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In this study, the four most important species in the Humboldt Current System (HCS), Engraulis ringens, Sardinops sagax, Trachurus murphyi, and Dosidicus gigas were linked to four climate indices, sea surface temperature (SST) and wind speed (WS) based on multivariate statistical analyses, aiming to explore their nonstationary responses to climate variability. Significant decadal variations in the catches were identified, with regime shifts in the mid-1970s, early 1990s, and late 1990s. These shifts corresponded well to climatic and environment regime shifts during these periods. However, the response patterns to climate and environmental variations varied among species. Compared with other physical drivers, seawater temperature, wind speed, the Pacific Decadal Oscillation (PDO), and the North Pacific Gyre Oscillation (NPGO) had greater ecological importance in driving changes in the four pelagic species. The variations in the important climate events influenced seawater temperature and wind speed fluctuations within the HCS, impacting on these commercially important pelagic species. Furthermore, non-stationarity was identified in the relationships between climate/environment and species catches, with different species showing different threshold years. The non-stationarity may be attributed to the transitions between warm and cold periods within the HCS, as well as shifts between strong and weak phases of pressure system. This study helps further understand changes in the HCS caused by fluctuations in climate and environment. [ABSTRACT FROM AUTHOR]

In trawl-acoustic methods, machine learning can objectively assign species composition to echo-traces, providing a reproducible approach for improving biomass assessments and the study of schooling behaviour. However, the automatic classification of schools in multispecies environments is challenging due to the difficulty of obtaining ground truth information for training. We propose a weakly supervised approach to classify schools into seven classes using catch proportions as probabilities. A balancing strategy was used to address high dominance of some species while preserving species mixtures. As the composition of schools from multispecific catches was unknown, model performance was evaluated at the school and haul level. Accuracy was 63.5% for schools from single-species catches or those identified by experts, and a 20.1% error was observed when comparing predicted and actual species proportions at the haul level. Positional and energetic descriptors were highly relevant, while morphological characteristics showed low discriminative power. The highest accuracies were obtained for juvenile anchovy and Muller's pearslide, while sardine was the most challenging to classify. Our multioutput approach allowed the introduction of a metric to assess the confidence of the model in classifying each school. As a result, we introduced a method to classify echo-traces considering prediction reliability. [ABSTRACT FROM AUTHOR]

This study investigated the potential use of fish paste from two pelagic species (Cetengraulis mysticetus or carduma in Colombia and Opisthonema sp. or plumuda in Colombia), either separately or combined, as a substitute for external fat sources in a Leberkäse product. Three stages were analyzed, evaluating biometric proportions, body performance, and meat batters containing different concentrations of fish pastes. Physicochemical and instrumental characterization analyses were performed to determine the effect of the type of fish paste and the level of its inclusion in the final product. Results showed that plumuda fish paste had higher protein and ash content than carduma fish paste, and the inclusion of carduma fish paste in meat batters led to a greater loss of liquid and lower emulsion and gel stability values. The study also established selection criteria for the two pelagic fish species that could be useful for the fishing industry. Overall, the study demonstrated that Leberkäse can be produced using these pelagic species with a relatively simple processing technology.

Bait-based remote underwater video (BRUV) systems are effective devices for remotely observing fish and other marine organisms in challenging environments. The development of a long duration (24 h) surface BRUV observation surveys allowed the monitoring of scarce and elusive pelagic sharks and the direct impact on non-targeted species of longline fishing in the Western Mediterranean. Technological limitations, such as the limited storage capacity and a single surface camera, were improved by (i) adding a deep camera equipped with light (below 80 m depth) and (ii) replacing Gopros with a multi-camera video surveillance system (surface and depth) with a storage capacity of several days and access to real-time observation. Based on a deployment effort of 1884 h video data, we identified 11 blue sharks (Prionace glauca) and one bluntnose sixgill shark (Hexanchus griseus), a deep-sea species that scarcely swims at the surface. The real-time observation capability was a powerful tool for reducing logistical costs and for raising environmental awareness in educational and outreach programmes. [ABSTRACT FROM AUTHOR]

Bait-based remote underwater video (BRUV) systems are effective devices for remotely observing fish and other marine organisms in challenging environments. The development of a long duration (24 h) surface BRUV observation surveys allowed the monitoring of scarce and elusive pelagic sharks and the direct impact on non-targeted species of longline fishing in the Western Mediterranean. Technological limitations, such as the limited storage capacity and a single surface camera, were improved by (i) adding a deep camera equipped with light (below 80 m depth) and (ii) replacing Gopros with a multi-camera video surveillance system (surface and depth) with a storage capacity of several days and access to real-time observation. Based on a deployment effort of 1884 h video data, we identified 11 blue sharks (Prionace glauca) and one bluntnose sixgill shark (Hexanchus griseus), a deep-sea species that scarcely swims at the surface. The real-time observation capability was a powerful tool for reducing logistical costs and for raising environmental awareness in educational and outreach programmes.

