Argentine Anchovy Research Articles

Using head, pectoral girdle bones and otoliths to estimate length and weight of Argentine anchovy (Engraulis anchoita), a key species in Patagonian marine ecosystem

The Argentine anchovy, Engraulis anchoita, plays a vital role as a key prey species for several marine predators in the north Patagonian marine ecosystem of the Atlantic Ocean. Reconstructing the length and weight of each consumed specimen is essential to provide a detailed description of the trophic ecology of top marine predators. Predictive linear regression equations were calculated for the Patagonian stock of Argentine anchovy to estimate parameters of length-weight relationships using measurements of whole individuals and diagnostic elements such as otoliths, head bones and pectoral fin bones. Among the diagnostic elements analyzed, the cleithrum and dentary exhibited the best fit. This study validates the use of head and pectoral girdle bones as reliable indicators for predicting the weight and length of Argentine anchovy across a wide size range, which corresponds to the target range of various predators. These relationships can contribute to the determination of body condition, estimation of consumed biomass, and calculation of energy density, providing valuable insights into the trophic ecology of predators in the southern Atlantic Ocean.

Contrasting distributional patterns of two co-occurring ctenophores in relation to ichthyoplankton and environmental features in the Southwestern Atlantic Ocean

Assessing the ecological role of ctenophores is crucial to understanding ecosystem functioning, including the recruitment of fish stocks. During austral summer in the North Patagonia Ecosystem (NPE) (41-48°S), the ctenophores Mnemiopsis leidyi and Pleurobrachia pileus co-occur with the peak of ichthyoplankton abundance of 2 important fishing resources: the Argentine anchovy Engraulis anchoita and the Argentine hake Merluccius hubbsi, in association with a highly productive tidal front system. We analyzed 367 plankton samples collected in the NPE over 13 yr (2005-2018) to determine the abundance and spatial distribution of M. leidyi and P. pileus, their spatial overlap with ichthyoplankton (eggs and larvae of hake and anchovy), and their relationship with environmental features. Both ctenophore species displayed contrasting distributional patterns, associated with different physical environments, particularly temperature. M. leidyi showed a higher spatial overlap with ichthyoplankton compared to P. pileus. In addition, we found a significant negative correlation between the biomass of M. leidyi and the abundance of both fish larvae, suggesting a potential negative impact (via predation and competition) on the survival and recruitment of these 2 fisheries resources.

Movements of satellite tracked Magellanic penguins (Spheniscus magellanicus) in a wintering area in southern Brazil

Food availability and oceanographic conditions drive the distribution and movement of marine vertebrates. Tracking efforts towards seabirds usually focus on their breeding period, tagging adults in colonies. In this study, we tracked four juvenile and one adult Magellanic penguin (Spheniscus magellanicus) with satellite transmitters. These individuals were caught incidentally in gillnets and were tagged at sea, with the exception of the adult that was rehabilitated and released on the beach. The penguins were tracked in their wintering grounds, where behavior and oceanographic characteristics of the area used were determined. All five birds remained along the coast of southern Brazil and Uruguay in neritic waters up to 10 km offshore and 50 m in depth. The four juveniles used a mean area of 1,426 km2, travelling on average at 7.4 km/h. The high turning angles observed and mean sinuosity of 2.46 indicated that the penguins were foraging. The adult penguin covered an area of 1,033 km2, at a mean speed of 4.6 km/h, and with low sinuosity (0.43), which is suggestive of either travelling movements or an experienced hunter who needs a few turning angles to forage. The adult travelled 538 km in total, reaching a maximal distance of 465 km. Locations were obtained over a period of 7–10 days, and all five penguins remained in waters of the coastal branch of the Malvinas Current, an area characterized by cold sea surface temperatures (SST, mean = 13.4 °C) and high primary productivity. Salinity values (34.06 PSU) were also typical of the Malvinas Current and were influenced by the La Plata River plume, whose waters are low in salinity and nutrient rich. All five penguins remained near the coast probably because these waters are rich in nutrients, and carry the penguins' main prey, the Argentine anchovy (Engraulis anchoita). Regarding conservation concerns involving these penguins, we highlight the current management of the anchovy fisheries and the development of offshore windfarms that could potentially cause major disturbances to the penguins’ foraging habitat. The establishment of the Albardão National Park in the nearshore area used by the penguins is highly desirable for the protection of the species and their feeding resources.

