Purse Seine Fishery Research Articles

Estimation of Preferred Habitats and Total Catch Amount of the Round Scad <i>Decapterus maruadsi</i> and Five Other Scad Species in the East China Sea and Sea of Japan

The preferred habitats of the round scad Decapterus maruadsi and five other scads (amberstripe scad D. muroadsi, mackerel scad D. macarellus, red scad D. akaadsi, roughear scad D. tabl, and shortfin scad D. macrosoma) in the East China Sea (ECS) and the Sea of Japan were examined based on catch records of Japanese large- and medium-type purse seine fisheries from 1993 to 2020. Delta-lognormal generalized additive models indicated that the habitats of the round scad and the other five scads were clearly segregated. A high round scad catch per unit effort (CPUE) was observed in the southwestern ECS on the continental shelf and coastal waters around Kyusyu, whereas for the other five scads, a high CPUE was observed around the shelf break and Kuroshio area. The standardized annual CPUEs of the scads decreased after 2010. Based on the proportion of round scad to all six scads calculated by spatial standardized CPUEs for each fishery grid, the total catch amount of round and the other five scads including coastal fisheries was approximately 2,071-13,382 tons and 3,496-24,617 tons, respectively. These estimates are important for scad stock assessment and developing effective management strategies.

The Catch of Pelagic Fish in Purse Seine Fisheries is Related to Oceanographic Parameters in the Water of the Makassar Strait Tolitoli Regency

This research aims to analyze oceanographic parameters and the number of pelagic fish caught in purse seine fisheries in the Makassar Strait, Toli-Toli Regency. The research was carried out using purposive sampling with purse seine catch data collected at 30 FADs (as research sites). Oceanographic data includes sea surface temperature, currents, pH, dissolved oxygen, and waves collected in situ. Meanwhile, nitrate and phosphate samples were analyzed at the Agricultural Science Study Program Laboratory, Tadulako University. Results of analysis of the composition of pelagic fish species caught in purse seine catches in February 2021 (4 types of fish are classified as economically important fish and the other three types are by-catch). In order of highest catches, they were kites (18,632 kg; 24 FADs), skipjack (15,203 kg; 27 FADs), tuna (4,290 kg; 12 FADs), mackerel tuna (3,060 kg; 4 FADs), tuna (4,500 kg; 1 FAD). ), katombo (253 kg; 2 FADs), and rattan (734 kg; 1 FAD). Close relationship and influence Parameters that have the strongest relationship and influence on fluctuations in pelagic fish catches in purse seine fisheries in the Makassar Strait are salinity, dissolved oxygen and nitrate.

Incidental mortality of dolphins in the eastern Pacific Ocean purse-seine fishery: correlates and their spatial association

A zero-inflated Poisson model was used to identify typical fishing practices that contributed to incidental mortality of dolphins in the eastern Pacific purse-seine fishery between 1993 and 2001. The presence of hazardous net conditions (net canopies and net collapses), the duration of the backdown procedure (the primary method of releasing dolphins from the net), the size and species composition of the encircled dolphin herd and the amount of tuna encircled, were all found to consistently contribute to increased dolphin mortality per set. In particular, the presence of net canopies and large biomass in the net contributed to both the development of problematic situations in which mortality could occur and to the mean mortality per set, once a problematic situation had developed. On the other hand, lengthy backdown procedures and the presence of net collapses contributed to the development of problematic situations, but had less effect on the mean mortality per set once a problematic situation had developed. Because some of these variables are partially correlated, the overall conclusion of this analysis is that one of the primary causes of dolphin mortality continues to be the encirclement of large herds. Dolphin mortality can increase with the number of dolphins encircled because: (1) the more animals encircled, the greater the likelihood of entanglement and mortality while confined in the net; and (2) the duration of the backdown procedure increases with the number of animals encircled. The duration of the backdown procedure may, in turn, contribute to increased dolphin mortality by: (1) keeping dolphins in close contact with the net for longer periods of time, thereby increasing the chances for entanglement; and (2) leading to the formation of net canopies. Dolphin mortality increases in the presence of net canopies because animals can be trapped below the sea surface in the areas of canopies. Spatial distributions of encircled herd size, duration of the backdown procedure, presence of net canopies and presence of dolphin mortality show similar patterns. Encircled herd size tended to be greatest south of the equator and north of the equator along the offshore margin of the fishery. In these areas, the duration of the backdown procedure tended to be longer and there was often an increased probability of net canopies and dolphin mortality, but also larger catches of tuna. These consistent spatial patterns suggest that reallocation of fishing effort to other areas may be an effective means of reducing the current level of dolphin mortality. Predictive models could be developed to assess tradeoffs between dolphin mortality and tuna catches at varying levels of fishing effort in areas where large herds are targeted by fishermen and different strategies for reallocation of fishing effort to other areas or to purse-seine sets on unassociated tunas.

