Growing global concern about the impacts of non-selective fisheries on marine mammals has resulted in an increase in international agreements and national regulations that pressure national governments, such as Chile, to develop scientifically based, cost-effective methods for assessment, monitoring, and reduction of bycatch. This study presents an expert elicitation approach to characterize bycatch mortality of marine mammals in small-scale fisheries in Chile, with particular focus on the Chilean dolphin (Cephalorhynchus eutropia). Given its restricted distribution and vulnerability to multiple anthropogenic threats, the Chilean dolphin represents a key candidate for piloting a comprehensive and scalable bycatch monitoring program. The methodology establishes baseline data on bycatch mortality by integrating an expert elicitation approach using the IDEA method to improve accuracy and reduce uncertainty, alongside regional stakeholder workshops and interview surveys with small-scale fishers. Results indicate that bycatch mortality occurs throughout the species' range with an average estimated value of 17 dolphins killed each year. Inshore gillnets were identified as the primary gear responsible for bycatch mortality. Fishers' perceptions of Chilean dolphin conservation were generally positive, suggesting openness to mitigation measures. Regular implementation of this cost-effective structured elicitation approach can support adaptive management and contribute to more effective fisheries regulations. It also represents a scalable approach that fisheries agencies can use as a starting point for improving bycatch monitoring efforts in other locations where small-scale fisheries are causing marine mammal bycatch.

Stable isotope analysis is a powerful tool that is widely used in modern marine ecology. However, its utility depends on researchers accounting for spatial and temporal variability in baseline values, e.g., for the correct interpretation of food web dynamics or animal movement in marine ecosystems. Here, we present the first observation-based δ13C and δ15N isoscapes for particulate organic matter (POM) in the southeastern Pacific, spanning 2300 km of the Chilean coastline. POM samples were collected during four research cruises (2017–2018) across three latitudinal zones. Using a Bayesian hierarchical modeling framework, we predicted spatial variation in δ13CPOM and δ15NPOM values based on in situ and satellite-derived environmental data. Because temporal overlap among stations was limited, these predictions represent integrated isotopic baseline estimates for 2017–2018 rather than season-specific surfaces. Results revealed a latitudinal gradient, with δ13C values increasing and δ15N values decreasing with latitude (i.e., southward). Best-fit models explained 61

Bycatch of marine mammals in fisheries is a critical conservation issue worldwide, and Chile is no exception. Pinnipeds such as the South American sea lion (Otaria byronia, SASL) frequently encounter fishing gear along the Chilean coast. Despite widespread evidence of these interactions, few studies have spatially assessed SASL bycatch risk across multiple fisheries for this species. This study applies the Bycatch Risk Assessment (ByRA) toolbox, a GIS-based model, to evaluate and compare the risk of SASL bycatch across nine Chilean purse-seine and trawl gear fisheries based on data from on-board scientific observer logs from 2015 to 2019. Our findings identify trawl fisheries, particularly those targeting southern hake (Merluccius australis), as posing the highest bycatch risk, especially during the non- reproductive season when SASL exhibit broader spatial distribution. Purse-seine fisheries presented lower risk overall, with the industrial northern fleet showing the highest relative risk. Spatial patterns revealed that risk is concentrated in nearshore areas, where the overlap between the distribution of SASL and fishing activity is the greatest. These results provide a robust, spatially explicit foundation for prioritizing mitigation measures, including the mandatory use of exclusion devices and seasonal restrictions. Our approach underscores the potential mitigation provided by evidence-based management of marine mammal bycatch in Chile and contributes information toward the assessment of compliance with domestic and international regulations.

