Patagonian Shelf Research Articles

Incidental capture of seabirds in Argentinean side-haul trawlers

SummaryBetween April 2008 and July 2015, we conducted a total of 18 trips on five different side-haul trawlers fishing within the Argentine Exclusive Economic Zone, monitoring 486 hauls. We observed 100% of the hauls and monitored trawl cables for 136.7 hours, about 5% of the trawl effort, to identify the levels of seabird bycatch from net entanglements and collisions with trawl cables. A total of 35 net entanglements of White-chinned Petrels Procellaria aequinoctialis, Great Shearwaters Ardenna gravis, Black-browed Albatrosses Thalassarche melanophris and Southern Royal Albatross Diomedea epomophora were recorded, all of which occurred during the autumn and winter. Additionally, 656 seabird collisions against trawl cables were recorded including 39 heavy, 96 medium and 521 light. Further, we recorded nine Black-browed Albatrosses and two Great Shearwaters potentially dead. Although in the study fishery the number of deaths in the trawl cables could surpass the number of birds incidentally killed in nets, the mortality rate caused by the latter type of interaction far exceeds those observed in nets from other trawl fisheries operating in the Patagonian Shelf. Fortunately, 26% of the seabirds entangled in the net were recovered and released alive, which indicates that awareness and training in safe bird handling and release may improve captured seabird survival rates. The main objectives of this work is to highlight a little-studied source of seabird mortality by entanglement, to generate discussion on potential technical mitigation measures for side-haul trawl fisheries, and to propose crew training in safe handling and release of seabirds as an immediate mitigation measure.

Anatomy of Subinertial Waves Along the Patagonian Shelf Break in a 1/12° Global Operational Model

AbstractThe Patagonian slope hosts a variety of waves. We used a state‐of‐the‐art ocean reanalysis to examine waves at the shelf break and in the core of the Malvinas Current (MC) at periods larger than 10 days. Statistics over 25 years indicated three types of signals: in phase signals at specific locations of the shelf break to the south of 47°S; fast propagating signals all along the shelf break (phase speed from 140 to 300 cm/s) at periods between 5 and 110 days; and slower signals in the core of the MC (phase speeds from 10 to 30 cm/s) at 20‐day, 60‐day, and 100‐day periods. The large zonal wind stress variations south of 47°S forced in‐phase along‐slope velocity variations and triggered fast propagating waves at distinct sites corresponding to abrupt changes in the shelf‐break orientation. The shelf‐break waves modulated the intensity of the inshore jet, which varied from 0 to 30 cm/s at 100 m depth, and had spatial and temporal structures and scales consistent with those of observed upwelling events. Slow propagating waves in the core of the MC had along‐slope wavelengths between 450 and 1,200 km and were not forced by the local winds. They were tracked back to the Drake Passage and the Malvinas Escarpment.

DOMOIC acid, Pseudo-nitzschia spp and potential vectors at the base of the pelagic food web over the northern Patagonian coast, Southwestern Atlantic

Plankton composition and density, and domoic acid (DA) content in microplankton and mesozooplankton were assessed over the northern Patagonian coastal shelf in late austral summer 2013. Maximum values of DA in these two plankton fractions as well as maximum densities of both Pseudo-nitzschia spp. (mainly the toxigenic P. australis) and DA potential vectors were only detected on the southern coast of San Matías Gulf and the eastern coast of Valdés Peninsula. In this zone, waters were characterized by low temperature, high nitrate, and intermediate values of silicic acid and phosphate. Based on the high association between the DA values recorded and the values of either micro- and mesozooplankton grazer density or biomass, we inferred that DA transfer from Pseudo-nitzschia spp. occurred largely through the small copepods Euterpina acutifrons and Oithona nana, Calanidae nauplii and Calanidae copepodites, Noctiluca scintillans, and euphausiid developmental stages. Small copepods, Calanidae nauplii and copepodites, and cladocerans were proposed as novel DA vectors although this suggestion requires experimental confirmation. This study provides the first lines of evidence of the co-occurrence of Pseudo-nitzschia spp. blooms with DA production and accumulation in mesozooplanktonic grazers at the base of the food web and of the environmental and oceanographic conditions that seem to favor these processes over the northern Patagonian shelf coasts.

