Tuna Larvae Research Articles

Navigating large scale ocean science in a Pacific small island developing state

Context In pursuit of protecting 30% of the ocean by 2030, large scale marine protected areas (LSMPAs) are rapidly increasing, especially in small island developing states (SIDS). Many SIDS have limited offshore research expertise or capacity to evaluate the efficacy of LSMPAs. The offshore Palau National Marine Sanctuary (PNMS) necessitated the Republic of Palau to develop its offshore research ability aimed at supporting science-based management. Owing to Palau’s important tuna fishery, investigating tuna reproductive biology in the PNMS was prioritized as a first step in evaluating the protective significance of the PNMS for tuna. Aims The aim of this study was to develop a useful and practical platform to conduct large scale ocean research within the context of SIDS. Methods A platform to conduct offshore research was developed. Reproductive histology and the presence and abundance of larvae were used to investigate tuna reproductive biology in the PNMS. Key results Most tunas sampled were mature, with 3 of the 59 sampled fish actively spawning. Twenty-two tuna larvae were collected across five offshore sites, and modeling results suggest larvae originated from these sites. Conclusions Findings suggest tuna spawn, to some extent, within the PNMS, and the PNMS provides local protection to tuna populations during this time. A research platform with five steps for developing, undertaking and understanding offshore research in SIDS was developed. Challenges and tips experienced are also detailed. Implications This platform can support the ever-increasing demand for offshore research in small island, large ocean states with limited resources and expertise.

Docosahexaenoic acid (DHA) is a driving force regulating gene expression in bluefin tuna (Thunnus thynnus) larvae development

This study elucidated the role of DHA-modulated genes in the development and growth of Atlantic bluefin tuna (Thunnus thynnus) larvae ingesting increasing levels of DHA in their rotifer prey. The effect of feeding low, medium, and high rotifer (Brachionus rotundiformis) DHA levels (2.0, 3.6 and 10.9 mg DHA g−1 DW, respectively) was tested on 2–15 days post hatching (dph) bluefin tuna larvae. Larval DHA content markedly (P < 0.05) increased in a DHA dose-dependent manner (1.5, 3.9, 6.1 mg DHA g−1 DW larva, respectively), that was positively correlated with larval prey consumption and growth (P < 0.05). Gene ontology enrichment analyses of differentially expressed genes (DEGs) demonstrated dietary DHA significantly (P < 0.05) affected different genes and biological processes at different developmental ages. The number of DHA up-regulated DEGs was highest in 10 dph larvae (491), compared to 5 (12) and 15 dph fish (34), and were mainly involved in neural and synaptic development in the brain and spinal cord. In contrast, DHA in older 15 dph larvae elicited fewer DEGs but played critical roles over a wider range of developing organs. The emerging picture underscores the importance of DHA-modulated gene expression as a driving force in bluefin tuna larval development and growth.

Bluefin tuna sperm production is hastened by surrogacy in small Euthynnus

Pacific bluefin tuna (Thunnus orientalis) remains heavily depleted due to overexploitation. Aquaculture and stock enhancement based on artificial seedlings could be effective solutions to this problem. However, widespread adoption of seedling production is limited because spawning in captivity of bluefin tuna, a large pelagic top predator, requires much space, time, cost, and labour. To downsize and shorten their generation time, here, we show that xenogeneic germ cell transplantation enables a surrogate production of functional bluefin tuna sperm in hybrid little tuna (genus: Euthynnus), which attain sexual maturity at a smaller body size and shorter time. Intraperitonially transplanted bluefin tuna germ cells migrate towards and are incorporated into the gonads of little tuna larvae. These recipients produce functional donor-derived bluefin tuna sperm at a mere 8 months of age and 1 kg of body size. This result represents an advance toward compact, low-cost, and time-efficient seedling production that will improve the efficiency of bluefin tuna aquaculture.

