Improvement in Survivorship: The Key for Population Recovery?

Interspecific interactions are key drivers of individual and population-level fitness in a wide range of animals. However, in marine ecosystems, it is relatively unknown which biotic and abiotic factors impact behavioral interactions between competing species. We assessed the impact of weather, marine productivity, and population structure on the behavioral agonistic interactions between South American fur seals (SAFSs), Arctocephalus australis, and South American sea lions (SASLs), Otaria byronia, in a breeding colony of SAFS. We hypothesized that agonistic interactions between SAFSs and SASLs respond to biotic and abiotic factors such as SAFS population structure, marine productivity, and weather. We found that SASL and SAFS interactions almost always resulted in negative impacts on the social structure or reproductive success of the SAFS colony. SASL adult males initiated stampedes of SAFS and/or abducted and predated SAFS pups. Adult SAFS males abundance and severe weather events were negatively correlated with agonistic interactions between species. However, proxies for lower marine productivity such as higher sea surface temperature and lower catches of demerso-pelagic fish were the most important predictors of more frequent agonistic interactions between SAFS and SASL. Under the current scenario of decline in marine biomass due to global climate change and overfishing, agonistic interactions between competing marine predators could increase and exacerbate the negative impacts of environmental change in these species.

Craniometrical data of male and female skulls collected from 1974 to 2007 were used to test the hypothesis that the somatic growth of South American sea lions Otaria flavescens in northern Patagonia has been affected by a reduction in the per capita food availability, due to a combination of the population recovery after cessation of sealing and the development of industrial fishing target- ing Argentine hake Merluccius hubbsi. Most of the 19 craniometric variables considered decreased through time in both sexes, and the same trend was found for a variable extracted by means of prin- cipal component analysis that was related to skull volume. Most of the reductions in skull size and volume have happened since 1990, when the sea lion population peaked and the hake population collapsed. This evidence, combined with a review of supplementary data derived from stable isotope analysis, supports the hypotheses that the somatic growth of South American sea lions is density- dependent and that industrial fishing has reduced the carrying capacity of the ecosystem for South American sea lions.

To understand the recovery process and population dynamics of species that were severely depleted, it is essential to monitor their population size and habitat changes throughout their distribution. The South American sea lion (SASL, Otaria flavescens) provides an opportunity to investigate the process of a reduction from sealing and the subsequent recovery in a marine mammal species. Its abundance was depleted throughout its distribution, but the most affected extraction areas were Peninsula Valdes (northern Patagonia) and Tierra del Fuego (Fuegian Archipelago). The aims of this work are to present recent estimates of the population abundance and then analyze changes in social composition, distribution, population size and trend of SASL at their sub-Antarctic distribution. We made an aerial survey of Fuegian Archipelago colonies and compared the results with historical compilation data registered since 1948. In total 49 colonies were surveyed (24 exclusive of SASL, 15 shared with South American fur seals and 10 sites were abandoned). An abundance of 7684 individuals (including 440 pups) was recorded. There was an increase of population abundance, with a change of the social composition and distribution of some colonies through time. The average annual percentage of population changes yields a growth of 8.8%. This value completes the population growth trend data throughout Southwestern Atlantic for SASL, and shows that there is an increasing latitudinal gradient of these rates. We discuss possible explanations related to differences in the beginning of the recovery, or in reactions to local environmental constraints, or migration from Pacific stocks.

Ingestion of fishing items by South American sea lion in southern Brazil: Indicating a neglected problem

Understanding the population dynamics of marine mammals is essential for assessing their resilience to historical harvesting pressures and current anthropogenic threats. The South American sea lion (SASL, Otaria byronia ), widely distributed along the South American coasts, represents the largest biomass of northern and central Patagonia. This species faces threats such as incidental fishing captures, aquaculture, and tourism, with well‐documented impacts on its population. However, the effects of Highly Pathogenic Avian Influenza (HPAI) H5N1 on its population dynamics are poorly understood. This study provides new insights into the impact of the 2023 avian influenza outbreak on the SASL in northern Patagonia. Population trends and age‐sex class composition of colonies were updated, incorporating the HPAI outbreak in the Río Negro rookeries to compare trends before and after the epizootic event. A positive trend in SASL abundance was observed from 2007 to 2022 across most age and sex classes. However, in the 2024 census, 7175 ± 145 individuals were counted across three colonies, with the largest, Punta Bermeja, recording a 27.6% decline. During the 2023 outbreak, 1476 deaths were reported, affecting all age and sex classes. These findings suggest the HPAI H5N1 outbreak significantly impacted the previously positive population trend.

