SPATIO-TEMPORAL PATTERNS OF JUVENILES IN EU PURSE SEINE FLEET CATCHES TARGETING TROPICAL TUNAS OVER THE PERIOD 1990-2019

The knowledge of the juvenile distribution in fisheries is essential to better manage the fishing effort on a stock. The exploration of a large dataset which covers 30 years of the purse seine fishery sampling enabled to study the spatio-temporal dynamic of the juvenile catches of the yellowfin and bigeye tunas. Results showed the existence of several areas of prime importance in terms of catch and concentration in juveniles with seasonal variations. Thus, the south of the fishing ground (Cape Lopez) was fished during winter month and the north during summer months (Cape Verde, Senegal y Mauritania). Offshore coastal zone and Gulf of Guinea were fished almost all along the year. This seasonal pattern is quite stable since the 90s but the proportion of juveniles in schools associated with floating objects tended to increase in both species. This preliminary study opened the way for further research on this important component of the fish stocks. La connaissance de la répartition des juvéniles dans les pêcheries est essentielle pour mieux gérer l'effort de pêche sur un stock. L'exploration d'un vaste jeu de données couvrant 30 ans d'échantillonnage de la pêcherie à la senne a permis d'étudier la dynamique spatio-temporelle des captures de juvéniles d'albacore et de thon obèse. Les résultats ont montré l'existence de plusieurs zones de première importance en termes de capture et de concentration des juvéniles avec des variations saisonnières. Ainsi, le sud de la zone de pêche (Cap Lopez) était pêché pendant les mois d'hiver et le nord pendant les mois d'été (Cabo Verde, Sénégal et Mauritanie). La zone côtière offshore et le golfe de Guinée ont été pêchés presque toute l'année. Bien que ce schéma saisonnier soit stable depuis les années 1990, la proportion de juvéniles dans les bancs associés à des objets flottants avait tendance à augmenter pour ces deux espèces. Cette étude préliminaire a ouvert la voie à d'autres recherches sur cette composante importante des stocks de poissons. El conocimiento de la distribución de los juveniles en las pesquerías es esencial para gestionar mejor el esfuerzo pesquero en un stock. La exploración de un gran conjunto de datos que abarca 30 años de muestreo de la pesquería de cerco permitió estudiar la dinámica espacio-temporal de las capturas de juveniles de rabil y patudo. Los resultados mostraron la existencia de varias zonas de importancia primordial en cuanto a la captura y concentración de juveniles con variaciones estacionales. Así, el sur del caladero (Cabo López) se pescaba durante el mes de invierno y el norte durante los meses de verano (Cabo Verde, Senegal y Mauritania). En la zona costera y en el golfo de Guinea se pescaba casi todo el año. Esta pauta estacional es bastante estable desde los años 90, pero la proporción de juveniles en los cardúmenes asociados a objetos flotantes tendió a aumentar en ambas especies. Este estudio preliminar abrió el camino a nuevas investigaciones sobre este importante componente de los stocks de peces.Versión del edito

Spatio-temporal patterns of juveniles in EU Purse sein fleet catch targetting tropical tunas over the period 1990-2019

The knowledge of the juvenile distribution in fisheries is essential to better manage the fishing effort on a stock. The exploration of a large dataset which covers 30 years of the purse seine fishery sampling enabled to study the spatio-temporal dynamic of the juvenile catches of the yellowfin and bigeye tunas. Results showed the existence of several areas of prime importance in terms of catch and concentration in juveniles with seasonal variations. Thus, the south of the fishing ground (Cape Lopez) was fished during winter month and the north during summer months (Cape Verde, Senegal y Mauritania). Offshore coastal zone and Gulf of Guinea were fished almost all along the year. This seasonal pattern is quite stable since the 90s but the proportion of juveniles in schools associated with floating objects tended to increase in both species. This preliminary study opened the way for further research on this important component of the fish stocks.Versión del edito

Spatio-temporal distribution of spinetail devil ray (Mobula mobular) in the eastern tropical Atlantic Ocean.

The distribution of the spinetail devil ray Mobula mobular in the eastern tropical Atlantic remains poorly known compared to the Pacific and Indian Oceans. We used fisherydependent data and generalized additive models to examine the environmental characteristics associated with the presence of M. mobular in the eastern Atlantic Ocean. Results revealed that the distribution of M. mobular is significantly associated with seasonal upwelling systems in coastal and pelagic areas. Our model predicted the presence of the species in areas where there is evidence of its occurrence, such as the Angolan upwelling system and the coast of Ghana. In addition, our model predicted new hotspot areas, including locations around the Mauritanian upwelling system, the Guinea coast, offshore Ghana and the south coast of Angola and Brazil, where sample sizes are limited. Those areas, as well as the environmental preferences depicted by the model, provide valuable information about the habitat and ecology of the spinetail devil ray. Future research lines derived from this study, as well as its limitations, are discussed. Furthermore, in light of our results we discuss the improvements that are needed to contribute to the conservation and management of this vulnerable species.Versión del edito

A preliminary analysis of spatiotemporal patterns in swordfish habitat distributions.

