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The shape of sagitta otoliths was used to compare individuals of little tunny (Euthynnus alleteratus) harvested on board commercial fishing vessels from the coastal areas along the Eastern Atlantic, including the Mediterranean Sea. Fish sampling and selection was designed to cover possible seasonal changes and tuna size. The research encompassed both morphometric and shape analyses of left sagittal otoliths extracted of 504 fish specimens. Four shape indices (Circularity, Roundness, Rectangularity, and Form-Factor) were significantly different between two groups, showing a statistical differentiation between two clear spatial units. The degree of divergence was even more pronounced along the rostrum, postrostrum, and excisura of the generated otolith outlines between these two groups. One group corresponds to the samples from the coastal areas in the Northeast Temperate Atlantic and Mediterranean Sea (NETAM Area) and a second group from the coastal areas off the Eastern Tropical Atlantic coast of Africa (ETA Area). This study is the first to use otolith shape to differentiate tunas from separate spatial units. These results could be used to re-classify previously collected samples and to correct time series of data collected.

Atlantic bluefin tuna are a symbol of both the conflict between preservationist and utilitarian views of top ocean predators, and the struggle to reach international consensus on the management of migratory species. Currently, Atlantic bluefin tuna are managed as an early-maturing eastern stock, which spawns in the Mediterranean Sea, and a late-maturing western stock, which spawns in the Gulf of Mexico. However, electronic tagging studies show that many bluefin tuna, assumed to be of a mature size, do not visit either spawning ground during the spawning season. Whether these fish are spawning in an alternate location, skip-spawning, or not spawning until an older age affects how vulnerable this species is to anthropogenic stressors including exploitation. We use larval collections to demonstrate a bluefin tuna spawning ground in the Slope Sea, between the Gulf Stream and northeast United States continental shelf. We contend that western Atlantic bluefin tuna have a differential spawning migration, with larger individuals spawning in the Gulf of Mexico, and smaller individuals spawning in the Slope Sea. The current life history model, which assumes only Gulf of Mexico spawning, overestimates age at maturity for the western stock. Furthermore, individual tuna occupy both the Slope Sea and Mediterranean Sea in separate years, contrary to the prevailing view that individuals exhibit complete spawning-site fidelity. Overall, this complexity of spawning migrations questions whether there is complete independence in the dynamics of eastern and western Atlantic bluefin tuna and leads to lower estimates of the vulnerability of this species to exploitation and other anthropogenic stressors.

The Scombridae family represents one of the most commercially valuable groups of pelagic fish, widely consumed across the globe. Despite their economic importance and high market demand, scientific data on Scombridae species in Aceh remains scarce. This study aimed to document Scombridae landings from Aceh waters. Fish samples belonging to the Scombridae family were collected from several Fish Landing Sites (TPIs) across Aceh Province. The collected samples were subsequently analyzed at the Genetics and Aquatic Biodiversity Laboratory, Faculty of Marine and Fisheries, Universitas Syiah Kuala. A total of ten Scombridae species were identified from the collected samples: Auxis rochei , Auxis thazard , Euthynnus affinis , Katsuwonus pelamis , Rastrelliger brachysoma , Rastrelliger kanagurta , Scomberomorus commerson , Scomberomorus guttatus , Sarda orientalis , and Thunnus albacares . Banda Aceh had the highest distribution of fish of the Scombridae family, followed by Meulaboh. The findings of this study provide critical baseline data for the future management and conservation of Scombridae fish, particularly in Aceh and Indonesia more broadly.

Growth models describe the change in length or weight as a function of age. Growth curves in tunas can take different forms from relatively simple von Bertalanffy growth curves (Atlantic bluefin, albacore tunas) to more complex two- or three-stanza growth curves (yellowfin, bigeye, skipjack, southern bluefin tunas). We reviewed the growth of the principal market tunas (albacore, bigeye, skipjack, yellowfin and the three bluefin tuna species) in all oceans to ascertain the different growth rates among tuna species and their implications for population productivity and resilience. Tunas are among the fastest-growing of all fishes. Compared to other species, tunas exhibit rapid growth (i.e., relatively high K ) and achieve large body sizes (i.e., high L ∞ ). A comparison of their growth functions reveals that tunas have evolved different growth strategies. Tunas attain asymptotic sizes ( L ∞ ), ranging from 75 cm FL (skipjack tuna) to 400 cm FL (Atlantic bluefin tuna), and reach L ∞ at different rates ( K ), varying from 0.95 year −1 (skipjack tuna) to 0.05 year −1 (Atlantic bluefin tuna). Skipjack tuna (followed by yellowfin tuna) is considered the “fastest growing” species of all tunas. Growth characteristics have important implications for population dynamics and fisheries management outcomes since tunas, and other fish species, with faster growth rates generally support higher estimates of Maximum Sustainable Yield (MSY) than species with slower growth rates.