Although the body size of consumers may be a determinant factor in structuring food webs, recent evidence indicates that body size may fail to fully explain differences in the resource use patterns of predators in some situations. Here we compared the trophic niche of three sympatric and sexually dimorphic air‐breathing marine predators (the South American sea lion,Otaria flavescens, the South American fur seal,Arctocephalus australis, and the Magellanic penguin,Spheniscus magellanicus) in three areas of the Southwestern Atlantic Ocean (Río de la Plata and adjoining areas, Northern Patagonia and Southern Patagonia), in order to assess the importance of body size and mouth diameter in determining resource partitioning. Body weight and palate/bill breadth were used to characterize the morphology of each sex and species, whereas the trophic niche was assessed through the use of stable isotope ratios of carbon and nitrogen. The quantitative method Stable Isotope Bayesian Ellipses in R (SIBER) was used to compute the area of the Bayesian ellipses and the overlap of the isotopic niches. The results showed that morphological similarity was significantly correlated with isotopic distance between groups within the δ13C–δ15N bi‐plot space in the Río de la Plata area, but not in Northern and Southern Patagonia. Furthermore, resource partitioning between groups changed regionally, and some morphologically distinct groups exhibited a large trophic overlap in certain areas, such as the case of male penguins and male sea lions in Southern Patagonia. Conversely, female sea lions always overlapped with the much larger males of the same species, but never overlapped with the morphologically similar male fur seals. These results indicate that body size and mouth diameter are just two of the factors involved in resource partitioning within the guild of air‐breathing predators considered here, and for whom – under certain environmental conditions – other factors are more important than morphology.

In Chile, since January 2023, a sudden and pronounced increase in strandings and mortality has been observed among South American (SA) sea lions (Otaria flavescens), prompting significant concern. Simultaneously, an outbreak of highly pathogenic avian influenza H5N1 (HPAIV H5N1) in avian species has emerged since December 2022. To investigate the cause of this unexpected mortality, we conducted a comprehensive epidemiological and pathologic study. One hundred sixty-nine SA sea lions were sampled to ascertain their HPAIV H5N1 status, and long-term stranding trends from 2009 to 2023 were analyzed. In addition, two animals were necropsied. Remarkably, a significant surge in SA sea lion strandings was observed initiating in January 2023 and peaking in June 2023, with a count of 4,545 stranded and deceased animals. Notably, this surge in mortality correlates geographically with HPAIV outbreaks affecting wild birds. Among 168 sampled SA sea lions, 34 (20%) tested positive for Influenza A virus, and 21 confirmed for HPAIV H5N1 2.3.4.4b clade in tracheal/rectal swab pools. Clinical and pathological evaluations of the two necropsied stranded sea lions revealed prevalent neurological and respiratory signs, including disorientation, tremors, ataxia, and paralysis, as well as acute dyspnea, tachypnea, profuse nasal secretion, and abdominal breathing. The lesions identified in necropsied animals aligned with observed clinical signs. Detection of the virus via immunohistochemistry (IHC) and real-time PCR in the brain and lungs affirmed the findings. The findings provide evidence between the mass mortality occurrences in SA sea lions and HPAIV, strongly indicating a causal relationship. Further studies are needed to better understand the pathogenesis and transmission.