A species distribution model (SDM) for swordfish that was in the development stage has been finalized. The model used detailed biological and oceanographic data to define the spatial distribution of Swordfish. The SDM adequately predicted Swordfish habitat (and thus fish) distributions such that it was found suitable for investigations into the spatiotemporal distribution of habitat. Results of this preliminary investigation supports the current hypothesized stock boundaries between the north and south Atlantic stocks used for management. Both the north and south Atlantic may be experiencing an expansion of habitat. This could result in decreased density of swordfish into a larger area and/or change MSY production metrics. A more detailed examination of this possibility is recommended.Versión del edito

PESQUERÍA DE PATUDO O TUNA (BIGEYE TUNA)

SUMMARY The main objective of this study is to carry out a detailed analysis of the bigeye tuna fishery (Thunnus obesus) in the Canary Islands during the period 1926 to 2020. The existence of this fishery dates back to the early 19th century on the island of La Gomera. Fishing effort has varied throughout the period under study. Catches of this species are analysed for the period 1965 to 2020. In the 1970s and 1990s, the maximum historical levels were reached i.e. 6,991 t and 9,325 t, respectively. The method of fishing on associated schools has modified the exploitation pattern. Catch seasonality has changed, shifting from the first and second quarters in the first period to the third and fourth quarters currently. The sizes of the catch taken on free schools and associated schools are different. In the 1980s and 1990s, the fishing areas were closer to each other. In the 2000s, the main fishing areas are located in the South, West and North of the islands, until Madeira and the Azores. RÉSUMÉ L'objectif principal de cette étude est de réaliser une analyse détaillée de la pêche du thon obèse (Thunnus obesus) dans les îles Canaries pendant la période 1926 à 2020. L'existence de cette pêche remonte au début du XIXe siècle à l'île de La Gomera. L'effort de pêche a varié tout au long de la période d'étude. Les captures de cette espèce sont analysées pour la période de 1965 à 2020. Dans les années 1970 et 1990, les niveaux historiques maximums ont été atteints avec 6.991 t et 9.325 t respectivement. La modalité de pêche sur mattes associées a modifié le schéma d'exploitation de l'espèce. La saisonnalité des captures a changé, passant du premier et deuxième trimestre de la première période au troisième et quatrième trimestre actuellement. Les tailles de capture réalisées sur bancs libres et mattes associées sont différentes. Dans les années 1980 et 1990, les zones de pêche étaient plus proches les unes des autres. Dans les années 2000, les principales zones de pêche se situent au sud, à l'ouest et au nord des îles, jusqu'à Madère et aux Açores. RESUMEN El principal objetivo de este estudio es realizar un análisis detallado de la pesquería de patudo (Thunnus obesus), también llamado tuna, en las islas Canarias, durante el período 1926 a 2020. La existencia de esta pesquería se remonta a principios del pasado siglo XIX en la isla de La Gomera. El esfuerzo pesquero ha variado a lo largo del período de estudio. Se analizan las capturas de esta especie para el período 1965 a 2020. En los 70 y 90 se produjeron los máximos históricos con 6991 t y 9325 t respectivamente. La modalidad de pesca “ a mancha” ha modificado el patrón de explotación de la especie. La estacionalidad de las capturas ha cambiado desde el primer y segundo trimestre de la primera época hacia el tercer y cuarto trimestre actualmente. Las tallas de captura son diferentes a banco libre y en mancha. En los 80 y 90 los caladeros de pesca estaban más cerca. En los 2000 las principales zonas de pesca están al sur, al oeste y al norte de las islas, llegando hasta Madeira y Azores.Versión del edito

