The Critical Role of Near-Surface Dynamics in Identifying Spawning Areas of Atlantic Bluefin Tuna in the Gulf of Mexico Authors

The Canary archipelago, which is part of the Atlantic biogeographical region of Macaronesia, provides suitable habitat for tropical and temperate-water large pelagic species. Atlantic bluefin tuna (ABFT) Thunnus thynnus occur year round in the Canary Islands. Life history traits of ABFT, specifically foraging patterns, have not been studied thus far in this region. We investigated ABFT trophic biology, combining stomach content and stable isotope analyses. A high proportion (~77%) of the stomachs contained prey, indicating active foraging. The diet primarily consisted of fishes, among which the snipefish Macroramphosus sp. was the major prey. Cephalopods and crustaceans were less important diet components. Moreover, a well-preserved specimen of Cory’s shearwater Calonectris borealis was found in a stomach sampled in 2018. Besides natural prey, 16.7% of the stomachs contained plastic debris. Inter-annual isotopic differences were detected in liver tissue samples, reflecting a dietary shift in 2018, where δ15N values were lower than in 2016 and 2017. Isotopic niche width estimations from stable isotope Bayesian ellipse in R and kernel utilization density analyses suggested a more diverse diet in 2017. Corrected and Bayesian standard ellipse area values from muscle and liver data indicated that the diet of ABFT in the Canary Islands is more euryphagous than in the Strait of Gibraltar (East Atlantic) but more stenophagous than it is in the Gulf of Saint Lawrence (West Atlantic). The present results show that the Canary archipelago represents a foraging ground for ABFT in spring.

Habitat use, vertical and horizontal behaviour of Atlantic bluefin tuna (Thunnus thynnus) in the Northwestern Mediterranean Sea in relation to oceanographic conditions

