Oceanographic conditions in the northern of the Humboldt Current System (NHCS) in 2023 were warm, due to the presence of El Niño 2023-2024. The Instituto del Mar del Peru (IMARPE) carried out five marine scientific activities applying hydroacoustic to observe the impact on fishery resources, with the support of fishing industry vessels. This article presents the impact generated on the distributional behavior and size structure of the anchoveta, as well as the oceanographic conditions of temperature, salinity, and oxygen. The results showed that anchoveta inertia was clearly elongated showing a very coastal spatial distribution throughout 2023, reaching up to 66 nm. At the vertical level, it reached up to 190.41 m depth due to the deepening of the Minimum Oxygen Zone (MOZ) and the approach to the coast of the warm water masses. Despite these conditions, the anchoveta maintained its usual characteristics of positive spatial autocorrelation due to the continuity along the coast, structured by the high concentration nuclei and variable in time due to the characteristics of the NHCS. The lengths were consistent in all marine research activities, what was observed in the summer survey reflected a growth mirrored in the spring survey; however, their body growth was slowed.

The squat lobster or munida (Pleuroncodes monodon) is one of the most abundant species in the coastal zone of the Peruvian Current. Due to its high incidence of occurrence and biomass, it has been monitored since 1998 by the Instituto del Mar del Perú (IMARPE) through the Hydroacoustic Assessment Surveys for Anchoveta and Other Pelagic Resources. In this study, 59 surveys conducted between 1998 and 2024 were analyzed to study the spatial distribution, abundance, and ecological relationship of munida with anchoveta (Engraulis ringens). The results showed that between 1998 and 2000, munida expanded its distribution northward along the Peruvian coast, while from 2001 onward its range remained relatively stable. A clear seasonal pattern was identified: during winter and spring, both the distribution area and inertia increased, and the species tended to occur farther from the coast, whereas in summer and autumn the distribution contracted, except during anomalous oceanographic events (e.g., warm or cold conditions). Vertically, munida generally inhabited the surface layer down to approximately 168 m, although during the 2015 -2016 El Niño event it was recorded as deep as 203 m. The average biomass throughout the study period was close to 2.04 million tons, with a maximum of 5.38 million tons recorded during survey 1703-04. Munida was also the species most closely associated with anchoveta, and when both occurred together, their interaction varied depending on the time of day, probably reflecting diel vertical migration and differential aggregation behaviors. These findings suggest that munida is a key component of the Peruvian Current ecosystem, whose variability is influenced both by seasonal cycles and by anomalous oceanographic conditions, and that its association with anchoveta may have implications for ecosystem functioning and fisheries management in the region.

This paper presents the spatial structure with geostatistical analysis and decadal spatiotemporal distribution of anchoveta according to the Pacific Decadal Oscillation index, its implications for the anomalous events of the oceanographic conditions of the Northern Region of the Humboldt Current System (NRHCS), and areas of high anchoveta abundance found in the analyzed period. The acoustic data came from the Hydroacoustic Pelagic Resources Assessment Surveys carried on by the Instituto del Mar del Peru (IMARPE), and the oceanographic data came from satellite images of sea surface thermal anomalies (SSTA) between 1985 and 2024. The results showed that anchoveta has had a positive linear trend, with a high positive spatial autocorrelation and a structure spatially dependent on invironmental conditions in space and time. In the cold decadal periods, anchoveta were found a little far from the coast, distributed in high concentrations mainly in the north-central region, while in the warm decadal periods, they were found close to the coast and with greater abundance towards the central zone; exceptional was in the warm period of 1985-1988, where anchoveta distribution was wide and generally dispersed. The trend in the warm decadal periods was negative, and in the decadal periods, it was positively influenced by El Ni & ntilde;o events: 1997-1998 and 2015-2016, with a decrease in biomass recorded in 1998 and 2015. In the last cold period, 2017-2024, it was influenced by the warm year of 2023. Between 2000 and 2024, anchoveta biomass averaged 8.26 million tons, with an average biomass of 7.46 million tons for the north-central region between 2004 and 2024.

