This paper reports the presence of the common dolphinfish, Coryphaena hippurus, in Argentinian waters for the first time, with a specimen collected by experienced sport fishermen near Mar del Plata (38 degrees S). This finding also represents the first record of a species from the Coryphaenidae family in Argentinian waters. The collection of these specimens coincided with sightings of other rarely-seen pelagic and oceanic fish species during the same period, providing further evidence supporting the influx of subtropical fish species from warmer Brazilian waters. These observations highlight the need for continued monitoring of fish populations and their distribution and the ecological dynamics within the region.

The identity of longnose skates (Dipturus-Zearaja-like skates) in the southern cone of the Americas has been a topic of extensive debate. This study employs a comprehensive analysis encompassing morphometrics, claspers, and the examination of COI and NADH2 sequence data to conclusively demonstrate the existence of only two longnose skate species in the southwestern Atlantic Ocean, extending south of 35 °S. Notably, Dipturus argentinensis Díaz de Astarloa, Mabragaña, Hanner and Figueroa, 2008 is revealed as a junior synonym of D. trachyderma (Krefft and Stehmann, 1975). Dipturus leptocaudus (Krefft and Stehmann, 1975) remains a northern valid species, but the specimen from the Falkland Islands (Malvinas) is recognized as a misidentification of D. trachyderma. Zearaja flavirostris (Philippi, 1892) and Dipturus lamillai Concha, Caira, Ebert and Pompert, 2019 are confirmed as junior synonyms of Zearaja brevicaudata (Marini, 1933). These findings contradict the previous report of six species within the same region over the last decade and underscore the presence of D. trachyderma and Z. brevicaudata south of 35 °S in the southwestern Atlantic. Additionally, this study notes the occurrence of only one specimen of Z. chilensis (Guichenot, 1848) in the Falkland Islands (Malvinas), suggesting an unusual frequency of this eastern Pacific skate in the southern Southwest Atlantic. Given that clasper morphology serves as the key distinguishing trait between Dipturus and Zearaja species, we provided a detailed analysis of the clasper characteristics of the Atlantic D. trachyderma, unequivocally situating it within Dipturus. The diagnostic characteristics include: (i) the presence of cartilage with the distal portion referred to as the sentinel, a feature absent in Zearaja; (ii) longer ventral terminal cartilage with the distal end referred to as the funnel, compared to Zearaja; and (iii) a non-spatulate distal lobe, a distinctive trait specific to Dipturus.

Here, we highlight the geological processes that resulted in the current conformation of the southern Southwest Atlantic Ocean, and explore the heterogeneous composition of the marine ichthyofauna found between 33 degrees and 56 degrees from a paleobiological perspective. During the early Cretaceous (140 Mya), the South Atlantic was still not formed, and Gondwana was probably a set of united plates with shallow continental waters. In the middle Cretaceous (112 Mya), the major Gondwanan plates started diverging from each other, allowing shallow marine intrusions and the diversification of an endemic fish fauna. By the end of the Mesozoic (66 Mya), the proto-South Atlantic connected with the North Atlantic, which was still part of the Tethys Sea, allowing its ichthyofauna to colonize the south and reach the Antarctic region. The opening of the Drake Passage in the Oligocene (33 Mya) enabled the cold waters of the Pacific Ocean to reach the South Atlantic, causing drastic effects on the thermophilic fauna and favoring the dispersion of cold-water species. Successive glaciations during the Quaternary (2 Myr to 10,000 years ago) resulted in the prevalence of Antarctic climatic conditions in the southern Southwest Atlantic. The long history of changing scenarios in the constitution of the southern Southwest Atlantic is reflected in the heterogeneous composition of the marine ichthyofauna between 33 degrees and 56 degrees S, which is characterized by a mixture of cosmopolitan, Tethyan, Pacific, Gondwanan, Antarctic, and endemic origins.