Environmental drivers of movement in a threatened seabird: insights from a mechanistic model and implications for conservation

AbstractAimDetermining the drivers of movement of different life‐history stages is crucial for understanding age‐related changes in survival rates and, for marine top predators, the link between fisheries overlap and incidental mortality (bycatch), which is driving population declines in many taxa. Here, we combine individual tracking data and a movement model to investigate the environmental drivers and conservation implications of divergent movement patterns in juveniles (fledglings) and adults of a threatened seabird, the white‐chinned petrel (Procellaria aequinoctialis).LocationSouth‐west Atlantic Ocean.MethodsWe compare the spatial distributions and movement characteristics of juvenile, breeding and non‐breeding adult petrels, and apply a mechanistic movement model to investigate the extent to which chlorophyll a concentrations (a proxy for food resources) and ocean surface winds drive their divergent distribution patterns. We also consider the conservation implications by determining the relative overlap of each life‐history stage with fishing intensity and reported fishing effort (proxies for bycatch risk).ResultsNaïve individuals fledged with similar flight capabilities (based on distances travelled, flight speeds and track sinuosity) to adults but differed in their trajectories. Comparison of simulations from the mechanistic model with real tracks showed that juvenile movements are best predicted by prevailing wind patterns, whereas adults are attracted to food resources on the Patagonian Shelf. The juveniles initially dispersed to less productive oceanic waters than those used by adults, and overlapped less with fishing activity; however, as they moved westwards towards South America, bycatch risk increased substantially.Main conclusionsThe use of a mechanistic framework provided insights into the ontogeny of movement strategies within the context of learned versus innate behaviour and demonstrated that divergent movement patterns of adults and juveniles can have important implications for the conservation of threatened seabirds.

Trace elements' reference levels in blood of breeding black-browed albatrosses Thalassarche melanophris from the Falkland Islands.

Trace elements' concentration in the ocean is fast growing and is a source of major concern. Being charismatic and at the top of food chains, seabirds are often used as biological monitors of contaminants. We studied the concentration of trace elements in blood of black-browed albatross from the Falklands Islands, which we here show, by tracking with geolocators, forage over most of the Patagonian Shelf. Levels of trace elements were measured in males and females from two different islands. Blood concentrations of trace elements were not significantly different between islands, which is consistent with observations from foraging behavior revealing that birds from both islands foraged in broadly the same areas in the months before sampling. Arsenic and selenium concentrations in females were higher than in males. Sex-related differences in the concentration of these elements may be related to unknown slight differences in diet or to differences in assimilation between sexes. These results provide reference values for monitoring elemental contamination in the Patagonian Shelf LargeMarine Ecosystem using black-browed albatrosses, one of the most abundant top predators and a suitable sentinel for the region's environmental health.

Statolith chemistry as a stock tag in the Argentine shortfin squid Illex argentinus

With annual catches that have exceeded 1 million tons, the Argentine shortfin squid (Illex argentinus) is among the most important fisheries in the Southwest Atlantic Ocean. The objective of this study was to assess the statolith multi-elemental signature as a tool to delimit I. argentinus stocks on the Patagonian shelf and slope (Argentina) during summer 2019. Squids were caught from the Southpatagonic (SPS) and Summer Spawning (SSS) Stocks, and mixing area. Statolith multi-elemental signature (Ba/Ca, Li/Ca, Mg/Ca, Mn/Ca, Na/Ca, Pb/Ca, Sr/Ca, Zn/Ca) was determined by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Ba/Ca, Mg/Ca, Mn/Ca, Sr/Ca and Zn/Ca were significantly different between catch areas (p < 0.05). PERMANOVA (p < 0.05) and linear discriminant analysis (mean jackknifed classification= 70.6%), were effective for discriminating between the three sampling areas. The ratios that most contributed to the discrimination between groups were Zn/Ca, Pb/Ca, Mn/Ca, and Ba/Ca. Statolith chemical analyzes suggest that the SSS and SPS are segregated, although there is some degree of mixing between them, which supports previous inferences about population stock from other biological parameters. This study showed that the statolith microchemistry is a useful tool to study the population stock of I. argentinus.

