The Tropical Eastern Pacific Ecosystem off Peru sustains important fisheries that contribute 12% of the annual fisheries landings of Peru, the world’s third-largest marine fisheries producer by catch volume. Although climate change is anticipated to negatively affect fish production in this region, species-specific vulnerability to climate change remains unclear. We implemented a trait-based Climate Vulnerability Assessment using expert elicitation to estimate the relative vulnerability of 35 fishery resources (benthic, demersal, and pelagic) to the impacts of climate change by 2055. Ten exposure factors (e.g., temperature, salinity, pH, chlorophyll) and 12 sensitivity attributes (biological and population-level traits) were used. No species were assessed as having “very high” vulnerability, five species were ranked with “high” vulnerability, 17 species with “medium” vulnerability, and 13 species with “low” vulnerability. The benthic group, particularly bivalves, were ranked the most vulnerable. The pelagic group was the second most vulnerable, with sharks amongst the most vulnerable. The demersal group was estimated with the lowest vulnerability. Temperature, primary productivity, salinity, pH, and chlorophyll were the principal drivers of exposure. This study allowed estimation of the most vulnerable fishery resources and the main exposure factors driving vulnerability, and detection of research and monitoring priorities in the region, which may be helpful to fisheries managers in developing climate change adaptation options and mitigation alternatives in the Tropical Eastern Pacific Ecosystem off Peru.

The last deglaciation provides an opportunity to assess the response of El Niño–Southern Oscillation to rapid warming and disruptions of the Atlantic Meridional Overturning Circulation, both projected in the near future. We present a reconstruction of deglacial El Niño–Southern Oscillation activity using finely laminated sediments from the El Niño–Southern Oscillation-sensitive Peruvian margin. An interannual record of titanium fluxes, a proxy for riverine discharge, shows that the frequency of extreme Eastern Pacific El Niño events and the amplitude of El Niño–Southern Oscillation variability were higher during the deglaciation and peaked during episodes of massive iceberg discharge into the North Atlantic. Maximum El Niño–Southern Oscillation variability occurred in the early phase of Heinrich event 1, at ~17.3–16.7 kyr BP, associated with at least five extreme floods per century in southern Peru. This proxy evidence linking El Niño–Southern Oscillation and the North Atlantic suggests a possible increase in El Niño-related extreme climatic events under future Atlantic Meridional Overturning Circulation weakening. El Niño–Southern Oscillation variability was not only stronger during the deglaciation but also correlated with North Atlantic records of iceberg discharge, according to analysis of finely laminated sediments from the Peruvian margin.

The biogeochemical characterization of sedimentary organic matter (OM) on continental shelves is fundamental for understanding organic matter cycling and benthic ecosystems functioning. This study assessed the composition, distribution, and biogeochemical state of organic matter (OM) along a bathymetric transect (48–178 m) across the central Peruvian continental shelf, beneath a highly productive coastal upwelling system and a persistent oxygen minimum zone (OMZ). Total and hydrolysable fractions of carbohydrates, proteins, and lipids, as well as photosynthetic pigments (chlorophyll-a and pheopigments), were analyzed and integrated into biogeochemical indices: Biogeochemical Quality Index (BI); Lipid Index (LI), Carbohydrate-to-Lipid ratio (C/L), Chlorophyll-a to Pheopigments ratio (Chl-a/Pheo-a) and Biopolymeric Carbon Index (BPC) to evaluate OM quality, origin, bioavailability, and early diagenetic processes. Undisturbed 50 cm-length sediment cores were collected in triplicate at four stations during ENSO-neutral period, sectioned at 1 cm intervals for the uppermost 10 cm-depth, and analyzed using spectrophotometric and fluorometric techniques adapted for marine sediments. The results suggest that sediments displayed a pronounced inner–outer shelf gradient: inner shelf sediments contained fresher, labile, and nutritionally rich OM, linked to high primary production and rapid burial, whereas outer shelf sediments showed selective preservation of lipids and refractory OM. Additionally, comparison with data obtained from the same study area suggests that temporal variability in phytopigments responded to oceanographic drivers (e.g. bathymetry, primary productivity, hydrodynamic, etc.) including anomalous events (e.g. post–La Niña and weak El Niño). These findings highlight the sensitivity of benthic biogeochemical processes to upwelling intensity and bottom-water oxygenation. Integration of hydrolysable fractions and biogeochemical indices may suggest strong benthic–pelagic coupling, selective OM degradation, and differential preservation along the shelf. These results underscore the interplay between primary productivity and sedimentary dynamics as key modulators of OM quality and distribution. This studyhighlights the key role of continental shelf sediments in carbon storage, nutrient recycling, and the biogeochemical processes that sustain benthic communities in highly productive upwelling systems. These findings underscore the importance of understanding sedimentary organic matter dynamics and their implications in the context of ongoing global warming.