The presence of ladyfish Elops smithi in Patagonian waters is a new addition to the ichthyological fauna of the Argentinean Sea. This record represents a southward extension of its known distribution by 8 degrees of latitude, similar to 1500 km. It is another example of the more frequent arrival of tropical or subtropical fish species to Patagonian waters.

Egg capsules of the multispine skate, Bathyraja multispinis (Norman, 1937), described here for the first time, are larger (180 mm in length without horns) than those of any Bathyraja species from the South-west Atlantic Ocean (SWA). The capsule’s surface texture is relatively smooth by the presence of woven-like fibres. However, below the fibres, it is rough to the touch by the presence of longitudinal ridges and prickles of different shapes and sizes, ending in two or more digitiform projections. An identification key to all described Bathyraja egg capsules occurring in the SWA from 34° to 55°S is provided.

Food habits and diet composition of Patagonian flounder Paralichthys patagonicus (Jordan, 1889) were studied on the basis of stomach content analyses from 828 specimens (512 females, 304 males, 12 unsexed) collected during 16 commercial cruises between February 2009 and April 2010 in the Argentine-Uruguayan Coastal Ecosystem (34° S-41° S). A total of 272 stomachs (32.9%) contained food (184 females and 84 males), among which 20 prey taxa were identified. The most important prey category was pelagic fish, primarily Argentine anchovy (Engraulis anchoita), followed by rough scad (Trachurus lathami). Evidence showed that females consumed a higher total wet weight of prey compared to males. Results also suggested a specialised diet over E. anchoita, across all sex and size groups. The estimated trophic level for the population of P. patagonicus was 4.16. This study suggests that P. patagonicus is a tertiary piscivorous consumer of the trophic food web in the region, and reveals changes in the prey consumption compared with previous studies.

En el presente estudio se determina la composición de la dieta y estrategia alimentaria del congrio de profundidad Bassanago albescens en el Atlántico Sudoccidental (35° S-45° S), a partir del análisis del contenido estomacal de 222 individuos. La dieta consistió de cefalópodos, seguidos por isópodos, anfípodos, ofiuroideos, braquiuros y poliquetos. Los resultados mostraron diferencias significativas en la composición de la dieta entre sexos, zonas y clases de tallas que se vieron reflejadas en los cambios de la estrategia de forrajeo. Se registró un aumento progresivo en el consumo de Illex argentinus con el aumento del tamaño de B. albescens, donde los individuos más grandes mostraron una especialización en el consumo de esta presa. Estos cambios alimentarios estarían relacionados a limitaciones morfológicas y habilidades asociadas al tamaño corporal de B. albescens, teniendo los individuos más grandes acceso a presas de mayor tamaño. Nuestros resultados ayudan a comprender la biología de una especie que tiene una distribución simpátrica con dos especies clave en las pesquerías de la Argentina: Merluccius hubbsi e I. argentinus, con evidencias de una fuerte interacción trófica entre ellas. Esta nueva información sobre los recursos involucrados permitiría una optimización del manejo pesquero bajo un criterio ecosistémico.

Evaluating the representativeness of species assemblages and species richness in a network of protected areas is key to reach a balanced and equitable network design. However, representativeness has not been assessed for sharks, rays and chimaeras (chondrichthyans), one of the most threatened vertebrate classes. Here, we evaluate the representativeness of chondrichthyan biodiversity in the current network of closed fishing areas (CFAs), and marine protected areas (MPAs), and on a proposed network of relevant conservation areas (RCAs) in the Southwest Atlantic, a large, globally significant region for chondrichthyan conservation. For each Southwest Atlantic bioregion, we estimated the geographic distribution of species richness, and related CFA, MPA and RCA coverage with species richness, using generalized linear and generalized additive models. Within each bioregion, large expanses of high species richness were, in general, not covered by CFAs, and one bioregion had no CFA coverage whatsoever. Three out of the six bioregions had null MPA coverage. Local areas of high species richness had negligible MPA coverage. RCA coverage of local high-richness areas was much higher than either MPA or CFA coverage. This represented a marked improvement; however, vast areas of high bioregional species richness had no coverage, and one bioregion lacked any RCA coverage. Current CFAs and MPAs do not provide adequate protection for the chondrichthyan biodiversity of the Southwest Atlantic, and must be improved to reach full representativeness. Global conservation agendas promoting big MPAs in remote seas should be integrated to regional networks to avoid unbalancing and halting future MPA networks.