Small-scale variation in the diet of the South American Sea lion (Otaria flavescens) in northern Patagonia (Argentina)

Individual specialisation is increasingly recognised to be an ecological and evolutionary process having important consequences for population dynamics of vertebrates. The South American fur seal (SAFS) and the South American sea lion (SASL) are two otariid species with similar ecology that coexist in sympatry in the Uruguayan coast. These two species have contrasting trends and widely different population sizes. The underlying reasons for these population trends, unique in their geographical ranges, remain unknown. We studied the foraging ecology of these otariid species over 2 years at the individual- and population levels using the isotopic ratios (δ13C–δ15N) in whiskers of both sexes. We compared the isotope ratios between species and sexes and used several metrics to characterise the degree of overlap and distinctiveness in the use of isotopic niche space at the individual- and population levels. Interspecific trophic niche overlap was minimal, thus ruling out interspecific competition as the cause for the contrasting population trends of both species. At the intraspecific level, both species had sexual segregation in their foraging areas, but each species had a large overlap in the isotopic niches between sexes. While SAFS had a wider niche and generalist individuals, SASL had the narrower niche with a higher degree of individual specialisation. Behavioural constraints during the breeding season, intraspecific competition and a major dependence on resources of the Uruguayan coastal shelf may explain why SASL had a higher trophic individual specialisation and a larger vulnerability in a heavily exploited habitat by fisheries and, by consequence, a locally declining population trend.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 384:273-286 (2009) - DOI: https://doi.org/10.3354/meps08017 Historic diet change of the South American sea lion in Patagonia as revealed by isotopic analysis M. Drago1,*, E. A. Crespo2, A. Aguilar1, L. Cardona1, N. García2, S. L. Dans2, N. Goodall3,4 1Department of Animal Biology, University of Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain 2Laboratory of Marine Mammals, Centro Nacional Patagonico (CENPAT-CONICET), and National University of Patagonia, Blvd. Brown 3600, 9120 Puerto Madryn, Argentina 3Acatushún Museum, 9410 Ushuaia, Tierra del Fuego, Argentina 4Centro Austral de Investigaciones Científicas (CADIC), Bernardo A. Houssay 200, V9410CAB Ushuaia, Tierra del Fuego, Argentina *Email: m.drago@ub.edu ABSTRACT: Carbon and nitrogen isotopic analyses of skull bone were used to investigate how sealing and the development of industrial fishing have affected the diet of the South American sea lion Otaria flavescens in northern Patagonia. Males from Tierra del Fuego were used as a control, as the species there was decimated by sealing, but industrial fishing is only poorly developed. The δ13C of both males and females from northern Patagonia increased from the 1940s to the 1970s, and then declined steadily. The decline in the slope was similar in both sexes, although females were more depleted in 13C than were males. The δ15N remained unaffected in males throughout the period, whereas that of females decreased from the 1940s to the 1970s and then stabilized. Conversely, no change was found in either the δ13C or δ15N in the skulls from Tierra del Fuego animals. As benthic prey off northern Patagonia are more enriched in 13C than are pelagic prey, the above results indicate increased consumption of benthic coastal prey in this region from the 1940s to the 1970s, when sea lions were decimated by commercial hunting, and increased consumption of pelagic prey since the 1970s, simultaneous with sea lion population recovery. Reinforced intraspecific competition and massive discard of pelagic fish likely contributed to the observed dietary shift, while the poorly developed industrial fishing off Tierra del Fuego did not facilitate a similar change there. Nevertheless, physical forcing related to regime changes observed in the Pacific Ocean since the 1970s may also have played a role. KEY WORDS: South American sea lion · Otaria flavescens · Dietary shift · Stable isotopes · Bone · Fishery interactions · Discarded fish Full text in pdf format PreviousNextCite this article as: Drago M, Crespo EA, Aguilar A, Cardona L, García N, Dans SL, Goodall N (2009) Historic diet change of the South American sea lion in Patagonia as revealed by isotopic analysis. Mar Ecol Prog Ser 384:273-286. https://doi.org/10.3354/meps08017 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 384. Online publication date: May 29, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Status of the population of South American sea lion (Otaria flavescens Shaw, 1800) in southern Argentina

