Interactions between Humans and South American Sea Lions (Otaria byronia) during an Avian Flu Outbreak in the Southeastern Pacific

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.

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.

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

Pups on mercury: Tracking early life exposure on South American fur seals (Arctocephalus australis) and South American sea lions (Otaria byronia) in the Southeastern Pacific.

The focus of this commentary is represented by the pandemic risk associated with the highly pathogenic avian influenza (HPAI) A(H5N1) virus, clade 2.3.4.4b. More in detail, the herein dealt pandemic alarm appears to be primarily justified by the huge and progressively growing number of virus-susceptible domestic and wild birds and mammals, including threatened marine mammal species like South American sea lions and elephant seals as well as harbour porpoises, bottlenose dolphins and polar bears. Of major concern is the susceptibility of dairy cattle to HPAI A(H5N1) virus, particularly the documented and unprecedented colonization of host's mammary gland tissue, resulting in viral shedding through the milk alongside a large series of cases of infection in dairy farm workers in several USA locations. Despite well-documented zoonotic capability, no evidences of a sustained and efficient HPAI A(H5N1) viral transmission between people have been hitherto reported. If this were to happen sooner or later, a new pandemic might consequently arise. Therefore, keeping all this in mind and based upon the lessons taught by the COVID-19 pandemic, a "One Health, One Earth, One Ocean"-centered approach would be absolutely needed in order to deal in the most appropriate way with the HPAI A(H5N1) virus-associated zoonotic and pandemic risk.

Fatty acids have been widely used as trophic biomarkers in marine mammals. However, for the South American sea lion, the most abundant otariid in the eastern South Pacific, there is no information about blubber fatty acids and their link to diet. Here, we compare fatty acid profiles of sea lions from two distinct oceanographic regions in northern and southern Chile. Their fatty acids vary greatly between regions, suggesting dietary differences at a spatial scale. The fatty acid C22:6ω3 was more abundant in sea lions from the northern region, likely associated with consumption of anchovy, cephalopods, and crustaceans, which are rich in that fatty acid, and have been reported as their main prey items. Sea lions from the southern region were richer in C22:1 and C20:1, characteristic of teleost fish, suggesting a piscivorous diet. Males displayed a more diverse fatty acid composition than females, suggesting a wider trophic niche. Few individual sea lions within the southern region had unusually high levels of C18:2ω6, commonly found in terrestrial environments. This suggests consumption of farmed salmon, whose diet is usually based on terrestrial sources. This demonstrates how human intervention is being reflected in the tissues of a top predator in a natural environment.

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.

Conditions experienced during the nonbreeding period have profound long‐term effects on individual fitness and survival. Therefore, knowledge of habitat use during the nonbreeding period can provide insights into processes that regulate populations. At the Falkland Islands, the habitat use of South American sea lions (Otaria flavescens) during the nonbreeding period is of particular interest because the population is yet to recover from a catastrophic decline between the mid‐1930s and 1965, and nonbreeding movements are poorly understood. Here, we assessed the habitat use of adult male (n = 13) and juvenile male (n = 6) South American sea lions at the Falkland Islands using satellite tags and stable isotope analysis of vibrissae. Male South American sea lions behaved like central place foragers. Foraging trips were restricted to the Patagonian Shelf and were typically short in distance and duration (127 ± 66 km and 4.1 ± 2.0 days, respectively). Individual male foraging trips were also typically characterized by a high degree of foraging site fidelity. However, the isotopic niche of adult males was smaller than juvenile males, which suggested that adult males were more consistent in their use of foraging habitats and prey over time. Our findings differ from male South American sea lions in Chile and Argentina, which undertake extended movements during the nonbreeding period. Hence, throughout their breeding range, male South American sea lions have diverse movement patterns during the nonbreeding period that intuitively reflects differences in the predictability or accessibility of preferred prey. Our findings challenge the long‐standing notion that South American sea lions undertake a winter migration away from the Falkland Islands. Therefore, impediments to South American sea lion population recovery likely originate locally and conservation measures at a national level are likely to be effective in addressing the decline and the failure of the population to recover.

Pacific and Atlantic sea lion mortality caused by highly pathogenic Avian Influenza A(H5N1) in South America

Goetz, S., Wolff, M., Stotz, W., and Villegas, M. J. 2008. Interactions between the South American sea lion (Otaria flavescens) and the artisanal fishery off Coquimbo, northern Chile. – ICES Journal of Marine Science, 65: 1739–1746. The South American sea lion (Otaria flavescens) forages in coastal waters, where it interacts with fisheries and causes considerable economic loss by removing some catch and damaging gear. This study describes for the fishery region of Coquimbo (Chile) where, when, and with what type of gear interactions occur, characterizes the animals involved (group size, sex, and age), and derives some management recommendations. The study was based on 55 interviews with fishers and observations aboard fishing vessels in the main fishing sectors between October 2003 and March 2004. Interactions were primarily at night (88% of interviewees fished at night), in the bay (“Bahía”) of Coquimbo (81% of interviewees fished in this sector), where shoaling fish were abundant, and with purse-seines (100% of interviewees used this gear). Although some large groups of sea lions were seen, most comprised 1–10 animals. Most animals that interacted with the fishing gear were males (67%), probably because of the different feeding strategies of the two sexes. Management options discussed include the adjustment of fisheries to foraging behaviour of sea lions, and the controlled elimination of conflicting animals.