Este artículo describe los actores que intervienen en la recomendación de la cuota de captura de anchoveta, previo a las temporadas de pesca para cada región (norte-centro y sur), así como el sesgo asociado a la misma. Los datos de las biomasas, cuotas y desembarques corresponden al período 2000-2022, mientras que las recomendaciones para la cuota total corresponden a 2019-2022. Para la región norte-centro, el Imarpe recomienda a Produce una tasa de explotación menor o igual a 0.35 mediante una tabla de decisión para cuatros escenarios probables de ambiente oceanográfico, considerando una biomasa remanente para asegurar su sostenibilidad. El cumplimiento de las cuotas de capturas de anchoveta en las primeras temporadas de pesca ha sido mayor a 90 %, mientras que en las segundas temporadas de pesca se han capturado inclusive menores a 50 %, como es el caso del: 2001, 2019, 2010 y 2017. Entre 2019 y 2022, Produce optó lo siguiente: i) con cuota menor a la recomendada en la tabla de decisión (I-2021, II-2020, I-2019) y ii) con cuota mayor a la recomendada en la biomasa a la tabla de decisión (I-2022, II-2021, II-2022, II-2019 y I-2020). El error de observación es menor (0.10) en los cruceros de verano y mayor (0.15) en invierno-primavera (cruceros de biomasa desovante e hidroacústicos).

Harmful algal bloom (HAB) events in front of Pisco River, inside Paracas Bay and Lagunillas inlet on the southern coast of Peru was identified from a satellite index (IOPifa) generated with daily high-resolution satellite data of phytoplankton absorption (aphy,GIOP) and non-algal detrital material plus CDOM (adCDOM,GIOP) from the Generalized Inherent Optical Properties (GIOP) model of Modis-Aqua, Viirs-Snpp and Viirs-Jpss1 satellites were used. Phytoplankton density field data sampling from HAB's monitoring programs of IMARPE of 2018 and 2019 were used to validate and identify the extent and spatio-temporal variability of these events. The satellite index (IOPifa) identified for Modis-Aqua 9 active HABs, 8 events in final conditions and 6 events that do not represent HAB conditions, while for Viirs-Snpp found 14 active HABs, 7 events in decaying bloom conditions and 13 events that do not represent HABs; and for Viirs-Jpss1 the index identified 7 active events, 14 in final bloom conditions and 6 that do not represent HABs conditions. The one-factor anova model was applied (p-value = 0.32 > 0.05), indicating that there is no evidence of a difference in the population means of the indices for each sensor. Subsequently, the pairwise multiple comparisons analysis with a 95 % confidence level of Tukey's test confirmed that there are no significant differences in the satellite index value, the differences could be associated with the spectral characteristics of the cell density of the species community and the oceanographic and environmental conditions. The spatial overlap between the in situ harmful algal blooms areas and the calculated satellite index, shows the capacity of the IOP satellite data for the HABs detection. However, it was also evidenced that some HAB events with high phytoplankton cell density had low IOPifa values, while other events with lower cell density were easily identified by the satellite index. This would indicate the ability of the ocean inherent optical properties to differentiate the phytoplankton types that cause algal blooms.

El 2021 se realizaron dos cruceros de Evaluación Hidroacústica de Recursos Pelágicos en toda la costa peruana, teniendo como apoyo de investigación embarcaciones industriales de la Sociedad Nacional de Pesquería (SNP). El primer crucero 2102-07, se efectuó del 17 de febrero al 01 de abril, completado del 19 de junio al 13 de julio, el segundo crucero 2109-11 fue del 22 de setiembre al 03 de noviembre 2021. En este artículo se presenta la distribución y biomasa de la anchoveta, así como del: jurel, caballa, samasa, bagre, munida, pota y vinciguerria en la Región Norte del Sistema de la Corriente de Humboldt (RNSCH). Los resultados mostraron que la anchoveta es la especie de mayor abundancia, su población se encontró saludable, favorecida por las condiciones oceanográficas ligeramente frías a neutras, manteniendo su comportamiento estacional; en el crucero 2102-07 se encontró hasta 80 mn de la costa con altas concentraciones y biomasa de 12,03 millones de toneladas; mientras que, en el crucero 2109-11 se detectó hasta 121 mn de la costa con mayor dispersión y biomasa de 8,03 millones de toneladas. Los descriptores acústicos de los cardúmenes de anchoveta variaron en ambos cruceros debido a la agregación y disgregación por variabilidad ambiental y la concentración de clorofila-a. La múnida, fue la segunda especie con mayor abundancia en la zona costera, que generalmente comparte distribución con anchoveta, su biomasa en los cruceros 2102-07 y 2109-11 fueron de 1,50 y 1,20 millones de toneladas, respectivamente. Las distribuciones de jurel y caballa se dieron en núcleos reducidos y aislados, solo en el crucero 2102-07 la caballa se estimó en 0,82 millones de toneladas por encontrarse en algunos núcleos de alta concentración de cardúmenes. La abundancia de las especies costeras samasa y bagre fue menor; mientras que, las mesopelágicas, pota y vinciguerria, se encontraron alejadas de la costa, solo la vinciguerria en el crucero 2109-11 tuvo biomasa de 1,06 millones de toneladas.

