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

Bluefin tuna larval indices in the western Mediterranean, ecological and analytycal sources of uncertainity

The main objective of this study is to provide the knowledge to design adequate sensitivity analyses on the assessment models used for the Eastern stock of Bluefin tuna. We analyze how different configuration for the same environmental variable (temperature in the mixed layer depth) and different modeling approaches (nonlinear Delta-log,delta-gamma, tweedy and bayesian) affects to the variability of the larval indices of the Eastern bluefin tuna from data collected in the Balearic Sea (Western Mediterranean). We also investigate the effects on the index caused from having differences in the total sampled area among years. We used these results to interpolate larval index values in years with not standard larval surveys but with some ichthyoplankton surveys available, and to propose a “revised version” of the index providing parameters of uncertainty

Albacore (Thunnus alalunga) larval index in the Western Mediterranean Sea, 2001-2015

Larval abundance indices express standardized abundances of larval densities from ichthyoplankton surveys. For more than two decades these indices have been used to assess the trends of the spawning stock biomass of various species in the Gulf of Mexico, being incorporated into the population models applied by ICCAT. Recently, the delta-lognormal models used for the calculation of the indices have been improved to incorporate the environmental variability and have been applied in the Balearic Sea to obtain a larval index for bluefin tuna (Thunnus thynnus). Here we apply the same methodological approach to calculate a larval index of albacore (Thunnus alalunga) from surveys conducted from 2001 to 2015 in the Balearic Sea, the most relevant spawning ground of this species in the Western Mediterranean. Results show a decreasing trend on albacore larval abundances and significant lower abundances from 2013 to 2015. This larval index, standardized for gears, sampling coverage, hour, salinity, date and sea surface temperature, attempt to provide information on the dynamic of the western Mediterranean stock of albacore, for which not much information available for assessment is availableLes indices d’abondance larvaire expriment les abondances standardisées de la densité larvaire à partir de prospections d’ichthyoplancton. Pendant plus de deux décennies, ces indices ont été utilisés pour évaluer les tendances de la biomasse du stock reproducteur de diverses espèces dans le golfe du Mexique et ont été incorporés dans les modèles de population utilisés par l’ICCAT. Récemment, les modèles delta log-normal utilisés pour calculer les indices ont été améliorés afin d’incorporer la variabilité environnementale et ont été appliqués dans la mer des Baléares afin d’obtenir un indice larvaire pour le thon rouge (Thunnus thynnus). La même méthodologie a été appliquée pour calculer un indice larvaire du germon (Thunnus alalunga) à partir des prospections réalisées entre 2001 et 2015 dans la mer des Baléares, la principale zone de frai de cette espèce de la Méditerranée occidentale. Les résultats présentent une tendance décroissante de l’abondance larvaire du germon et une abondance significativement plus faible de 2013 à 2015. Cet indice larvaire, standardisé pour les engins, la couverture de l'échantillonnage, l’heure, la salinité, la date et la température à la surface de la mer, vise à fournir des informations sur la dynamique du stock de germon de la Méditerranée occidentale, au sujet duquel il existe peu d’informations pour l’évaluationLos índices de abundancia de larvas expresan abundancias estandarizadas de densidades de larvas a partir de prospecciones de ictioplancton. Durante más de dos décadas estos índices se han utilizado para evaluar las tendencias de la biomasa reproductora del stock de varias especies en el golfo de México, y se han incorporado en los modelos de población aplicados por ICCAT. Recientemente los modelos delta lognormal utilizados para calcular los índices se han mejorado para incorporar la variabilidad medioambiental y se han aplicado al mar Balear para obtener un índice de larvas para el atún rojo (Thunnus thynnus). En este caso se ha aplicado el mismo enfoque metodológico para calcular un índice larvario de atún blanco (Thunnus alalunga) a partir de prospecciones realizadas desde 2001 a 2015 en el mar Balear, la zona de reproducción más importante para esta especie en el Mediterráneo occidental. Los resultados muestran una tendencia decreciente en la abundancia de larvas de atún blanco y unas abundancias significativamente inferiores de 2013 a 2015. Con este índice de larvas, estandarizado para los artes, la cobertura de muestreo, la hora, la salinidad, la fecha y la temperatura de la superficie del mar se intenta proporcionar información sobre la dinámica del stock de atún blanco del Mediterráneo occidental, para el que no se dispone de mucha información con vistas a su evaluaciónVersión del edito

RETROCALCULATED LARVAL ABUNDANCE INDEX OF ATLANTIC BLUEFIN TUNA IN THE WESTERN MEDITERRANEAN SEA, 2001-2020

This document presents the update of the bluefin tuna retrocalculated larval abundance indices from the Balearic archipelago (western Mediterranean). The index has been calculated following methods presented in 2020 (SCRS/2020/067) and 2021 (SCRS/2021/033). The abundance index shows an increasing trend with a maximum value in 2020. A previous version of the index (SCRS/P/2019/055) is also provided for comparison.En prensa