Food Preference of Bullet Tuna (<i>Auxis rochei</i> Risso, 1810) in Prigi Coast of Trenggalek Regency, East Java

As a commercial fish, bullet tuna is constantly caught in purse seine fisheries to provide economic benefits for coastal communities. Biological information such as food preference has to be known due to their sustainability in the future. This research aims to figure out the food composition and preference of bullet tuna (Auxis rochei Risso, 1810) in Prigi Coast, Trenggalek Regency East Java. A total of 294 fish landed by purse seine fishermen have been collected from March up to May 2018. Each individual was measured in its total length and weight, then was dissected for sex determination, measured the length of intestine, and analyse the stomach content. The data analysis encompasses frequency distribution of total length, relative gut length, frequency of occurrence, index of preponderance, trophic level, niche breadth, and food overlapping. The research result indicates that the main foods of Auxis rochei are fish and crustacean, while the complementary and additional foods were copepod, mollusc, annelid, and debris. Bullet tuna was a carnivorous fish with the trophic level of 3.7 and shows the existence of competition for food resources. Overlapping of feeding occurred in the 19-20 cm long group against the 23-24 cm long group in male fish and the 19-20 cm size group against the 21-22 cm length group in female fish. Bullet tuna use the same feed resources among the size groups of fish, where females use feed over a wider area than males.

Assessment and management recommendations for the status of Japanese sardine Sardinops melanostictus population in the Northwest Pacific

Japanese sardine (Sardinops melanostictus) is one of the main species caught in the high seas purse seine fishery in the Northwest Pacific Ocean and its resources gradually recovered in recent years. This paper used the historical yearly catch data of Japanese sardine from 1990 to 2021 and biological data (manily for body length) in April-November 2020–2022 to assess its maximum sustainable yield (MSY) and stock resource status using Catch-MSY and LBB models, respectively. And then based on the evaluation results of Japanese sardine MSY, we analyzed the stock management strategies on this species by the Kobe II Strategy Matrix (K2SM). The results were as follows: (1) the Catch-MSY model assessed its MSY as 170.0 × 104 t with a 95 % confidence interval of 134.1 × 104 t ∼ 211.4 × 104 t; (2) the LBB model assessed the biological parameters for the last three years (2020–2022) with the interval range of Lc/Lc_opt was 0.76–0.95, B/BMSY was 0.79–0.84, and B/B0 was 1.9–2.3, which indicate that Japanese sardine resource is healthy and recovering; (3) the results of these two models and the Kobe Ⅱ management strategy matrix are combined to predict future resource status probability values. The management target range for the medium term (5-10 years) should be set 100 % TAC to MSY values, i.e., 102.0 × 104 t–170.0 × 104 t as TAC, and for the long term (10–20 years) can be set to 120 % TAC to MSY values, i.e., 122.4 × 104 t–170.0 × 104 t. Japanese sardine fishery resource can be sustainably used on a longer time scale.