Perkembangan Morfologi dan Tingkah Laku Larva Ikan Tuna Sirip Kuning Yellowfin Tuna (Thunnus albacares)

The yellowfin tuna (Thunnus albacares) is a pelagic fish with distinct morphological development and behavioral traits. Understanding the early stages of morphology and behavior in yellowfin tuna larvae is crucial for successful cultivation efforts, particularly during the hatchery phase. This study aimed to observe and document the developmental progression and behaviors of yellowfin tuna larvae at the Tuna Laboratory of Balai Besar Riset Budidaya Laut and Penyuluhan Perikanan Gondol, Bali. Yellowfin tuna larvae were reared in 700 L round tanks at a density of 10,000 larvae per tank. Larval rearing was monitored over a period of 13 days, specifically on days 1 (D1), 3 (D3), 5 (D5), 7 (D7), 10 (D10) and 13 (D13) post-hatching. Morphological changes in the larvae were observed over time. On day 1, the larvae were transparent and planktonic, with closed mouths and eyes and the presence of melanophore pigments in their bodies. By day 3, the larvae had opened their mouths and eyes, becoming capable of feeding. The mouth opening measured between 0.34-0.68 mm (90°) and 0.18-0.37 mm (45°) on day 5 post-hatching. As the larvae grew, improvements in swimming ability were noted, correlating with the development of the swim bladder, tail fin, and dorsal fin.

Effects of triploidization on light sensitivity in larval stage of Pacific bluefin tuna Thunnus orientalis.

Triploidization influences various biological characteristics of fish, which is associated with reductions in the number of multiple cell types in different tissues/organs. Our behavioral analyses revealed that triploid Pacific bluefin tuna (Thunnus orientalis) larvae exhibit lower sensitivity to light compared to diploids. Furthermore, histological analyses revealed a reduction in the number of ganglion cells and an increase in their size in the retinas of triploid T. orientalis larvae. Our findings provide the first evidence indicating that triploidization reduces sensory perception during the larval stage of fish.

Maternal Effects and Trophodynamics Drive Interannual Larval Growth Variability of Atlantic Bluefin Tuna (Thunnus thynnus) from the Gulf of Mexico.

Two cohorts of Atlantic bluefin tuna (Thunnus thynnus) larvae were sampled in 2017 and 2018 during the peak of spawning in the Gulf of Mexico (GOM). We examined environmental variables, daily growth, otolith biometry and stable isotopes and found that the GOM18 cohort grew at faster rates, with larger and wider otoliths. Inter and intra-population analyses (deficient vs. optimal growth groups) were carried out for pre- and post-flexion developmental stages to determine maternal and trophodynamic influences on larval growth variability based on larval isotopic signatures, trophic niche sizes and their overlaps. For the pre-flexion stages in both years, the optimal growth groups had significantly lower δ15N, implying a direct relationship between growth potential and maternal inheritance. Optimal growth groups and stages for both years showed lower C:N ratios, reflecting a greater energy investment in growth. The results of this study illustrate the interannual transgenerational trophic plasticity of a spawning stock and its linkages to growth potential of their offsprings in the GOM.

The effect of continuous lighting on the rearing of yellowfin tuna (Thunnus albacares) larvae

Yellowfin tuna (Thunnus albacares) has important economic value in the world market. This study aims to determine the effect of continuous lighting on survival, growth, stomach contents, and histology of the eye of larvae. Larval rearing was conducted on 6 concrete tanks with 60 m3 in volume that support the water circulation and aeration system with an initial stocking of 20 eggs/liter. The treatments tested were A: Larval rearing by a 40-watt fluorescent lamp (TL) which was positioned 1 m above the surface of the water surface for 24 hours and B: Without lights (control). Each treatment used 3 repetitions and data analysis with a t-test. The parameters observed were larval survival and growth stomach content and eyes histology. The results showed that the rearing of larvae in treatment B can with a survival of 0.26±0.0231% and a final total length of 3 6.2 ± 7.3 mm which is significantly higher (P<0.05) compared to treatment A (0.10±0.057% and 24.3 ± 5.5 mm). From the observation of stomach contents at night in treatment B still eats rotifers while in treatment A stomach is empty. The inner nuclear layer cell arrangement of larval eyes is more tenuous than control. From these results, it can be concluded that the provision of continuous lighting treatment can improve the survival, growth, stomach content, and vision ability of larvae.