Phytoplankton production represents the ultimate source of organic matter in the ocean; thus, the study of organic compounds can give us information related to organic matter (OM) origin and transformations. Usually less than 1% of the OM produced in the ocean surface reaches the seafloor, although in highly productive regions nearly 10% can be buried and subjected to further degradation. The Peruvian upwelling system is among the most productive marine ecosystems in the world ocean, with high primary production sustained mainly in a year-round upwelling. Along the Peruvian continental margin, variations in primary production, bottom dissolved oxygen, and depth influence OM accumulation and preservation, and thus determine the existence of different depositional environments. Previous geochemical and palaeoceanographic studies have shown that the best records of well-preserved OM are found towards the central area of the Peruvian continental margin, between 12°S and 14°S. Therefore, the study of organic compounds, particularly lipids, deposited in surface sediments could give us information regarding early diagenetic processes related to OM degradation/preservation. The objective of this study was to characterize both the solvent extractable OM fraction (i.e. free lipids) and the insoluble OM fraction (i.e. protokerogen) in order to elucidate possible preservation mechanisms involved in OM accumulation. A total of 14 surface sediment samples from different locations between 12°S and 14°S were analyzed by means of gas chromatography mass spectrometry. Organic compounds such as short-chain and long-chain alkanes and fatty acids were quantified in the solvent-extractable OM fraction, which allowed the calculation of a pristane/phytane index and a carbon preference index. In the insoluble OM fraction, alkanes and fatty acids were also quantified together with dithiophene and benzothiophene compounds and organic sulfur heterocompounds. Overall, our results allowed a detailed geochemical molecular characterization of the OM deposited in surface sediments beneath one of the most productive areas of the Peruvian coast. The differences observed in both the n-alkane and fatty acids distribution between the solvent-extractable OM fraction and the insoluble OM fraction, together with the quantification of sulfur compounds in the insoluble fraction, suggests that complex diagenetic processes occur in surface sediments. An important part of the freshly-produced OM in the highly productive surface waters off central Peru reaches the seafloor and undergoes preservation mechanisms mainly related to natural sulfurization and selective preservation, tightly coupled to the reduced conditions that characterize surface sediments in the area.

This study presents a regionally trained version of the “CArbonate system and Nutrients concentration from hYdrological properties and Oxygen using a Neural network” (CANYON) method, named CANYON-PU, for estimating primary macronutrients (phosphates, silicates, and nitrates) in the Peruvian Upwelling System (PUS). Using a neural network approach, the model was trained using extensive biogeochemical data spanning between 2003 and 2021, collected by the Peruvian Institute of Marine Research (IMARPE). Variables representing the low-frequency variability related to ENSO were introduced in the training and significantly improved the performance of the algorithm. The performance of CANYON-PU was validated against independent datasets and demonstrated an improvement in accuracy over the global CANYON model that struggled to represent the nutrient distribution in the PUS mainly due to the lack of samples in its training. Therefore, CANYON-PU successfully captured nutrient variability across different spatial and temporal scales, showcasing its applicability to diverse datasets, including high-frequency data such as profiling floats or gliders. This work highlights the effectiveness of neural networks for representing the nutrient distribution within highly variable ecosystems like the PUS.

The Peruvian coastal upwelling system (PCUS) is one of the most productive in the world ocean. The Peruvian Marine Research Institute (IMARPE) has been monitoring the PCUS since the 1960’s with an increase in the frequency and spatial distribution of measurements since the early 2000’s focusing on temperature, salinity and oxygen. In recent years, autonomous gliders have started to be routinely deployed by IMARPE, collecting a large amount of profiles. However, there is still a gap for the high-resolution sampling of biogeochemical parameters such as nutrients (nitrate, phosphate and silicate).New methods using machine learning to reconstruct missing data have been developed recently with promising results (Sauzède et al, 2017; Bittig et al., 2018; Fourrier et al., 2020). In particular, a recent global approach using neural networks (NN) named CANYON-B (CArbonate system and Nutrientes concentration from hYdrological properties and Oxygen using a Neural network) was developed in order to fill those gaps and infer nutrients’ concentrations from the more sampled variables of temperature, salinity and oxygen (Bittig et al., 2018).In this work we show the application of this global CANYON-B algorithm to the PCUS using all the historical IMARPE’s CTD casts. Moreover, we trained a new NN and compared its outputs with the ones from CANYON-B, demonstrating the benefits of training the NN with the extensive regional data set collected by IMARPE.