Makassar Strait has been identified as an area of interesting studies for marine science and operational fisheries. It provides the unique ocean structures such as topographic feature, the main path of the Indonesia Throughflow (ITF) and dynamics of thermal fronts. The aims of this study were to map the dynamic spatial and temporal of the thermal fronts, and to describe their implications to the pelagic fisheries. We used satellite data of sea surface temperature (SST) for the period of January-December 2018 with spatial and temporal resolutions of 4 km and monthly, respectively. For fishery data, we used sampling data of skipjack tuna fishing ground distributions in October and December 2018. Thermal fronts throughout the year were estimated using a Single Image Edge Detection (SIED) algorithm and the available fishing ground data were overlain on the SST front map. The results showed that the spatial distributions of thermal fronts along Makassar Strait tended to be different every month. However, the thermal fronts were consistently detected near the upwelling area from June to September. Skipjack tuna fishing grounds associated with fish aggregating devices (FADs) developed in the northern area of upwelling in October. Two month later, the FADs and free swimming skipjack fishing grounds again well formed around the same location. It implies that the formation of the thermal fronts after upwelling contributes the positive effect on development of pelagic fishery especially skipjack in Makassar Strait.

Small-scale fisheries (SSF) contribute to nearly half of global landings and provide multiple socioeconomic benefits to coastal communities. The Pacific coast SSF represents 37% of the total fisheries landings in Colombia. Scientific literature continually shows that tropical marine habitats are most vulnerable to oceanic changes associated with climate change. This study prioritized three pelagic species (Euthynnus lineatus, Scomberomorus sierra, and Cynoscion albus) based on their landing statistics to develop potential current and future species distributions using five ensembled machine learning models including Artificial Neural Network (ANN), Maximum Entropy (MaxEnt), Boosted Regression Tree (BRT), Random Forest (RF), and Classification Tree (CT). Future distributions of these species in the medium-term (2050s) and long-term (2080s) were modeled using the Representative Concentration Pathways (RCP) 2.6 and 8.5 emission scenarios for four ensembled General Circulation Models (GCMs) obtained from the Coupled Model Intercomparison Project Phase 5 (CMIP5). In addition, change detections were calculated to identify contraction and expansion of areas, and the distributional core shift was determined to estimate the spatial movements. Results indicate that E. lineatus and S. sierra will potentially move to deeper waters away from the coastline. Alternatively, C. albus could be a species to potentially gain more importance for the fishing sector due to potential variations in climate. These results constitute a critical scientific basis for evaluating the climate change vulnerability of the fishing sector and the decision-making process in the future of small-scale fishery management in the southern Colombian Pacific Ocean.

Climate‐induced nonlinearity in biological variability and non‐stationary relationships with physical drivers are crucial to understand responses of marine organisms to climate variability. These phenomena have raised concerns in the northeastern North Pacific, but are out of the spotlight in the northwestern North Pacific in spite of potential implications for this productive system under increased climate variability. Pelagic communities in the Kuroshio ecosystem have both ecological and economic importance. However, patterns of climate‐induced nonlinearity in pelagic communities are not well understood, and existence of non‐stationarity in their relationships with physical drivers remains obscure. Here, we compile large numbers of climatic, oceanic and biological long‐term time‐series data and employ diverse statistical techniques to reveal such climate‐induced nonlinearity and non‐stationarity. Results show that pelagic communities in the Tsushima and Pacific areas (major areas in the Kuroshio ecosystem) had regime shifts in the late 1990s and late 1980s, respectively. Winter sea surface temperatures in the Kuroshio Current path and in the eastern part of East China Sea, which are respectively affected by the Kuroshio Current and Siberian High, correlate with dominant variability patterns in their pelagic communities. Furthermore, non‐stationarity was identified with threshold years in the 1990s in the Tsushima area and in the 1980s in the Pacific area as a possible result of the declined variances in the Siberian High and Aleutian Low, respectively. Our findings provide insights on spatial differentiation of climate‐induced nonlinearity and non‐stationarity, which are valuable for the management of pelagic communities in the northwestern North Pacific under changing climatic conditions. [ABSTRACT FROM AUTHOR]

