Natalia A. Dellabianca

The Beagle Channel, located south of Tierra del Fuego (~54° S), is South America’s southernmost intracoastal ecosystem. Here, we applied environmental DNA metabarcoding using a partial sequence of the 12sRNA mitochondrial gene to evaluate the seasonal and spatial dynamics of marine vertebrate communities along the longitudinal gradient of the Beagle Channel. Water samples were collected across seasons and sites spanning the central and eastern sectors of the channel. Vertebrate DNA was amplified and analyzed against a custom reference database enriched with locally generated sequences. A total of 43 vertebrate taxa were detected, including 25 fish, 13 mammals, and 5 seabirds. Vertebrate assemblages were spatially structured along the longitudinal gradient of the Beagle Channel, with the central sector characterized by higher relative abundances of Fuegian sprat (Sprattus fuegensis), Southern elephant seal (Mirounga leonina), South American fur seal (Arctocephalus australis), and domestic species, whereas the eastern sector showed higher relative abundances of fish species including silversides (Odontesthes spp.), Magellanic rockcod (Paranotothenia magellanica), and striped rockcod (Trematomus hansoni), as well as mammals including southern sea lion (Otaria flavescens), North American beaver (Castor canadensis), and native grass mice (Abrothrix spp.). This spatial differentiation was associated with contrasting environmental conditions. No significant seasonal effect was detected. This study provides the first environmental DNA-based baseline of marine vertebrates on the Beagle Channel and validates this approach for ecosystem-scale biodiversity monitoring in subantarctic coastal environments.

The marine ecosystem provides numerous goods and services, dampens the impacts of floods and storms, and provides climate control, through the regulation of carbon fluxes, nutrient cycling, and the bioremediation of human waste and tourism. However, the ocean is vulnerable to anthropogenic threats and has been severely altered by humans. Seabirds and marine mammals are long lived, highly mobile, easily identifiable, and occupy the upper levels of trophic webs. These ecological features make them suitable as sentinels of the marine ecosystem. Sighting data collected during eight oceanographic surveys were analysed to describe and compare the biodiversity of the communities of top predators within the marine protected areas (MPAs) of Namuncurá/Burdwood Bank I and II and the surrounding areas in two contrasting seasons (summer and winter). Data were grouped into six zones based on depth and geographic position. Twenty‐five species of seabirds and 13 species of marine mammals were recorded in 113 days of surveys between 2014 and 2018. Top predator community composition varied seasonally in the different zones. A suite of indicator species was identified according to their specificity and fidelity to a particular zone. Most of the species identified as potentially useful indicators differed between summer and winter, highlighting the importance of conducting systematic surveys in both periods. The MPAs Namuncurá/Burdwood Bank I and II are key areas for top predator communities in the region, mainly in summer when the number and abundance of species increase. However, the waters around Isla de los Estados and the channel between Isla de los Estados and Burdwood Bank were also identified as a relevant habitat for many species. This knowledge should be included to create a regional network of areas under special management considerations that connect the established MPAs with other key pelagic and coastal areas (as found in this study) for the conservation of subantarctic marine megafauna.

Common dolphins, Delphinus delphis, in the southwestern Atlantic Ocean are subject to incidental mortality in fishing gear. However, no information on trends in abundance or estimates of bycatch mortality are available to evaluate the impact of this threat on the population. This study presents estimates of life history parameters using postmortem data obtained over a 17‐year period in Argentina. Ages were determined for 93 specimens, and reproductive organ samples were examined (n = 89). Immature animals ranged from 0 to 6 years in females and from 0 to 9 years in males. Mature animals ranged from 7 to 21 years in females and from 6 to 23 years in males. The asymptotic body length (L_∞) described by a Gompertz model fit to age‐length data was 196 cm, 95% CI [192.45, 199.76] for females and 210.75 cm, 95% CI [206.64, 215.30] for males and was attained at 14 years in females and 15 years in males. Comparison to other populations showed that L_∞ were shorter than estimates from New Zealand, similar to L_∞ from eastern North Atlantic, and longer than estimates from North Pacific common dolphins. L_max reported here were shorter than New Zealand ones but similar to those previously reported from other populations.