Atlantic bluefin tuna Thunnus thynnus (ABFT) is a fish of high market value which has recently become strongly overexploited, notably in the Mediterranean Sea. This area is an essential habitat for ABFT reproduction and growth. We present here an approach for deriving the daily mapping of potential ABFT feeding and spawning habitats based on satellite-derived sea surface temperature (SST) and chl a concentration. The feeding habitat was mainly derived from the simultaneous occurrence of oceanic fronts of temperature and chl a content while the spawn- ing habitat was mostly inferred from the heating of surface waters. Generally, higher chl a con- tents were found to be preferred for the feeding habitat and a minimum SST value was found for the spawning habitat. Both habitats were defined by the presence of relevant oceanographic fea- tures and are therefore potential and functionally-linked habitats. This approach provides, for the first time, a synoptic view of the potential ABFT habitats in the Mediterranean Sea. The model performs well in areas where both satellite data and ABFT observations are available, as 80% of presence data are in the vicinity of potential habitats. The computed monthly, seasonal and annual maps of potential feeding and spawning habitat of ABFT from 2003 to 2009 are in good agreement with current knowledge on ABFT. Overall, the habitat size of ABFT is about 6% of the Medi - terranean Sea surface. The results displayed a strong seasonality in habitat size and locations as well as high year-to-year variations (30 to 60%), particularly for the potential spawning habitat, which is key information for evaluating the utility of ABFT Marine Protected Areas in the Medi - terranean Sea.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 400:245-265 (2010) - DOI: https://doi.org/10.3354/meps08394 Movements and diving behavior of Atlantic bluefin tuna Thunnus thynnus in relation to water column structure in the northwestern Atlantic Gareth L. Lawson1,2,*, Michael R. Castleton1, Barbara A. Block1 1Tuna Research and Conservation Center, Stanford University, Hopkins Marine Station, 120 Oceanview Boulevard, Pacific Grove, California 93950, USA 2Present address: Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA *Email: glawson@whoi.edu ABSTRACT: We analyzed the movements and diving behavior in relation to water column structure of 35 electronically tagged Atlantic bluefin tuna (176 to 240 cm in length at tagging) during their spring–fall period of occupancy of the Gulf of Maine, Canadian Shelf, and neighboring off-shelf waters from 1999 to 2005. Tagged fish arriving in this study region in March–April initially occupied weakly stratified off-shelf waters along the northern Gulf Stream. As waters over the continental shelf warmed in June, the fish shifted onto the shelf. Sea surface temperatures occupied were relatively constant in both off- and on-shelf waters (April–September monthly medians varying from 16.1 to 19.0°C). Dives made in the stratified waters of the shelf during summer and fall were significantly more frequent (up to 180 dives d–1) and fast (descent rates up to 4.1 m s–1) than in weakly stratified off-shelf waters occupied during spring, defining dives as excursions below tag-derived estimates of the surface isothermal layer depth (ILD). The duration and depth of dives also decreased significantly in association with changing water column structure, from medians in off-shelf waters during April of 0.45 h and 77.0 m, respectively, to 0.16 h and 24.9 m in August. Analyses of tag measurements of internal body temperature and feeding proxies suggest that both the horizontal movement of the fish onto the continental shelf and the dives made from the warm surface layer into colder waters at depth represent a balance between the maintenance of preferred ambient temperatures and foraging opportunities. KEY WORDS: Atlantic bluefin tuna · Thunnus thynnus · Electronic tagging · Gulf of Maine · Diving behavior Full text in pdf format Supplementary material PreviousNextCite this article as: Lawson GL, Castleton MR, Block BA (2010) Movements and diving behavior of Atlantic bluefin tuna Thunnus thynnus in relation to water column structure in the northwestern Atlantic. Mar Ecol Prog Ser 400:245-265. https://doi.org/10.3354/meps08394Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 400. Online publication date: February 11, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Simple SummaryThe Atlantic bluefin tuna Thunnus thynnus is a species characterized by complex trans-oceanic migrations linked to size, which rely on the delicate trade-off between somatic growth and reproduction before and during the migratory movements to reach spawning grounds. Therefore, understanding the processes that drive reproduction and elucidating its age-related regulation is essential in the context of sustainable fishery management. In this study, carried out in the Mediterranean Sea, older bluefin tuna females were found to have greater reproductive performances than younger females according to a molecular biology approach (i.e., gene expression), a result that likely mirrors a better physical condition, different habitat usage or migratory behaviour. This result highlights the importance of preserving large females for their major reproductive contribution at a stock level. Furthermore, the gonad-specific mir-202, which belongs to a class of non-coding RNA, called miRNA, that regulate the post-transcription of protein-coding genes, was identified as a potential candidate to play a role in egg quality and quantity (i.e., fecundity) during ovarian maturation through age- or stage-dependent reproductive processes. Overall, the present study contributes to improve the sustainability of the Atlantic bluefin tuna fishery in the Mediterranean Sea.In the Mediterranean Sea, a demographic substructure of the Atlantic bluefin tuna Thunnus thynnus has emerged over the last decade, with old and young individuals exhibiting different horizontal movements and spatial–temporal patterns of gonad maturation. In the present study, histology and molecular reproductive markers were integrated with the gonad-specific mir-202 gene expression and ovarian localization to provide a comprehensive picture of the reproductive performances in young and old females and investigate the role played by the mir-202 during gonadal maturation. During the reproductive period, old females (>100 kg; 194.6 ± 33.9 cm straight fork length; 11.3 ± 2.7 years old) were found to have greater reproductive performances than younger females (<80 kg; 139.3 ± 18.8 cm straight fork length; 8.4 ± 1.1 years old) according to gene expression results, suggesting a prolonged spawning season, earlier arrival on spawning grounds and/or better condition in older females. The mir-202-5p showed no global changes; it was abundantly expressed in granulosa cells and faintly present in the ooplasm. On the other hand, the mir-202-3p expression profile reflected levels of oocyte maturation molecular markers (star, lhr) and both histological and molecular (casp3) levels of follicular atresia. Overall, old females exhibited greater reproductive performances than younger females, likely reflecting different reproductive dynamics linked to the physical condition, habitat usage and migratory behaviour. These results highlight the importance of preserving large and old females in the context of fishery management. Finally, the mir-202 appears to be a good candidate to regulate the reproductive output of this species in an autocrine/paracrine manner through either stage- or age-dependent processes.

