Drifting Fish Aggregating Devices (dFADs) are currently made with synthetic and non-biodegradable materials contributing to the increase of marine litter and other potential ecosystem impacts. Tuna RFMOs have promoted the research and progressive replacement of existing FADs by non-entangling biodegradable FADs (bioFADs). Here, we present the results of the first large-scale biodegradable FAD project in the Indian Ocean to develop and implement the use of non-entangling biodegradable dFADs. The bioFAD tested were fully non-entangling without netting minimizing completely the risk of entanglement. Tested bioFADs significantly contribute to the reduction of the synthetic plastic-based materials, increase the use of biodegradable materials and reduce the total material weight used in FADs, reducing their overall ecosystem impacts. The results of testing 771 bioFADs in real fishing conditions, showed that the fishing performance regarding presence/absence of tuna around dFADs, first day of tuna detection, proportion of FADs occupied by tuna, biomass aggregation underneath the FADs and catch per set between bioFADs and conventional dFADs were similar. This provides support for the efficacy of bioFADs regardless of the degradation experienced by the biodegradable materials tested. Although some bioFADs lasted up to one year, the degradation of the biodegradable material was important and some bioFADs lost their original structure after the study period, suggesting the need to find alternative designs for bioFADs that will suffer less structural stress than those bioFADs made of biodegradable material but with conventional design. The lessons learnt in this large-scale trial will contribute to refining the future designs of biodegradable FADs.

An acoustic survey was performed in the Bay of Biscay (usual summer feeding area for bluefin tunas) during July 2015 to 2019 on-board a baitboat fishing vessel, using a long-range 90kHz sonar and a SIMRAD EK60 scientific echosounder (upgraded to EK80 in 2018) working at three frequencies, of which 38 kHz, used for echointegration. The survey followed systematic transects defined according to 2000-2011 baitboat catch locations. All bluefin detections by sonar and echosounder were recorded. In each aggregation, species identification or sizesampling were performed through no-kill fishing events, stereoscopic camera and/or multibeam sonar. The spatial distribution of detected bluefin schools is shown, as well as the estimated number and size of individuals in the detected schools, and the estimated number of individuals by age-group. The detected abundance and distribution of bluefin tuna is analyzed by sizegroup and in terms of spatial variability. The goal of this survey is to produce an acousticsbased, fishery independent abundance index in the Bay of Biscay as an alternative to the current one, based on catch rates, that is being used in the stock assessment.

Marine species have exhibited trends in their geographic distribution and phenology in recent decades, and these changes are triggered by climate variability or anthropogenic pressures. Northeast Atlantic albacore has recently been identified to show changes of this nature, although the underlying causes are still uncertain. The aim of this work was to analyse the Northeast Atlantic albacore distribution shifts and phenological changes during the trophic migration that juveniles undertake from late spring to autumn and to identify potential causes of such variability. Specifically, time series of albacore catches of the Basque trolling fleet were studied and compared with trends derived from a null ecological niche model using very large number of catch observations (27,982). The results showed an earlier albacore migration of 2.3 days per decade during the period of 1981-2017, which was partly associated with the recent warming of the sea. The trend analysis of the catch distribution also detected a significant north-westward trend in catch observations and a northward trend in species habitat. In contrast, both latitudinal trends were uncorrelated. This result suggests that interannual species distribution shifts are mainly related to factors other than oceanic-climatic variability, such as fleet behaviour or prey changes.

Fisheries are constrained by ecosystem productivity and management effectiveness. Climate change is already producing impacts on marine ecosystems through overall changes in habitats, productivity and increased variability of environmental conditions. The way how these will affect fisheries is under debate and, also there is uncertainty on the best course of action to mitigate climate change impacts on fisheries. Harvest control rules are sets of pre-agreed rules that can be used to determine catch limits periodically and describe how harvest is automatically controlled by management in relation to the state of some indicator of stock status. In 2017, the International Commission for the Conservation of Atlantic Tunas adopted a harvest control rule for North Atlantic albacore. This harvest control rule was evaluated using Management Strategy Evaluation against the main sources of uncertainty inherent to this fishery. Here, we used the same framework to evaluate the robustness of the adopted rule against two types of potential climate change impacts on North Atlantic albacore dynamics. First, we evaluated how the control rule would perform in the event of overall changes in productivity in the North Atlantic and second, against increases in climate driven recruitment variability. Overall, our results suggest that the adopted harvest control rule is robust to these climate driven impacts and also suggests bounds at which the current management framework would be vulnerable to climate change. Throughout the manuscript we also discuss the potential of harvest control rules and harvest strategies to adapt fisheries management to a changing environment. Our main conclusion is that despite the many uncertainties on climate impacts on fisheries, efficient fisheries management and HCRs will be critical to ensure the sustainability of fisheries in the future.