Large-scale climatic variability and emerging diseases can reshape trophic interactions and ecosystem functioning in highly productive upwelling systems. Here, we evaluate how El Niño conditions and the 2022–2023 avian influenza outbreak affected the population trophic niche of the South American sea lion (Otaria byronia) across the central–southern Humboldt Current System. Within an Optimal Foraging Theory framework, we tested whether environmental forcing and changes in prey availability promote trophic niche contraction or expansion. Trophic metrics, including total niche width (TNW), standardized Levins’ index, and taxonomic richness, were estimated from prey remains in scats collected at multiple colonies over several years along the Chilean coast. Local environmental variability associated with El Niño was quantified using daily sea surface temperature anomalies (SST; local Niño index, LIN), together with a categorical index of avian influenza occurrence (IAA) and an index of relative prey abundance (RPA). TNW declined with increasing El Niño intensity, although responses differed among sites and years, indicating spatially heterogeneous climatic effects. In contrast, avian influenza was associated with localized increases in TNW at some colonies, potentially reflecting altered competitive dynamics or shifts in prey exploitation following population impacts. Overall, O. byronia exhibited context-dependent trophic responses to climatic and epidemiological disturbances, underscoring the role of upper trophic predators as sentinels of marine environmental change and trophic restructuring in the Humboldt ecosystem.

This study characterizes seasonal hydrography and mixing processes in Almirantazgo Fjord, a sensitive ecosystem in southern Chilean Patagonia. Although estuarine and tidal forcing conventionally explain fjord dynamics, wind stress effects remain less understood in this high-latitude region. The study analyses a comprehensive six-month dataset including a moored time-series of temperature, salinity, and dissolved oxygen, cross-fjord CTD transects, and hydrographic profiles derived from seal-deployed sensors. Observations indicate distinct seasonality, shifting from a stratified water column in summer – defined by low-salinity surface water from glacial melt – to a mixed winter state with significantly reduced vertical stability. The analysis identifies persistent, topographically channelled up-fjord winds as a primary physical driver. By applying the Wedderburn number (Wb) and mechanical energy balance calculations, we determined that strong wind stress perturbs the pycnocline (Wb > 1). During stratified summer periods, strong wind events (above the 90th percentile) generated wind power of the same order of magnitude as that of the estuarine circulation. Under such conditions, wind forcing amplifies vertical mixing, modulates the pressure gradient, and supports oxygenation in the upper and subsurface layers. First-order estimates indicate that the upper brackish layer is flushed in approximately one week, reflecting a dynamic surface exchange governed by the interplay of freshwater buoyancy and wind stress. These results indicate that wind constitutes a primary mechanism regulating the hydrographic structure and biogeochemical function of the Tierra del Fuego inner sea.

Body condition is a key proxy of fitness in pinnipeds, reflecting nutritional status and maternal investment. In the South American sea lion (Otaria flavescens), pup growth and survival depend on maternal foraging success, making pup condition a sensitive indicator of local environments. We quantified spatial and interannual variation in pup body condition across five Chilean breeding colonies spanning 21-53°S during the austral summers of 2024 and 2025. We captured 157 live pups (95 males, 62 females), measured morphometrics and calculated a body condition index (BCI = mass/length). To account for seasonal effects, BCI values were standardized to allow comparisons across sites and years. We tested the effects of sex, year, locality and satellite-derived net primary productivity (NPP). Male pups consistently showed higher standardized BCI than females. Locality was the strongest predictor: Isla Marta (southern limit) exhibited significantly higher values than all other sites, followed by Isla Metalqui. Cobquecura, Isla Choros and Punta Lobos showed lower or intermediate values. Year alone had no effect, but a significant locality × year interaction indicated interannual variability in northern colonies, particularly Punta Lobos. NPP was not retained in top-ranked models, suggesting broad-scale productivity does not directly predict pup condition at this resolution. The pronounced latitudinal gradient, with larger, better-conditioned pups at higher latitudes, is consistent with expectations under Bergmann's rule, which refers to the tendency of animals to be larger in colder climates and smaller in warmer ones. These results underscore the combined influence of local ecological conditions, maternal effects and intrinsic sex differences on pup condition and reinforce the value of South American sea lion pups as sentinels of ecosystem variability along the Chilean coast.