Trophic ecology of Patagonian flounder Paralichthys patagonicus (Jordan, 1889) in the Argentine-Uruguayan Coastal Ecosystem

Food habits and diet composition of Patagonian flounder Paralichthys patagonicus (Jordan, 1889) were studied on the basis of stomach content analyses from 828 specimens (512 females, 304 males, 12 unsexed) collected during 16 commercial cruises between February 2009 and April 2010 in the Argentine-Uruguayan Coastal Ecosystem (34° S-41° S). A total of 272 stomachs (32.9%) contained food (184 females and 84 males), among which 20 prey taxa were identified. The most important prey category was pelagic fish, primarily Argentine anchovy (Engraulis anchoita), followed by rough scad (Trachurus lathami). Evidence showed that females consumed a higher total wet weight of prey compared to males. Results also suggested a specialised diet over E. anchoita, across all sex and size groups. The estimated trophic level for the population of P. patagonicus was 4.16. This study suggests that P. patagonicus is a tertiary piscivorous consumer of the trophic food web in the region, and reveals changes in the prey consumption compared with previous studies.

Marine fish imported from Argentina as source of human diphyllobothriosis in Europe? Ecological evidence from dolphins.

Diphyllobothriosis caused by the Pacific broad tapeworm Adenocephalus pacificus (syn. Diphyllobothrium pacificum) is an emerging parasitic disease reported also from non-endemic areas, including Europe (Spain). The origin of these human cases is unknown but should be related to fresh marine fish imported from endemic areas. In this study, we molecularly confirmed common dolphins Delphinus delphis off Argentina as euparatenic transit hosts of A. pacificus. Preliminary analysis of their stomach content, together with data from previous studies from the Southwest Atlantic, showed that common dolphins feed almost exclusively on schooling Argentine hake Merluccius hubbsi and Argentine anchovy Engraulis anchoita. Therefore, we suggest that Argentine hake and Argentine anchovy may represent the intermediate hosts of A. pacificus in the Southwest Atlantic, but also in Europe to where M. hubbsi is imported on ice (unfrozen).

Isotopic niche plasticity in a marine top predator as indicator of a large marine ecosystem food web status

As marine ecosystems are harvested or modified by anthropogenic or natural factors, there is an increasing demand for indicators of trophic web health or status. The Magellanic Penguin (Spheniscus magellanicus) is a widely distributed species that forages in the Patagonian Shelf. During breeding, this species is a central-place forager that feeds mainly on schooling fish, with Argentine anchovy (Engraulis anchoita) being the dominant prey in the north and Fuegian sprat (Sprattus fuegensis) in the south of the Argentine Patagonian distribution (40–55°S). Like most forage fish, both prey species display large natural interannual recruitment fluctuations. We used stable isotope analysis of adult Magellanic penguin blood obtained at twelve colonies along its Patagonian latitudinal range to assess changes in isotopic niche and in trophic level as a response to interannual changes in abundance and spatial segregation of forage fish size classes, respectively. Magellanic penguins showed large isotopic niche fluctuations among breeding seasons, explained by the contribution of forage fish in their diet. Furthermore, the size of the isotopic niche negatively correlated with forage fish biomass estimated from acoustic surveys and with their contribution in penguin diet. We defined an isotopic niche size threshold that indicates low abundance of forage fish in nearby feeding grounds. In addition, the trophic level of Magellanic penguins increased with latitude, which corresponds to the size-distribution of both main forage fish species, showing that penguins from different colonies target different size classes of their main prey. We present here a simple and easy to implement indicator to monitor the status of the base of the food web in one of the most productive marine areas in the world, which constitutes the feeding ground of a diverse group of high trophic level predators and sustains large-scale fisheries.

Seabirds, environmental features and the Argentine anchovy Engraulis anchoita in the southwestern Atlantic Ocean

As top predators in marine environments, seabirds frequently respond to the presence of their main prey, and both predators and prey are usually associated with specific environmental features. We investigated the variability in the presence and density of flying seabirds (mostly Procellariiformes and Charadriiformes) and Magellanic penguinsSpheniscus magellanicusalong the southwestern (SW) Atlantic continental shelf. Five acoustic assessment surveys were conducted to determine the biomass of the Argentine anchovyEngraulis anchoita, and seabird counts and the collection of oceanographic data were conducted simultaneously with the surveys between June and October 2010. Generalized linear mixed models (GLMMs) were fitted to test the effect of anchovy density and environmental variables on seabird density. Sea surface temperature was significant for the presence of flying seabirds. Bottom water temperature and anchovy density were key variables affecting the presence and density of penguins, while bottom water salinity was also important for penguin presence. Based on Akaike’s information criterion, the most important factor explaining the density of flying seabirds was the difference between surface and bottom salinity (ΔS), while for penguin density, the most important factor was anchovy density. These results highlight that the subtropical shelf front in the SW Atlantic Ocean is a key feature influencing the aggregation of flying seabirds and confirm the close association of penguins and anchovies. Bottom water intrusion, originating from the sub-Antarctic shelf water, is an important factor explaining the presence of penguins, which tend to aggregate in areas with high anchovy densities on the SW Atlantic continental shelf.