In the Eastern temperate North Atlantic, the Bay of Biscay is a well-known summer feeding area for juvenile bluefin tunas (ages 1 to 4). An acoustic survey was performed in the Bay of Biscay during July 2015, 2016, 2017 and 2018 on-board a baitboat fishing vessel, using a long-range 90kHz sonar and a SIMRAD EK60 38kHz scientific echosounder (upgraded to EK80 in 2018). The survey followed systematic transects throughout the fishing ground defined according to bluefin tuna catch locations by baitboats in the summers 2000 to 2011. Along these transects, all bluefin tuna detections by sonar and echosounder were recorded. In each aggregation, no-kill fishing events or direct observations through stereoscopic camera were conducted to verify the species as well as to sample the sizes of the bluefin individuals. The spatial distribution of detected bluefin schools is shown, and the estimated number and size of individuals in the detected schools is provided. The goal of this survey is to produce an acoustic, fishery independent abundance index in the Bay of Biscay as an alternative to the current one, based on catch rates, that is being used in the stock assessment. The detected abundance and distribution of bluefin tuna is analyzed by size-group and in terms of spatial variability.

Tuna are globally distributed species of major commercial importance and some tuna species are a major source of protein in many countries. Tuna are characterized by dynamic distribution patterns that respond to climate variability and long‐term change. Here, we investigated the effect of environmental conditions on the worldwide distribution and relative abundance of six tuna species between 1958 and 2004 and estimated the expected end‐of‐the‐century changes based on a high‐greenhouse gas concentration scenario (RCP8.5). We created species distribution models using a long‐term Japanese longline fishery dataset and two‐step generalized additive models. Over the historical period, suitable habitats shifted poleward for 20 out of 22 tuna stocks, based on their gravity centre (GC) and/or one of their distribution limits. On average, tuna habitat distribution limits have shifted poleward 6.5 km per decade in the northern hemisphere and 5.5 km per decade in the southern hemisphere. Larger tuna distribution shifts and changes in abundance are expected in the future, especially by the end‐of‐the‐century (2080–2099). Temperate tunas (albacore, Atlantic bluefin, and southern bluefin) and the tropical bigeye tuna are expected to decline in the tropics and shift poleward. In contrast, skipjack and yellowfin tunas are projected to become more abundant in tropical areas as well as in most coastal countries' exclusive economic zones (EEZ). These results provide global information on the potential effects of climate change in tuna populations and can assist countries seeking to minimize these effects via adaptive management.

From 2005 to 2010, 136 internal archival tags and 29 pop-up satellite archival tags were used to track juvenile Atlantic bluefin tuna in the Bay of Biscay. Information from 15 pop-up and 5 internal archival tags was recovered. The analysis was adapted for a common treatment of both types of tag data, allowing classification of overwintering distribution patterns, fidelity to the Bay of Biscay feeding area, as well as of horizontal and vertical habitat utilization. Results show substantial geographic dispersion from autumn to spring, with high habitat concentration in the Bay of Biscay during summer, when bluefin tuna inhabit in the mixed layer. Of the individuals that left the Bay of Biscay towards the end of the year, a high percentage returned the next year, suggesting a strong fidelity to the area. Thirty-three percent of records during the overwintering periods revealed residency in the Bay of Biscay and surrounding areas. Half of the fish overwintered in the mid-Atlantic, near the Azores or Madeira Islands, while three (17%) made trans-Atlantic round trips, and one individual travelled to and remained off the eastern coast of the United States. These findings challenge previous assumptions regarding the seasonality and annual movements of bluefin tuna from the Bay of Biscay, while demonstrating extensive spatio-temporal dispersion.