The effect of ocean acidification on otolith morphology in larvae of a tropical, epipelagic fish species, yellowfin tuna (Thunnus albacares)

Increasing ocean acidification is a concern due to its potential effects on the growth, development, and survival of early life stages of tuna in oceanic habitats and on the spatial extent of their suitable nursery habitat. To investigate the potential effects of increasing CO2 on otolith calcification of 9-day old pre-flexion stage yellowfin tuna (Thunnus albacares), an experiment was conducted at the Inter-American Tropical Tuna Commission's Achotines Laboratory in Panama during 2011. Fertilized eggs and larvae were exposed to mean pCO2 levels that ranged from present day (355 μatm) to two levels predicted to occur in some areas of the Pacific in the near future (2013 and 3321 μatm), and to an extreme value equivalent to long-term projections for 300 years in the future (9624 μatm). The results indicated significantly larger otoliths (in area and perimeter) with significant, and increasing, fluctuating asymmetry at acidification levels similar to those projected for the near future and long-term. Otoliths increased significantly in size despite a significant decrease in somatic length with increasing pCO2. A consistent correlation between otolith and somatic growth of yellowfin tuna larvae among treatments was evident (i.e., larger otoliths were still associated with larger larvae within a treatment). The observed changes in otolith morphology with increasing ocean acidification have the potential to indirectly affect larval survival through dysfunction of the mechanosensory organs, but this remains to be verified in yellowfin tuna larvae.

Evidence of isotopic maternal transmission influence on bluefin tuna (Thunnus thynnus) larval growth

Pre-flexion stages of Atlantic bluefin tuna (Thunnus thynnus) larvae were collected in 2014 during the peak of spawning in the two main spawning areas: Gulf of Mexico (GOM) and Mediterranean Sea (MED). We examined daily growth, otolith biometry, and stable isotopes and found that the GOM grew at a faster rate, had larger otoliths, wider daily increments, and significantly lower values of δ15N when compared to the MED. In addition, an intra-population comparative analysis between slow- and fast-growing individuals (deficient vs. optimal growth groups, respectively) showed that optimal growth groups had significantly lower δ15N within each spawning area, implying a direct relationship between growth potential, development, and maternal transmission of isotopic signatures. A third pre-flexion larval group that was aquaculture-reared also exhibited the same pattern to the wild larval groups. In addition, for the first time, we estimated the maternal trophic niches using models developed with field-captured pre-flexion larvae. The estimated maternal trophic niches for the GOM were narrower than the MED, implying differences in the maternal trophodynamics from each nursery area. Overall, the inter-population (GOM vs. MED) and intra-population growth groups (deficient vs. optimal) grew faster and had narrower maternal niches. This study shows the advantages that larval SIA research can aid in the understanding of the trophodynamics of their breeders by examining the trophic relationship of a spawning stock jointly with the development of growth potential in offspring within the same breeding season.

High throughput identification of tuna (Thunnus spp.) larvae in the Gulf of Mexico using unlabeled-probe high-resolution melting analysis (UP-HRMA).

The genus Thunnus (family Scombridae) comprises eight species of tunas of which all but one are targeted by industrialized fisheries. While intact individuals of these species can be distinguished by morphological characteristics, researchers and managers often rely on dressed, frozen, juvenile, or larval fish samples which often necessitates molecular species identification. Here we investigate short amplicon (SA) and unlabeled probe (UP) high-resolution melting analysis (HRMA) as a low-cost, high-throughput molecular genotyping assay capable of distinguishing between albacore tuna (T. alalunga), blackfin tuna (T. atlanticus), bigeye tuna (T. obesus), Atlantic bluefin tuna (T. thynnus), and yellowfin tuna (T. albacares) in the Gulf of Mexico. While SA-HRMA of variable regions in the NADH dehydrogenase subunit 4 (ND4) and subunit 5 (ND5), and subunit 6 (ND6) of the mitochondrial DNA (mtDNA) genome did yield some species-specific diagnostic melting curves (ex. ND4 assay can reliably distinguish Atlantic bluefin tuna) genotype masking produced excessive variation in melting curves for reliable multi-species identification. To minimize the genotyping masking of SA-HRMA a 26 base pair long UP containing four SNPs was developed within a 133 bp segment of ND4. The UP-HRMA is able to reliably distinguish Gulf of Mexico species T. thynnus, T. obesus, T. albacares, and T. atlanticus by UP melting temperature at 67°C, 62°C, 59°C, and 57°C respectively. The developed UP-HRMA assay is a lower-cost, higher-throughput, alternative to previously published molecular assays for tuna identification that can be easily automated for large data sets including ichthyological larval surveys, fisheries specimens lacking distinguishing morphological characteristics, or detection of fraudulent trading of tuna species.