Age estimates for female eastern and whitebelly spinner dolphins (Stenella longirostris) incidentally killed in the eastern tropical Pacific tuna purse-seine fishery from 1973-82

Age was estimated from teeth for 1,267 female eastern spinner dolphins (Stenella longirostris orientalis) and 1,071 female whitebelly spinner dolphins (S. longirostris) incidentally killed in the eastern tropical Pacific yellowfin tuna purse-seine fishery between 1973 and 1982. The final age assigned to each specimen was the mean of two readers’ age estimates made independently and without knowledge of the corresponding biological data for each specimen. The oldest eastern spinner dolphin was estimated to be 24.5 years and the oldest whitebelly spinner dolphin was 26 years. Age bias plots revealed nonlinear systematic bias between readers while a measure of overall precision, coefficient of variation (CV), indicated equivalent difficulty in estimating age for each population. The age frequency distributions generated in this study document the age structure of dolphins sampled from the observed incidental kill, which will facilitate further assessments of the impact of the fishery on these dolphins.

Towards non-entangling and biodegradable drifting fish aggregating devices – Baselines and transition in the world’s largest tuna purse seine fishery

Drifting Fish Aggregating Devices (dFAD) are widely used in purse seine tuna fisheries globally. DFADs are often lost or abandoned by the fishing industry which can lead to marine pollution, entanglement of sensitive species and habitat damage. They are considered as a high-risk lost or abandoned fishing gear due to their common construction with long-lasting synthetic materials, including netting. This study used data collected by fishery observers to investigate materials and designs used in dFAD construction over the last 10 years in the Western and Central Pacific Ocean (WCPO). Results indicated that apart from bamboo, which is commonly used in dFAD rafts with other synthetic materials for buoyancy, very few natural materials are used. The depth of dFAD appendages varied, with a median of 50 m. Most dFADs used netting of various mesh sizes in some aspect of their construction. There is limited information to assess the uptake of lower entanglement risk dFAD designs. Transition towards more environmentally friendly dFAD designs is being promoted by management measures imposed by the Western and Central Pacific Fisheries Commission that include banning of netting by 2024 and encouraging the use of natural materials. Scientific trials are underway to support industry adoption of biodegradable dFAD materials. This paper provides important baseline data to detect and monitor future changes in dFAD construction and materials in response to management measures, and also highlights limitations to data collected by observers that will need to be improved to better monitor these changes.

The Environmental Niche of the Tuna Purse Seine Fleet in the Western and Central Pacific Ocean Based on Different Fisheries Data

Understanding the spatial pattern of human fishing activity is very important for fisheries resource monitoring and spatial management. The environmental preferences of tropical tuna purse seine fleet in the Western and Central Pacific Ocean (WCPO) were constructed and compared at different spatial scales based on the fishing effort (FE) data from the available automatic identification system (AIS) and commercial fishery data compiled from the Western and Central Pacific Fisheries Commission (WCPFC), using maximum entropy (MaxEnt) methods. The MaxEnt models were fitted with FE and commercial fishery data and remote sensing environmental data. Our results showed that the area under the curve (AUC) value each month based on the commercial fishery data (1°) and FE at 0.25° and 0.5° spatial scales was greater than 0.8. The AUC values each month based on the FE data at a 1° scale ranged from 0.775 to 0.829. The AUC values based on commercial fishing data at the 1° scale were comparable to the model results based on FE data at the 0.5° scale and inferior to the model results based on FE data at the 0.25° scales. Overall, the sea surface temperature (SST), temperature at 100 metres (T100), oxygen concentration at 100 metres (O100) and total primary production (PP) had the greatest influence on the distribution of the purse seine tuna fleet. The oxygen concentration at 200 metres (O200), distance to shore (DSH), dissolved oxygen (Dox), EKE, mixed layer depth (Mld), sea surface salinity (SSS), salinity at 100 metres (S100) and salinity at 200 metres (S200) had moderate influences, and other environmental variables had little influence. The suitable habitat areas varied in response to environmental conditions. The purse seine tuna fleet was mostly present at locations where the SST, T100, O100, O200 and PP were 28–30 °C, 27–29 °C, 150–200 mmol/m3 and 5–10 mg/m−3, respectively. The MaxEnt models enable the integration of AIS data and high-resolution environmental data from satellite remote sensing to describe the spatiotemporal distribution of the tuna purse seine fishery and the influence of environmental variables on the distribution, and can provide forecasts for fishing ground distributions based on future remote sensing environmental data.