Uncertainties regarding the Atlantic bluefin tuna stock state and regarding the reliability of fishery-dependent abundance indices raise the need to develop fishery-independent abundance indices for this species. An acoustic survey was performed in the Bay of Biscay during July 2015 and 2016 on-board a baitboat fishing vessel, using a long-range sonar and an echosounder comprising a set of two vertically and horizontally oriented transducers. The survey followed systematic transects defined according to bluefin tuna catch locations by baitboat in the 2000-2011 period. Along these transects, all bluefin tuna detections by sonar and echosounder were recorded, and no-kill fishing events were done in order to identify the species and sample the sizes of the individuals present in each aggregation. In this document the detections by day are shown for 2015 and 2016 surveys. For the 2015 survey, we also present the analyses done to determine the dimensions, volume, number of individuals in each bluefin tuna aggregation observed, as well as an estimation of the spatial density of bluefin tuna. RÉSUMÉ

This study presents a methodology for the automated analysis of commercial medium range sonar signals for detecting presence/absence of bluefin tuna (Tunnus thynnus) in the Bay of Biscay. The approach uses image processing techniques to analyze sonar screen shots. For each sonar image we extracted measurable regions and analyzed their characteristics. Scientific data was used to classify each region into a class ("tuna" or "no-tuna") and build a dataset to train and evaluate classification models by using supervised learning. The methodology performed well when validated with commercial sonar screenshots, and has the potential to automatically analyze high volumes of data at a low cost. This represents a first milestone towards the development of acoustic, fishery-independent indices of abundance for bluefin tuna in the Bay of Biscay. Future research lines and additional alternatives to inform stock assessments are also discussed.

1. Whale shark, the world's largest fish, is believed to be particularly vulnerable owing to its biological characteristics (slow growth, late maturation, great longevity) and is listed as Vulnerable by IUCN and included in Appendix II of CITES.2. Whale sharks are occasionally encircled in tropical tuna purse-seine nets, throughout this global fishery. Although apparent immediate survival rates following encirclement and release have recently been assessed through scientific onboard observer programmes, a more rigorous methodology is still required for studying post-released survival.3. This work provides a method for applying pop-up satellite tags and reports an enhanced release procedure for whale sharks. The first assessment of survival after release from purse-seine nets involved six whale sharks tagged between May and September 2014 in the eastern tropical Atlantic Ocean. Five tags transmitted data: three popped up as programmed (after 30 days), while two surfaced prematurely (one after 21 and the other after 71 days (programmed to pop off after 30 and 90 days, respectively)) but showed no sign of unusual behaviour.4. Overall, whale sharks survived at least 21 days (one at least 71 days) after release from purse-seine nets. These observations based on five large individuals (total length > 8 m), suggest that whale sharks have a good chance of survival when released with the proposed method.5. Additional tagging in this and other oceans, especially of juveniles which may be more sensitive to encirclement and release operations, is essential to further assess whale shark post-release survival rates in tuna purse-seine fisheries. Copyright (C) 2016 John Wiley & Sons, Ltd.

An ecological niche modelling (ENM) approach was used to predict the potential feeding and spawning habitats of small (5-25 kg, only feeding) and large (>25 kg) Atlantic bluefin tuna (ABFT), Thunnus thynnus, in the Mediterranean Sea, the North Atlantic and the Gulf of Mexico. The ENM was built bridging knowledge on ecological traits of ABFT (e.g. temperature tolerance, mobility, feeding and spawning strategy) with patterns of selected environmental variables (chlorophyll-a fronts and concentration, sea surface current and temperature, sea surface height anomaly) that were identified using an extensive set of precisely geo-located presence data. The results highlight a wider temperature tolerance for larger fish allowing them to feed in the northern high chlorophyll levels latitudes up to the Norwegian Sea in the eastern Atlantic and to the Gulf of Saint Lawrence in the western basin. Permanent suitable feeding habitat for small ABFT was predicted to be mostly located in temperate latitudes in the North Atlantic and in the Mediterranean Sea, as well as in subtropical waters off north-west Africa, while summer potential habitat in the Gulf of Mexico was found to be unsuitable for both small and large ABFTs. Potential spawning grounds were found to occur in the Gulf of Mexico from March April in the south-east to April May in the north, while favourable conditions evolve in the Mediterranean Sea from mid-May in the eastern to mid-July in the western basin. Other secondary potential spawning grounds not supported by observations were predicted in the Azores area and off Morocco to Senegal during July and August when extrapolating the model settings from the Gulf of Mexico into the North Atlantic. The presence of large ABFT off Florida and the Bahamas in spring was not explained by the model as is, however the environmental variables other than the sea surface height anomaly appeared to be favourable for spawning in part of this area. Defining key spatial and temporal habitats should further help in building spatially-explicit stock assessment models, thus improving the spatial management of bluefin tuna fisheries. (C) 2016 The Authors. Published by Elsevier Ltd.