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

Fish 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 < 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.En prensa3,38

Spawning site distribution of a bluefin tuna reduces jellyfish predation on early life stages

Bluefin tunas across the world migrate long distances to spawn in particularly warm and oligotrophic areas constrained by oceanographic fronts. The low abundance of predators in these areas increases survival chances of their early life stages, but its importance for choice of spawning habitat is unknown. Here, we use estimated clearance rates and data on spatial distributions of Atlantic bluefin tuna larvae Thunnus thynnus and metaephyrae of the jellyfish Pelagia noctiluca to quantify predation at a major spawning ground in the Mediterranean Sea. We found that high densities of P. noctiluca can rapidly deplete tuna eggs and preflexion larvae, but their patchy distribution and low spatial and temporal overlap results in overall low predation. The specific distribution of the spawning sites suggests that bluefin tunas may use local oceanography as cues to spawn outside areas with high predator densities.Postprint3,38

Abundance of Pelagia noctiluca early life stages in the western Mediterranean Sea scales with surface chlorophyll

Pelagia noctiluca is the most successful and well-studied jellyfish in the Mediterranean Sea. This species tolerates a wide range of water temperatures and succeeds in low to medium food regimes, but factors driving its distribution and population dynamics remain poorly understood. Here we applied a multiscale analytical approach using survey data and a physical-biochemical coupled model to assess how environmental factors affect the 3-dimensional distribution and seasonal abundance of P. noctiluca early life stages. The surveys took place after the spring bloom, when warm water favors fecundity and growth, but food shortage limits the reproductive investment and early survival. We found that most early life stages of P. noctiluca remained above the shallow thermocline and upper mixed layer where temperature is warm. Their spatial distribution was positively correlated with surface chlorophyll concentration, and over 90% of the variation in interannual abundance was explained by basin-scale productivity in June. Warmer water during winter and spring seasons coupled with protracted spring blooms increase the population of P. noctiluca, and this explains the trend of increasing outbreaks observed in the western Mediterranean Sea over the past decades.Postprin

Enhancing maternal sensitivity in contexts of urban extreme poverty in Sierra Leone: a pilot study

This pilot study presents preliminary data on the efficacy of Strong Bonds, Strong Pikin (SBSP), a brief intervention program that aims to enhance sensitivity among mothers who care for their preschool children in a slum settlement in Freetown (Sierra Leone). SBSP adapts principles of attachment theory to intervention within a non-Western cultural setting, where families suffer from extreme poverty. A combination of psychoeducation, group work, video-feedback, and storytelling defines the methodology of the program. Maternal sensitivity, parenting stress, and the use of violent discipline practices were measured before (pretest) and after the intervention (posttest) in a sample of 43 mothers who participated in the program. Analyses showed a significant increase in observed maternal sensitivity, as well as a decrease in mother-reported parenting stress, child problems, and use of violent discipline practices from pretest to posttest. These results are discussed in terms of the potential value of culturally sensitive, attachment-centered interventions with caregivers who raise their children in non-Western settings affected by economic vulnerability.Education and Child Studie

Spatially Explicit Modeling Reveals Cephalopod Distributions Match Contrasting Trophic Pathways in the Western Mediterranean Sea

Populations of the same species can experience different responses to the environment throughout their distributional range as a result of spatial and temporal heterogeneity in habitat conditions. This highlights the importance of understanding the processes governing species distribution at local scales. However, research on species distribution often averages environmental covariates across large geographic areas, missing variability in population- environment interactions within geographically distinct regions. We used spatially explicit models to identify interactions between species and environmental, including chlorophyll a (Chla) and sea surface temperature (SST), and trophic (prey density) conditions, along with processes governing the distribution of two cephalopods with contrasting life-histories (octopus and squid) across the western Mediterranean Sea. This approach is relevant for cephalopods, since their population dynamics are especially sensitive to variations in habitat conditions and rarely stable in abundance and location. The regional distributions of the two cephalopod species matched two different trophic pathways present in the western Mediterranean Sea, associated with the Gulf of Lion upwelling and the Ebro river discharges respectively. The effects of the studied environmental and trophic conditions were spatially variant in both species, with usually stronger effects along their distributional boundaries. We identify areas where prey availability limited the abundance of cephalopod populations as well as contrasting effects of temperature in the warmest regions. Despite distributional patterns matching productive areas, a general negative effect of Chla on cephalopod densities suggests that competition pressure is common in the study area. Additionally, results highlight the importance of trophic interactions, beyond other common environmental factors, in shaping the distribution of cephalopod populations. Our study presents a valuable approach for understanding the spatially variant ecology of cephalopod populations, which is important for fisheries and ecosystem management.Versión del editor4,411