Uncertainties surrounding the evolutionary origin of the epipelagic fish family Scombridae (tunas and mackerels) are symptomatic of the difficulties in resolving suprafamilial relationships within Percomorpha, a hyperdiverse teleost radiation that contains approximately 17,000 species placed in 13 ill-defined orders and 269 families. Here we find that scombrids share a common ancestry with 14 families based on (i) bioinformatic analyses using partial mitochondrial and nuclear gene sequences from all percomorphs deposited in GenBank (10,733 sequences) and (ii) subsequent mitogenomic analysis based on 57 species from those targeted 15 families and 67 outgroup taxa. Morphological heterogeneity among these 15 families is so extraordinary that they have been placed in six different perciform suborders. However, members of the 15 families are either coastal or oceanic pelagic in their ecology with diverse modes of life, suggesting that they represent a previously undetected adaptive radiation in the pelagic realm. Time-calibrated phylogenies imply that scombrids originated from a deep-ocean ancestor and began to radiate after the end-Cretaceous when large predatory epipelagic fishes were selective victims of the Cretaceous-Paleogene mass extinction. We name this clade of open-ocean fishes containing Scombridae \"Pelagia\" in reference to the common habitat preference that links the 15 families.

Prior aquatic animal image classification research focused on distinguishing external features in controlled settings, utilizing either digital cameras or webcams. Identifying visually similar species, like Short mackerel (Rastrelliger brachysoma) and Indian mackerel (Rastrelliger kanagurta), is challenging without specialized knowledge. However, advancements in computer technology have paved the way for leveraging machine learning and deep learning systems to address such challenges. In this study, transfer learning techniques were employed, utilizing established pre-trained models such as ResNet50, Xception, InceptionV3, VGG19, VGG16, and MobileNetV3Small. These models were applied to differentiate between the two species using raw images captured by a smartphone under uncontrolled conditions. The core architecture of the pre-trained models remained unchanged, except for the removal of the final fully connected layer. Instead, a global average pooling layer and two dense layers were appended at the end, comprising 1024 units and by a single unit, respectively. To mitigate overfitting concerns, early stopping was implemented. The results revealed that, among the models assessed, the Xception model exhibited the most promising predictive performance. It achieved the highest average accuracy levels of 0.849 and 0.754 during training and validation, surpassing the other models. Furthermore, fine-tuning the Xception model by extending the number of epochs yielded more impressive outcomes. After 30 epochs of fine-tuning, the Xception model demonstrated optimal performance, reaching an accuracy of 0.843 and displaying a 11.508% improvement in predictions compared to the model without fine-tuning. These findings highlight the efficacy of transfer learning, particularly with the Xception model, in accurately distinguishing visually similar aquatic species using smartphone-captured images, even in uncontrolled conditions.

To quantitatively evaluate the distribution of tuna larvae relative to oceanographic conditions, we conducted investigations off the Nansei Islands in the western North Pacific in June from 2015 to 2017. Five species, namely Pacific bluefin tuna Thunnus orientalis (PBF), yellowfin tuna T. albacares (YFT), skipjack tuna Katsuwonus pelamis (SKJ), frigate tuna Auxis thazard, and bullet tuna A. rochei (BT), were collected in each year. The most dominant species was BT throughout the 3 yr period, followed by SKJ in 2015 and YFT in 2016 and 2017. The horizontal larval distributions of the 5 species were largely influenced by the Kuroshio Current: larvae of the 2 Auxis species were distributed in the Kuroshio and the Kuroshio inshore waters, whereas those of the other species were found in the Kuroshio offshore waters. These differences are consistent with the differences in spawner distributions among the tunas. Generalized additive models (GAMs) indicated that the larval densities were affected by the sea surface height anomaly and that the larvae were not always amassed by horizontal transport. Sea surface temperature (SST) and salinity possibly influenced the larval physiology and survival, thereby determining their densities. In the GAMs, PBF and YFT showed similar responses to SST, and YFT and SKJ similarly responded to salinity. To avoid overlapping their ecological niches, the larvae of 3 species (PBF, YFT, and SKJ) are expected to differ in other ways, including their vertical distributions and feeding habits.