Thin sections in pinniped canines from the Second Component of Túnel I site (mid-Holocene) hunting strategies focused on adult and subadult males of South American fur seal (Arctocephalus australis) in the Beagle Channel region, these captures would occur outside the reproductive period. However, recent zooarchaeological studies of the entire occupation sequence show a more heterogeneity pattern in the mortality profiles based on the study of postcranial bones. In order to expand previous knowledge about pinniped exploitation strategies, in this paper we estimated ages and the seasons of death through thin sections of pinniped canines from archaeological assemblages of the middle and late Holocene. The results indicate consistency with the mortality profiles previously informed from zooarchaeological studies of the postcranial bones. In turn, the results also indicate a seasonally diverse pattern in the pinniped captures during the middle and late Holocene. We finally argue that pinniped harvesting strategies have temporarily varied in the Beagle Channel, in accordance with subsistence changes proposed in a human peopling model for the region. Durante varias décadas, las interpretaciones sobre las pautas de explotación de pinnípedos en el canal Beagle se basaron sobre los conjuntos zooarqueológicos recuperados en el Segundo Componente de Túnel I. En los últimos años, el análisis sistemático de un número mayor de contextos distribuidos en distintos sectores de la costa norte del canal Beagle generó información para momentos más recientes de la secuencia de ocupación. Aunque se mantiene una tendencia en la explotación de machos adultos y subadultos de Arctocephalus australis durante el Holoceno medio, se observa heterogeneidad en el tipo de presas explotadas en el Holoceno tardío en relación con los perfiles de sexo y edad. En este trabajo se presentan y discuten los resultados de cortes delgados efectuados en 15 caninos de pinnípedos a fin de ampliar estimaciones sobre edad y estación de muerte de especímenes recuperados en contextos del Holoceno tardío en el canal Beagle. Los resultados indican variabilidad en los perfiles de edad respecto de los determinados previamente y capturas de pinnípedos en todas las estaciones del año durante el Holoceno tardío. Se concluye que es posible que las estrategias de aprovechamiento se hayan diversificado hacia momentos tardíos en la historia de ocupaciones de dicha región.

Commerson’s dolphins (Cephalorhynchus c. commersonii) and Peale’s dolphins (Lagenorhynchus australis) are two of the most common species of cetaceans in the coastal waters of southwest South Atlantic Ocean. Both species are listed as Data Deficient by the IUCN, mainly due to the lack of information about population sizes and trends. The goal of this study was to build spatially explicit models for the abundance of both species in relation to environmental variables using data collected during eight scientific cruises along the Patagonian shelf. Spatial models were constructed using generalized additive models. In total, 88 schools (212 individuals) of Commerson’s dolphin and 134 schools (465 individuals) of Peale’s dolphin were recorded in 8,535 km surveyed. Commerson’s dolphin was found less than 60 km from shore; whereas Peale’s dolphins occurred over a wider range of distances from the coast, the number of animals sighted usually being larger near or far from the coast. Fitted models indicate overall abundances of approximately 22,000 Commerson’s dolphins and 20,000 Peale’s dolphins in the total area studied. This work provides the first large-scale abundance estimate for Peale’s dolphin in the Atlantic Ocean and an update of population size for Commerson’s dolphin. Additionally, our results contribute to baseline data on suitable habitat conditions for both species in southern Patagonia, which is essential for the implementation of adequate conservation measures.

Total mercury (THg) and selenium (Se) concentrations were determined in hepatic, renal, and muscle tissues of seven specimens of Commerson’s dolphins incidentally captured in artisanal fisheries of Tierra del Fuego, Argentina, by instrumental neutron activation analysis. Liver yielded the mean highest concentration of THg 9.40 (9.92) μg g⁻¹ dry weight (DW) (standard deviation of the average in parenthesis); kidney and muscle showed similar values, ranging from 2.34 to 3.63 μg g⁻¹ DW. Selenium concentrations were similar in hepatic and renal tissues, with values from 13.62 to 14.56 μg g⁻¹ DW; the lowest concentration was observed in muscle, 4.13 (2.05) μg g⁻¹ DW. Among the specimens analyzed, the maximum concentrations of THg and Se were observed in the single adult female studied. An increasing age trend is observed for THg concentrations in tissues analyzed. The molar ratio of Se/Hg in the hepatic, renal, and muscle tissues were 8.7 (9.6), 13.2 (9.5), and 9.0 (11.4), respectively, suggesting Se protection against Hg toxicity. Silver concentrations in the three tissues were included, and the Se/(Hg + 0.5×Ag) molar ratio showed values closer to 1. Both Hg and Se concentrations in liver and kidney were comparable to those found in other small odontocetes from Argentine and Brazilian waters. This study constitutes the first joint description reported of Hg and Se concentrations in liver, kidney, and muscle of the Commerson’s dolphin species.