First evidence of polycyclic aromatic hydrocarbons in sediments from a marine protected area within Argentinean Continental Shelf

This study evaluated for the first time, the distribution, sources, and ecological risk assessment of 16 polycyclic aromatic hydrocarbons (PAHs) in sediments collected along the northern Patagonian shelf in the Argentine Sea –included in a Marine Protected Area (MPA). Total concentration of the PAHs varied from 19.47 to 183.17 ng/g dry weight and low molecular weight compounds, such as Anthracene and Naphthalene were the dominants. The selected PAHs ratios suggested a predominance of petrogenic sources and ecotoxicological risk evaluation based on the sediment quality guidelines model, indicated that some PAHs might cause occasional adverse biological effects in the study area.

First Insights Into the Growth and Population Structure of Cottoperca trigloides (Perciformes, Bovichtidae) From the Southwestern Atlantic Ocean

The aim of this work was to describe the growth of Cottoperca trigloides, a notothenioid species with a non-Antarctic distribution, and to test the existence of different nursery areas and fish stocks through changes in the otolith elemental composition. Fish were collected during spring 2009 over the Patagonia continental shelf, including the Marine Protected Area Namuncura/Burdwood Bank, in the southwestern Atlantic Ocean. The age and growth analysis were performed by counting marks in sagittae, assuming an annual periodicity of their deposition, and identified 8-year classes (0+ to 7+). Given the size range of the fish, length-at-age data were fitted to the Gompertz growth model TLt = 55.45 [exp ((exp) -0.32 (t – 1.89))], explaining more than 95% of the growth pattern. Moreover, the chemical composition of otolith core and edge areas was analyzed by laser ablation inductively coupled plasma mass spectrometry. The canonical analysis of principal coordinates successfully allocated 72.92% of the fish for the core and 91.67% for the edge area of the otolith, in three groups corresponding to ‘northern Patagonia shelf’, ‘southern Patagonia shelf’ and ‘Marine Protected Area Namuncura/Burdwood Bank’ areas, suggesting a high segregation among them over the Patagonian shelf. Thus, otolith elemental composition has proven to be an efficient approach to identify different nursery areas and stocks for the species. Present results provide new information on the growth and the population structure of C. trigloides, from a geographical area where information on this issue is still scarce, constituting an essential tool to develop conservation principles for the species.

Microbial plankton configuration in the epipelagic realm from the Beagle Channel to the Burdwood Bank, a Marine Protected Area in Sub-Antarctic waters.

