Dg Vales

Studying trophic feeding habits and their variation over time is crucial for understanding individual and population success. Although many generalist feeders’ populations appear to use diverse trophic resources, they are often composed of individuals that specialize in only a subset of these resources, a phenomenon known as individual trophic specialization (ITS). The South American sea lion (SASL) (Otaria flavescens), widely distributed along the South American coast, is an opportunistic and generalist predator with a diverse diet, making it a good model for studying ITS. We aimed to estimate the diet composition and the degree of ITS among SASL females on Isla Arce, Argentina, over a period of three years (2012 to 2014). For that, we analysed stable isotopes (δ15N and δ13C) in vibrissae from 12 females. Over the three years studied, females from this colony primarily fed on pelagic prey. At the population level, the most commonly consumed prey varied between the Argentine anchovy (Engraulis anchoita) in 2012 and 2014 and the Patagonian squid (Doryteuthis gahi) in 2013. Consuming mostly pelagic resources throughout the year, unlike previous studies in nearby colonies, suggests the existence of different foraging strategies in lactating females. Although the prey contribution varied between years, the analysis indicated that SASL females breeding on Isla Arce show some degree of ITS, which could be a mechanism adopted by individuals to mitigate the potential competition given by sustained population increases.

Humans have altered marine ecosystems over very long-time scales and historical data is often needed to understand the true magnitude of human impacts. The Southwest Atlantic Ocean has a long history of large-scale removal of marine vertebrates due to whaling, sealing, and fishing in the past three centuries. Historical catch records are crucial in assessing the conservation status of these historically over-exploited populations and setting suitable recovery goals. However, several gaps in the history of exploitation of many populations limit our ability to judge recoveries success. This study examines the history of the Spanish fishing company, the Real Compañía Marítima (Royal Maritime Company), and reconstructs its catches of marine mammals in Patagonia and on the north coast of the Río de la Plata. The analysis of a wide range of historical sources reveals that, between the years 1790 and 1804, the Company extracted less than 100 southern right whales Eubalaena australis, some 200,000 South American fur seals Arctocephalus australis and South American sea lions Otaria flavescens, and a few southern elephant seals Mirounga leonina. Although the Company’s whale catch is negligible compared to that of other nations in the same whaling grounds, the amount of fur seals and sea lions removed from the ecosystem deserves attention. This historical survey provides us with the first estimate of the catches made by the Real Compañía Marítima. However, these figures only represent a small part of the extractive activities that took place in the region and further research is encouraged to assess the true dimension of human impacts on Southwest Atlantic ecosystems. The incorporation of retrospective data into ecological studies can be laborious and may have inherent biases, but it also provides valuable information for comprehending modern ecosystems and formulating appropriate conservation plans.

The northern coast of the San Jorge Gulf, Atlantic Patagonia, is recognised as a marine biodiversity hot spot and is designated as a priority conservation area. Among marine mammals, three species of pinnipeds inhabit the region. While South American sea lions ( Otaria flavescens) have a higher abundance and a larger number of colonies than South American fur seals ( Arctocephalus australis), a few individuals of the Southern elephant seal ( Mirounga leonina) reside in the region. Nevertheless, little is known about the abundance and distribution of these pinnipeds before the 18th century, when various extractive activities became widespread, including the unregulated exploitation of furs and oil. This study aims to examine whether the distribution and relative abundance of ancient pinnipeds differ from present-day populations. To achieve this, we conducted inter-specific identification of pinniped bone remains coming from archaeological assemblages dated from 6000 to 600 ¹⁴C years BP and reviewed historical sources to contrast these retrospective data with modern ecological literature. The results suggest changes over time in the relative abundances of species within the pinniped community. The relative abundance of fur seals was greater than or equal to that of sea lions in most Late-Holocene pinniped assemblages. Additionally, fur seals have been recorded in historical and Late-Holocene periods in places where they are currently very rare. These findings are consistent with the higher relative abundance of fur seals recorded in other archaeological sites along the Patagonian coast, suggesting that modern distribution and abundance have been heavily affected by commercial hunting. This study contributes to a better understanding of the nature and magnitude of the anthropic impact on the marine ecosystem of the northern coast of the San Jorge Gulf. It also provides historical baseline information to strengthen conservation policies and restoration efforts.