Molecular Antioxidant Functions are Enhanced in Atlantic Bluefin Tuna (Thunnus Thynnus, L.) Larvae Fed Selenium-Enriched Rotifers Brachionus Rotundiformis.

Selenium (Se) is an essential trace element for fish with more than 40 selenoproteins identified, many exhibiting antioxidant functions. This study investigated the effect of dietary Se supplementation on physiological parameters, selenoprotein and antioxidant enzyme gene expression in Atlantic bluefin tuna (ABT, Thunnus thynnus) larvae. First-feeding ABT larvae were divided into triplicate groups and fed rotifers Brachionus rotundiformis enriched with five different levels of Se (0, 3, 10, 30, and 100 µg Se·L-1) until 14 days after hatching. Both rotifers and ABT larvae effectively accumulated Se achieving maximum levels in the Se100 treatment (30.05 μg Se·g-1 and 194 ± 38 μg Se·g-1 dry mass, respectively). Larvae showed highest total length when fed Se3 rotifers, whereas flexion index was highest in larvae fed Se10. Selenium supplementation increased the gene expression of selenoproteins gpx1, msrb1, trxr2, selenom, selenop, and selenoe compared to the non-supplemented control (Se0), but only marginal differences were detected between supplementation levels. In contrast, expression of the antioxidant enzymes cat and sod1 were lowest in larvae fed Se100. To conclude, non-Se-enriched rotifers may be suboptimal for first feeding ABT larvae, which showed improved selenoprotein and antioxidant gene expression when fed a diet containing 4.42 μg Se·g-1 dry mass.

Succession of the intestinal bacterial community in Pacific bluefin tuna (Thunnus orientalis) larvae.

We investigated the succession process of intestinal bacteria during seed production in full-cycle aquaculture of Pacific bluefin tuna (Thunnus orientalis). During the seed production, eggs, healthy fish, rearing water, and feeds from three experimental rounds in 2012 and 2013 were collected before transferring to offshore net cages and subjected to a fragment analysis of the bacterial community structure. We identified a clear succession of intestinal bacteria in bluefin tuna during seed production. While community structures of intestinal bacteria in the early stage of larvae were relatively similar to those of rearing water and feed, the bacterial community structures seen 17 days after hatching were different. Moreover, although intestinal bacteria in the late stage of larvae were less diverse than those in the early stage of larvae, the specific bacteria were predominant, suggesting that the developed intestinal environment of the host puts selection pressure on the bacteria in the late stage. The specific bacteria in the late stage of larvae, which likely composed 'core microbiota', were also found on the egg surface. The present study highlights that proper management of the seed production process, including the preparation of rearing water, feeds, and fish eggs, is important for the aquaculture of healthy fish.

Bluefin Larvae in Oligotrophic Ocean Foodwebs, investigations of nutrients to zooplankton: overview of the BLOOFINZ-Gulf of Mexico program

Abstract Western Atlantic bluefin tuna (ABT) undertake long-distance migrations from rich feeding grounds in the North Atlantic to spawn in oligotrophic waters of the Gulf of Mexico (GoM). Stock recruitment is strongly affected by interannual variability in the physical features associated with ABT larvae, but the nutrient sources and food-web structure of preferred habitat, the edges of anticyclonic loop eddies, are unknown. Here, we describe the goals, physical context, design and major findings of an end-to-end process study conducted during peak ABT spawning in May 2017 and 2018. Mesoscale features in the oceanic GoM were surveyed for larvae, and five multi-day Lagrangian experiments measured hydrography and nutrients; plankton biomass and composition from bacteria to zooplankton and fish larvae; phytoplankton nutrient uptake, productivity and taxon-specific growth rates; micro- and mesozooplankton grazing; particle export; and ABT larval feeding and growth rates. We provide a general introduction to the BLOOFINZ-GoM project (Bluefin tuna Larvae in Oligotrophic Ocean Foodwebs, Investigation of Nitrogen to Zooplankton) and highlight the finding, based on backtracking of experimental waters to their positions weeks earlier, that lateral transport from the continental slope region may be more of a key determinant of available habitat utilized by larvae than eddy edges per se.