El análisis de los morfogrupos de foraminíferos bentónicos se realizó en una secuencia de sedimentos laminada (B1404-11) que abarca los últimos 300 años. El testigo fue colectado en el talud continental (302 m de profundidad) al noroeste de bahía Independencia, Pisco (14°7,755S, 76°30,253W), con influencia de la Zona de Mínimo de Oxígeno (ZMO). El morfogrupo de testas aplanadas-elongadas fue predominante, muy por encima del resto de morfogrupos identificados (aplanado, cónico, plano-convexo, biconvexo, biumbilicado, lenticular y ovoidal). El análisis de agrupamiento jerárquico mostró dos grandes asociaciones considerando la contribución de los morfogrupos más importantes. La primera asociación representó los intervalos en los cuales el morfogrupo cónico y biumbilicado fueron de mayor significancia mientras que el morfogrupo aplanado y plano convexo conformaron la segunda asociación. Los resultados sugieren que la presencia de los morfogrupos con mayor contribución evidencia las propiedades estructurales de la ZMO en esta región.

Earth system models (ESMs) are the main tool for understanding the impacts of global change and are regularly updated to provide more reliable scenarios of the future. However, their confrontation with observations reveals biases that need to be corrected, especially for impact applications where the absolute scale of the environmental variable is relevant. In addition, marine regional impact studies require fine-scale projections for strategic planning and management actions. Statistical downscaling provides a fast way to produce regional forcings from ESMs and can additionally produce bias-corrected outputs necessary for marine impact applications driven by or fitted to observed data. Statistical downscaling can use different parametric distributions depending on the variables used, and generalised regression can provide a flexible approach for this purpose. We propose a multi-model approach based on non-parametric generalised regression and a set of indicators to select a robust statistical downscaling model that can be used to project future scenarios for marine ecosystems. The empirical cumulative distribution of the variables to be downscaled is modelled, ensuring that not only the mean but also the variance and quantiles (including minima and maxima) are properly represented, improving the prediction of extreme events and taking into account spatial autocorrelation. We incorporated future bias indicators alongside traditional evaluation metrics for model selection to identify and mitigate potential extrapolation errors in future scenario projections, ensuring more robust and plausible downscaled climate outputs. The approach presented here is applied to two contrasted regional case studies, the Bay of Biscay-Celtic Sea ecosystem and the Northern Peru Current ecosystem, using sea surface temperature from the IPSL-CM5A-LR ESM. The results show that a multi-model selection approach is appropriate, as individual model performance is case-specific.

The accidental release of around 11,000 barrels of crude oil off the central Peruvian coast (11.92 degrees S, 77.18 degrees W) on January 15, 2022, affected similar to 70 km of shoreline. This study analyzes the spatiotemporal variation of metal concentrations in intertidal and subtidal zones from October 2022 to September 2023, and their effects on benthic foraminiferal communities. Metal concentrations were found to exceed background levels established by the Peruvian Environmental Inspection Agency. Although no temporal trends were detected, spatial differences were recorded. Intertidal sites showed enhanced concentrations of V, Fe, Cr, and Mn. Notably, the site closest to the spill (Ventanilla Beach; 11.87 degrees S), recorded the highest concentrations of Pb, Cu, Zn, and As. In the subtidal zone, concentrations increased with water depth and reduced hydrodynamic conditions. The more sheltered site (Punta Mulatos; 11.76 degrees S) had higher Ni, Pb, Cu, Cd, Zn, and As levels compared to the more dynamic site (Bahia Blanca; 11.83 degrees S). Furthermore, a contribution associated with natural rock leaching was detected. These findings suggest that the spill's influence on metal concentration is amplified by low hydrodynamics, low oxygen, high productivity and riverine inputs. Dominant benthic foraminiferal taxa, typical of oxygen-poor environments, were associated with enhanced Cd, Cu, Ni, Cr, and Pb. However, isolating spill effects is challenging due to natural species tolerance and concurrent El Nino conditions affecting oxygen levels and organic matter fluxes. Finally, 18 months after the spill, heavy metals persist in both environments, underscoring the need for long-term monitoring and mitigation.