IntroductionSmall marine carnivores inhabiting fragmented rocky coastlines are increasingly exposed to anthropogenic pressures, yet mortality drivers in these systems remain poorly quantified.MethodsWe analyzed 22 years of carcass records (2003–2024) and standardized necropsies to evaluate the contribution of anthropogenic causes and their spatial and temporal patterns in marine otters (Lontra felina) from north-central Chile.ResultsWe documented 173 mortality events involving 181 individuals. Space–time permutation analyses revealed three significant peri-urban clusters associated with areas of high human activity. Among cases with assigned cause, anthropogenic drivers predominated, particularly free-ranging dog attacks, followed by fisheries bycatch and non-specific trauma. Although seasonal differences were not statistically significant, anthropogenic mortality contributed proportionally more during summer months.DiscussionOur findings highlight terrestrial human-related pressures, particularly free-ranging dogs, as underrecognized mortality pathways in marine otters inhabiting human-dominated coastlines. Recurrent spatial clustering indicates predictable mortality risk hotspots and demonstrates the utility of spatio-temporal approaches for informing conservation and management strategies integrating terrestrial and marine systems.

The Chilean Patagonia, between 40°S and 56°S, hosts one of the world’s largest and most productive estuarine systems, where oceanic waters mix with freshwater from rivers, runoff, glaciers, and snowmelt, creating a complex and dynamic estuarine environment. Understanding the factors influencing salinity fluctuations in this region is key to elucidating its ecosystem complexity. This study evaluates the forcings driving salinity variability in the mixed layer of West Patagonia’s coastal zone. A salinity balance was done using GLORYS reanalysis and atmospheric variables from ERA5. Spatiotemporal variability of the salt balance terms was investigated using Hovmöller diagrams focusing on three key sites. Results showed significant seasonal and interannual variability in the mixed layer. Advective terms, particularly the zonal component, were crucial in modulating salinity. A clear annual cycle emerged in the northern sector (40–48°S). Empirical Orthogonal Function analysis identified significant interannual fluctuations, with positive atypical periods in 1997–2005 and 2010–2015, and negative periods in 2006–2008 and 2018–2020. These fluctuations were primarily linked to the dynamics of San Quintín Glacier (∼47°S), which induced anomalous salinity conditions along the coastal domain. Notably, these variations did not exhibit a direct relationship with large-scale climate modes. These findings underscore the intricate nature of salinity variability in West Patagonia’s coastal waters, driven by a complex interplay of local hydrological processes and glacial dynamics. Understanding these mechanisms is essential for anticipating future changes in this fragile and ecologically significant region.

In phocid seals, the fatty acid composition of blubber can be modified during energetically demanding periods, such as fasting, when lipid reserves are mobilised to meet metabolic demands. This study describes the fatty acid composition of the inner, middle, and outer blubber layers of recently moulted southern elephant seals from Southern Patagonia to evaluate blubber stratification during the moulting fast. For this, 8 adult females and 9 juvenile males were sampled during January of 2024 and 2025 in Jackson Bay, Tierra del Fuego, Chile (54°26′53′′ S 69°00′06′′ W). The fatty acid composition across the blubber depth showed stratification, with the inner and outer blubber layers exhibiting the largest dissimilarities. Monounsaturated fatty acids were dominant across blubber layers, while polyunsaturated fatty acids showed the lowest contributions, especially 20:5n-3. Blubber was highly stratified during the moult, which was best explained by the variable sex, followed by standard length. The stratification index showed marked variability among individuals, with adult females exhibiting higher stratification than juvenile males. This greater stratification observed in adult females is presumably due to greater energy expenditure during the breeding season, when they nurse a pup whilst fasting, followed by a shorter foraging trip before moulting compared to juvenile males, and is consistent with the lower lipid content found in the inner blubber layer of adult females. Our findings confirm a high stratification of the blubber during moulting and reflect the importance of considering physiological condition in studies based on the blubber layer.