Marine microbial plankton hold high structural and functional diversity, however, high-resolution data are lacking in a large part of the Global Ocean, such as in subpolar areas of the SW Atlantic. The Burdwood Bank (BB) is a submerged plateau (average depth 100 m) that constitutes the westernmost segment of the North Scotia Ridge (54°–55°S; 56°–62°W). The BB hosts rich benthic biodiversity in low chlorophyll waters of the southern Patagonian Shelf, Argentina, declared Namuncurá Marine Protected Area (NMPA) in 2013. So far, the pelagic microorganisms above the bank have not been described. During austral summer 2016, we assessed the microbial plankton (0.2–200 μm cell size) biomass and their taxonomical and functional diversity along a longitudinal transect (54.2–55.3°S, 58–68°W) from the Beagle Channel (BC) to the BB, characterized by contrasting hydrography. Results displayed a marked zonation in the composition and structure of the microbial communities. The biomass of phytoplankton >5 μm was 28 times higher in the BC, attributed mainly to large diatom blooms, than in oceanic waters above the BB, where the small coccolithophore Emiliania huxleyi and flagellates <10 μm dominated. In turn, the biomass of microheterotrophs above the BB doubled the biomass in the BC due to large ciliates. Notably, toxic phytoplankton species and their phycotoxins were detected, in particular high abundance of Dinophysis acuminata and pectenotoxins above the bank, highlighting their presence in open subpolar regions. Picophytoplankton (<2 μm), including Synechococcus and picoeukaryotes, were remarkably important above the BB, both at surface and deep waters (up to 150 m). Their biomass surpassed by 5 times that of phytoplankton > 5 μm, emphasizing the importance of small-sized phytoplankton in low chlorophyll waters. The homogeneous water column and high retention above the bank seem to favor the development of abundant picophytoplankton and microzooplankton communities. Overall, our findings unfold the plankton configuration in the Southern Patagonian Shelf, ascribed as a sink for anthropogenic CO2, and highlight the diverse ecological traits that microorganisms develop to adjust their yield to changing conditions.

Internal solitary waves from L-band SAR over the Argentine inner Patagonian shelf

ABSTRACTInternal waves represent an important mechanism of energy exchange influencing primary production through the turbulent transport of nutrients and changes in the intensity of light available for photosynthesis. Internal solitary waves (internal solitons) appear in packages and retain their shape and speed even after interacting with other internal waves. We detected solitons in the inner Patagonian shelf with the active L-band microwave satellite sensor (ALOS-PALSAR). Packages found in the satellite images were digitized. Generation mechanisms and propagation speeds were assessed using historical CTD profiles near the detected waves, assuming linear theory and atwo-layer vertical structure. The estimated propagation speeds of the waves ranged from 0.5 to 0.7m s−1. The generation regimes of waves originated at asill near the coast were classified as subcritical or near-critical according to the Froude number. We hypothesize that at this site, the generation mechanism starts leeward from the sill (lee wave mechanism), after the relaxation of the tidal current. Generation mechanisms of waves detected elsewhere over the shelf are not so obvious. More images are necessary to better determine the wave generation site. We will continue the analysis with L-band images aboard the SAOCOM 1A (CONAE), put in orbit in October 2018.

Long-Term Stability in the Trophic Ecology of a Pelagic Forager Living in a Changing Marine Ecosystem

Natural or human-induced environmental changes can modify the structure of ecological communities and thus alter food web interactions. After the collapse of hake stocks (Merluccius hubbsi) provoked by fisheries over the Patagonian shelf in 1997 profound changes have taken place in the community, including long-term dietary shifts in some marine vertebrate predators. Stable carbon (δ13C) and nitrogen (δ15N) isotope ratios in bone collagen of subadult and adult male South American fur seals (Arctocephalus australis) were measured for the period 1976-2017 to investigate if the changes occurred in the marine community from northern and central Patagonia affected the diet of this predator. Suess corrected δ13C values and δ15N values in bone collagen of fur seals did not change significantly over the study period. According to this, male fur seals have remained as pelagic foragers without changing their trophic position nor switching their main preys in the Patagonian food web over the last four decades. This long-term stability in the diet of fur seals contrasts with dietary changes reported for benthic foragers in the region. Although long-term diet studies are restricted to a few marine predators in the region, current evidence suggests that benthic-demersal foragers were more prone to dietary shifts than pelagic ones after perturbations that occurred in the marine community of northern and central Patagonia.