Linking cadmium and mercury accumulation to nutritional intake in common dolphins (Delphinus delphis) from Patagonia, Argentina

Bioaccumulation of Hg and Cd from food is a complex ecological process that has been oversimplified in the past. Common dolphins (Delphinus delphis) provide a powerful model to biomonitor metal concentrations in marine environments worldwide. We combined proportions-based nutritional geometry with metal analysis, stomach content analysis and the proximate composition of prey, to yield novel insights into the accumulation of Hg and Cd. Our analysis showed an age-related accumulation trend for Cd and Hg in kidney and liver, with highest concentrations found at 18 years of age. When viewed through the lens of nutritional ecology, Argentine anchovy (58.1 Mass %) and South American long-finned squid (22.7 Mass %), provided most of the dietary intake of protein (P) and lipids (L) (P:L ratio = 2.6:1.0) and also represented the main source for Cd and Hg levels accumulated in their bodies. This study presents unprecedented evidence on metal accumulation in relation to age and nutritional intake in a marine predator.

Energy Density Predictors for Argentine Anchovy Engraulis anchoita, a Key Species of the Southwestern Atlantic Ocean

AbstractForage fishes have a cosmopolitan distribution and constitute key species in marine trophic webs throughout the world. We estimated the energy density of the Argentine Anchovy Engraulis anchoita, a key component of the base of the food web in a large fraction of the southwestern Atlantic Ocean. We also examined the relationships between energy density and different proxies (condition factor, fork length, and percent dry weight) and compared the relationship of energy density to percent dry weight for Argentine Anchovy to this relationship in other forage fishes. A regression model that includes percent dry weight and fork length was the best predictor for the energy density in this species. The Argentine Anchovy had similar energy density to percent dry weight to all species in the Engraulidae family (anchovies) and to most of the species in the Clupeidae family (sardines). Engraulidae species showed smaller mean energy density and smaller energy density to percent dry weight compared with the Clupeidae species. The difference in energy density between these two families could have direct implications on population dynamics of predators in oscillating sardine–anchovy systems or in regions where these two families are spatially segregated.

Forage fish to growing chicks: shared food resources between two closely related tern species

The assessment of the relevance of forage fish in seabird diet and how different species partition food resources is fundamental to understand predator–prey relationships. We assessed the importance of forage fish in the diet of Royal (Thalasseus maximus maximus) and Cayenne (T. sandvicensis eurygnathus) terns and their partitioning of food resources during the early and late chick stages of 2013 and 2014 at a colony in Argentina. Direct observation of prey deliveries during chick provisioning showed that diet composition of Royal and Cayenne terns comprised at least 16 and 9 prey species, respectively. In both tern species, Argentine Anchovy (Engraulis anchoita) and five species of silversides (Odontesthes spp.) were the main prey fed to chicks (over 90% contribution, anchovy and silversides pooled). Both tern species fed their chicks with similar prey species, but Royal terns delivered, in general, larger prey than Cayenne terns. Based on carbon and nitrogen isotopic values from chick whole blood samples, Bayesian mixing models showed that anchovies and silversides contributed similarly to the diet of both tern species’ chicks. Both conventional and stable isotope methods showed a high overlap in their trophic niches. Prey sizes delivered to chicks were larger in the late chick stage and the second study season. Wind speed did not have a significant effect on the frequency of the different prey species and sizes delivered to chicks by both tern species. As anchovies and silversides are fishery targets, tern trophic requirements should be considered when planning future fisheries development and management.