ABSTRACTThis work examined the diet of the porbeagle shark Lamna nasus in the south‐west Atlantic Ocean (SWAO, Argentina, 52° S–56° S) by analysing the stomach content information obtained by scientific observers who sampled specimens captured as by‐catch on‐board commercial fishing vessels from 2010 to 2020. A total of 148 fishing sites were analysed, in which the estimated catch was composed mainly of hoki Macruronus magellanicus (56.00%) and southern blue whiting Micromesistius australis (33.13%). From 413 porbeagle sharks sampled (292 females and 121 males) ranging from 71 to 241 cm total length (LT) (mean: 179.76 ± 26.74 cm), 310 (75.06%) contained food in the stomachs. The forage fish were mainly hoki M. magellanicus (23.53%) and southern blue whiting M. australis (19.05%), followed by the Patagonian sprat Sprattus fuegensis (4.48%) and nototheniids (1.4%). Cephalopods and crustaceans accounted for 10% of the diet. The estimated trophic level was 4.35. Generalized linear models revealed that the consumption of hoki M. magellanicus and southern blue whiting M. australis increased with the LT of the porbeagle shark. Moreover, smaller porbeagle sharks preyed upon both small and large teleost fish, whereas larger porbeagle sharks predated exclusively upon large fish. The diet of porbeagle shark involved interactions with fisheries as it fed upon the fish species that constituted the main catch in the analysed fishing sites, as well as the main catches of the austral trawl fisheries. The ecological role of porbeagle shark observed in the SWAO exposed implications for fisheries management from a multispecies perspective.

This study aimed to determine the diet composition and feeding strategies of the hairy conger eel Bassanago albescens in the Southwest Atlantic (35° S-45° S), from stomach contents analysis of 222 specimens. The diet consisted mainly of cephalopods, followed by isopods, amphipods, ophiuroids, brachyurous and polychaetes. Results showed significant differences in the composition of the diet between sexes, regions and size classes that were reflected in the changes in the foraging strategy. The consumption of squid Illex argentinus progressively increased with a growing predator size, where the largest individuals showed specialization in the consumption of this particular prey. We propose these dietary changes would be related to morphological limitations and abilities associated with the body size of B. albescens, with larger individuals having access to larger prey. Our results help to understand the biology of a species that has a sympatric distribution with two key species in the Argentine fisheries: hake Merluccius hubbsi and I. argentinus, with evidence of a strong trophic interaction between them. This new information on the resources involved would allow an optimization of the fisheries management under an ecosystem-

Seahorses (Genus Hippocampus) are rarely reported as prey items. Their low population numbers, their ability to blend with the environment and their low palatability are the features making them an unsuitable option for predators. Five individuals of the Patagonian seahorse Hippocampus patagonicus were found in the stomach of a single narrownose smooth-hound shark Mustelus schmitti from a sample of 959 stomachs analyzed. This rare record in a single stomach out of hundreds analyzed suggests that these individuals might have clustered in a group which was detected by the opportunistic M. schmitti.

This study reports the phenotypic and genetic differences between individuals of puyen Galaxias maculatus from two sites in the same river basin in Tierra del Fuego National Park, southern South America. Individuals from the two sampling sites presented morphometric and genetic differences. The morphometric differences indicated that individuals from Laguna Negra (LN) were short and more robust and had large eyes, whereas those from Arroyo Negro (AN) were thin and elongated and had small eyes. Genetic differences showed that AN individuals had a greater genetic structuration and an older demographic history than LN individuals. The results of this study affirmed that the individuals from the two sampling sites belong to different populations with a high degree of isolation. The demographic history could indicate that the individuals of G. maculatus which migrated to northern areas during the last glaciation settled in the Beagle Channel after its formation. The LN population could have originated after the retreat of the glaciers, migrating from AN.