Del 03 al 15 de enero 2018 (verano austral), se realizó el crucero de investigación ANTAR XXV, abarcando desde la isla Trinidad, por el estrecho de Bransfield, alrededor de la isla Elefante, hasta la bahía Almirantazgo. Se efectuaron 14.970 mediciones superficiales que comprendieron: la presión parcial de CO2 para determinar los flujos de CO2 en el estrecho de Bransfield y alrededor de la isla Elefante, así como temperatura, salinidad, oxígeno disuelto, clorofila-a; además, se determinaron las masas de aguas transicionales de Bellingshausen (TBW), Weddel (TWW) y del mar de Escocia. También, se identificó el frente de Bransfield, definido por la isoterma de 1 °C el cual se ubicó en la zona intermedia del estrecho, donde los valores del oxígeno disuelto superficial estuvieron entre 330 y 340 µmol kg-1 en la mayor parte del estrecho y valores entre 350 y 360 µmol kg-1 alrededor de la isla Elefante, asociados al deshielo de los glaciares contiguos al continente. Se determinaron concentraciones de clorofila-a, como un indicador de fitoplancton y productividad primaria, con concentraciones mayores a 0,7 µg L-1 en las TBW asociado al mayor contenido de nutrientes del derretimiento de los glaciares de las islas Shetland del Sur. La velocidad de los vientos fue menor a 6 m s-1 en el estrecho, mientras que, en los alrededores de la isla Elefante las velocidades fueron cercanas a 10 m s-1. Los valores de (pCO2) in situ estuvieron entre 427,7 y 574,6 µatm con flujos positivos de CO2 entre 5 y 20 mmol m-2 día-1 en el estrecho de Bransfield y para el área alrededor de la isla Elefante entre 25 y 35 mmol m-2 día-1. Por otra parte, las concentraciones de clorofila-a en las masas de agua TBW se asocian con la disminución del pCO2 del agua de mar y en consecuencia en los flujos de CO2 en comparación con la zona sur del estrecho cerca de la península que tiene el efecto de las TWW menos productivas. La zona este de la isla Elefante presentó el mayor flujo de CO2, asociado a los vientos más intensos. Los resultados muestran que el estrecho de Bransfield e Isla Elefante se comportan predominantemente como fuente de CO2 con un flujo promedio de 11,3 mmol m-2 día-1.

Coastal hypoxia can occur naturally in inshore areas of the Eastern Boundary Upwelling Systems, influenced by the nutrient-rich and low-oxygen upwelling waters. This study aims to explore the influence of water stratification and winds on bottom-water hypoxia of the Paracas Bay, an area subjected to the most intense alongshore winds and active coastal upwelling in the Peruvian coast. Monitoring data of the Pisco-Paracas water properties (dissolved oxygen, temperature, salinity and estimated stratification), the Pisco River flow, and the intensities of surface winds of the outside upwelling area, and of the local area, were analysed for the period 2006 to 2015. Bottom waters deeper than 8 m in the bay were shown undergoing a hypoxic regime (oxygen <1.4 mL L-1) that becomes more frequent towards austral summer and less frequent towards winter. This seasonal difference was associated with changes in the oxygen content of incoming upwelling waters and changes in the intensity of both local and upwelling winds that drive the hydrodynamics of the bay. High frequency data analysis revealed that synoptic time-scale fluctuations of the upwelling-favourable and local winds modulate the intra-seasonal variability of hypoxia. Fluctuations of the former drive the inshore expansion of mixed and less hypoxic upwelling waters during June-September, whereas fluctuations of the latter during December-April drive the entrance and circulation of more hypoxic upwelling waters, and the development of stratification events that contribute to the persistence of bottom hypoxia.