Putting the pieces together: Recent growth, nutritional condition, and mortality of Engraulis anchoita larvae in the Southwest Atlantic

AbstractDynamics of clupeiform fish populations such as anchovy are frequently impacted by environmental variations which can affect the success of the species recruitment. Herein, we have analyzed recent otolith growth rate, RNA/DNA nutritional condition index (sRD), and mortality rate of argentine anchovy larvae Engraulis anchoita from three different nursery areas in the Southwest Atlantic. We have evaluated the relationship between the environmental variables (abundance of copepod nauplii, temperature, chlorophyll‐a concentration, and abundance of E. anchoita larvae) and larval endogenous variables (size, weight, age, and otolith radius) to sRD and recent growth rate. Fast larval growth rates were observed toward the northern sector of the studied area, characterized by higher temperature. High values of sRD were associated with higher nauplii abundance in the proximity of coastal fronts. The larvae with the lowest growths and lowest minimum values of nutritional condition coincided with the area where there was less abundance of nauplii and higher larval mortality. Larval size and nauplii abundance were positive explanatory factors for both recent growth rate and sRD index. Temperature had a positive effect on recent growth rate and a negative effect on sRD index. This condition index was poorly explained in terms of model fit in comparison with the growth model. The results herein provided could be significant to better understand the recruitment of the species, as to determining favorable areas for the growth and survival of anchovy larvae.

Shared dietary niche between sexes in Magellanic Penguins

AbstractPrey use by male and female Magellanic Penguins (Spheniscus magellanicus) was quantified during chick rearing in northern Golfo San Jorge, Argentina and the dietary niches and diet composition of each sex were assessed and compared. A total of 67 males and 45 females were flushed during the chick stages of 2011 and 2012. Argentine Anchovy (Engraulis anchoita) was the main prey in terms of importance by mass in males and females in all stages and years (52.4–86.6% and 83.8–88.7%, respectively), except during the old chick stage in 2011 when the main prey in males and females was the Shortfin Squid (Illex argentinus) (63.1% and 44.4%, respectively). Analyses of similarity showed that diet composition in terms of contribution by mass of the main prey species was similar between sexes. Based on the isotopic values of δ13C and δ15N corresponding to 38 males and 21 females, the Bayesian mixing model outputs showed that Argentine Anchovy was also the main prey. In both years and chick stages, the isotopic niche of males and females was similar. The similarity in the dietary niche between male and female Magellanic Penguins raising chicks may be due to the high availability of Argentine Anchovy during the study period and the consequent dominance of this forage species in the diet of both sexes.

Diet composition of expanding breeding populations of the Magellanic Penguin

ABSTRACTThe Magellanic Penguin (Spheniscus magellanicus) is the most abundant and widely distributed seabird breeding on the Patagonian Coast of Argentina. We combined conventional stomach content and stable isotope analysis to assess Magellanic Penguin diet during the chick rearing stage at the two northernmost colonies in an area subject to fisheries. In 2011 and 2013, Thornfish (Bovichtus argentinus) was the main prey by mass at Complejo Islote Lobos (63.0% and 32.3%, respectively) and Argentine Anchovy (Engraulis anchoita) at Estancia San Lorenzo (85.2 and 63.3%, respectively). Magellanic Penguins from both colonies showed low isotopic niche overlap in 2011 (36%) and no overlap in 2013, suggesting a different use of prey species and/or foraging areas. Stable isotope mixing models showed that Argentine Anchovy (52.8%) and Thornfish (65.9%) were the main prey at Complejo Islote Lobos in 2011 and 2013, respectively, while Patagonian Redfish (Sebastes oculatus) (46.4%) and Squat Lobster (Munida gregaria) (50%) were the main prey at Estancia San Lorenzo in 2011 and 2013, respectively. Results show that in addition to Argentine Anchovy, previously recognized as main prey for breeding Magellanic Penguins in northern Patagonia, other juvenile or small sized fish are important diet items. Diet results suggest different scenarios of food conditions for each colony, despite the relative short distance between breeding locations. The low contribution of Argentine Hake (Merluccius hubbsi) and Argentine Shortfin Squid (Illex argentinus) suggests a low trophic overlap with commercial fisheries. The information provided is key to understand changes in the marine ecosystem and potential penguin-fishery interactions.

Dinoflagellates Amyloodinium and Ichthyodinium (Dinophyceae), parasites of marine fishes in the South Atlantic Ocean.