Biogeographic regionalization identifies natural species assemblages of a given region. In this study, the geographic distribution of chondrichthyan species richness and species assemblages for the Southwest Atlantic were identified. The geographic distribution of 103 chondrichthyans was estimated through modelling. Based on the obtained binary maps, the distribution of chondrichthyan richness was obtained at four taxonomic levels: class Chondrichthyes (chondrichthyans), subclass Holocephali (chimaeras), division Selachii (sharks), and division Batomorphi (batoids). The continental shelf off Uruguay and southern Brazil presented the highest levels of chondrichthyan richness, and a smaller peak was found in El Rincón (northern Argentina). Shark richness concentrated mainly off Lagoa dos Patos (southern Brazil). Batoid richness was maximal off Uruguay and northern Argentina, including modes in El Rincón, San Jorge Gulf, and slope of the Argentinean shelf. Classification analyses revealed the presence of a hierarchical regionalization, with three main and six minor assemblages. Main assemblages are hierarchically identifiable as provinces and minor ones as ecoregions or districts. Two of the main assemblages correspond with the Argentinean and Magellanic Provinces; the third one is identified here for the first time, the Patagonian Slope Province. This regionalization provides the basis for the design of protected area networks for conservation or management purposes.

Identifying the ecological traits of threatened species may help to identify species vulnerable to exploitation and habitat loss, predict future declines in abundance and provide the basis for their conservation. We assessed the relationship of dietary and habitat niche breadth on conservation status of skate species (Chondrichthyes, Rajiformes). We hypothesized that skate species with a narrow niche breadth have a higher conservation concern than skate species with wide niche breadth. Conservation status (IUCN), dietary and depth range data on 57 skate species were collected. Generalized linear mixed effect models were fitted with taxonomic level (genera nested within family) included as a random effect term in each model. In each model, body size of skate species was included as a variable because this life history trait is a known predictor of vulnerability. A model selection approach to test the level of support for alternative models was applied. Our results support the hypothesis that a narrow niche breadth is related to high vulnerability. Skate species with high probability of being of conservation concern have a narrow trophic niche breadth and a large body size. We conclude that dietary niche breadth together with body size may be an important trait to identify potentially vulnerable skate species. Conservation biology faces the challenge of identifying what species are vulnerable to anthropogenic stressors and to determine why this is so. The predictive value of our results may allow to know a priori which species should receive prioritary attention.

Long-term data on spatial and bathymetric distributions, preferred bottom temperatures, length and weight of blue hake Antimora rostrata caught off the Atlantic coast of South America are presented based on published and unpublished materials. The species frequently occurred in waters of southern Argentina where catches were considerably higher as compared with Brazilian waters. The blue hake were captured at depths from 97 to 2162 m (average depth 1279 m). Most of the specimens (65.1%) were collected at depths from 700 to 1300 m, similar to depths in other parts of the species’ range. Bottom temperatures at sites of blue hake captures in Brazilian waters were 2.18–4.20°C (average 2.93°C). Specimens in bottom trawl catches were 9–61 cm in total length, averaging 34.84 cm. The bulk of the catches (85.5% of individuals) were fish of 25–45 cm. Body weight ranged from 70 to 1380 g (average 437.5 g). Frequency of occurrence decreased from southern Argentina to northern Brazil; complete absence of records in the Central Western Atlantic might relate to different means by which the blue hake colonized the Pacific and Atlantic coasts of South America.

The population of Galaxias maculatus studied here, Arroyo Negro (54° S), is located at the southern extreme of the species distribution. This is the first work on growth and other life history traits of a Fueguian diadromous population based on otoliths study. This species is part of the native fish fauna of Patagonia. Furthermore, studies on the growth and reproduction of G. maculatus in South America mostly refer to freshwater populations of Andean-Patagonian lakes and rivers (about 41° S). Size cohorts were studied; age and growth parameters were estimated, the latter using the VBGM. Four size cohorts were established, and 3+ was determined as maximum age class. No differences were found in growth curves between males and females. The 1+ age class was by far not only the most numerous in the population but also the most represented in the reproductive population. The relation between mean TL and latitude was positive (r = 0.62) for South American populations; however, further studies are needed to determine whether it is this population’s life strategy, the local adaptation of a peripheral population or countergradient growth. The results are interpreted in the context of the information available for other populations, and provide important information about the plasticity in life history traits of this species.