The Atlantic bluefin tuna is an ecologically and commercially important species, acting as an apex predator and supporting a valuable fishery. Current management of the western stock of this species recognizes the Slope Sea off the Northeast USA as a spawning site, albeit one of unknown persistence and importance, supporting the need for studies into the use of this region by spawning adults as well as larval behavior and success. Stable isotope analysis using tissues of Atlantic bluefin tuna larvae captured in the Slope Sea was performed to measure δ¹³C, δ¹⁵N, and the C:N content ratio. The Slope Sea larvae were found to have a significantly more enriched δ¹³C signature compared to their Mediterranean Sea and Gulf of Mexico counterparts based on prior literature. Their δ¹⁵N, an indicator of trophic position, overlapped with Atlantic bluefin tuna larvae of the Mediterranean Sea and eastern Gulf of Mexico, but was significantly more enriched than those in the western Gulf of Mexico. The C:N ratio of the Slope Sea larvae indicates a healthy body condition. A secondary ion mass spectrometer (SIMS) ion microprobe approach was used to measure δ¹⁸O signatures in the otoliths of Atlantic bluefin tuna larvae from the Slope Sea, Gulf of Mexico, and Mediterranean Sea. This is the first study that uses SIMS ion microprobe technology to analyze larval otoliths of any species. Using this method, it was determined that the variable conditions of the Slope Sea result in a wide range of δ¹⁸O otolith signatures that both overlap with the Gulf of Mexico larvae and also include more depleted δ¹⁸O signatures. Otoliths from five adult specimens captured in the Gulf of Maine were analyzed using the same SIMS ion microprobe method to generate a δ¹⁸O transect from core to edge. This provides a temperature and salinity-based map of their migratory history from spawning to capture. This study found that western adults frequent the Slope Sea region during the summer while aged three to five years. The results of this work provide justification for more extensive development of spawning site baselines and additional analyses of adult Atlantic bluefin tuna to improve understanding of stock structure. The methods outlined can be a useful tool for the same applications in other fisheries.

In recent decades, abundance, spatial distribution, and physical condition of Atlantic bluefin tuna Thunnus thynnus (ABFT) have shifted, in part due to changes in the composition, distribution, and condition of available prey. Dietary studies conducted in the Gulf of Maine (GOM) over the past 30 yr have identified lipid-rich Atlantic herring Clupea harengus (‘herring’) as the primary ABFT prey, but recent stock assessments indicate poor spawning stock biomass and recruitment. Given these declines in abundance, we hypothesized that ABFT diet dominance would shift to an alternative, more abundant prey. Stomach content analysis from 379 ABFT collected in the GOM in 2018 and 2019 showed a reduced reliance on herring and an increased consumption of northern shortfin squid Illex illecebrosus, the dominant prey in frequency of occurrence (56.3%) and weight (23.0%). Atlantic mackerel Scomber scombrus was a secondary prey with similar presence (35.7%) in stomach samples as herring (23.5%). Other clupeids, such as Atlantic menhaden Brevoortia tyrannus, alewives Alosa pseudoharengus, and blueback herring A. aestivalis, were more prevalent relative to previous studies, with menhaden and northern shortfin squid co-dominating the primary prey in 2019. ABFT condition increased seasonally in the GOM and was significantly greater than in ABFT from neighboring foraging habitats where herring were the dominant prey. Our results document a historic diet shift on primary seasonal foraging grounds and suggest that continued monitoring of ABFT diet and prey energetics are essential to understanding future ABFT presence and condition in the GOM.