The morphology and molecular phylogeny of the parasitic dinoflagellates Ichthyodinium chabelardi and Amyloodinium ocellatum was investigated off Brazil (South Atlantic Ocean). This is the first record of Ichthyodinium and the first molecular data of both parasites from the southern hemisphere. I. chabelardi infected the yolk of eggs of wild populations of Argentine anchovy Engraulis anchoita (Engraulidae) and Brazilian sardinella Sardinella brasiliensis (Clupeidae) in different seasons. The small subunit (SSU) rRNA and internal transcribed spacer (ITS) gene sequences were identical and confirmed Ichthyodinium as a host generalist. The new sequences clustered with the type species I. chabelardi from the North Atlantic and environmental sequences from the Pacific Ocean. A second species from the western Pacific remains undescribed. A. ocellatum was isolated from the gills of a cultured cobia Rachycentron canadum after causing mortality. The SSU rRNA gene sequence of the Brazilian isolate was almost identical to those from the northern hemisphere. This suggests a single species with a widespread distribution, although it is uncertain whether the species has a natural pantropical distribution or is the result of artificial distribution due to human-induced fish transport.

A hydrodynamic analytical model of fish tilt angle: Implications regarding acoustic target strength modelling

We implement a simple hydrodynamical model to study the behavioural swimming tilt angle of open swimbladder fish. For this purpose we analysed the force stability which act upon a fish swimming horizontally at a constant velocity. Furthermore, the open swimbladder compression at depth is modelled by Boyle's law. With these, our model gives us an analytical solution relating depth with body tilt angle and velocity. An interesting result that surges from steady horizontal swimming is that the body tilt decreases with velocity almost like v−1. Moreover, we provide an expression for the tilting as function of depth that asymptotically yields the maximum tilt angle. Additionally, by introducing the assumption of constant swimming power we can relate the swimming velocity to the tilting. We also show that the hydrodynamical influence of a temperature gradient produced by a thermocline does not seem to affect fish tilting significantly. Finally, we obtain reasonable results by comparing our hydrodynamics solutions with acoustic observations and simulations obtained from of Target Strength simulations of Argentine anchovy (Engraulis anchoita).

Trophic ecology of Magellanic penguins (Spheniscus magellanicus) during the non-breeding period

Some top predators couple their migration with the migration of their main prey. Magellanic penguins, Spheniscus magellanicus, migrate north from their Patagonian colonies during their non-breeding period, supposedly following the Argentine anchovy, Engraulis anchoita, a keystone species and their main prey item in the southwestern Atlantic Ocean. However, previous studies based on stranded carcasses suggest that cephalopods are the main food item for the penguins at their Brazilian wintering grounds. Moreover, anchovy stocks are in the early stages of commercial exploitation in southern Brazil. This study aims to investigate the importance of the Argentine anchovy in the diet of Magellanic penguins, including penguins of different age classes, both healthy and debilitated individuals, and in different parts of their annual cycle, using stomach content analysis and stable isotope analysis of multiple tissues, representing different time windows. Juvenile and adult penguins were collected (n = 54), either stranded on the beach or incidentally killed during gillnet fishing in adjacent waters. Penguins collected at sea had higher body mass indexes compared to stranded, demonstrating that they were healthy individuals. Among adult penguins from both areas (n = 21), fish was the main food item in their stomachs (prey-specific index of relative importance, PSIRI = 86%), with high contribution of Argentine anchovy. Cephalopods were the main food item (PSIRI = 71%) for juveniles (n = 20), with a predominance of the squid Doryteuthis sanpaulensis. In liver, muscle and feathers of penguins, mixed models based on δ13C and δ15N values demonstrated large contribution of the Argentine anchovy in the diet of the juveniles (95% credibility interval = 46–98.6%) and adults (39.8–98.9%), despite the high importance of cephalopods in the juvenile diet as identified in the stomach content analysis. Adults and juveniles presented isotopic niche overlap for all the tissues analysed, despite the differences in isotopic niche areas (= niche width) among the age classes. In 29% of the stomach contents, plastic debris was also found. Our results highlight the importance of using complementary techniques to study trophic ecology, as stomach content analysis of individuals found dead on beaches may not provide reliable information on diet. The strong reliance of penguins on the Argentine anchovy as a key resource throughout its annual cycle suggests that the stocks of this small pelagic fish should be exploited sustainably, ensuring the minimal forage biomass needed not only for seabirds but also for other consumers.