Review of potential line-transect methodologies for estimating abundance of dolphin stocks in the eastern tropical Pacific

A twelve-year hiatus in fishery-independent marine mammal surveys in the eastern tropical Pacific Ocean (ETP), combined with a mandate to monitor dolphin stock status under international agreements and the need for reliable stock status information to set dolphin bycatch limits in the tuna purse-seine fishery, has renewed debate about how best to assess and monitor ETP dolphin stock status. The high cost of replicating previous ship-based surveys has intensified this debate. In this review, transect methods for estimating animal abundance from dedicated research surveys are considered, with a focus on both contemporary and potential methods suitable for surveying large areas for dolphin species that can form large, multi-species aggregations. Covered in this review are potential improvements to the previous ship-based survey methodology, other ship-based methods, alternative approaches based on high-resolution imagery and passive acoustics, and combinations of ship-based and alternative approaches. It is concluded that for immediate management needs, ship-based surveys, with some suggested modifications to improve precision, are the only reliable option despite their high cost. However, it is recommended that a top research priority should be development of composite methods. Pilot studies on the use of high-resolution imagery and passive acoustics for development of indices of relative abundance to be used in composite methods should be part of any future ship-based survey efforts.

Environmental Characteristics Associated with the Presence of the Pelagic Stingray (Pteroplatytrygon violacea) in the Pacific High Sea

The pelagic stingray (Pteroplatytrygon violacea), perhaps the only stingray to inhabit open ocean waters, is highly interactive with longline and purse seine fisheries. The threat to P. violacea posed by high bycatch mortality has received widespread attention. To date, the environmental preference of P. violacea, which is important in designing conservation and management measures, has not been well studied. Based on data collected during a 2016–2019 survey in the Pacific Ocean by national observers of tuna longline fisheries, the relationship between the presence of P. violacea and spatiotemporal and environmental variables was first analyzed using the Generalized Additive Model. The results showed that geographic location (latitude and longitude) was the most influential variable. Monthly, P. violacea is frequently present in the Pacific high sea from December to May. The El Niño–Southern Oscillation had a significant impact on the presence of P. violacea in the Pacific high sea, with both the cold (Ocean Nino Index <−0.5) and warm (Ocean Nino Index >1) phases leading to a decrease in its presence. Regarding the environmental factors, we found that high presence was associated with low salinity (33.0~34.5 psu), a relatively high concentration of chlorophyll (0.2–0.35 mg/m3), and warm water (>20 °C). P. violacea was most likely observed in the waters offshore, closer to seamounts, and with water depths between 4000 and 5000 m. Four areas, including those east of the Solomon Islands and east of Kiribati, areas west of the Galapagos Islands, and areas near the coastal upwelling of northern Peru, related to upwelling systems or seamounts, were identified as the potential key habitats of P. violacea. Predicted distribution maps showed a significant seasonal variation in the presence of P. violacea. Moreover, the yearly change in the presence of P. violacea in the Pacific high sea indicated a possible decreasing trend in recent years. The information first provided here is essential for developing conservation and management measures for P. violacea to prevent the unavoidable ecological consequences of bycatch or other anthropogenic factors.

