un mont sous-marin. Les perspectives de recherches sur l'association sous-marins et thons et sur l'exploitation rationnelle de ces micro-structures sont discutées. Les positions et les profondeurs des monts sous-marins étant actuellement facilement repérées grâce aux satellites à radar altimétrique, la localisation systématique de ces structures est possible et revêt pour les pêcheurs un intérêt potentiel évident pour réduire les temps de prospections des thoniers.

An ultrasonic tagging program for tuna was conducted in 1988 and 1989 within the Regional TunaProject of the Indian Ocean Commission. Three yellowfin and six skipjack tuna were tagged withtemperature or depth sensitive transmitters in the North-western part of the Mozambique Channel(12°S-44°E) around Anjouan island (Comoros Archipelago) where several fish aggregating devices(FADs) were previously moored. The horizontal and vertical movements observed during 8 tracks (3yellowfin and 5 skipjack tuna) whose duration was between 3 and 24 hours, are analysed in terms ofswimming depth, temperature encountered and position of the tracked tuna relative to the FAD orcoast line. Comparison between recorded depth of tracked tuna and echo sounded fish indicatedtracked tuna were schooling.Two of the 3 tagged yellowfin tuna displayed a behaviour of association with FADs. The optimaldistance between 2 anchored FADs, to avoid adverse interference in the attraction of tuna, is estimatedas 11 nautical miles. A very small percentage of time is spent by yellowfin tuna near the surface. Themean swimming depths encountered in the daytime by yellowfin tuna are much deeper (70-110 m)than they are at night (40-70 m). The relative homogeneity in the observed behaviour of yellowfintuna and the fair general agreement with previous results obtained in the Pacific Ocean, should allowapplication of ultrasonic tagging results to fishing and prospecting purposes in the future.The movements of the 5 tracked skipjack tuna do not indicate a behavioural association withFADs, and do not present marked differences between the swimming depths encountered by nightand during the daytime. The high variability observed in the behaviour of the different trackedskipjack tuna, and the bad agreement with previous results obtained in the Atlantic and in the PacificOceans have to be emphasized. A high turnover of the skipjack tuna concentrated around FADs dueto an intense and pelmanent migratory flow through the area of Comoros Islands could partly explainthese apparent discrepancies.