Eduardo Marcelo Acha

The Agujero Azul sector of the Patagonian shelf-break (44–47°S) is a hydrographically dynamic transition zone where continental shelf, subantarctic, and deep ocean waters interact, generating distinct biogeochemical signatures. This study investigated how hydrographic forcing influenced the distribution of inorganic nutrients, particulate organic matter (POM), and the optical properties of dissolved organic matter (DOM) during late austral spring 2021. Water masses were identified from temperature–salinity characteristics and compared with the spatial variability of nutrients, chlorophyll a (Chl a), POM, and DOM optical properties. Surface biogeochemistry differed markedly among Subantarctic Shelf Water (SSW), Patagonian Shelf-Break Front Water (PSBFW), and Subantarctic Surface Water (SASW). SASW was associated with comparatively nitrate- and phosphate-rich waters to the shelf-break, whereas SSW exhibited nutrient depletion, elevated Chl a, and enhanced CDOM absorption, reflecting intense biological uptake and in situ DOM production. PSBFW displayed intermediate nutrient and DOM characteristics together with relatively elevated ammonium, consistent with active organic matter regeneration. At depth, Subantarctic Mode Water/Antarctic Intermediate Water (SAMW/AAIW), Upper Circumpolar Deep Water (UCDW), and North Atlantic Deep Water (NADW) exhibited contrasting nutrient and DOM signatures that reflected differences in water-mass origin and subsequent biogeochemical processing. Optical DOM indices, particularly the absorption coefficient (a254) and spectral slope (S275-295), varied consistently with water masses and closely followed the hydrographic structure. These findings demonstrate that hydrographic forcing governs the development of distinct biogeochemical signatures across the Agujero Azul shelf-break, emphasizing the fundamental role of water-mass interactions in shaping nutrient dynamics and organic matter transformation across continental shelf-break systems of the southwestern Atlantic.

Fisheries management often relies on single‐species assessments, overlooking multispecies dynamics while facing the added challenge of nonlinear environmental variability. Marine landings of most commercially exploited species in the Southwestern Atlantic have declined for decades and are projected to decrease further under climate change, as ocean warming is expected to reduce fisheries catches and revenues. Despite these trends, multispecies studies linking regional landings to environmental forcing remain scarce. Addressing this gap, we propose an integrated approach to examine multiscale environmental influence on fisheries landings within the Argentinean–Uruguayan Common Fishing Zone, a complex hydrographic region strongly influenced by the Río de la Plata discharge. We applied time‐series alignment and latent factor modeling to identify common patterns across multivariate landing series. These patterns served as response variables in lagged generalized linear and additive models, incorporating as predictors: riverine runoff, sea surface temperature, salinity, and turbidity, wind mixing, and large‐scale climatic indices such as the El Niño–Southern Oscillation (ENSO), the Southern Annular Mode (SAM), and the Southern Oscillation Index (SOI). Time‐lagged analyses show that environmental forcing at local and basin scales explains much landings variability. Turbidity and salinity were the most consistently retained variables, while the best‐fitting model (82% deviance explained) incorporated the combined effects of SAM and turbidity. Our findings demonstrate that diverse fisheries landings can be summarized into common multivariate patterns, which in turn can be linked to multiscale environmental forcing. This provides a robust basis for climate‐informed management, supporting a transition from isolated single‐species assessments to integrated multispecies frameworks.

The ”Agujero Azul” (AA) sector of the Patagonian shelf-break (44 – 47°S) constitutes a dynamic transition zone where continental shelf waters interact with subantarctic and deep waters transported by the Malvinas Current. In this study, we analyze the spatial distribution of inorganic nutrients, chlorophyll a (Chl a), particulate organic matter, and chromophoric dissolved organic matter (CDOM) optical properties during late austral spring 2021. Surface and vertical observations were interpreted in relation to water mass structure identified through temperature–salinity analysis and supported by multivariate clustering. Surface biogeochemistry was primarily structured by the mixing of Subantarctic Shelf Waters (SSW), Patagonian Shelf-Break Front Waters (PSBFW), and Subantarctic Surface Water (SASW). SASW supplied elevated nitrate (8 – 10 µM) and phosphate (0.6 – 1.1 µM) to the shelf-break, while SSW exhibited nutrient depletion (<5 µM nitrate) associated with enhanced Chl a and higher CDOM absorption, reflecting biological uptake and in situ dissolved organic matter (DOM) production. PSBFW showed transitional nutrient and DOM characteristics and elevated ammonium, indicative of active regeneration processes. Vertical distributions revealed a clear stratification from productive surface waters to nutrient-rich intermediate layers associated with Subantarctic Mode Water/ Antarctic Intermediate Water, and deeper Upper Current Deep Waters integrating contributions from North Atlantic Deep Water. In deep waters (1160–1760 m), nitrate ranged between 15 and 22 µM, while silicate reached 42 – 50 µM, consistent with the combined influence of circumpolar and North Atlantic sources. CDOM optical indices, including total CDOM (250–450 nm), absorption coefficient a254, and spectral slope (S275–295), effectively discriminated water masses and mirrored the multivariate structure identified by cluster analysis. Overall, the combined analysis of hydrography, nutrients and CDOM demonstrates that inorganic nutrient variability and DOM optical signatures in the ”AA” region are largely governed by water mass identity, modulated by frontal mixing and local biological processing.