Over the past decade, there has been a significant increase in low oxygen conditions within marine coastal areas, profoundly impacting ecosystem processes and living coastal resources. Coastal bays in highly productive upwelling regions, where hypoxia occurs naturally, are special areas affected by both local and adjacent shelfrelated processes. Paracas Bay (13.8 degrees S) is a traditional shellfish fishing and intense farming area highly influenced by one of the most active upwelling centers of the Peruvian coast. Despite the small dimensions of the bay (35 km2), a key feature is its complex physical dynamics and high environmental variability. Recently, important efforts have been made in the study of both the spatial and temporal oxygen concentration variability, nevertheless, information regarding the ecological and biological impact of hypoxic events is still lacking. In this study, the spatial and temporal distribution of hypoxic events was analyzed across Paracas bay at different depths by means of high-frequency hourly dissolved oxygen records collected by data-loggers deployed across the bay during the periods September 2012 - February 2013 and March 2015 - February 2017. To study the ecological impact of hypoxic events, we developed a hypoxia intensity index, while the biological impact was studied through the development of a hypoxia biological effect index using as model species the Peruvian scallop (Argopecten purpuratus). Our results showed that hypoxic events have an intrinsic variability across the bay. The deeper areas of the bay, towards the northwest and center, were characterized by long, intense, and lethal events, while the southeast and southwest, shallower areas, were characterized by shorter events of low intensity and either sublethal or innocuous. We propose that the observed variability is not only related to the large-scale environmental context in which the events occurred, but also to small-scale variability linked to local circulation, biological activity, and sediment biogeochemistry. We expect that our research will be useful not only for scientific purposes, but also for coastal resource management and aquaculture, underlining the importance of developing high-resolution oxygen monitoring systems in coastal bays.

The circulation and stratification in the shallow semi-enclosed bay of Paracas located downstream of the main upwelling cell off the Peruvian coast were studied during the summer season using a regional circulation model and in situ observations. A downscaling strategy based on a series of three embedded grids, from 10 km to 500 m resolution in the bay allows to take into account the influence of remote perturbations on the bay dynamics. Debiased surface winds from a high-resolution regional atmospheric model were used to force the model. The shortwave absorption depth was parameterized using satellite measurements of surface chlorophyll.Sensitivity experiments to the model forcing and parameterizations were performed to investigate the impact of the wind diurnal variability, tidal forcing, freshwater discharge from a nearby river and shortwave absorption depth on the bay stratification. Results show that: debiasing the wind intensity reduced the model cold bias in the bay and increase the stratification; a shallow shortwave absorption depth induced a cooling of the subsurface water, increasing the stratification; freshwater discharge from the Pisco river north of the bay increased slightly the stratification in the bay during days of weak wind. The high sensitivity of the bay stratification to the at-mospheric forcing calls for the need to use more realistic wind forcing products. The circulation in the bay under strong (>5.5 m s-1) and weak (<3 m s-1) winds was also examined. The summer circulation during strong upwelling-favorable wind conditions was characterized by northward surface currents transporting the bay surface waters outward and subsurface currents transporting cold deeper waters into the bay along its western shore. During weak wind conditions, the current is outward in the bottom layer and a surface southward current related to the poleward undercurrent flowing over the continental slope and shelf transported warm waters into the bay, generating a cyclonic circulation in the bay.

In recent decades, there has been a divergence in the evidence (models, observations, reanalysis data) about the trend of coastal upwelling driving winds in the current global warming scenario over the Humboldt Current System. Herein, we present a 150 yr, sub-decadal grain size distribution record of a laminated sediment core (B0405-6) retrieved from the continental shelf of the Pisco region (similar to 14 degrees S) within the wind-driven coastal upwelling system of South-Central Peru. This area is characterized by local aeolian inputs from seasonal dust storms called Paracas Winds (PW). This study aims to reconstruct the variability of surface wind intensity using the Geometric Median Diameter (GMDs) and frequency (A%) of aeolian particles in a high temporal resolution sediment core and to unravel the mechanisms that control this variability. In addition, we propose to evaluate these GMDs as a better proxy of local surface wind strength and thus the variability of upwelling favorable winds (UFWs) in these near-source conditions. Our results show a progressive intensification of the UFWs in the region throughout the last 150 years, which agrees with other records along the South Pacific coast. In addition, good correspondence was found between the UFW wind proxy and the region's sea surface temperature (SST) trends, suggesting an intensification of the driving mechanisms linked to these events. It also suggests that UFW intensification could continue as the local coastal atmospheric jet strengthens. A comparison of indirect oceanic and atmospheric records from the South American Pacific coast is shown at the regional scale, suggesting a recent progressive expansion and intensification of the South Pacific Subtropical High (SPSH).