To examine habitat use in Atlantic bluefin tuna Thunnus thynnus, we used time series records from 20 archival tags and 7 pop-up satellite archival tags. Daily vertical profiles were classified into 3 dive types: (1) profiles restricted to surface waters by either bathymetry or thermal constraints; (2) profiles with frequent V-shaped dives that may be associated with transiting or searching behaviors; and (3) U-shaped profiles associated with putative foraging behavior. Fixed kernel probability contours were calculated for each of the dive profile classes. Key potential North Atlantic foraging habitats were identified in the NW Atlantic (Gulf of Maine/Scotian Shelf, Grand Banks and Flemish Cap), off Florida and the Bahamas and in the NE Atlantic. These ‘hotspot’ regions encompass areas of high seas that may be important to future conservation and management of the species. U-shaped dive profiles were shallower and surface returns were more frequent in areas where subsurface temperatures were coldest. The presence of Atlantic bluefin tuna coincided with peak productivity and sea surface temperatures in 3 of the 5 hotspot areas. Further analyses examined spatial and temporal patterns of transatlantic migrations and deep diving behavior in the Strait of Gibraltar.

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 2:239-252 (2012) - DOI: https://doi.org/10.3354/aei00042 Spatial and temporal extension of wild fish aggregations at Sparus aurata and Thunnus thynnus farms in the north-western Mediterranean Kathrin Bacher1,*, Ana Gordoa1, Oscar Sagué2 1Centro de Estudios Avanzados de Blanes (CEAB-CSIC), 17300 Blanes, Spain 2Federació Catalana d’Activitats Subaquàtiques, 08930 Sant Adrià del Besòs, Spain *Email: kbacher@ceab.csic.es ABSTRACT: Fish farms cause wild fish to aggregate nearby and thus act to modify their distribution, but the spatial and temporal extent of the attraction effect around farms is still poorly understood. We examined attraction using an integrated approach combining 3 factors: spatial extent, depth and season. We analysed an Atlantic bluefin tuna Thunnus thynnus (ABT) and a gilthead seabream Sparus aurata (SB) farm off the north-eastern coast of Spain which represent different fish farming models in the Mediterranean. Underwater visual counts were conducted from summer 2010 to spring 2011. We recorded 39 species at the SB farm and 17 species at the ABT farm. The analysis of fish abundance and biomass at 3 stations located along a distance gradient from the farm (SB: 0, 30, 200 m; ABT: 0, 100, 200 m) showed significantly higher values next to the cages than at more distant stations, revealing that the spatial extent of the attraction effect was mainly restricted to the cage rather than following a gradient. The intensity of the cage effect varied according to farm, season and depth, reflecting species-specific behaviours. At the SB farm, the cage effect persisted year round, varying with depth, whereas at the ABT farm, the effect was only detected in summer and spring. These distinct spatial and temporal aggregation patterns suggest that implementation of fishery regulatory measures to protect wild fish should be farm-specific. This study emphasizes the importance of using an integrated approach to study wild fish aggregations at farms. KEY WORDS: Sea-cage . Aquaculture . Wild fish . Attraction effect . Sparus aurata . Thunnus thynnus . Mediterranean Full text in pdf format PreviousNextCite this article as: Bacher K, Gordoa A, Sagué O (2012) Spatial and temporal extension of wild fish aggregations at Sparus aurata and Thunnus thynnus farms in the north-western Mediterranean. Aquacult Environ Interact 2:239-252. https://doi.org/10.3354/aei00042 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 2, No. 3. Online publication date: June 25, 2012 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2012 Inter-Research.

A combination of stomach contents, nitrogen stable-isotope and tissue C:N values are presented to demonstrate feeding activity of Atlantic bluefin tuna Thunnus thynnus on the Gulf of Mexico (GOMEX) spawning grounds. Diets include teleosts, cephalopods, crustaceans and a pelagic tunicate (Pyrosoma atlanticum). Results reveal the need to classify the GOMEX as a T. thynnus feeding ground.