Turtles, TEDs, tuna, dolphins, and diffusion of innovations: key drivers of adoption of bycatch reduction devices

AbstractFisheries extension programmes frequently fail to secure mandatory or voluntary adoption of bycatch reduction devices and techniques. Approaches for improving the outcomes of extension programmes are often based on ad hoc assessments and do not consider human behaviour or change theories. This paper offers an in-depth analysis of extension activities that led to various adoption outcomes in two prominent bycatch case studies in the United States: turtle excluder devices in shrimp trawl fisheries and dolphin bycatch in the tuna purse seine fishery. Using a grounded theory approach to text analysis of interviews and documents, I examine five periods of voluntary or mandatory adoption efforts. I explain the outcomes through the lens of diffusion of innovation theory. The most effective extension programme involved informative and persuasive efforts, enforced regulations, and commercially practical bycatch reduction devices. Voluntary adoption occurred under exceptional circumstances of public and political pressure and a device that offered substantial benefits to the adopter. The two periods of successful adoption applied the most core principles of diffusion theory. This paper concludes with recommendations for how change agents can apply diffusion theory to future fisheries extension programmes to improve the adoption of bycatch reduction devices.

Co-management of large-scale and medium-scale fisheries: An assessment of the fishery tax system in Indonesia

Many fish stocks are jointly exploited by industrial vessels that employ modern fishing technologies and small- to medium-scale vessels that rely on simple gears. For the effective management of these shared stocks, it is imperative to understand how different policy options influence the behavior of fishing vessels of different sizes. A fishery tax could be a viable option where other popular market-based instruments, such as individual transferable quotas, cannot be adopted. In this study, we developed a model that incorporates the interaction between large- and medium-scale fishing vessels to evaluate the impact of alternative tax schemes. The model is parameterized using the skipjack (Katsuwonus pelamis) purse-seine fishery in Indonesia, which has over 20 years of experience in fishery taxes. The results show that the current tax system has a limited impact on reducing fishing pressure, as tax payments are determined by the pre-production characteristics of fishing entities. Moreover, vessels below 30 GT are exempt from taxes, giving incentive for fishers to invest in vessels below or far above 30 GT. When taxes are imposed on only one vessel group, the harvest reduction by this vessel group could be offset by an increase in the harvest by untaxed vessels. Imposing a production-based tax on both large and medium vessels results in a more balanced outcome in terms of the distribution of fishery benefits and vessel capacity across regions. We discuss the social and institutional implications of implementing a production-based taxation system to promote efficient and equitable resource use in Indonesian fisheries.

Vitality as a measure of animal welfare during purse seine pumping related crowding of Atlantic mackerel (Scomber scrombrus)

The impacts of wild capture fishing on animal welfare are poorly understood. During purse seine fishing for Atlantic mackerel (Scomber scrombrus), catches are crowded to high densities to facilitate pumping onboard. This study aimed to monitor fish welfare during crowding events in the Norwegian purse seine fishery, and to identify relevant drivers. We first correlated a suite of neuro-endocrine, physiological and physical stress responses (integrated into a single measure of welfare using multivariate analysis) to the behavioural vitality of individual mackerel in controlled crowding trials in aquaculture cages. Vitality was found to be a useful measure of welfare. We then assessed individual fish vitality onboard a commercial purse seiner. Catch welfare, measured using vitality, was observed to be negatively impacted during pumping related crowding. Larger catches and longer crowding exposure times resulted in greater negative impacts. Vitality was not significantly impacted by crowding density or dissolved oxygen concentrations inside the net, although methodological limitations limited accurate measurement of these parameters. Blood lactate levels correlated negatively with vitality, suggesting that high-intensity anaerobic locomotory activity was associated with the reduction in welfare. Based on these findings, catch welfare could be improved by targeting smaller schools to minimise crowding exposure times.