Dynamical analysis of the oceanic circulation in the Gulf of San Jorge, Argentina

Abstract This study identifies the dynamical mechanisms driving seasonal variations in oceanic circulation and water mass characteristics of the Gulf of San Jorge (GSJ) and its exchanges with the Patagonian Shelf (PS). A suite of process-oriented numerical experiments indicates that GSJ circulation is mainly driven by tidal forcing and modulated by wind forcing and intrusions from the PS. During late spring and summer, stratification decouples the upper and deeper layers of the gulf, leading to a shallow, wind-forced surface circulation and a deeper, density driven, cyclonic geostrophic flow. The subsurface circulation is induced by differential tidal mixing in coastal and deep areas and its intensity is strongly affected by the temporal variability of the atmospheric heat flux, which increases from spring to summer and fades from fall to winter. As stratification weakens, circulation patterns are replaced by wind-driven anticyclonic gyres in the south and an open cyclonic loop in the north. Passive tracer diagnostics show that in summer, surface and subsurface waters from the GSJ northern coast are exported and replaced by waters from the coastal portion of PS currents. The renewal of bottom waters is slower: A small portion upwells in the southwestern coast but most are ventilated by winter convection in the southern region and by intrusions of PS waters in the northern region.

The Falkland Islands (Malvinas) as sub-Antarctic foraging, migratory and wintering habitat for southern right whales

AbstractThe historical and contemporary presence of southern right whales (SRWs;Eubalaena australis) around the Falkland Islands (Malvinas) has received little recognition. We assessed SRW occurrence in the Falklands via whaling records, a literature review, systematic surveys (boat, aerial and shore-based), and citizen science sightings. The combined data sources indicated a year-round (peaking in austral summer) presence of SRWs in pelagic areas around the Falklands. In contrast, most nearshore records originated in the austral late autumn and winter (May to August), including a marked increase in sightings along the north-east coast during 2017 compared with previous years. The data support spatio-temporal variation in the use of Falklands waters by SRWs. Pelagic waters appear to comprise summer foraging habitat, and may also be used by animals migrating between the Patagonian shelf and feeding grounds located further south and east. The peak numbers observed in nearshore waters occurred earlier in the winter (July) than those on the Argentinean or Brazilian calving grounds (Aug–Oct). Consequently, some whales may have continued migrating northwards to established breeding areas after departing Falklands waters. A component of the south-west Atlantic population could also be using the islands as a novel wintering destination, for mating and/or socializing (no calving has been confirmed to date). The importance of Falklands waters as a multi-use SRW habitat appears to be increasing. The region is important in the context of addressing current knowledge gaps regarding feeding grounds and migratory corridors highlighted in international SRW conservation and management plans for the wider South-west Atlantic.

Spatial ecology, phenological variability and moulting patterns of the Endangered Atlantic petrel Pterodroma incerta

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 40:189-206 (2019) - DOI: https://doi.org/10.3354/esr00991 ESR Special: Biologging in conservation Spatial ecology, phenological variability and moulting patterns of the Endangered Atlantic petrel Pterodroma incerta Marina Pastor-Prieto1,*, Raül Ramos1, Zuzana Zajková1,2, José Manuel Reyes-González1, Manuel L. Rivas1, Peter G. Ryan3, Jacob González-Solís1 1Institut de Recerca de la Biodiversitat (IRBio) and Departament de Biologia Evolutiva, Ecologia i Ciències Ambientals (BEECA), Universitat de Barcelona, 08028 Barcelona, Spain 2Center for Advanced Studies of Blanes (CEAB-CSIC), 17300 Girona, Spain 3FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, University of Cape Town, Rondebosch 7701, South Africa *Corresponding author: marina.pastor6@gmail.com ABSTRACT: Insights into the year-round movements and behaviour of seabirds are essential to better understand their ecology and to evaluate possible threats at sea. The Atlantic petrel Pterodroma incerta is an Endangered gadfly petrel endemic to the South Atlantic Ocean, with virtually the entire population breeding on Gough Island (Tristan da Cunha archipelago). We describe adult phenology, habitat preferences and at-sea activity patterns for each phenological phase of the annual cycle and refine current knowledge about its distribution, by using light-level geolocators on 13 adults over 1-3 consecutive years. We also ascertained moulting pattern through stable isotope analysis (SIA) of nitrogen and carbon in feathers from 8 carcasses. On average, adults started their post-breeding migration on 25 December, taking 10 d to reach their non-breeding areas on the South American shelf slope. The pre-breeding migration started around 11 April and took 5 d. From phenological data, we found evidence of carry-over effects between successive breeding periods. The year-round distribution generally coincided with the potential distribution obtained from habitat modelling, except during the non-breeding and pre-laying exodus periods, when birds only used the western areas of the South Atlantic. Moulting occurred during the non-breeding period, when birds spent more time on the water, and results from SIA helped us to distinguish feathers grown around Gough Island from those grown in the non-breeding area. Overall, our results bring important new insights into the spatial ecology of this Endangered seabird, which should help improve conservation strategies in the South Atlantic Ocean. KEY WORDS: Atlantic petrel · Year-round movements · At-sea behaviour · Carry-over effects · Patagonian Shelf Full text in pdf format Supplementary material PreviousNextCite this article as: Pastor-Prieto M, Ramos R, Zajková Z, Reyes-González JM, Rivas ML, Ryan PG, González-Solís J (2019) Spatial ecology, phenological variability and moulting patterns of the Endangered Atlantic petrel Pterodroma incerta. Endang Species Res 40:189-206. https://doi.org/10.3354/esr00991 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 40. Online publication date: November 14, 2019 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2019 Inter-Research.