This study investigated the potential use of fish paste from two pelagic species ( Cetengraulis mysticetus or carduma in Colombia and Opisthonema sp. or plumuda in Colombia), either separately or combined, as a substitute for external fat sources in a Leberkäse product. Three stages were analyzed, evaluating biometric proportions, body performance, and meat batters containing different concentrations of fish pastes. Physicochemical and instrumental characterization analyses were performed to determine the effect of the type of fish paste and the level of its inclusion in the final product. Results showed that plumuda fish paste had higher protein and ash content than carduma fish paste, and the inclusion of carduma fish paste in meat batters led to a greater loss of liquid and lower emulsion and gel stability values. The study also established selection criteria for the two pelagic fish species that could be useful for the fishing industry. Overall, the study demonstrated that Leberkäse can be produced using these pelagic species with a relatively simple processing technology., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 Published by Elsevier Ltd.)

The conservation of marine biodiversity is firmly embedded in national and international policy frameworks. However, the difficulties associated with conducting broad-scale surveys of oceanic environments restrict the evidence base available for applied management in pelagic waters. For example, the Oceanic Shoals Australian Marine Park (AMP) was established in 2012 in a part of Australia’s continental shelf where unique topographic features are thought to support significant levels of biodiversity, yet where our understanding of ecological processes remains limited. We deployed mid-water baited remote underwater video systems (mid-water BRUVS) in the Oceanic Shoals AMP to provide the first non-extractive baseline assessment of pelagic wildlife communities in the area. We used these observations and high-resolution multibeam swaths of the seafloor to explore potential relationships between prominent geomorphological features and the (i) composition, (ii) richness, and (iii) relative abundance of pelagic communities. We documented 32 vertebrate species across three sampling areas, ranging from small baitfish to large sharks and rays, and estimated that up to nearly twice as many taxa may occur within the region as a whole. This highlights the Oceanic Shoals AMP as a reservoir of biodiversity comparable to other documented offshore oceanic hotspots. Our results also confirm the AMP as a possible distant foraging destination for IUCN red listed sea turtles, and a potential breeding and/or nursing ground for a number of charismatic cetaceans. Model outputs indicate that both species richness and abundance increase in proximity to raised geomorphic structures such as submerged banks and pinnacles, highlighting the influence of submarine topography on megafauna distribution. By providing a foundational understanding of spatial patterns in pelagic wildlife communities throughout a little studied region, our work demonstrates how a combination of non-destructive sampling techniques and predictive models can provide new opportunities to support decision-making under data shortage.

Small- and intermediate-size pelagic fisheries are highly impacted by environmental variability and climate change. Their wide geographical distribution and high mobility makes them more likely to shift their distribution under climate change. Here, we explore the potential impact of different climate change scenarios on the four main commercial pelagic species in the North-East Atlantic (NEA): Atlantic mackerel (Scomber scombrus), European sprat (Sprattus sprattus), Atlantic herring (Clupea harengus) and blue whiting (Micromesistius poutassou). We used a process-based fisheries model (SS-DBEM), where all the target species were exploited at their maximum sustainable yield (MSY), to project future potential catches under a high- and low-future-greenhouse-gas scenario (RCP 2.6 and 8.5, respectively). Two ocean biogeochemical models (GDFL and MEDUSA) were used to force the environmental conditions. Mackerel and sprat are projected to have increases in a potential catch under both scenarios. Herring and blue whiting are projected to increase under the RCP2.6, but future projections under RCP8.5 show mixed responses with decreases or no changes forecasted. Overall, the potential catch is projected to increase in the northern area of the NEA but is projected to decrease in the southern area. These projected changes are mainly driven by changes in temperature and primary production. Shifts in the distribution of pelagic resources may destabilize existing international agreements on sharing of straddling resources as exemplified by the dispute in sharing of quota for Atlantic mackerel. Novel climate-ready policy approaches considering full species distribution are needed to complement current stock-based approaches. [ABSTRACT FROM AUTHOR]