In recent years, albacore (Thunnus alalunga) catches decreased strongly in the Eastern part of the Bay of Biscay. In order to understand the drivers of local albacore catches by fisheries in this area, we analyzed the influence of temperature, salinity and trophic parameters on albacore daily catches by three fleets (baitboat, trolling line and pelagic trawling) traditionally operating in the Bay of Biscay and its surrounding waters. For this, we used oceanographic data obtained from the operational model Regional Ocean Model System (ROMS), for each catch date and location. A Principal Component Analysis performed on these oceanographic data, on Julian day, latitude and longitude, yielded three synthetic variables used as explanatory variables in Generalized Additive Models (GAMs). The first one synthesized most of the variability related to temperature, plankton concentration and longitude. The second one synthesized most of the variability related to surface mixing associated with a seasonal trend. The third one synthesized most of the variability related to salinity and latitude. GAMs revealed a non-linear effect of salinity and latitude on daily catches for all fleets. The effect of mixing was negative for surface gear catches and positive for trawl catches. The trophic and planktonic component had a clear influence only on baitboat and trolling catches. The results are discussed in terms of albacore habitat preferences, vertical distribution and feeding behavior. We suggest that these environmental influences should be considered when using albacore catch data for stock assessment and extrapolating the effects of climate change on albacore abundance in the Bay of Biscay.

Three out of eight albacore (Thunnus alalunga) tagged with pop-up satellite archival tags (PSATs) in the greater Bay of Biscay area of the North East Atlantic were predated as indicated by missing light level data, sudden increases in temperature, and substantial changes in depth profiles. Recorded stomach temperatures and differences between stomach and ambient water temperatures were consistent with shortfin maim (Isurus oxyrinchus) and porbeagle (Lamna nasus) sharks. Vertical behavior in the form of diel migrations, deep dives and extensive periods spent close to the surface during day and night time was again consistent with Lamnid sharks. The observed predation rate was considered to be elevated due to irregular post-release behavior as opposed to symptomatic of natural mortality. (C) 2014 Elsevier B.V. All rights reserved.

The growth equation currently used for Atlantic bluefin tuna, Thunnus thynnus (L.), eastern stock (L-t = 318.85 [1-e(-0.093(t + 0.97))]) is validated using several approaches. The first method involved a comparison of studies with von Bertalanffy parameter estimates in which, different methods for the age estimation are utilized, taking as references the maximum size of this species (L-max = 319.93 +/- 11.3 cm) and the growth equation of the western Atlantic stock (L-t = 314.90 [ 1-e(-0.089(t + 1.13))]). The result of this analysis showed that the growth equation used by ICCAT's Standing Committee on Research and Statistics Atlantic bluefin tuna assessment group for the eastern stock perfectly fits L-max. Second, an analysis was realized from first dorsal spine rings, 578 samples (age groups 0 to 3) of ABFT collected from the Bay of Biscay and the Mediterranean Sea, enabled the interpretation of the wide opaque bands (fast growth), formed during the boreal late spring and completed by autumn (June to November), and the translucent rings (hyaline rings, slow growth), formed during boreal autumn to late spring (November to May-June). In addition, first dorsal spine sections bands of two recovered fish that had carried conventional and electronic archival tags are also consistent. The chronological analysis of the opaque bands and hyaline rings of one fish tagged with an archival tag and recovered in the Bay of Biscay (the first time such a spine had been available for such analysis) revealed that transatlantic migrations may lead to double hyaline ring formation in the spine. Finally, the validation of the ABFT growth equation is made by superimposing tag-recovery data from tagging surveys in the Bay of Biscay, western Mediterranean and western Atlantic (N = 131) and spine readings (N = 299) to the eastern stock ABFT growth equation and analysing residuals. The coefficient of determination (R-2 = 97.98) and the residual's distribution indicated good performance of the model. Although no important differences between the growth model of the eastern stock and that of the western stock are found, in all cases studied, the predictive accuracy indicators are better for the eastern model.