Effect of Organic Acids on Physical-Mechanical and Antifungicidal Properties of Anchovy Protein Films

ABSTRACTThe use of active biodegradable films from renewable sources like anchovy, with the incorporation of organic acids, such as sorbic acid (SA) and benzoic acid (BA), is an alternative to decrease environmental pollution and minimize the development of fungi in foods. This study investigated the respective influences of SA and BA at 0, 0.50, 0.75, and 1.50% on the growth of Aspergillus flavus and Rhizopus oryzae and on Argentine anchovy protein film properties (L*, a*, b*, tensile strength, elongation at break, solubility in water, water vapor permeability, and Fourier transform infrared spectroscopy (FTIR)). Results showed that the incorporation of SA or BA at different levels significantly increased the water vapor permeability, water solubility, and elongation at break of the films, but decreased the tensile strength and L* parameter (p < 0.05). FTIR evidenced an interaction between the BA and Argentine protein isolate. Also, the influences of the SA or BA concentration on antifungal activity was observed. The greatest effectiveness was obtained for films containing SA against R. oryzae compared to BA film treatments. In conclusion, the Argentine anchovy protein films could retain their antifungal property by incorporation of these organic acids.

Induced Regurgitation Versus Stomach Sampling: Assessing Their Value for the Characterization of Imperial Cormorant (Phalacrocorax atriceps) Diet

Abstract. Several studies have applied induced regurgitations to characterize the diet of cormorants, but none have presented quantitative information indicating complete stomach contents were obtained. Our goal was to test the value of induced regurgitations for the assessment and monitoring of Imperial Cormorant (Phalacrocorax atriceps) diet. Stomach samples were obtained from male and female breeding adults bringing food back to the colony during the chick rearing stage (n = 22) at Isla Arce, Argentina. Samples were obtained through induced regurgitation, and immediately afterward each individual was flushed with sea water. The diet of the Imperial Cormorant consisted of at least 23 prey taxa, mostly fish complemented by crustaceans, cephalopods and polychaetes. However, only Argentine anchovy (Engraulis anchoita) and rockcods (Patagonotothen spp.) showed a significant contribution by mass (70.7% and 25.3%, respectively). Analysis of similarity indicated that prey composition between samples obtained b...

Relevance of forage fish in the diet of Magellanic penguins breeding in northern Patagonia, Argentina

ABSTRACTWe quantified the trophic niche of Magellanic penguins (Spheniscus magellanicus) breeding and moulting in Golfo San Jorge, Argentina, through conventional stomach content and stable isotope analysis. A total of 112 adults were flushed during the early and late chick stages of 2011 and 2012 at Isla Vernacci Norte, and at least 15 prey taxa were found, including fishes, cephalopods, crustaceans and polychaetes. Overall, Argentine anchovy (Engraulis anchoita) showed the highest contribution in terms of importance by mass (68.1–85.3%, depending on chick stage and year), except for the old chick stage in 2011 when the shortfin squid (Illex argentinus) was the main prey consumed (56.0%). Based on carbon and nitrogen isotopic values from a total of 256 blood samples, corresponding to young and old chicks and to adults of both sexes sampled throughout the incubation, chick and moult stages at the above mentioned colony and years, Bayesian mixing model outputs showed that Argentine anchovy was always the main prey (48–86%). Bayesian mixing model outputs obtained from adults of both sexes and their chicks during the late chick stage of 2013 at Isla Vernacci Norte, Isla Tova and Isla Leones also showed that Argentine anchovy was the main prey consumed. This is the first comprehensive assessment of Magellanic penguin diet composition in northern Patagonia, quantifying the relative contribution of prey in the diet of adults and chicks at different stages of the annual cycle and years, and confirms the relevance of a forage fish such as the Argentine anchovy in its trophic ecology.

Assessing the trophic niche of South American Terns integrating conventional and isotopie methods

Conventional dietary studies combined with stable isotope analysis allowed the characterisation of the trophic niche of South American Terns (Sterna hirundinacea) breeding in Argentina. Direct observation of prey deliveries during mate-and chick-provisioning showed that the diet of South American Terns comprised at least 18 prey items, mainly pelagic schooling fish with smaller proportions of marine invertebrates. Argentine Anchovy (Engraulis anchoita) was the main fish prey. Adults delivered a higher proportion of fish and smaller prey to their chicks than to their mates. Analysis of stable isotope ratios in blood samples, using Bayesian stable isotope mixing models, indicated that adult Terns used a higher proportion of marine invertebrates for self-feeding than for mate-or chick-provisioning. Analyses of stable isotopes ratios in blood samples from chicks were consistent with the determination of diet from direct observation, and indicated differences from adults in both the proportion of different prey in the diet and trophic niche. In addition, isotopic niche analysis showed that chicks had a significantly higher trophic position compared with self-feeding adults during both mate-provisioning and chick stages. The results highlight the importance of combining stable isotope and conventional methods to adequately assess the food requirements of a population during the breeding season.