Enrique Alberto Crespo

The instantaneous diet of South American sea lions ( Otaria byronia ) and South American fur seals ( Arctocephalus australis ) was analyzed using scats collected from shared haul‐out islands in the northern region of San Jorge Gulf, Patagonia, Argentina. Prey species were identified using otoliths, squid beaks, and crustacean exoskeletons during a long‐term project from 1999 to 2024. Sea lions and fur seals share several prey species, as well as with the fishing fleet, since most of them are commercial species. The diet of fur seals was predominantly pelagic, with Argentine anchovy ( Engraulis anchoita ) as a key prey, whereas sea lions showed a more demersal feeding pattern, with Argentine hake ( Merluccius hubbsi ) as the main fish prey. Argentine shortfin squid was also a major dietary component in both species, particularly during the early years of the study, when it dominated several sampling periods. Over time, both species exhibited a consistent shift in diet composition, characterized by a decrease in fish and cephalopods and an increasing contribution of crustaceans. The changes observed over the 26‐year period generally include a decrease in fish and an increase in crustaceans in the diet of both pinnipeds. The most important crustaceans were Argentine red shrimp and squat lobster, although their relative contribution differed between species. These changes, observed over a multi‐decadal period, are consistent with a broader reorganization of the Patagonian marine ecosystem. The observed patterns likely reflect changes in prey availability associated with sustained fishing pressure, including the extraction of key fish stocks and the input of fishery discards, acting in combination with environmental variability. Overall, our results support the use of pinnipeds as sentinel species for detecting long‐term trophic changes, as their diet integrates ecosystem‐level responses across multiple trophic levels.

Teeth provide valuable information about an individual’s life cycle and serve as a powerful tool for visualizing population-level changes associated with density-dependent processes. In pinnipeds, teeth are used to estimate the age of individuals based on the count of growth layer groups (GLG) in the dentine. In this study, we analyzed changes in tooth size and GLG widths in the canines of Otaria byronia throughout the past 100 years, linking these to fluctuations in population abundance. A total of 76 male individuals from Patagonia were analyzed, classified into two periods: harvest and postharvest. The length and diameter of each tooth were measured prior to sagittal sectioning. Only for the postharvest period body length was recorded. Longitudinal sections of the upper canine were prepared, age was determined and the width of each GLG was measured in the resulting half-tooth. Results indicated a positive correlation (F = 62.90; p < 0.001; n = 50; r² = 0.59) between body length and tooth length in postharvest individuals, suggesting that tooth growth is a reliable indicator of body growth. Individuals from the harvest period had narrower GLGs (t = 3.75; p < 0.001) and smaller tooth size (t = 3.48; p < 0.001) compared to those from the postharvest period. These results indicate that somatic growth of individuals may vary with population numbers and resources available. Also, hard structures like teeth are excellent tools for visualizing density-dependence effects.

Studying trophic feeding habits and their variation over time is crucial for understanding individual and population success. Although many generalist feeders’ populations appear to use diverse trophic resources, they are often composed of individuals that specialize in only a subset of these resources, a phenomenon known as individual trophic specialization (ITS). The South American sea lion (SASL) (Otaria flavescens), widely distributed along the South American coast, is an opportunistic and generalist predator with a diverse diet, making it a good model for studying ITS. We aimed to estimate the diet composition and the degree of ITS among SASL females on Isla Arce, Argentina, over a period of three years (2012 to 2014). For that, we analysed stable isotopes (δ15N and δ13C) in vibrissae from 12 females. Over the three years studied, females from this colony primarily fed on pelagic prey. At the population level, the most commonly consumed prey varied between the Argentine anchovy (Engraulis anchoita) in 2012 and 2014 and the Patagonian squid (Doryteuthis gahi) in 2013. Consuming mostly pelagic resources throughout the year, unlike previous studies in nearby colonies, suggests the existence of different foraging strategies in lactating females. Although the prey contribution varied between years, the analysis indicated that SASL females breeding on Isla Arce show some degree of ITS, which could be a mechanism adopted by individuals to mitigate the potential competition given by sustained population increases.