Highly mobile odontocetes need habitats with environmental conditions with the potential of aggregating enough and high-quality prey, to maximize foraging success. Until now, the characterization of those habitats was in terms of physical and biological indicators of high production, capable of attracting and sustaining prey. Nevertheless, there has been no approach to quantifying the effects of a biophysical characteristic of the ocean with proven effects on the vertical distribution of prey for cetaceans: The oxygen minimum zone (OMZ) depth. In the northern branch of the Humboldt Current System off Peru (~6-18° S), a shallow OMZ (30-50 m) affects the distribution of the Peruvian anchovy ( Engraulis ringens ), main prey for several marine predators, including dolphins. We hypothesized these predators would aggregate in productive areas, but with preference for places where the relative OMZ depth can constrain prey vertically, making it more accessible and maximizing foraging success. We fitted Bayesian habitat models for three dominant odontocete species in this region, with multiple combinations of environmental covariates, smoothing techniques, and temporal and spatial random effects. Cetacean data came from 23 dedicated surveys spanning 2001-2019. Habitat predictors included the spatial anomalies of sea surface temperature, surface chlorophyl- a , pycnocline depth and OMZ depth. Dusky ( Lagenorhynchus obscurus ) and common dolphins ( Delphinus delphis ) preferred productive, cold areas with a very shallow OMZ, regardless of the season, while bottlenose dolphins ( Tursiops truncatus ) aggregated in both cold and warm waters, also with shallow OMZ. The former two species of higher metabolic demands would maximize energy intake by selecting areas with highly aggregated prey, while the latter, of more moderate metabolic needs and more diverse prey, would exploit less restricted habitats.

This study has considered anchoveta acoustic data from the Pelagic Resources Hydroacoustic Assessment Surveys carried out by the Peruvian Sea Institute (IMARPE) and free access satellite data (HYCOM and MODIS from the USA) of some oceanographic variables between the period 2011 and 2021, to know the oceanographic conditions, characteristics of schools and size structure in the optimum zone (OZ) and in the physiological stress zone (PSZ), of their total distribution. The OZ is determined by the extent of the Cold Coastal Waters (CCW), and the PSZ is determined by the mixing of waters, to the north by the CCW-ESW (Equatorial Surface Waters) and to the west between the CCW-SSW (Subtropical Surface Waters). The range of sea surface temperature and salinity in the PSZ (16.1-25.0 degrees C and 34.65-35.29, respectively) was wider than in the OZ (14.5-24.0 degrees C and 34.65-35.20, respectively), where a higher number of schools were recorded. Our analyses showed that the morphometric and energetic acoustic descriptors of anchoveta schools in the summer were higher during summers compared to springs. In terms of positional characteristics, the mean depth of the schools in the PSZ was slightly greater than in the OZ. The total size structure of anchoveta in the OZ consisted mainly of juvenile specimens (less than 12 cm total length) in the summer of 2011 and 2013-2014 and in the spring between 2014-2017 and 2021. In the PSZ, adult specimens (greater than 12 cm total length) predominated in summer between 2011-2013, 2015, 2018, and 2021 and in spring between 2011-2013, 2015, and between 2018-2021. However, specimens greater than 10 cm in total length were found in the PSZ. Knowledge of the location of this zone away from the coast will allow a high probability of anchoveta capture of adult specimens during fishing periods.