de la Torriente, A., Quiñones, R. A., Miranda-Urbina, D. A., and Echevarría, F. 2010. South American sea lion and spiny dogfish predation on artisanal catches of southern hake in fjords of Chilean Patagonia. – ICES Journal of Marine Science, 67: 294–303. The South American sea lion (Otaria flavescens) is a pinniped known to interact with fisheries, potentially damaging gear and lowering catches. Predation by O. flavescens and spiny dogfish (Squalus acanthias) on artisanal southern hake (Merluccius australis) catches in fjords of Chilean Patagonia is estimated and compared. Observations were made in the Gulf of Ancud and Comau Fjord in southern Chile from October 2005 to September 2006. Losses of southern hake catches to O. flavescens predation were 1.6% of the total catch of the species, and to spiny dogfish predation were slightly higher, at 3.3%. The predation of both species on southern hake catches varied throughout the year, but was lower in summer. Both predators showed a preference for adult southern hake over juveniles. There was no significant relationship between predation on southern hake catches by the sea lion and the availability of adult and juvenile southern hake on longlines (AHCL). However, there was a significant relationship (p < 0.05) between AHCL and spiny dogfish predation. Most O. flavescens interaction events (81.4%) were during longline retrieval. Our results showed minimal interactions between O. flavescens and the artisanal southern hake fishery in the area, so with the present abundance of O. flavescens, there is no justification for reducing the sea lion population by hunting.

Our understanding of how air-breathing marine predators cope with environmental variability is limited by our inadequate knowledge of their ecological and physiological parameters. Because of their wide distribution along both coasts of the sub-continent, South American sea lions (Otaria byronia) provide a valuable opportunity to study the behavioral and physiological plasticity of a marine predator in different environments. We measured the oxygen stores and diving behavior of South American sea lions throughout most of its range, allowing us to demonstrate that diving ability and behavior vary across its range. We found no significant differences in mass-specific blood volumes of sea lions among field sites and a negative relationship between mass-specific oxygen storage and size, which suggests that exposure to different habitats and geographical locations better explains oxygen storage capacities and diving capability in South American sea lions than body size alone. The largest animals in our study (individuals from Uruguay) were the shallowest and shortest duration divers, and had the lowest mass-specific total body oxygen stores, while the deepest and longest duration divers (individuals from southern Chile) had significantly larger mass-specific oxygen stores, despite being much smaller animals. Our study suggests that the physiology of air-breathing diving predators is not fixed, but that it can be adjusted, to a certain extent, depending on the ecological setting and or habitat. These adjustments can be thought of as a 'training effect': as the animal continues to push its physiological capacity through greater hypoxic exposure, its breath-holding capacity increases.

Five years of behavioral observations revealed significant effects of high air temperatures and breeding site topography on the mating system of South American sea lions in Peru. Unlike most polygynous mammals that defend females or fixed territories, male sea lions in Peru maintained positions along the shoreline where females passed each day to thermoregulate, and where most copulations occurred. Sex ratios (1 male per 17 females) and male mating success were extremely skewed (14% of males achieved 50% of the copulations, and 25% of them did not copulate at all). The mass daily movements of females toward the water and cool substrate of the shoreline, along with a highly skewed sex ratio, accentuated the difficulty for males to monopolize and restrict female movements. Females moved freely and chose their mates, unlike in temperate regions of their range where male South American sea lions control groups of females or access to tide pools. Our observations indicate that the South American sea lion in Peru has a lek‐like breeding system. This is a rare alternative to the common male strategies of defending females and resources, and is likely an evolutionary product of their highly skewed sex ratio, protracted breeding season, and the extreme subtropical climate where they breed.

Apex marine predators alter their foraging behavior in response to spatial and/or seasonal changes in natural prey distribution and abundance. However, few studies have identified the impacts of aquaculture that represents a spatially and temporally predictable and abundant resource on their foraging behavior. Using satellite telemetry and stable isotope analysis we examined the degree of spatial overlap between the South American sea lion (SASL) and salmon farms, and quantify the amount of native prey versus farmed salmonids in SASL diets. We instrumented eight SASL individuals with SRDL-GPS tags. Vibrissae, hair and skin samples were collected for δ13C and δ15N analyses from five of the tagged individuals and from four males captured in a haul-out located adjacent to salmon farms. Tracking results showed that almost all the foraging areas of SASL are within close proximity to salmon farms. The most important prey for the individuals analyzed was farmed salmonids, with an estimated median (±SD) contribution of 19.7 ± 13.5‰ and 15.3 ± 9.6‰ for hair and skin, respectively. Using vibrissae as a temporal record of diet for each individual, we observed a remarkable switch in diet composition in two SASL, from farmed salmonids to pelagic fishes, which coincided with the decrease of salmon production due to the infectious salmon anemia virus that affected salmon farms in Chile at the end of 2008. Our study demonstrates the usefulness of integrating stable isotope derived dietary data with movement patterns to characterize the impacts of a non-native prey on the foraging ecology of an apex marine predator, providing important applied implications in situations where interactions between aquaculture and wildlife are common.

South American Sea Lion: Otaria flavescens