Despite being an important source of wealth and food security for many countries, most of the small tuna stocks in the Atlantic Ocean and Mediterranean Sea remain unassessed. In this study, we summarized the current state of knowledge of this group of species reviewing the information available on life history parameters, stock structure, historical catches, size frequency distributions and current knowledge of stock status. In relation to the life history parameters, data are overall scarce and mainly missing in the Eastern Atlantic where small tunas are relevant in small-scale fisheries. From the 27 defined stocks, only 11 have been quantitatively assessed. From those, the Northwest wahoo and the Southeast little tunny stocks may be experiencing overfishing, deserving priority management attention. Length-based rather than catch-based methods showed a more promising applicability for small tunas, although representative length distributions from the catch are scarce for some stocks. Historical catch time series for small tuna are still incomplete, however, the last two decades are the most accurate and could be considered in future assessment methods. The gaps of knowledge related mainly to life history parameters and historical catches are the main reason why most of these stocks remain unassessed and unmanaged.

The copepod family Shiinoidae Cressey, 1975 currently comprises nine species of teleost parasites with unusual morphology and a unique attachment mechanism. Female shiinoids possess greatly enlarged antennae that oppose a rostrum, an elongate outgrowth of cuticle that originates between the antennules. The antennae form a moveable clasp against the rostrum which they use to attach to their host. In this study, we use micro-computed tomography (microCT) to examine specimens of Shiinoa inauris Cressey, 1975 in situ attached to host tissue in order to characterize the functional morphology and specific muscles involved in this novel mode of attachment and to resolve uncertainty regarding the segmental composition of the regions of the body. We review the host and locality data for all reports of shiinoids, revise the generic diagnoses for both constituent genera Shiinoa Kabata, 1968 and Parashiinoa West, 1986, transfer Shiinoa rostrata Balaraman, Prabha & Pillai, 1984 to Parashiinoa as Parashiinoa rostrata (Balaraman, Prabha & Pillai, 1984) n. comb., and present keys to the females and males of both genera.

Abstract In fisheries, the phenomenon known as fishing down food webs is supposed to be a consequence of overfishing, which would be reflected in a reduction in the trophic level of landings. In such scenarios, the resilience of carnivorous, top predator species is particularly affected, making these resources the first to be depleted. The Serra Spanish mackerel, Scomberomorus brasiliensis, exemplifies a predator resource historically targeted by artisanal fisheries on the Brazilian coast. The present work analyzes landings in three periods within a 50-year timescale on the Parana coast, Southern Brazil, aiming to evaluate whether historical production has supposedly declined. Simultaneously, the diet was analyzed to confirm carnivorous habits and evaluate the trophic level in this region. Surprisingly, the results show that from the 1970’s to 2019 Serra Spanish mackerel production grew relatively to other resources, as well as in individual values. The trophic level was calculated as 4.238, similar to other Scomberomorus species, consisting of a case where landings increase over time, despite the high trophic level and large body size of the resource. The results agree with a recent global assessment that has demystified a necessary correlation between high trophic level and overexploitation, but possible factors acting on the present findings are discussed. Resumo Na pesca, o fenômeno fishing down food webs, ou ‘pescando teias tróficas abaixo’, expressa a redução do nível trófico na composição das capturas, e tem origem tradicionalmente atribuída à sobrepesca. Sob intenso extrativismo, a resiliência das espécies carnívoras, predadoras de topo, é particularmente afetada, sendo seus estoques os primeiros a entrarem em depleção. A cavala, ou serra, ou sororoca, Scomberomorus brasiliensis, é exemplo de recurso predador historicamente alvo da pesca artesanal, de pequena escala, na costa brasileira. O presente trabalho analisa os valores de desembarque do recurso em três períodos ao longo de 50 anos na costa paranaense, sul do Brasil, com objetivo de avaliar se sua produção tem efetivamente diminuído. Ainda, estuda-se a dieta da espécie na região, para confirmar seus hábitos carnívoros e avaliar o nível trófico na região. Os resultados mostram que, surpreendentemente, dos anos 1970 para 2019 a produção de S. brasiliensis tem aumentado em valores absolutos, bem como relativamente à de outros recursos, em que pese o nível trófico 4,238, similar a outras espécies do gênero. Constata-se que a pesca da cavala na região de estudo constitui um caso de aumento nos desembarques a despeito de elevado nível trófico e grande tamanho corpóreo. Os resultados concordam com recente levantamento em nível mundial, que nega existir correlação necessária entre sobrepesca e nível trófico alto, mas fatores que podem explicar os resultados do presente trabalho são discutidos.