Increased liver apoptosis and tumor necrosis factor expression in Atlantic bluefin tuna (Thunnus thynnus) reared in the northern Adriatic Sea

Effects of age on growth in Atlantic bluefin tuna (Thunnus thynnus)

Pelagic fish have historically been a challenge to study because of their large size and highly migratory movements. Previous technological limitations have recently been overcome using archival and pop-off satellite tags, enabling studies of long-term movements, oceanographic preferences and behaviors. Archival tags record information on depth, ambient and internal temperatures, and light levels. Their major advantage lies in the extensive detail of this information and the ability to extract geolocation and oceanographic information in addition to biological data. We have deployed 279 archival tags in Atlantic bluefin tuna (Thunnus thynnus thynnus) in the western North Atlantic. To date, 40 of these have been reported as recaptured from both the western Atlantic and the Mediterranean Sea. Detailed records up to 3.6 years in length have been obtained demonstrating that Atlantic bluefin prefer the top 200 m of the water column and spend more than half their time in the upper 40 m. Atlantic bluefin maintain a high internal body temperature despite encountering a wide range of ambient temperatures (2–30°C). Patterns of feeding behavior have emerged providing data on how often and when fish feed at sea. Geolocation estimates for electronic tagged western Atlantic bluefin derived from archival and pop-up satellite archival tags indicate these bluefin show visitation and aggregation in New England, Carolina, the Gulf of Mexico as well as the Mediterranean. Pop-up satellite tags have been deployed on 120 west Atlantic bluefin tuna. Ninety percent of the pop-up tags scheduled to transmit have delivered data or position information on time. Both types of electronic tag data can be combined with oceanographic data to reveal a complete picture of how and where these fish forage in the pelagic realm.

Objective The Atlantic Bluefin Tuna Thunnus thynnus is a highly migratory, internationally managed species whose stock structure and dynamic life history are challenging to capture in scientific advice for management. The large measurement and process uncertainty generated by Atlantic Bluefin Tuna stock identification using stable isotope chemistry, the central method of individual stock identification for the stock assessment, suggests that a more thorough examination of the methodology is needed. The Gulf of Maine, United States, is a key commercial fishing area where substantial mixing occurs between two Atlantic Bluefin Tuna stocks. The goal of this study was to determine the influence of alternative stable isotope baselines (adults and yearlings) and different random forest input parameters and decision thresholds on the stock assignment of Atlantic Bluefin Tuna caught in the Gulf of Maine. Methods Using different stable isotope baselines, random forest modeling was used to explore the impact of sample baseline assumptions, training–test set proportions, and probability thresholds on stock identification in the Gulf of Maine. Baseline-to-baseline classification was conducted to examine the alignment between presupposed and predicted identities. Results Baseline-to-baseline classification revealed that when samples from one baseline were treated as unknown and reclassified using a random forest model trained on another baseline, the assigned stock identities differed from their original classifications. Additionally, baseline choice and model specifications altered classification performance metrics, thus affecting the perceived mixing proportions and age structure in the Gulf of Maine. Conclusions Critical examination of baselines and establishment of robust approaches for addressing new baselines are necessary because their inclusion has the potential to influence stock perceptions in areas of significant fishing pressure and stock mixing.

In the present work, we assembled and characterized a de novo larval transcriptome of the Atlantic bluefin tuna Thunnus thynnus by taking advantage of publicly available databases with the goal of better understanding its larval development. The assembled transcriptome comprised 37,117 protein-coding transcripts, of which 13,633 full-length (>80% coverage), with an Ex90N50 of 3061bp and 76% of complete and single-copy core vertebrate genes orthologues. Of these transcripts, 34,980 had a hit against the EggNOG database and 14,983 with the KEGG database. Codon usage bias was identified in processes such as translation and muscle development. By comparing our data with a set of representative fish species, 87.1% of tuna transcripts were included in orthogroups with other species and 5.1% in assembly-specific orthogroups, which were enriched in terms related to muscle and bone development, visual system and ion transport. Following this comparative approach, protein families related to myosin, extracellular matrix and immune system resulted significantly expanded in the Atlantic bluefin tuna. Altogether, these results provide a glimpse of how the Atlantic bluefin tuna might have achieved early physical advantages over competing species in the pelagic environment. The information generated lays the foundation for future research on the more detailed exploration of physiological responses at the molecular level in different larval stages and paves the way to evolutionary studies on the Atlantic bluefin tuna.