Survival of Atlantic bluefin tuna (Thunnus thynnus) larvae hatched at different salinity and pH conditions

In this study, we assessed the effect of environmental salinity and pH as independent factors on larval survival of Atlantic bluefin tuna (ABFT –Thunnus thynnus) together with their whole-body Na+/K+-ATPase and v-type H+-ATPase activities. Fertilized eggs of ABFT were obtained from a spontaneous spawning of broodstock in the farming facilities at El Gorguel (Cartagena, SE Spain) and were transferred to facilities of the Spanish Institute of Oceanography (IEO) in Mazarrón (SE Spain). In a first experiment, eggs (200 fertilized eggs L−1 per treatment, in 3 replicates) were exposed to different salinities treatments and constant pH 8.0 (control) until hatch was completed (50 h post-fertilization, hpf, at 23 °C): 27, 30, 33, 36, 37, 38 (control), 39, 40, 43, 46 and 49 ppt. In a second experiment eggs (200 fertilized eggs L−1, in 3 replicates) were exposed to seawater salinity (SW: 38 ppt) and four reduced pH treatments until hatch was completed (50 hpf at 23 °C): 8.0 (control), 7.7, 7.5 and 7.3. An inverse “U-shaped” relationship was observed between environmental salinity and number of hatched larvae. An opposite pattern was observed for both Na+/K+-ATPase and H+-ATPase activities in hatched larvae, increasing both activities in groups exposed to extreme salinities. Thus, larval survival was higher at intermediate salinities and lower at the extreme salinities tested. These results suggest higher survival rates with lower active pumps activities. No significant differences in larval survival were observed with pH treatment, but lower H+-ATPase activity was detected at control environmental pH (pH 8.0). Survival results are discussed in terms of osmoregulatory cost adapting to a salinity and pH predicted for the near future scenarios.

Small fish eat smaller fish: A model of interaction strength in early life stages of two tuna species

AbstractFish larvae are rarely a major driver of fish mortality, but tunas can produce large batches of larvae that rapidly develop the capacity to kill other fish. We combine a model for the killing potential from Atlantic bluefin tuna (BFT) larvae on larval albacore (ALB) with field observations at a major spawning ground. Both species spawn from June to August, but BFT has a narrow spawning peak at the beginning of the season that results in priority effects. Our model shows that, following a recent stock recovery, BFT larvae have increased their killing pressure, leaving areas of up to 1000 km2 with &lt; 1% chance of ALB daily survival. Such increase in killing pressure suggests larval ALB has reduced chances to survive; yet in large areas with few BFT, other drivers of early survival prevail over BFT predation. This shows that strong predatory interactions can occur during larval stages in some fishes.

Environmental Conditions along Tuna Larval Dispersion: Insights on the Spawning Habitat and Impact on Their Development Stages

Estimated larval backward trajectories of three Tuna species, namely, Atlantic Bluefin Tuna (Thunnus thynnus, Linnaeus, 1758), Bullet Tuna (Auxis Rochei, Risso, 1801) and Albacore Tuna (Thunnus alalunga, Bonnaterre, 1788) in the central Mediterranean Sea, were used to characterize their spawning habitats, and to assess the impact of changes due to the major environmental parameters (i.e., sea surface temperature and chlorophyll-a concentration) on larval development during their advection by surface currents. We assumed that the environmental variability experienced by larvae along their paths may have influenced their development, also affecting their survival. Our results showed that the Tuna larvae underwent an accelerated growth in favorable environmental conditions, impacting on the notochord development. In addition, further updated information on spawning and larval retention habitats of Atlantic Bluefin Tuna, Bullet and Albacore Tunas in the central Mediterranean Sea were delivered.

Similarities of distributions and feeding habits between Bullet tuna, Auxis rochei, and Pacific bluefin tuna, Thunnus orientalis, larvae in the southern Sea of Japan