This study compares the δ ¹⁵ N values and the trophic position of two seabird species throughout the late Holocene in three regions in the southwestern Atlantic Ocean to assess the hypothesis that the decimation of megafauna led to changes in the trophic position of mesopredators. Modern and ancient mollusk shells were also analyzed to account for changes in the isotopic baseline through time. Results revealed that modern Magellanic penguins have higher δ ¹⁵ N values than their ancient conspecifics in the three regions, after controlling for changes in the isotopic baseline. This was also true for modern Imperial shags compared with ancient unidentified cormorants/shags from the two areas where ancient specimens were recovered (southern Patagonia and the Beagle Channel). Such temporal variability might be caused by three non–mutually exclusive processes: decreased availability of pelagic squat lobster resulting from decreasing primary productivity through the late Holocene, increased availability of small fishes resulting from the sequential depletion of other piscivores (South American fur seal and sea lion and Argentine hake) since the late eighteenth century, and modification of the migratory patterns of Magellanic penguins. Although disentangling the relative contribution of all those processes is impossible at this time, the results reported here demonstrate that the ecology of Magellanic penguins and Imperial shags has undergone major changes since the late Holocene.

Natural or human-induced environmental changes can modify the structure of ecological communities and thus alter food web interactions. After the collapse of hake stocks (Merluccius hubbsi) provoked by fisheries over the Patagonian shelf in 1997 profound changes have taken place in the community, including long-term dietary shifts in some marine vertebrate predators. Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios in bone collagen of subadult and adult male South American fur seals (Arctocephalus australis) were measured for the period 1976–2017 to investigate if the changes occurred in the marine community from northern and central Patagonia affected the diet of this predator. Suess corrected δ¹³C values and δ¹⁵N values in bone collagen of fur seals did not change significantly over the study period. According to this, male fur seals have remained as pelagic foragers without changing their trophic position nor switching their main preys in the Patagonian food web over the last four decades. This long-term stability in the diet of fur seals contrasts with dietary changes reported for benthic foragers in the region. Although long-term diet studies are restricted to a few marine predators in the region, current evidence suggests that benthic-demersal foragers were more prone to dietary shifts than pelagic ones after perturbations that occurred in the marine community of northern and central Patagonia.

Arctocephalus australis y Otaria flavescens son las dos especies de otáridos que aparecen con mayor frecuencia en el registro zooarqueológico de sitios costeros de Sudamérica. La similitud en los huesos del esqueleto postcraneal en estos otáridos ha limitado la identificación específica, constituyéndose en una de las mayores dificultades encontradas para emprender estudios zooarqueológicos pormenorizados en estos animales. El objetivo de este trabajo es presentar criterios descriptivos claros que puedan ser empleados en la identificación de estas dos especies recuperadas en el registro zooarqueológico. La utilización de rasgos diagnósticos junto a otros abordajes existentes (estudios osteométricos, cronograma de fusión de huesos) permitirá investigar aspectos particulares que involucren el registro fósil de estos animales. A partir de una muestra de 24 individuos adultos actuales se revisaron los criterios propuestos previamente por otro autor y como resultado se presenta una nueva lista de 36 rasgos diagnósticos para huesos del esqueleto postcraneal, sólidamente sustentada.

Stable carbon and nitrogen isotope ratios in the skeletal elements of both ancient and modern marine species from the Beagle Channel were used to compare the structure of Late Holocene and modern food webs, and predict potential changes as a result of a Sea Surface Temperature (SST) increase in the region. Complementary, ancient and modern shells of limpets and mussels were isotopically analysed to explore changes in the isotopic baseline and compare marine food webs through time after an appropriate correction for baseline shifts. Results confirmed a declining pattern of marine primary productivity during the Late Holocene in the Beagle Channel. In general, the isotopic niches overlapped largely in the ancient food web in comparison to the current marine one, with the exception of that of cormorants (Phalacrocorax sp.). Our data suggest that all the species that have undergone intense human exploitation (Arctocephalus australis, Otaria flavescens and Merluccius sp.) significantly increased their trophic levels. The most important finding of this work was the very high isotopic overlap between snoek (Thyrsites atun) and hake (Merluccius sp.) during the Late Holocene. Increasing SST as a result of global warming could favour the recolonization of the southern South‐Western Atlantic Ocean by snoek from the South‐Eastern Pacific Ocean, with a potential impact on the landings of the economically important Argentine and Austral hake. These findings highlight the relevance of using zooarchaeological remains for providing predictions about marine food webs changes in the near future.