Fil: Diaz de Astarloa, Juan Martin. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

We updated the distribution and habitat patterns of Maurolicus stehmanni in the Southwest Atlantic Ocean by compiling data obtained from research surveys conducted on the Argentinean continental shelf, as well as from opportunistic records. This paper confirms the presence of M stehmanni in the Argentinean continental shelf, extending its southernmost distributional limit by ca. 1000 km (from 43.0 degrees S to 52.2 degrees S). Adult specimens of M. stehmanni were collected in various locations from 2004 to 2016. Eggs and larvae of Maurolicus spp. were caught during ichthyoplankton tows carried out from 2003 to 2013. The present paper furthermore extends the habitat type in which this species was recorded: specimens were found in the inner continental shelf (between 46.2 degrees S and 52.2 degrees S) instead of the shelf break and continental slope. Two specimens were found lying dead upon the beach of Puerto Madryn, Nuevo Gulf (42.8 degrees S). The presence of eggs and larvae in coastal embayments (San Maths and San Jose gulfs), in concomitant occurrence with adults, may suggest the establishment of this species in the region.

The presence of the telescope fish Mendosoma lineatum in Patagonian waters of Argentina is reported. Mendosoma lineatum is the second species of the Latridae recorded in the south-west Atlantic Ocean and its presence in Patagonia is an addition to both the ichthyological fauna of the Argentinean Sea and the south-west Atlantic Ocean.

Skates of the genera Dipturus and Zearaja present a particular challenge for fishery management and conservation, since they have been subject to intense exploitation in the last years. In the Argentine Sea, these genera are represented by D. leptocauda, D. trachyderma, D. argentinensis and Z. chilensis. These last three are sympatric species since they overlap in depth and geographic distribution. Their behavioral habits and the morphological similarity make these species, especially in juvenile stages, difficult to identify. The use of the mitochondrial gene Cytochrome C Oxidase I (COI) as a DNA Barcode (genetic barcode), is a useful molecular tool to identify morphologically similar species. In this work, we used the DNA Barcode to identify specimens of Z. chilensis that presented a different thorny pattern in their dorsal side and tail instead of the common pattern found in that species. Also, we compared the DNA Barcode with other sympatric skates’ species to obtain a molecular characterization of the Dipturus and Zearaja species from the Argentine Sea. The DNA Barcode was obtained from 23 individuals collected along the Argentine continental shelf. The specimens were classified as D. argentinesis, Z. chilensis and Z. chilensis with a distinct different spinal pattern (specimens ZSP). The specimens were identified at species level by comparing their barcodes with reference sequences of specimens from the Pacific and Atlantic ocean in Barcode of Life Data System (BOLD), and also by the intra and interspecific Kimura two-parameter (K2P) distance. The ZSP individuals were identified as Z. chilensis with more than 99% of similarity, and they had a K2P distance of 0.24% with the reference sequences collected in the Argentine Sea. The K2P distance between D. argentinensis and Z. chilensis was 3.1%, this value could suggest that both species are the same Genus Zearaja. We found that the specimens’ reference sequences of Z. chilensis from the Pacific had a high divergence (3.46%) from the Z. chilensis of the Argentine Sea, which would indicate two different species, suggesting that the Argentine form should be called Z. flavirostris (Philippi, 1892). From this work, we conclude that the DNA Barcode is a useful and efficient molecular marker to identify skates’ species. The obtained genetic distance data contributes to the characterization of these sympatric species from the Argentine Sea and is a useful tool as a reference parameter for the differentiation of the species.