A rise in pinniped-fisheries interactions has been observed due to the global decline in fish populations primarily attributed to overfishing, and/or due to the recent population recovery of several pinniped species. Although many studies have quantified these interactions, a limited number delve into their behavioral aspects. We consulted 374 studies on pinniped-fisheries interactions from 1980 to 2020 and analyzed which of them addressed the interaction from a behavioral perspective. Additionally, we examined the role of learning in pinnipeds and their ability to capture prey from fishing gear. The stimulus-reward relationship in operational interactions was addressed in 51 (14%) studies, involving 10 (19%) of the world’s 54 pinniped species or subspecies. Depredation behavior (43%) and attack behavior (35%) were frequently reported during fishing interactions. Understanding associative and non-associative learning mechanisms has the potential to reduce economic losses from fishing activity, advance efficient mitigation measures to minimize conflicts, and establish pragmatic conservation priorities based on a better understanding of the behavioral aspects of these interactions. More research is needed to explore the effectiveness of deterrents in different species, improve methods of reducing habituation, and evaluate long-term behavioral effects, fostering effective strategies for minimizing conflicts and promoting coexistence between humans and pinnipeds.

In recent decades, the growth, physiology and distribution of many elasmobranch species have been altered as a result of environmental changes that affect prey abundance, availability and composition. Consequently, variations in nutrient input during climate events could manifest in the growth of their hard tissues. This study focuses on assessing the impact of the El Niño‐Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) on the growth of Shorttail Yellownose skate (Zearaja brevicaudata) in Patagonia, Argentina. To achieve this, vertebrae from 115 Z. brevicaudata specimens were analysed, and growth rings were dated and measured. By using cubic splines with varying flexibility, we constructed three standard chronologies. Generalized additive models (GAMs), the chronology with the best the R‐bar ( ) and expressed population signal (EPS) were employed and values obtained from them linked to annual time series data of the Multivariate ENSO Index (MEI) and SAM, considering lags in the biological response. Surprisingly, no significant association was found with the MEI time series. However, a noteworthy positive association emerged between the chronology and the SAM time series lagged by 1 year, suggesting that SAM‐related climatic conditions could delay their transfer into the Patagonian marine ecosystem, subsequently impacting the growth of this ectothermic predator.

Studying the abundance, distribution, and habitat use of dolphins can provide essential information for preserving marine biodiversity, managing coastal ecosystems, and enhancing our understanding of aquatic life. Herein, we investigated the abundance, distribution, and habitat use of two dolphin populations—Guiana dolphins (Sotalia guianensis) and common bottlenose dolphins (Tursiops truncatus)—in the Gulf of Urabá, Colombian Caribbean. Between 2017 and 2020, 34 non-systematic surveys were conducted across the studied region, amounting to an effort of 176.69 hours and covering 3,658.33 km, with a dolphin encounter probability rate of 8.65%. The Guiana dolphin population was estimated at 63 (95% CI = 53 to 76) individuals, whereas the common bottlenose dolphin population was estimated at 50 (95% CI = 43 to 58) individuals. The dolphins were mainly found in the central region of the Gulf, particularly around the Atrato River mouth and the east side of the estuary. Both species showed a preference for coastal areas with maximum depths of 20 m, and the Guiana dolphins showed a permanent presence in the Gulf of Urabá region. These findings indicate that the Gulf of Urabá acts as a crucial habitat and feeding ground for both Guiana and common bottlenose dolphins. Therefore, systematic monitoring programmes aiming to protect dolphin populations and their ecosystems from threats posed by coastal development, which currently endanger both species in the area, should be implemented.

Interactions between whale‐watching vessels and cetaceans have raised questions regarding the sustainability of whale‐watching. This study aimed to build a model for managing whale‐watching activity. The approach involved establishing vessel‐exposure thresholds based on changes in short‐term behavioral responses of southern right whales in the Bahía San Antonio Marine Protected Area of Argentina. The model serves as a source of information for management decision‐making in whale‐watching operations, with an estimated framework for the maximum carrying capacity dictating the vessel‐exposure level that can be maintained with no significant changes in the whales' activity budgets. The model, based on Markov chains, indicated that surface active behavior was the form most sensitive to the presence of tourism vessels. However, vessel exposure always remained below nonsustainability threshold, defined as the amount of time that a whale could be disturbed by vessels without significantly changing its activity budget. Therefore, the observed changes were biologically insignificant. Thus, whale watching in this area is developing with minimal impact on southern right whales. An understanding of the exposure thresholds is essential for establishing management strategies that enable sustainable whale watching. This approach is crucial for setting limits within a scenario of future growth and reducing activity when demand exceeds the carrying capacity.