Introduction: Scientific information is often needed to guide management decisions, but marine protected areas usually lack such information. Further, these protected areas face the challenge of protecting highly-mobile pelagic species that move between protected areas in different countries and across fishing zones. In general, the dissociation that commonly exists between academic and conservation groups, which work under different objectives and reward systems, serves as an obstacle for producing the information that is needed by wildlife managers. This limitation is further enhanced in oceanic islands, such as Isla del Coco because of their mere remoteness, a condition that dramatically increases the economic and operational costs for doing research. Objective: To illustrate the challenge of generating useful scientific information for conservation decision making in protected areas, using Isla del Coco National Park in Costa Rica as a case study, and to propose possible solutions. Results: In order to produce the scientific information that these areas require, it is necessary to: i) distinguish between biologically relevant information, and information required for decision-making, ii) generate information about the threats to biodiversity, even in the absence of information about the species themselves, iii) establish clear goals and objectives for monitoring plans, and iv) build strong links between two types of groups: those that work from mainland and those that operate offshore; this includes working alongside fishing vessels. Conclusions: It will be a great challenge to articulate such relationships between groups, but this option seems more viable (in terms of associated logistic and economical costs) than attempting to collect the required data from an isolated academic platform. Also, this articulation appears to be the only way of generating information that is crucial for stock management, such as the accurate characterization of the fishing activity. [ABSTRACT FROM AUTHOR]

Yellowfin tuna (Thunnus albacares) are highly valued pelagic fisheries target species. Regional fisheries management organizations (RFMOs) are the principal mechanism that manage yellowfin tuna fisheries. Determining changes in population abundances is crucial for effective conservation and management. We use multiple methods for monitoring biomass trends and evaluating the status of yellowfin tuna in each ocean basin and show how additional, multiple lines of evidence can enhance our understanding of the conservation and exploitation status of this species. Our analysis of regional biomass trajectories and Catch-MSY++ assessments corroborate the findings of the most recent RFMO stock assessments suggesting yellowfin tuna in the Indian Ocean are in critical condition, while the Eastern Pacific yellowfin tuna population shows the lowest levels of exploitation. These results are supported by fisheries-independent data from baited remote underwater video systems (BRUVS), showing that the Indian Ocean yellowfin tuna population is the least common, least abundant, and smallest across all oceans. Our findings support previous claims of systematic and widespread overfishing of yellowfin tuna in the Indian Ocean and thus confirm calls to reduce current fishing levels to ensure the long-term viability of the species. [Display omitted] • Multiple lines of evidence corroborate RFMOs enhancing our understanding of yellowfin tuna conservation and exploitation. • CMSY++ assessments confirm that Indian Ocean (IO) yellowfin tuna are overfished and subject to overfishing. • IUCN classifies Indian Ocean yellowfin tuna as 'Vulnerable' and biomass trajectories estimate a decline of ∼70% since 1950. • Ecological data from BRUVS indicate that IO yellowfin tuna are least common, least abundant, and smallest across all Oceans. • This approach opens up additional avenues to understanding the conservation status of other large pelagic species. [ABSTRACT FROM AUTHOR]

Species composition of fish is decribed for the Japan Sea on the data of Pacific Fish.Res.Center (TINRO), Russia (about 10,000 bottom and pelagic research trawlings at the depth 5-750 m obtained in 1980-2005), National Fish.Res.Dev.Inst. (NFRDI), Rep.Korea (about 100 research cruises conducted since 1994 with trawling at the depth 30-2550 m), coastal fishery statistics, and cited data. All past revisions in the taxonomy are registered. Some general ecological and zoogeographical features of the Japan Sea are revealed. In total, 962 fish species dwell in the Japan Sea, and 738 of them (77 %) are registered in the EEZ of Russia and Korea. In the analyzed TINRO and NFRDI surveys, 419 fish species were found, mainly in research trawls (389) and patially only in commercial catches in coastal waters (30). On the other hand, 872 fish species (91 % of the total list) occur in the EEZ of Japan. The species belong to 42 orders (Perciformes absolutely dominates among them by number of species - 432) and 215 families (the most numerous are Cottidae - 51 species, Gobiidae - 48 species, and Stichaeidae - 41 species). From zoogeographic point of view, they have mostly tropical-subtropical (488 species), lowboreal-subtropical (210 species), and lowboreal Asian (128 species) origin; only 14 species are endemics of the Japan Sea, 17 species are endemics of the Japan and Okhotsk Seas, and 171 species are endemics of the southern part of the North-West Pacific (Japan Sea, Yellow Sea, East China Sea, and Pacific coast of Japan). The major part of fish species in the Japan Sea inhabit mainly sublittoral (28 %) and elittoral (28 %) biotopes; diversity of stenobathic species decreases both shoreward and toward the continental slope. Bottom (46 %) and near-bottom (26 %) species absolutely prevail over pelagic ones (20 %), whereas 8 % of the species are considered as bottom-pelagic ones.