Se han descrito tacticas reproductivas para machos y hembras en sistemas reproductivos poliginicos, dentro de las cuales, una respuesta conductual sexo-especifico seria esperable para maximizar el ixito reproductivo. El presente estudio da cuenta de un seguimiento conductual del lobo marino comun Otaria flavescens durante la epoca reproductiva (ER) y no reproductiva (ENR) en el Santuario de la Naturaleza Loberia Cobquecura, Chile central. Se registraron patrones conductuales de machos, hembras, juveniles y crias entre mayo de 2008 y diciembre de 2009. Los machos presentaron mas registros de conductas asociadas a agresion, desplazamiento y reconocimiento durante ER, mientras que la conducta descanso fue mayor durante ENR. Hembras y juveniles presentaron mayores registros de reconocimiento durante ENR mientras que las otras categorias conductuales no presentaron diferencias entre ER y ENR. Las conductas agresivas por parte de los machos asi como las relacionadas al cuidado parental por parte de las hembras podrian ser estrategias conductuales desarrolladas por ambos sexos para asegurar la viabilidad poblacional. Este estudio contribuye al conocimiento de los patrones conductuales reproductivos de la especie y forma parte de uno de los seguimientos conductuales reproductivos mas continuos desarrollados en la actualidad en el lobo marino comun. Dado que el estudio se realiza en un area protegida dentro del marco legal de Santuario de la Naturaleza, los resultados expuestos seran de utilidad para futuras comparaciones con loberas reproductivas afectadas por actividad antropica.

Los pinipedos muestran una alta predictibilidad en su distribucion, tanto espacial como temporal, y tienden a congregarse en parches, lo que permite un facil acceso de turistas. Sin embargo, la presencia de dichos turistas puede generar un impacto negativo sobre los animales. El objetivo de este estudio fue evaluar, por primera vez en Chile, el efecto del ecoturismo sobre el comportamiento del lobo marino comun Otaria flavescens durante la epoca reproductiva. Registramos un total de 44 visitas de embarcaciones a la lobera reproductiva de Isla Chanaral. La mayoria de los turistas mostro una actitud de calma, seguida por moderada y perturbadora. La respuesta de los lobos marinos fue mayoritariamente de escape, seguida de inactiva y alerta. La respuesta de los lobos marinos se relaciono negativamente con la distancia de aproximacion de la embarcacion a la colonia, pero no se relaciono ni con el tiempo de permanencia de la embarcacion en la colonia ni con la conducta de los turistas. Nuestros resultados indican que el lobo marino comun es afectado negativamente por la presencia de turistas, especialmente debido al escape de los individuos desde la colonia al mar. Dichos escapes pueden generar efectos fisiologicos negativos sobre el animal, lo que puede incidir sobre su adecuacion biologica. Sugerimos que futuros estudios evaluen el comportamiento de respuesta de los lobos marinos durante la epoca reproductiva y en otros periodos del ano, ademas de analizar posibles diferencias entre clases de edad y sexo, lo que permita contar con herramientas adecuadas para el manejo del turismo sobre el lobo marino comun en Chile.

Knowledge, attitudes and behavioural intentions of gillnet fishermen towards the South American sea lion in two marine protected areas in southern Brazil

This study describes operational interactions between coastal gillnet fishing and South American sea lions (Otaria flavescens) off the southern Brazilian coast. In total, 263 onboard surveys were carried out during three periods between 1992 and 2012 in fishing boats from two harbours on the northern coast of Rio Grande do Sul State: Passo de Torres (29°19'S; 49°43'W) and Imbé (29°58'S; 50°07'W). Interactions of South American sea lions were observed in 116 (24.0%) out of 484 fishing operations. These interactions were more frequent in fishing boats from Passo de Torres (frequency of occurrence FO = 42.8%) than those from Imbé (FO = 14.8%; P < 0.001) and during autumn and winter months. Interactions between South American sea lions and fishing activities with fixed bottom gillnets in Imbé were most frequent during period III of the study (2011/2012) (FO = 52.0%; P = 0.032). These results demonstrated that interactions are not as high as reported/complained about by the local fishermen who tend to exaggerate the impact of these interactions. It is suggested that reduced fish stock and increased fishing effort during recent decades is raising the frequency of encounters with South American sea lions during fishing activities off the southern Brazilian coast. Therefore, the implementation of fishery management measures that reduce fishing effort and that integrate environmental education programmes are essential to reduce conflicts between fishing activities and the sea lions in the region. Copyright © 2015 John Wiley & Sons, Ltd.