Gamete biology: Perspectives for Bluefin Tuna Aquaculture

Taking care of fish reproductive physiology and gamete biology allowed significant progresses in fry production control for many commercially interesting fish. Can it be a similar situation for bluefin tuna? Fish gamete production results from long processes controlled mainly by climatic conditions, mediated by neuroendocrine and endocrine factors. The possibility to monitor the development of germinal cells by successive sampling in individual fish which easily breed in captivity, has allowed learning about the sequences of gametogenesis and their control, as well as important characteristics of fish gamete biology. The female ovarian cycle involves a progressive accumulation of yolk in the oocytes (i.e., vitellogenesis), followed by cytoplasmic and nuclear events related to maturation and ovulation. The phases of vitellogenesis and maturation are of different duration in different species. In captive fish the endocrine regulation of reproduction may be disrupted by stress, thus preventing spontaneous spawning, while the application of exogenous hormones at the conclusion of gametogenesis allowed production of good quality gametes. In males, gamete production is not continuous as in mammals. Spermatozoa are produced after a cycle that includes a resting period, followed by continuous or discontinuous sequences of spermatogenesis (spermatogenesis sensu stricto, spermiogenesis and spermiation). The discontinuity of fish sperm production may induce a phenomenon of ageing along the period of spermiation, which decreases the quality of semen with time. Wild bluefin tuna breed in specific areas during a short summer spawning season. When kept in cages in the area of Cartagena (Spain), they present developed gamete stages at the same time as wild fish, but, until now, neither mating behavior nor eggs have been observed as was the case in Japan. It has not been possible to monitor individual gonad recrudescence by successive sampling, due to inability to handle the fish without causing mortality, so that the reproduction failure remains unexplained. Hormonal stimulation may be an interesting alternative but its use requires an assessment of gonadal stage to be performed properly. The high post-handling mortality of bluefin tuna in captivity is a real bottleneck for reproduction control. The improvement of handling and the use of less stress-susceptible individuals may be a major progress for bluefin tuna reproduction control. The occurrence of a second generation of juveniles in Japan, subjected to first domestication selection may provide very interesting experimental fish.EU 5FP REPRODOTT (Q5RS-2002-01355

Listado de especies de peces (excluyendo túnidos) capturadas de forma accesoria por la flota de cerco tropical española en el área ICCAT

El objetivo principal del presente estudio es mostrar una lista verificada de las capturas accesorias de peces (excluidas las especies de túnidos) por parte de la flota española de cerco tropical en el área de ICCAT. Se ha identificado un total de 76 especies de peces (excluidas las especies de túnidos) durante el período de estudio (2003-2017). También se han identificado dos taxones que necesitan confirmación (Kajikia audax y Makaira mazara)

Accounting for fishing days without a fishing set in the CPUE standardization of yellowfin tuna in free schools for the EU purse seine fleet operating in the eastern Atlantic Ocean during the 1993-2018 period

The time series of EU purse seine fleet catches per unit effort (CPUE) of yellowfin tuna (YFT) from the Atlantic Ocean were standardized using an extension of the Delta-lognormal GLMM to three components. The aim was to depict the trend in abundance for adult YFT observed in free schools (FSC). The originality of this work relied on the inclusion of i) null sets, considered as presence of YFT FSC, ii) fishing days without set, considered as absence of FSC, iii) EU fishing agreement in the exclusive economic zones driving EU purse seine fleet presence in these areas, and iv) time spent by centroid cell by boat by day to constrain detectability. Standardized CPUE for FSC was thus defined as the product of the number of set (positive and null) by spatio-temporal strata, the proportion of sets with large YFT (>10 kg) and the catch per large YFT set. To detect strata without sets, all activities recorded in captain logbooks were used for the period 1993-2018. This new standardization approach, therefore, represents a significant advance over previous efforts, though there are a number of avenues for future progress.Versión del edito

A hypothesis of a redistribution of North Atlantic swordfish based on changing ocean conditions

Conflicting trends in indices of abundance for North Atlantic swordfish starting in the mid-to late 1990s, in the form of fleet specific catch-per-unit-effort (CPUE), suggest the possibility of a spatial shift in abundance to follow areas of preferred temperature. The observed changes in the direction of the CPUEs correspond with changes in trends in the summer Atlantic Multidecadal Oscillation (AMO), a long term mode of variability of North Atlantic sea surface temperature. To test the hypothesis of a relation between the CPUE and the AMO, the CPUEs were made spatially explicit by re-estimating using an “areas-as-fleets” approach. These new CPUEs were then used to create alternative stock histories. The residuals of the fit were then regressed against the summer AMO. Significant, and opposite, relations were found in the regressions between eastern and western Atlantic areas. When the AMO was in a warm phase, the CPUEs in the western (eastern) areas were higher (lower) than predicted by the assessment model fit. Given the observed temperature tolerance limits of swordfish, it is possible that either their preferred habitat, prey species, or both have shifted spatial distributions resulting in conflicting CPUE indices. Because the available CPUE time series only overlaps with one change in the sign of the AMO (~1995), it is not clear whether this is a directional or cyclical trend. Given the relatively localized nature of many of the fishing fleets, and the difficulty of separating fleet effects from changes in oceanography we feel that it is critical to create CPUE indices by combining data across similar fleets that fish in similar areas. This approach allowed us to evaluate area-specific catch rates which provided the power to detect basin-wide responses to changing oceanography, a critical step for providing robust management advice in a changing climate.Postprin

Tuna regional fisheries management organizations and the conservation of sea turtles: a reply to Godley et al

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