Baleen whale classical pattern of summering in high latitude and wintering in low latitude has been framed within a continuum of migratory schemes. Here, we aim to understand fin whale distribution and migratory patterns off South America by summarizing dedicated visual surveys, passive acoustic monitoring, and telemetry data from Chile, Argentina, and Brazil. Our results agree with findings from other fin whale populations and whaling records from South America, supporting the existence of multiple migratory schemes including year-round residency and classic migration. An unprecedented case of a “seasonally inverted migration”, with an individual summering in low-mid latitudes and wintering in high latitudes is presented as the first description of a fin whale round trip migratory route in the Southern Hemisphere. Our results reinforce the notion that baleen whale migratory movements are more diverse than previously thought and highlight the relevance of international cooperation for the study and conservation of migratory species.

Interactions between the South American sea lion (Otaria flavescens, SASL) and artisanal fisheries represent a growing conflict in Chile and other Southern Cone countries, with ecological and economic implications. Various factors, such as prey availability, proximity to breeding colonies, environmental conditions, and operational characteristics of fishing,can influence the frequency and intensity of these interactions. This study evaluated ecological, environmental, and operational variables affecting the number and interaction of SASL with artisanal common hake (Merluccius gayi gayi) fisheries in central Chile. A total of 96 fishing operations conducted between November 2020 and November 2021 were analyzed using generalized linear models to assess SASL abundance and fishery interaction. The interaction frequency was 44.8% for gillnets and 31% for longlines, with most events occurring during the hauling phase. Seabird presence, fishing depth, cloud cover, and gear type were significant predictors of the number of SASL individuals observed. The probability of interaction increased with the number of SASL present, although most events involved small groups (<= 4 individuals), suggesting opportunistic behavior. These results indicate that interactions are not random but respond to specific environmental and operational conditions. Furthermore, they suggest that artisanal fishing may act as a trophic facilitator, offering energetically accessible resources for SASL. This study provides key evidence that could support the design of mitigation strategies to reduce conflict between SASL and fisheries in Chile and across South America.

Mercury (Hg) is a toxic metal that biomagnifies through food webs, posing ecological and human health risks. The anchovy (Engraulis ringens), a key forage fish in the Humboldt Current System, sustains major fisheries and transfers energy to top predators. However, spatial patterns of Hg accumulation in this species along the Chilean coast remain poorly understood. We quantified total mercury (THg) in 179 adult anchovies collected along the Chilean coast between 18° - 39°S and evaluated biological (length, mass, trophic position) and environmental (latitude, coastal proximity) drivers using generalized additive models. THg ranged from 7.7 to 56 μg/kg dry mass (mean 26 ± 9 μg/kg). The final model, which included latitude and trophic position, explained 39.5% of the variance in THg concentrations. Latitude was the dominant predictor, while trophic position had only a minor, non-significant effect. Two spatial hotspots of elevated THg were detected near 21 - 24°S and 33 - 36°S, likely linked to industrial emissions and regional oceanography. These results indicate that spatial environmental gradients, rather than diet, govern THg variability in anchovy. This baseline information is essential for ecological risk assessments and supports spatially targeted strategies to mitigate marine pollution, particularly in industrialized coastal zones.

Abstract. The fjords and channels of Chilean Patagonia form a complex estuarine system where freshwater input, tidal currents, and stratification interact to modulate vertical mixing. We combined velocity microstructure profiles (VMP-250) and CTD-SRDL observations collected between 2023 and 2025 to quantify turbulent kinetic energy dissipation (ε) and vertical diffusivity (Kshear) across northern (42–46° S) and southern (52–55° S) Chilean Patagonia. Dissipation rates spanned 10-9–10-5 W kg-2 with maxima near sills and narrow passages such as Paso Desertores, where semidiurnal tides dominate energy input. Northern Patagonia exhibited seasonal stratification driven by freshwater inputs, while southern Patagonia remained weakly stratified and vertically well mixed throughout the year, aided by strong tidal currents and westerly winds. The tidal mixing parameter h/U³ indicated that semidiurnal tides account for ~ 97 % of energy dissipation in the north and ~ 77 % in the south. These findings highlight the strong spatial heterogeneity of turbulent mixing in Patagonian fjords and the key role of the interaction between tidal forcing and stratification in controlling vertical exchange. The results provide a framework for understanding how fjord systems may respond to changing freshwater inputs and atmospheric forcing under a warming climate.