Bullet tuna (Auxis rochei: BT) larvae and juveniles are found during summer in the Sea of Japan, where those of Pacific bluefin tuna (Thunnus orientalis: PBF) also occur. However, the ecology of BT larvae and their interactions with the PBF larvae are both unclear. To identify the differences in the spatial distributions and feeding habits between BT and PBF larvae at the larval stages, they were evaluated in the Sea of Japan during the summer. The distributions were assessed using generalized additive models (GAMs) in 2016, 2017, and 2018, and the feeding habits of both species were investigated using a metagenetic technique in 2017 and a morphological technique in 2017 and 2018. The BT and PBF larvae were the only members of the family Scombridae found during the study. The GAMs indicated that BT larvae occur in warm water (>24.3 °C), and PBF larvae are found at similar temperatures (>23.5 °C). BT larvae occurred in more saline conditions than PBF larvae. The ecological niche breadth was estimated with a diversity of environments at which the target species are present, and that of BT was estimated to be greater than that of PBF. Morphologically identified gut contents of BT larvae consisted mainly of copepods and cladocerans, and appendicularians, with sagitta being added to this list through metagenetic identification, and the PBF larvae had the same prey. The breadth of the feeding niche, the diversity of the feeding contents, of the BT larvae were wider than those of the PBF, and their feeding niches highly overlapped. The number of different species in the gut of BT larva was significantly lower than that in PBF larva, suggesting feeding behavior of PBF larvae is superior to that of BT larvae. These results show that PBF larvae are the competitors of BT larvae and may have a competitive advantage; however, environmental characteristics that are unique to the BT larvae are present. These interspecies interactions keep the coexistence of BT and PBF at the juvenile period in the Sea of Japan.

Atlantic bluefin tuna spawn early to avoid metabolic meltdown in larvae.

To predict shifts in phenology and distribution of organisms we need to understand how survival through early life stages depends on environmental conditions. Here, we present a mechanistic model of development, feeding and bioenergetics of early life stages in bluefin tuna and predict the optimal time of the year for them to be born. We find that the availability of prey, particularly nauplii, is sufficient for fast growth in tuna larvae while temperature is moderate during midsummer, but not when temperatures increase later in summer. High temperatures benefit egg and yolk-sac stages, but the metabolic needs of feeding larvae are hard to sustain during the warmest periods. Heatwaves, such as the one in 2003, increase larval survival potential, but shorten the viable part of the season for the larvae. Atlantic bluefin tuna is a large, highly migratory marine top predator that spawns while temperatures are rising, but before the heat leads to a metabolic meltdown in larvae. This means that food resources modulate how temperature change shifts optimal phenology.

Support for the Slope Sea as a major spawning ground for Atlantic bluefin tuna: evidence from larval abundance, growth rates, and particle-tracking simulations

Atlantic bluefin tuna (Thunnus thynnus) are commercially and ecologically valuable, but management is complicated by their highly migratory lifestyle. Recent collections of bluefin tuna larvae in the Slope Sea off northeastern United States have opened questions about how this region contributes to population dynamics. We analyzed larvae collected in the Slope Sea and the Gulf of Mexico in 2016 to estimate larval abundance and growth rates and used a high-resolution regional ocean circulation model to estimate spawning locations and larval transport. We did not detect a regional difference in growth rates, but found that Slope Sea larvae were larger than Gulf of Mexico larvae prior to exogenous feeding. Slope Sea larvae generally backtracked to locations north of Cape Hatteras and would have been retained within the Slope Sea until the early juvenile stage. Overall, our results provide supporting evidence that the Slope Sea is a major spawning ground that is likely to be important for population dynamics. Further study of larvae and spawning adults in the region should be prioritized to support management decisions.

Unveiling the Relationship Between Sea Surface Hydrographic Patterns and Tuna Larval Distribution in the Central Mediterranean Sea

Thunnus thynnus (Atlantic bluefin tuna, ABT) and other tuna species reproduce in the Mediterranean Sea during the summer period. Despite the Central Mediterranean Sea, the Strait of Sicily in particular, being a key spawning site for many tuna species, little is known on the effects of oceanographic variability on their larval distribution in this area. The abundance and presence-absence of larval specimens for three tuna species (ABT, bullet tuna and albacore) were modeled in order to examine their relationships with environmental factors, by analysing historical in situ information collected during seven annual surveys (2010–2016). The results revealed that most tuna larvae for the three species were found in the easternmost part of the study area, south of Capo Passero. This area is characterized by a stable saline front and warmer nutrient-poor water, and it has different environmental conditions, compared with the surrounding areas. The models used to investigate the presence-absence and abundance of the three species showed that ABT was the most abundant, followed by bullet tuna and albacore. The presence and abundance data collected are comparable with those of other spawning areas in the Mediterranean. Regarding biological and physical parameters, the results suggest that temperature, salinity, and day of the year are the key factors for understanding the ecological mechanisms and geographical distribution of these species in this area. Temperature affects the presence of ABT larvae and salinity, which, with a physical barrier effect, is a key factor for the presence-absence of bullet and albacore and for albacore abundance.