The presence of harmful microalgae in aquaculture sites represents a risk for production and human health, so surveillance of these species is relevant for early warning of harmful algal blooms. Here we examine the monitoring results of potentially toxic phytoplankton in Peruvian coastal sites associated with the cultivation of Argopecten purpuratus and natural banks of other mollusks. We evaluated the density, frequency, temporal and spatial distribution of these species, as well as blooms occurred from 2011 to 2019. Results showed that the most abundant species was Heterosigma akashiwo, and the most frequent ones were Pseudo-nitzschia delicatisima and seriata complexes. The majority of blooms were caused by H. akashiwo (21 events) and Dinophysis acuminata (19 events). Canonical correspondence analysis revealed the preference of dinoflagellates to warmer sea surface temperatures and more stable conditions (indicated by low wind velocities) than Pseudo-nitzschia species. Generalized additive models (GAMs) indicated that wind velocities > 3.7 m s-1 and El Nin similar to o conditions favor Pseudo-nitzschia species while warm temperatures (> 20 degrees C), weaker winds (< 3.7 m s-1), and cold periods associated with La Nin similar to a promoted higher densities of D. acuminata complex. A recent increasing trend in the density of D. acuminata was observed. This information is useful to understand the dynamics of potentially toxic species in upwelling regions.

The Northern Humboldt Current System sustains one of the most productive fisheries in the world. However, climate change is anticipated to negatively affect fish production in this region over the next few decades, and detailed analyses for many fishery resources are unavailable. We implemented a trait-based Climate Vulnerability Assessment based on expert elicitation to estimate the relative vulnerability of 28 fishery resources (benthic, demersal, and pelagic) to the impacts of climate change by 2055; ten exposure factors (e.g., temperature, salinity, pH, chlorophyll) and 13 sensitivity attributes (biological and population-level traits) were used. Nearly 36% of the species assessed had “high” or “very high” vulnerability. Benthic species were ranked the most vulnerable (gastropod and bivalve species). The pelagic group was the second most vulnerable; the Pacific chub mackerel and the yellowfin tuna were amongst the most vulnerable pelagic species. The demersal group had the relatively lowest vulnerability. This study allowed identification of vulnerable fishery resources, research and monitoring priorities, and identification of the key exposure factors and sensitivity attributes which are driving that vulnerability. Our findings can help fishery managers incorporate climate change into harvest level and allocation decisions, and assist stakeholders plan for and adapt to a changing future.

The authors declare that they have no conflict of interest. Appendix S1. Boxplots of the abundance in sampling rookeries of SAFS and SASL by age-class during breeding and non-breeding months during study period (2015–2018). Appendix S2. Table of prey items identified in samples of SAFS and SASL with ecological grouping categories. Appendix S3. Boxplots of the seasonal (a) SST and (b) SSTA for study period 2015–2018 collected in San Juan de Marcona. Spearman correlation charts (P < 0.05) for trophic and environmental indices for SAFS and SASL. Appendix S4. Values of Importance Index (IIMP) for all prey items found in South American fur seal (SAFS) and South American sea lion (SASL) samples for each season and year. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Determining trophic habits of predator communities is essential to measure interspecific interactions and response to environmental fluctuations. South American fur seals, Arctocephalus australis (SAFS) and sea lions Otaria byronia (SASL), coexist along the coasts of Peru. Recently, ocean warming events (2014–2017) that can decrease and impoverish prey biomass have occurred in the Peruvian Humboldt Current System. In this context, our aim was to assess the effect of warming events on long-term inter- and intra-specific niche segregation. We collected whisker from SAFS (55 females and 21 males) and SASL (14 females and 22 males) in Punta San Juan, Peru. We used δ13C and δ15N values serially archived in otariid whiskers to construct a monthly time series for 2005–2019. From the same period we used sea level anomaly records to determine shifts in the predominant oceanographic conditions using a change point analysis. Ellipse areas (SIBER) estimated niche width of species-sex groups and their overlap. We detected a shift in the environmental conditions marking two distinct periods (P1: January 2005—October 2013; P2: November 2013—December 2019). Reduction in δ15N in all groups during P2 suggests impoverished baseline values with bottom-up effects, a shift towards consuming lower trophic level prey, or both. Reduced overlap between all groups in P2 lends support of a more redundant assemblage during the colder P1 to a more trophically segregated assemblage during warmer P2. SASL females show the largest variation in response to the warming scenario (P2), reducing both ellipse area and δ15N mean values. Plasticity to adapt to changing environments and feeding on a more available food source without fishing pressure can be more advantageous for female SASL, albeit temporary trophic bottom-up effects. This helps explain larger population size of SASL in Peru, in contrast to the smaller and declining SAFS population.