This study investigates the interactions between South American sea lions (Otaria byronia) and trawling fisheries in central-southern Chile, using underwater video technology. From August 2017 to August 2018, a total of 32 underwater filming sessions were conducted across trawl fisheries targeting Patagonian grenadier (Macruronus magellanicus), nylon shrimp (Heterocarpus reedi), and Chilean hake (Merluccius gayi gayi). The records revealed a total of 15 sea lions, including adult and subadult males and females. These individuals were observed engaging in specific behaviors, such as swimming within the trawl nets and feeding at escape panels of bycatch reduction devices (BRDs). Notably, we documented one subadult male reaching 425 meters. This finding suggests a probable significant adaptability and potential predation behavior at extreme depths. Our findings highlight the importance of further monitoring and research to address conflicts between marine mammal populations and the fishing industry, while enhancing the of conservation strategies to ensure their effectiveness.

This research investigated the incidences of marine mammal bycatch reported by artisanal fishers in six fishing coves from San Antonio to Quisco, central Chile, including socioeconomic aspects of the fishery that provide context to this important livelihood. A total of 153 semi-structured and unstructured interviews were conducted with artisanal fishers and their representatives. Responses indicate a low incidence of marine mammal bycatch in the local artisanal fishing sector and raise concern about the possibility of underreporting. In addition, interviews reveal the importance of fishing as a key source of economic and nutritional security for hundreds of thousands of Chileans, including the families of over 1600 registered artisanal fishers in the southern part of central Chile. Results also indicate that fishers have considerable distrust towards marine governance institutions, which may affect their willingness to participate in resource management and marine mammal bycatch reduction programs. Understanding the complexities of local artisanal fisheries and communities can allow for effective fishery management that considers both ecological and socioeconomic importance of artisanal fisheries, especially those that address the protection of protected species such as marine mammals, and the impact of policies on individual harvesters and their communities.

Ship strikes are a worldwide threat to large whales as a major cause of mortality and injury. In the Southeast Pacific, this has been poorly studied. In the last decade, an increase in ship strikes has been observed off Chile. This study assesses ship strike mortality in large whales off Chile using data on fatal strandings from the past 52 years, (1972-2023) and vessel traffic patterns. In 63 out of 226 strandings (28 %), ship strike was the direct or probable cause of mortality, i.e. the primary cause of non-natural death in whales. Fin whales (B. physalus) suffered highest total ship strikes (n = 23; 37%), followed by humpback (M. novaeangliae) (n =13; 21 %), blue whales (B. musculus) (n = 7; 11 %), sei (B. borealis) and sperm whales (P. macrocephalus) (n = 6; 10 %). Ship strikes were highest in the Regions of Valparaiso, Coquimbo, Atacama and Antofagasta (Central-Northern Chile), Los Lagos, Aysen and Magallanes (Southern Chile). Since 2013, when necropsies began to be systematically performed, an average of 5 individuals/year have been killed by ships, mostly between January and May. We review all ship strike studies globally and compare rates in Chile with those elsewhere. Based on data between 2013 and 2023, Chile is the country with the highest ship strike mortality globally; considering the entire time series since 1972, Chile ranks number six worldwide. We identify major knowledge gaps and recommend policy measures, including establishing High-Risk Areas and the implementation of shipping lanes modifications and vessel speed restrictions.