Carbon footprint, economic benefits and sustainable fishing: Lessons for the future from the Western Mediterranean

Ensuring an economically viable, sustainable and low CO2 emission extractive fishery is critical in order to achieve the life below water UN sustainable development goals and the climate change commitments of Paris agreement. This challenge is even more relevant in the most overexploited region of the world: The Mediterranean Sea. Here, we use the socio-ecological system of the Spanish Mediterranean commercial fisheries (Northern Alboran Sea, Northern Spain and the Balearic Islands) to develop an integrative impact assessment, including detailed socio-economic, ecosystem indices of the trophic structure of extractive fishery and CO2 emission analyses combining different gear, vessel size classes as well as a wide range estimation of carbon release from the seafloor by bottom trawling. Northern Alboran Sea preferentially requires reduction in purse seine fishery while in Northern Spain bottom trawling should be reduced first to reach sustainable exploitation. Fuel CO2 footprint of purse seine and bottom trawling are among the lowest footprints of animal protein production, but considering sweeping released CO2 from the seafloor the bottom trawling footprint becomes the animal protein production with the highest footprint. Moreover, the lowest bottom released CO2 estimation overrides 2.7–10 times the CO2 buried in the seafloor through the biological pump in trawled areas potentially turning the continental shelf from a CO2 sink to a CO2 source. Net profit per fuel derived CO2 emission for all fleets is lower than 1€ kgCO2−1, being lowest for large bottom trawler (0.025 € kgCO2−1).Thus, urgent mitigation and adaptation measures are necessary to obtain sustainable fishery in terms of net profit, sustainable seafood extraction and CO2 emission reduction. Our study provides scientific bases to develop these measures such as the restriction of harmful fishing gear in carbon rich river influenced areas, reduction of bottom contact of the fishing gear, favouring purse seine fishery and smaller bottom trawlers.

Comparison of catch rate by operation time of Korean tuna purse seine fishery in the Western and Central Pacific Ocean

Comparison of catch rate by operation time of Korean tuna purse seine fishery in the Western and Central Pacific Ocean

Low anthropogenic mortality of humpback (Megaptera novaeangliae) and killer (Orcinus orca) whales in Norwegian purse seine fisheries despite frequent entrapments

AbstractFishery inspector logbooks were used to estimate fishing gear interaction rates for humpback (Megaptera novaeangliae) and killer (Orcinus orca) whales in Norwegian purse seine fisheries for herring from 2011 to 2020. Estimated rates were applied to fisheries data to estimate fleet‐wide totals. Estimates showed that in a 10‐year period, a total of 78 humpback whales, 95% CI [41, 145] and 100 killer whales, 95% CI [63, 176] were entrapped in purse seines. Most whales were disentangled alive, with an estimated mortality of 5%, CV 0.69, 95% CI [0.0, 11.8] and 6%, CV 0.48, 95% CI [0.3, 11.9], respectively. The average yearly mortality over the study period was thus approximately 0.60 killer whales and 0.39 humpback whales corresponding to 0.008% and 0.007% of the respective abundance estimates for these whale species in Norwegian waters. Given the Potential Biological Removal sustainability limits of 98 humpbacks and 161 killer whales per year, it may be concluded that, by itself, the average yearly mortality incurred by these whale populations by Norwegian fisheries does not constitute a significant risk to either of these species, but bycatch in Norwegian purse seine fisheries may not be the only source of anthropogenic mortality.

An integrated scheme for the management of drifting fish aggregating devices in tuna purse seine fisheries

AbstractDrifting fish aggregating devices (dFADs) are extensively used in modern tuna purse seine fisheries. The use of dFADs has greatly improved fishing efficiency and generated substantial economic returns in purse seine fisheries, but adverse impacts on tuna juveniles, associated species and marine ecosystems are still of concern. Based on an analysis of current challenges in dFAD management measures in tuna regional fishery management organisations (t‐RFMOs), we explored opportunities to strengthen dFAD management in tuna fisheries. An integrated dFAD management scheme with multiple tools that account for different usage stages of a dFAD needs to be organised to regulate, track, monitor and recover in tuna purse seine fisheries. We recommend that (1) dFAD‐associated definitions should be standardised to provide operational guidance for dFAD activities; (2) all deployed dFADs should be counted towards dFAD limits on active dFADs, except those reported as lost and abandoned; (3) a regional dFAD tracking and monitoring program should track dFAD paths based on daily position reported to RFMOs directly, in addition to mandatory dFAD marking requirements; and (4) a framework of compensation mechanisms should provide financial support for joint dFAD recovery and eco‐compensation.