Habitat, trophic levels and migration patterns of the short-finned squid Illex argentinus from stable isotope analysis of beak regions

Illex argentinus is an ecologically and economically important species, assumed to be restricted to the Patagonian Shelf and around the subtropical convergence. Beaks found in diet samples from black-browed albatrosses Thalassarche melanophris during chick rearing initially suggested that it may also inhabit Antarctic waters until it was appreciated that I. argentinus is used as fishing bait by commercial longliners within albatrosses foraging areas. Here, we applied a new methodology involving stable isotope analysis (δ13C and δ15N) in two regions [tip of the rostrum (juvenile) and wing (adult)] of lower beaks obtained from diet samples of black-browed albatrosses breeding at Bird Island (South Georgia). The aims were to (1) assess if I. argentinus could inhabit Antarctic waters somewhere in the life cycle (2) determine the trophic ecology of I. argentinus, and (3) discuss possible migration patterns of I. argentinus and whether its distribution may change in the future. Values of δ13C (proxy for habitat) were − 18.4 ± 0.7‰ and − 17.1 ± 0.4‰ during the juvenile and adult life stages, respectively, indicating a northwards ontogenetic shift, and that this species exclusively inhabits waters north of the Antarctic Polar Front. Values of δ15N was lower in juveniles (+5.9 ± 1.1‰) than adults (+8.4 ± 1.3‰), indicating an increase of one trophic level throughout the squid’s life, suggesting a diet shift from zooplankton to fish and squid. Based on predicted effects of climate change, the distribution of I. argentinus may become more restricted as the northern limit moves southwards because of warming ocean temperature.

First record of Burmeister\u2019s porpoise (Phocoena spinipinnis) in the Falkland Islands (Malvinas)

The Burmeister’s porpoise Phocoena spinipinnis is a small, poorly-studied, and Near Threatened cetacean species, with a limited geographic range comprising the Pacific and Atlantic coastal temperate waters of five South American countries. Here we describe a stranding of a freshly-dead adult male Burmeister’s porpoise that was discovered opportunistically on the eastern coast of the Falkland Islands (51°40.9′S, 57°43.2′W) on 29 June 2019. Unfortunately the carcass was removed by an unknown source prior to any scientific sampling, but the morphological features revealed in photographs taken of the dead animal were sufficient to verify the species identification. This is the first known record of Burmeister’s porpoise in the Falklands, confirming a sixth range state for the species and expanding its known distribution range eastwards from the previous nearest documented occurrence in Tierra del Fuego by at least 600 km across the Patagonian Shelf.