In recent years, the growth of fishing activities has led to increased interactions between marine fauna and fisheries. Among these, gillnet fisheries are recognized for exerting significant impact. Despite this, our comprehension of their effect on marine fauna is still limited. This study, therefore, aims to elucidate the operational interaction and bycatch of seabirds and marine mammals in the artisanal gillnet fishery off southern Chile. From January to November 2007, scientific observers documented 66 fishing sets to monitor and describe these interactions. The observations revealed substantial encounters. A total of 103 South American sea lions, one Burmeister's porpoise, 272 petrels, 140 gulls, 82 albatrosses, 54 cormorants, and 46 pelicans were observed during these sets. Sea lions were involved in 29 of the 66 sets mainly damaging the catch, while seabirds interacted in 16 sets, leading to gear damage. Furthermore, additional species such as spiny dogfish, crabs, and benthic amphipods were also found interacting with the gillnets. The study recorded the mortality of three marine mammals (1 porpoise and 2 sea lions) and 71 seabirds (63 penguins and 8 cormorants). Notably, no porpoises or penguins were observed during net setting or hauling, indicating that entanglements occur during the net soak time. These findings underscore the broader range of species affected by gillnet operations and highlight the potentially underestimated impact on marine wildlife. In conclusion, this research provides crucial insights into the interactions between artisanal gillnet fisheries and marine fauna in Southern Chile. By detailing these interactions and their associated mortalities, it emphasizes the urgent need for enhanced conservation measures and sustainable fishing practices to mitigate the ecological consequences of gillnet fisheries on marine biodiversity.

The composition of marine mammal blubber is influenced by factors such as diet and environmental conditions. Here, we investigate the thermal influence on fatty acid composition and degree of unsaturation in the blubber of 151 South American sea lions (Otaria byronia). Samples were collected at ten locations along the Chilean coast and spanned a latitudinal range of approximately 2500 km, an arc of 23 degrees. We found a significant latitudinal gradient in the biochemical composition of sea lion blubber. At higher colder latitudes the endogenous fatty acids in the blubber were more unsaturated, as indicated by the desaturation index. In cold conditions the modification of fatty acids from saturated to unsaturated improves fluidity of cell membranes, which is important for thermal insulation. Thus, the higher degree of unsaturated endogenous fatty acids at higher latitudes may help sea lions maintain thermal balance in colder environments. For the dietary-sourced fatty acids however, we found the opposite latitudinal pattern, here the overall degree of unsaturation decreases with latitude. The lower proportion of polyunsaturated fatty acids in blubber at higher latitudes may be influenced by the sea lion's dietary choices. Additionally, the presence of extremely high levels of 18:2n-6 in some sea lions south of 40 degrees S, values more typical of terrestrial origin, suggests they consumed farmed salmon. The observed variation in fatty acid profiles across the latitudinal gradient implies that differences in fatty acid composition are not solely attributed to dietary variation, but potentially also to endogenous metabolism in response to environmental conditions.

AbstractPinnipeds face increasing challenges that affect how maternal foraging and nursing strategies transfer key resources for immune function and ultimately the survival of their offspring. We evaluated how foraging strategies and maternal care in South American fur seals (Arctocephalus australis) affect male and female pup growth, physiology, and immune health. We used capture and recapture data for mothers and their pups and daily monitoring during the austral summers of 2015-2016, 2021-2022, and 2022-2023 to assess maternal care. We collected pup morphometric data, blood, and vibrissae to assess their growth rates, health, and immune competence. We found that mothers shifted their diet from demersal to more pelagic prey between 2015 and 2023 because of a decrease in their main demersal prey item, the southern hake (Merluccius australis). This shift in diet was associated with reduced maternal foraging time and increased nursing time, which differentially affected the health of male and female pups. Male pups grew faster, emphasizing energy reserves, especially in years with a higher abundance of demersal prey, while slower-growing female pups prioritized the development of the immune system, especially during years with a decline in demersal fish and an increase in the use of pelagic fish by their mothers, suggesting sex-specific adaptation for the long-term survival of offspring. This study suggests that prey scarcity could differentially impact the development and immune health of male and female offspring of marine top predators.