The Hydroacoustic Pelagic Resources Assessment survey (Cruise 1909-11) was conducted along the Peruvian coast (03°23'S-18°21'S) between 29 September and 15 November 2019 with the participation of three scientific research vessels from the Peruvian Marine Research Institute (Instituto del Mar del Peru, IMARPE), the R/V Jose Olaya Balandra, the R/V Flores Portugal and the R/V Humboldt. Using the acoustic data collected by the three scientific vessels we estimated the anchoveta biomass using seven hydroacoustic methodologies by applying the following three types of techniques in the processing and subsequent analysis of the eco-acoustic records for the frequencies of 120 and 38 kHz: stratification by isoparalitoral areas; stratification by transects; and by geostatistics. The three best anchoveta biomass estimates were 8.37 million tons obtained with the method of stratification by isoparalitoral areas using the 120 kHz acoustic frequency data; 8.47 million tons obtained with the transect stratification method using data from the 38 kHz frequency; and 8.22 million tons obtained with the geostatistical delta method using the 120 kHz frequency data with coefficients of variation of 5.44%, 13.71%, and 33.21%, respectively. Special attention was paid in the analyzes of the size distribution, in the length-weight relationship of the anchovy obtained in the survey 1909-11 and the use of the Target Strength (TS) equations, taking into account the great influence these may have on the population biomass estimates irrespective of the hydroacoustic technique being used. Based on the results obtained, we conclude that the anchoveta population in the Peruvian marine ecosystem is in an abundant and healthy state, although its abundance and in particular its distribution pattern may be affected by anomalous climatic events.

Land use change is one of the major drivers of soil degradation, affecting the ability of soils to supply multiple ecosystem services (ES). Despite the growing importance of soil-related ES, there is a lack of comprehensive methodologies to systematize how land use change affects the ability of soil to supply them. Here, by using primary information on soil properties, we develop a series of indices to assess the impact of land use change on the ability of soil to supply five soil-related ES: support for plant growth (SES1), C storage (SES2), nutrient cycling (SES3), erosion control (SES4), and water regulation and aeration (SES5). We focus our analysis on the rainforest-pasture transition for extensive ranching in the Colombian Amazon. Despite the global importance of the Amazon Forest biome, the existing methodological and knowledge gaps restrict our understanding of the impacts of land use change in the region???s soil-related ES. The results revealed that the extensive conversion of forest to pasture degraded the soil???s ability to supply all measured soil-related ES, with a higher impact for SES2 (47% of soil C storage reduction), SES1, and SES4 (40% and 31% decline of related indices, respectively). Ac-cording to the average scores for the three sites, the capacity of the soil to supply related ES is severely threatened by extensive ranching, causing a decline in the index from 99% in forest sites to 73% in pasture sites. A sig-nificant correlation among most indices revealed that the supply of the five soil-related ES is interdependent, with the indices of soil C storage and erosion control services being the major drivers of synergies and trade-offs. Our study highlights the importance of re-adjusting management practices to mitigate the negative historical impacts of pasture conversion on soil properties linked to soil-related ES. Superscript/Subscript Available

Climate change is expected to affect marine mercury (Hg) biogeochemistry and biomagnification. Recent modeling work suggested that ocean warming increases methylmercury (MeHg) levels in fish. Here, we studied the influence of El Niño Southern Oscillations (ENSO) on Hg concentrations and stable isotopes in time series of seabird blood from the Peruvian upwelling and oxygen minimum zone. Between 2009 and 2016, La Niña (2011) and El Niño conditions (2015-2016) were accompanied by sea surface temperature anomalies up to 3 °C, oxycline depth change (20-100 m), and strong primary production gradients. Seabird Hg levels were stable and did not co-vary significantly with oceanographic parameters, nor with anchovy biomass, the primary dietary source to seabirds (90%). In contrast, seabird Δ199Hg, proxy for marine photochemical MeHg breakdown, and δ15N showed strong interannual variability (up to 0.8 and 3‰, respectively) and sharply decreased during El Niño. We suggest that lower Δ199Hg during El Niño represents reduced MeHg photodegradation due to the deepening of the oxycline. This process was balanced by equally reduced Hg methylation due to reduced productivity, carbon export, and remineralization. The non-dependence of seabird MeHg levels on strong ENSO variability suggests that marine predator MeHg levels may not be as sensitive to climate change as is currently thought.