Fishing is one of the most important economic and cultural activities in Galapagos and Hg presence in aquatic ecosystems is a serious problem for human health, so its concentrations should be studied. We sampled five demersal species (Caulolatilus princeps, Caulolatilus affinis , Mycteroperca olfax, Hyporthodus mystacinus and Pontinus clemensi) and four pelagic species (Coryphaena hippurus , Acanthocybium solandri , Thunnus albacares and Seriolella violacea) to evaluate Hg concentration in muscle, liver and gonads. Hg was analyzed by Cold Vapor Atomic Absorption Spectrophotometry with Flow Injection System (CV-AAS-FIAS). Demersal species had higher Estimated Weekly Intakes (EWI) of Hg than pelagic species. According to the Codex Alimentarius (1995), EFSA (2018), FDA (2021) regulations, and according to the regulations in Europe, A. solandri , P. clemensi, and H. mystacinus were found above the maximum allowed concentration (MAC) (0.65, 0.65 and 1.26 mg/kg wet weight, respectively) so they could not be ingested nor commercialized. The Margin of Safety (MoS) of these species was above 1, so they could pose a risk to human health. We hypothesize that the Hg concentrations found in the studied species could come from the volcanism of the archipelago, since no major sources of anthropogenic Hg contamination can be found in the islands. • solandri, P. clemensi and H. mystacinus were above the MAC for its commercialization in Europe. • solandri , P. clemensi and H. mystacinus could pose a risk to human health. • hippurus , S. violacea and M. olfax showed the lowest concentrations of mercury in muscle. • Mercury concentration in M. olfax 's liver do not coincide with the bioaccumulation process. • Mercury levels in S. violacea 's gonads suggests that this species could be in their reproduction period. [ABSTRACT FROM AUTHOR]

Nano-sized palladium (nano-Pd) is used in catalytic converters of automobiles, where it can be released into the environment by abrasion. Although these particles may subsequently be transported into surface water bodies, no data estimating their fate and toxicity in aquatic systems exists. This study characterized the particle size development of nano-Pd (advertised size ~12 nm; hydrodynamic size ~70 nm) in media with variable ionic strength (IS). Additionally, the particles' acute toxicity for daphnids and chironomids was assessed. While nano-Pd agglomerated more quickly with increasing IS, it caused only marginal effects in both test species after 96 h of exposure. After 144 h of exposure, however, an EC value of 1.23 mg nano-Pd/L for daphnids was determined indicating effects over the long run. When considering the relatively low environmental concentration of elemental Pd in surface waters (usually ng/L), though, this study suggests only a low aquatic risk in response to nano-Pd. [ABSTRACT FROM AUTHOR]

An empirical approach was used to determine the sample size of transects in acoustic surveys to estimate the abundance of three pelagic species in northern Chile. Relationships between the coefficient of variation of fish density and modified degree of coverage were established, where the modified degree of coverage is proportional to the distance sailed and the surface occupation index (Co) of the species and inversely related to the square root of the study area. From this relationship, an equation was obtained to estimate the number of transects required in order to obtain a predefined level of precision, given a known level of occupation. The surface occupation index corrects the degree of coverage and explains to a large degree the differences in the estimated coefficients of variation among the different species. Results showed that sample size declined with an increase in the surface occupation index of the species, and the magnitude of that reduction was appreciably greater for higher levels of precision. The number of transects must be limited to sample sizes with a minimum transect separation in order to assure independence between transect densities. The empirical procedure used for the estimation of the number of transects can be applied to other species situations if the information is available from previous surveys, since the approach only requires repeated echo integrator surveys. [ABSTRACT FROM AUTHOR]

The article presents a study on the origin of yellowtail kingfish from Lord Howe Island, Australia. Researchers examined the otolith chemistry from juvenile kingfish collected from the island, New South Wales and Elizabeth and Middleton Reefs. Results show a strong distinction in otolith signatures from different locations with error rate of classification ranging from 3.5% to 9.9%. Results also go to show that a significant proportion of the adult kingfish sampled may have originated in the waters around Lord Howe Island or nearby Elizabeth and Middleton reefs.