Durante la migración, las aves marinas se concentran en áreas oceánicas claves asociadas a una alta productividad. Los Pingüinos de Magallanes (Spheniscus magellanicus) y Penacho Amarillo (Eudyptes chrysocome chrysocome) pasan la mayor parte de la temporada no-reproductiva migrando en el Mar Argentino. Aquí comparamos las distancias y fenologías de los viajes migratorios entre ambas especies que nidifican en colonias cercanas (< 20 km de distancia en Puerto Deseado, Santa Cruz). Además, evaluamos la asociación de estas colonias y otras colonias de Pingüinos de Magallanes a los frentes marinos durante la migración. Entre 2017 y 2024, analizamos 186 geolocalizadores recuperados de individuos adultos de ambas especies. Los Pingüinos Penacho Amarillo recorrieron distancias totales mayores y se desplazaron más mar adentro que los Pingüinos de Magallanes, pero las distancias máximas alcanzadas fueron similares. Los Pingüinos de Magallanes partieron y regresaron de la colonia antes que los Pingüinos Penacho Amarillo, manifestando una alocronía reproductiva interespecífica. El frente más utilizado por ambas especies fue el de El Rincón. En el caso del Pingüino de Magallanes, el frente del Río de la Plata parece actuar como el límite oriental en la migración de individuos de las colonias del norte (60% de la población evaluada), en tanto que el frente de la Corriente Patagónica es utilizado por los individuos de las colonias del sur (16%). Ante anomalías térmicas, los Pingüinos Penacho Amarillo usaron además el frente del talud. Estos hallazgos evidencian una segregación espacial y temporal en la utilización de hábitats de estas especies y resaltan la importancia de áreas clave para su conservación, como las aguas de El Rincón y el Río de la Plata.

Time‐series modeling of fisheries provides insights into stock tendencies and enables short‐term forecasting of landings, aiding decision makers in establishing management priorities. The Rio de la Plata Estuary and its maritime front sustain valuable fisheries for Argentina and Uruguay, with striped weakfish (Cynoscion guatucupa), whitemouth croaker (Micropogonias furnieri), and Argentine hake (Merluccius hubbsi) historically representing highest catches. However, their landings have declined in recent decades. To support resource management, we investigated the effectiveness of Autoregressive Integrated Moving Average (ARIMA) models in capturing fishery landing dynamics and providing reliable short‐term predictions. The best models exhibited a good fit and accurately captured the overall trends of landings. Residual variability unaccounted for by the model was analyzed in relation to time‐lagged environmental conditions. A wavelet coherence analysis was employed to examine the effect of the most significant variables on landings. Results revealed that environmental conditions affect differentially landings of each species as a result of their particular ecological traits. Turbidity and salinity affected mainly M. furnieri, which inhabits the innermost part of the estuary. Additionally, C. guatucupa, inhabiting the outer estuary and coastal region, exhibited a stronger association with river runoff compared to M. hubbsi, which inhabits the continental shelf. This study provides the first evidence of ARIMA models' reliability in representing the temporal evolution of catch in these fisheries, offering valuable tools for short‐term landings forecasting and facilitating sustainable management. Wavelet analysis findings will also contribute to enhancing our comprehension of trends in the correlation between environmental conditions and commercial landings.

The Argentine shortfin squid (Illex argentinus) sustains one of the world's largest squid fisheries. This squid presents strong interannual fluctuations in abundance, attributed to its semelparous life strategy coupled with environmental influences on recruitment. Several stocks have been identified, but the south patagonic stock (SPS) is the most abundant and the main support (ca. 80%) of the Argentine fishery. SPS spawns in autumn–winter, but there are controversies regarding the spawning ground location. We studied the relationship between the recruitment variability and oceanographic conditions to which eggs and paralarvae are exposed, considering two possible spawning ground locations: Patagonia and Southern Brazil. We tested the hypothesis that the SPS recruitment variability could be controlled by oceanographic fluctuations related to the transport of the egg masses spawned on each of the two grounds, to their retention on the continental shelf and to the attainment of the thermal habitat required for eggs hatching. We used a 24‐ years long time series (1993–2017) of catch per unit effort of the squid fishery, and a shorter stock‐assessment series as recruitment proxies; and satellite data of SST and of geostrophic velocities derived from sea surface height. This information was employed to model the advection of the squid egg masses along the external shelf and slope and to estimate the annual recruitment success. Results show that if spawning occurs in Patagonia, 52% of the recruitment variability could be explained. On the other hand, if spawning occurs in southern Brazil, it does not result in successful recruitments for the SPS.