Impact of the Bottlenose Dolphins (Tursiops truncatus) Depredation on Purse-Seine Fishery in the Region of M’diq (Northwestern Morocco)

Impact of the Bottlenose Dolphins (Tursiops truncatus) Depredation on Purse-Seine Fishery in the Region of M’diq (Northwestern Morocco)

End-of-life fishing gear in Spain: Quantity and recyclability

European Commission has approached the challenge of End-Of-Life (EOL) fishing gear and Abandoned, Lost, or otherwise Discarded Fishing Gear (ALDFG) by focusing on circular economy. Current directives highlight the need to provide a proper management to EOL fishing gears, fostering their separate collection, transport, and treatment from a circular perspective. They also request Member States to set collection and treatment targets. However, this is far from being widely implemented in a coordinated manner. In the quest to explore the Spanish case, this contribution aims at providing insights on the amount and type of EOL fishing gear and management practices carried out in different Spanish ports, as well as recycling options for such gears. Data was collected through an online survey, interviews to stakeholders, and visits to ports. Composition, degradation and mechanical recyclability of EOL samples were assessed. Yearly, 1643 tonnes of EOL fishing gear (mainly nets) are discarded in Spanish ports from trawling (97.5%), gillnet/trammel nets (2.3%) and purse seine (0.2%) fisheries. High-density polyethylene (from trawling nets) is the most common discarded polymer, followed by polyamide 6 (from gillnets/trammel net and purse seine nets). EOL fishing gear management is diverse in Spain as it depends on the nature of the port (who governs it, either regional or national govern), special agreements between local fishers’ guilds and waste managing companies, the waste managers in port, etc. Polyamide nets are degraded but in good condition to be recycled mechanically; for trawl nets chemical recycling is more suited due to their degraded state. Currently, few recycling companies exists in Spain that are engaged on mechanical recycling of EOL fishing gears, none in chemical recycling. Therefore, a more comprehensive analysis, coordination, and smart logistics are needed to make the collection and recycling of EOL fishing gear possible.

Multi‐species hotspots detection using self‐organizing maps: Simulation and application to purse seine tuna fisheries management

Abstract To fulfil fisheries management objectives that often include implementing the precautionary and ecosystem‐based approaches, multispecies fisheries data need to be analysed. Amongst the different methods dealing with these multidimensional data, self‐organizing maps (SOMs) remain rarely used, although they are highly flexible in data input and offer visualization possibilities particularly suited to summarize complex datasets. Here, we propose to combine SOMs with a clustering approach to break down data complexity and produce simple geographic maps showing catch hotspots, which can indicate sensitive zones in terms of fishery management. To promote this approach, we tested it first on simulated datasets and then on the open‐access ICCAT commercial catch database of the tropical tuna fisheries of the Atlantic Ocean. We aimed to detect drifting fish aggregating devices (dFADs) catch hotspots of juveniles of two tuna species, bigeye and yellowfin tunas and of the silky shark, a commonly bycaught vulnerable shark species, in tropical tuna purse seine fisheries. Simulations on datasets increasing in complexity (in number, geographic and duration extent of the hotspots and number of species in the analysis) informed us about the method's sensitivity and limits. Our findings showed that, in the context of multi‐specific fisheries, the detection of the hotspot is dependent on a certain level of catch within the hotspot and that adding species to the analysis tended to mask small and short‐duration hotspots. Applied to tropical tuna fisheries' data, the method confirmed the empirical knowledge on which first time‐area closures were based and provided scientifical support. All in all, the visual support provided by the method, its interpretability and its potential transferability to other fisheries' systems constitute its main strengths and imply a possible implementation in management decisions; specifically, as a tool to reach agreement between stakeholders in the definition of regulated areas for protecting juveniles of tunas and vulnerable associated species to dFAD practices.