Soil enzymes mediate key processes and functions of the soils, such as organic matter decomposition and nutrient cycling in both natural and agricultural ecosystems. Here, we studied the activity of five extracellular soil enzymes involved in the C, N, and P-mineralizing process in both litter and surface soil layer of rainforest in the northwest region of the Colombian Amazon and the response of those soil enzymes to land use change. The experimental study design included six study sites for comparing long-term pasture systems to native forest and regeneration practices after pasture, within the main landscapes of the region, mountain and hill landscapes separately. Results showed considerable enzymatic activity in the litter layer of the forest, highlighting the vital role of this compartment in the nutrient cycling of low fertility soils from tropical regions. With the land use transition to pastures, changes in soil enzymatic activities were driven by the management of pastures, with SOC and N losses and reduced absolute activity of soil enzymes in long-term pastures under continuous grazing (25 years). However, the enzyme activities expressed per unit of SOC did not show changes in C and N-acquiring enzymes, suggesting a higher mineralization potential in pastures. Enzymatic stoichiometry analysis indicated a microbial P limitation that could lead to a high catabolic activity with a potential increase in the use of SOC by microbial communities in the search for P, thus affecting soil C sequestration, soil quality and the provision of soil-related ecosystem services.

The East Pacific (EP) leatherback population is listed by the IUCN Red List of Threatened Species as Critically Endangered. Despite conservation efforts, mainly focused on nesting beaches, its population has declined by over 90% since the 1980s. A major current threat is fisheries bycatch, which has been primarily documented in small-scale gillnets and longlines within South American migration and foraging habitats, but scarcely reported in fisheries that operate in areas near nesting beaches (i.e., inter-nesting areas). To assess the impact of small-scale fisheries on EP leatherbacks inhabiting waters north of the equator we conducted rapid bycatch assessments interviews in five countries (Mexico, Nicaragua, Costa Rica, Panama and Colombia), some of which host the main EP leatherback nesting beaches and inter-nesting areas. A total of 1778 interviews were conducted across 79 fishing ports (Mexico = 37, Nicaragua = 6, Costa Rica = 5, Panama = 17 and Colombia = 14). Leatherback bycatch was reported in all countries, and in 54% of ports assessed by 7% (n = 125) of fishers interviewed. Interviews enabled identification of inter-nesting areas where leatherback bycatch was higher and periods during which fisheries interaction events were more frequent. Bycatch events were most frequently reported in gillnets and secondarily in longlines. Data were extrapolated across fishing fleets to estimate that 345 ± 210 (mean ± SD) individual leatherbacks are caught annually in the ports assessed. Our study provides a first evaluation of leatherback bycatch by small-scale fisheries in countries of the eastern Pacific Ocean where leatherbacks nest, and it highlights areas close to index nesting beaches where conservation efforts targeting bycatch reduction and bycatch mortality may be focused.

Anchovy (Engraulis ringens) is the most important exploited fish species in the Northern Humboldt Current System (NHCS) off Peru. This species, as well as most other pelagic resources, mainly forage on zooplankton. The NHCS is bottom-up controlled at a variety of scales. Therefore, fish biomass is driven by the abundance of their prey. In this context, we studied the spatiotemporal patterns of zooplankton biomass in the NHCS from 1961-2012. Data were collected with Hensen net all along the Peruvian coast. To transform zooplankton biovolume into biomass we used a regression that was calibrated from 145 zooplankton samples collected during four surveys and, for which, precise information was available on both biovolume and wet weight. The regression model was then applied on a time-series encompassing 158 cruises performed by the Peruvian Institute of the Sea (IMARPE) between 1961 and 2012. We observed a clear multidecadal pattern and two regime shifts, in 1973 and 1992. Maximum biomass occurred between 1961 and 1973 (61.5 g m(-2)). The lowest biomass (17.8 g m(-2)) occurred between 1974 and 1992. Finally, the biomass increased after 1993 (26.6 g m(-2)) but without reaching the levels observed before 1973. A seasonal pattern was observed with significantly more biomass in spring than in other seasons. Spatially, zooplankton biomass was higher offshore and in northern and southern Peru. Interestingly, the zooplankton sampling was performed using classic zooplankton net that are well fitted to mesozooplankton and are known to underestimate the macrozooplankton; however, the spatiotemporal patterns we observed are consistent with those of macrozooplankton, in particular euphausiids. This suggests that in the NHCS, when and where macrozooplankton dominates it also dominates the biomass obtained using classic zooplankton net samples. Finally, until now, in the NHCS only time-series on zooplankton biovolume were available. The biomass data we provide are more directly usable in trophic or end-to-end models.