Little research has been focused to date on the juvenile fraction of Atlantic bluefin tuna (Thunnus thynnus, BFT) populations. For instance, although the baitboat CPUE from the Bay of Biscay is used as the only recruitment index for the eastern stock, little is known about the role of this juvenile feeding area within the life cycle of bluefin tuna. This, together with recent changes in the bluefin tuna management context, might jeopardize the usefulness of the CPUEderived index. One objective of the ongoing “Hegalabur 2009” project is to analyze the possibility of using acoustic technologies (long-range sonar and ecoshounder) to get abundance indices of bluefin tuna in the Bay of Biscay. On the other hand, the project aims to understand the role of the Bay of Biscay in the life cycle of BFT, by identifying the origin of the bluefin tuna present in the Bay of Biscay, and the variability of the proportion of individuals of different origins. Acoustic surveys (scientific echosounders and commercial sonars), biological sampling and tagging (conventional and electronic) have been conducted. Some posibilities for developing acoustic indices of abundance are discussed, as well as the perspectives for different analyses (genetics, otolith microchemistry, reproduction, tagging).

The goal of the present study is to analyze the small scale vertical behaviour of juvenile albacore tuna (Thunnus alalunga) in relation to the abundance and distribution of their main prey, which has particular importance regarding catchability by surface fishing gears, such as trolling. A total of six juvenile albacore were tracked in the south east Bay of Biscay in July and August 2005, using ultrasonic transmitters. Two echosounders working at 38 and 120 kHz on the tracking vessel were used to collect data on the biotic environment (krill, small pelagic fish and planktonic layers) between the surface and 200 m depth. These data were echo-integrated in order to relate tuna vertical movements to food availability. The stomach contents of 97 albacore caught during the surveys were analyzed, the comparison of prey occurrences respectively in the stomachs and on the echograms showed selectivity for blue whiting. However, the biotic factors considered in this study had no significant influence on the depth of albacore, which possibly feed during night-time in surface waters. The tracked albacore had a shallow depth distribution and did not exhibit any regular deep-diving behaviour. A significant effect of time of day and body size on albacore depth was shown, all fish remaining deeper during daytime, and smaller fish having a shallower vertical distribution.

Since 2001, AZTI-Tecnalia has conducted opportunistic tagging activities onboard sport fishing vessels operating in the Bay of Biscay. The activities involve training fishermen on tagging methods and promoting tag and release activities within tournaments and during regular fishing trips. In the last six years, the number of fish tagged on this basis has increased exponentially, with 2531 tunas tagged in 2006 (mainly albacore and bluefin, Table 1).

Different stock-recruitment models were fitted to North Atlantic albacore (Thunnus alalunga) recruitment and spawning stock biomass data. A classical density dependence hypothesis, a recent environmental-dependence hypothesis and a combination of both were considered. For the latter case, four stock-environment-recruitment models were used: Ricker, Beverton-Holt, Deriso's General Model (modified to take into account environmental effects) and conditioned Neural Networks. Cross-validation analysis showed that the modified Deriso model had the best predictive capability. It detected an inverse effect of the North Atlantic Oscillation (NAO) on recruitment, a Ricker-type behaviour with density dependent overcompensation when environmental conditions are unfavourable and a Beverton-Holt-type behaviour towards an asymptotic recruitment carrying capacity with favourable environmental conditions. The Neural Network model also detected that under favourable environmental conditions high spawning stock biomass does not necessarily have a depensatory effect on recruitment. Moreover, they suggest that under extremely favourable environmental conditions, albacore recruitment could increase well above the asymptotic carrying capacity predicted by Beverton-Holt-type models. However, the general decrease in spawning stock biomass in recent years and increasing NAO trends suggest that there is low probability of exceptionally large recruitment in the future and instead there is a danger of recruitment overfishing.