Variations in fat content of the Peruvian anchovy after “El Nin˜o” phenomenon (July 1998–August 1999) are presented confirming the correlation between fat content and spawning of fish as a consequence of this natural disruption. Results obtained show extremely low values (fat content of 0.91% in July 1998). A gradual recovery of the species to normal values of 11.20% was observed in June 1999. [Copyright &y& Elsevier]

This present study documents the incidence of plastic digestion by shortfin mako shark (Isurus oxyrinchus), caught by the Taiwanese small-scale tuna longline fishery in the Northwest Pacific Ocean (between the northeast coast of Taiwan and Japan). In 20 stomachs of shortfin mako, nearly 10% of samples contained at least one piece of plastic debris. The ingested plastic debris was found in the forms of films (5.0 cm) and fragments (3.0 mm) and was identified as polypropylene (PP) based on its polymer characteristics. The results from the analysis provide evidence for the anthropogenic origin and potential intake pathway of direct engulfment of ingested plastics. Our results also confirmed the low incidence of plastic ingestion in shortfin mako, suggesting that pelagic marine species may be relatively less affected by plastic pollution. Future research efforts are thus needed to assess the long-term impact of plastic pollution on marine species. • A low incidence of plastic ingestion (nearly 10%) was found in shortfin mako. • One obtained plastic-like fragment was in the microplastic size range (<5 mm). • The ingested plastics were identified as polypropylene. • Polymer characteristics were identified using SWIR and ATR-FTIR spectroscopy. • Plastics seemed to be directly engulfed from the marine environment. [ABSTRACT FROM AUTHOR]

Small-scale fisheries (SSF) contribute to nearly half of global landings and provide multiple socioeconomic benefits to coastal communities. The Pacific coast SSF represents 37% of the total fisheries landings in Colombia. Scientific literature continually shows that tropical marine habitats are most vulnerable to oceanic changes associated with climate change. This study prioritized three pelagic species ( Euthynnus lineatus , Scomberomorus sierra , and Cynoscion albus ) based on their landing statistics to develop potential current and future species distributions using five ensembled machine learning models including Artificial Neural Network (ANN), Maximum Entropy (MaxEnt), Boosted Regression Tree (BRT), Random Forest (RF), and Classification Tree (CT). Future distributions of these species in the medium-term (2050s) and long-term (2080s) were modeled using the Representative Concentration Pathways (RCP) 2.6 and 8.5 emission scenarios for four ensembled General Circulation Models (GCMs) obtained from the Coupled Model Intercomparison Project Phase 5 (CMIP5). In addition, change detections were calculated to identify contraction and expansion of areas, and the distributional core shift was determined to estimate the spatial movements. Results indicate that E. lineatus and S. sierra will potentially move to deeper waters away from the coastline. Alternatively, C. albus could be a species to potentially gain more importance for the fishing sector due to potential variations in climate. These results constitute a critical scientific basis for evaluating the climate change vulnerability of the fishing sector and the decision-making process in the future of small-scale fishery management in the southern Colombian Pacific Ocean., Competing Interests: The authors declare no conflict of interest., (© 2022 The Author(s).)

The longline is the most common fishing gear used to catch pelagic fish species. It consists of a principal line or mother line from which secondary lines with hooks hang. This fishing gear has demonstratedits efficiency to catch tuna, shark and billfish. The relative specific selectivity, according to some authors, seems to be influenced byfactors like fishing strategy, horizontal and vertical species distribution, and the kind and size of bait. In this paper, a practical method to estimate hook operating depth is proposed, taking into consideration the catenary line formed by the mother line in each section. This estimate was validated with data obtained by means of a CTD meter placed at the same depth as the hooks during the longline operation. Moreover, an analysis of the species composition of the catch at each hook depth was performed. The results indicate that there is a difference of more than 30 m between operating depths in each section. Likewise, significant differences (at level a = 0.05) among catches ateach operating level were observed. [ABSTRACT FROM AUTHOR]