To better understand and characterize the distribution of the dolphinfish Coryphaena hippurus in the Pacific Ocean off Peru, we analyzed spatio-temporal catch per unit effort (CPUE) data from the artisanal longline dolphinfish fishery and oceanographic variables measured from October-March during 2010-2017. A Delta-GAM approach determined that high dolphinfish CPUE occurred during the period from November-January between 9-11 degrees S at an average of 190 nautical miles (nm) from the coast. From February-March, the highest CPUE was located along the coast up to 115 nm offshore between 12-13 degrees S, which suggested that dolphinfish migrate to the southeast during austral summer. However, there was no evidence of a reverse migration towards the northwest, although this result must be corroborated with data taken outside of the dolphinfish fishing season (October-April) in future studies. According to the environmental variables, dolphinfish preferred to stay in waters with sea surface temperatures (SST) that ranged from 22-24 degrees C, low chlorophyll-a concentrations (CHL; < 1 mg m(-3)), and surface sea heights (SSH) that ranged from 0.10-0.20 m. The information derived from this study, such as the maps, spatial indicators, and time series, contribute to the knowledge of how the spatial distribution of the dolphinfish and dolphinfish CPUE may vary under future climate conditions and provide some clues that will facilitate fishing ground forecasts in both the short and long term. Finally, our results may provide tools to develop or improve the conservation and management strategies of this species, which supports one of the most important artisanal fisheries in Peru.

The Humboldt Current System (HCS) has the highest production of forage fish in the world, although it is highly variable and the future of the primary component, anchovy, is uncertain in the context of global warming. Paradigms based on late 20th century observations suggest that large-scale forcing controls decadal-scale fluctuations of anchovy and sardine across different boundary currents of the Pacific. We develop records of anchovy and sardine fluctuations since 1860 AD using fish scales from multiple sites containing laminated sediments and compare them with Pacific basin-scale and regional indices of ocean climate variability. Our records reveal two main anchovy and sardine phases with a timescale that is not consistent with previously proposed periodicities. Rather, the regime shifts in the HCS are related to 3D habitat changes driven by changes in upwelling intensity from both regional and large-scale forcing. Moreover, we show that a long-term increase in coastal upwelling translates via a bottom-up mechanism to top predators suggesting that the warming climate, at least up to the start of the 21st century, was favorable for fishery productivity in the HCS.

Physical forcing of the surface ocean includes a variety of energetic processes, ranging from internal wave (IW) to submesoscale and mesoscale. Recent works based on acoustic data showed that, off Peru, the vertical displacements of the oxycline depth provide a robust proxy of isopycnals displacements over a wide range of horizontal scales. These studies revealed the importance of ephemeral hotspots (oases), which concentrate organisms ranging from zooplankton to seabirds, enhancing trophic interactions. Here, we address the question of the potential impact of climate variability on these fine-scale oases for life. Indeed, temperature and salinity changes induced by climate change are expected to lead to an ocean near-surface stratification increase that could have a negative impact on the intensity of physical small-scale structures and, consequently, on patterns distribution of marine life. For that we use 35 000 physical structures from acoustic data collected during twelve scientific surveys conducted between 2002 and 2011 off Peru. We estimate the strength of these structures, its power of aggregation on zooplankton and small pelagic fish and also ocean stratification conditions. Results show that higher the ocean stratification, less the strength and the power of aggregation of the fine scale physical structures. Climate variability, and potentially climate change, could thus lead to a reduction of the size and density of organisms patches with a potential impact on consequent trophic interactions.