Telecoupling analysis of the Patagonian Shelf: A new approach to study global seabird-fisheries interactions to achieve sustainability

The Southwest Atlantic Ocean, particularly the extended Patagonian Shelf, constitutes a complex, globally-relevant ecosystem. It is a highly productive area, and it maintains a high diversity and abundance of seabird species. At the same time, the Patagonian Shelf experiences pressues, such as fisheries that have been identified as a main stressor for marine ecosystems worldwide, including being a principal cause of seabird population declines. Using the telecoupling framework - which incorporates natural and socioeconomic interactions over large distances - we present here a holistic look at the dynamics of threatened seabird- fisheries interactions for the Patagonian Shelf over space and time. Based on the best-available public data for seabird presence, we used machine learning and geographic information systems to model-predict the at-sea distribution of seabirds. Then, maps were overlaid with fisheries distributions to show spatial correlation and hotspots for co-occurrence between seabirds and fisheries. We found that even this remote corner of the Atlantic Ocean is globally connected to XXX nations and XXX other outside-stakeholders through fisheries. By identifying and characterizing the systems, flows, agents, causes and effects involved in this telecoupling process, we highlighted specific complexities, bottlenecks and sensitivities that must still be addressed to achieve both biodiversity conservation and management as well as fisheries sustainability not only in this study area, but worldwide.

On the origins of the low-frequency sea surface height variability of the Patagonia shelf region

In this study, we identify the drivers of the dominant mode of sea surface height interannual variability over the Patagonian shelf using a suite of process-oriented numerical experiments. Consistent with altimetry, the dominant mode of the model sea surface height interannual variability, which accounts for approximately 84% of the total variance, exhibits a robust deterministic low-frequency variability. The weak sea surface height gradients indicate that this mode has a weak dynamical effect, but the contribution of the steric effect is shown to be non significant. Here we demonstrate that the temporal variability of this mode is not driven by heat or freshwater fluxes but by the propagation of sea surface height perturbations generated in the Pacific. In particular, we show that sea surface height interannual variability over the Patagonian shelf is influenced by wind stress forcing in the offshore region of southern Chile and by the propagation of equatorial sea surface height anomalies.

Pelagic seabirds as biomonitors of persistent organic pollutants in the Southwestern Atlantic.

Persistent Organic Pollutants (POPs) are accumulated through time and can exert different effect on ecosystems. POPs and Chlorpyrifos, a current use pesticide, were assessed in body feathers of males and females of Black-browed albatross (Thalassarche melanophris, BBA) and Cape petrels (Daption capense, CAP) during their non-breeding seasons at the Patagonian Shelf, Argentina. Chlorpyrifos showed the highest values among all pollutants in both species (49.56-84.88 ng g-1), resulting from current agricultural practices. The pattern OCPs > PCBs > PBDEs was observed in both species, and CAP showed higher concentrations than BBA probably as a consequence of higher lipid mobilization and pollutants availability during dispersion. Non-significant differences between sexes about POPs levels were found; however a slight tendency was observed, females>males in CAP, and males>females in BBA. More attention and further studies are needed to understand seabirds' physiology and its relationship with the pollutants distribution in their tissues and considering breeding season.

South American sea lions Otaria byronia as biological samplers of local cephalopod fauna in the Patagonian shelf marine ecosystem

AbstractCephalopods are important prey in the diet of top predators, such as marine mammals and seabirds. However, detailed information on their trophic relationships in the Patagonian marine ecosystem is scarce, including those cephalopod species with commercial interest. The aims of this study were to evaluate the composition of the cephalopod component in the diet of Otaria byronia and determine the habitat use and trophic levels of their main cephalopod prey by measuring the stable isotopic signature of cephalopod beaks. Between May 2005 and February 2009, fresh faecal samples were collected from two sea lions rookeries in San Matias Gulf. Cephalopods occurred in 39.4% of the 1112 samples collected during the whole period of study. The dominant prey species was Octopus tehuelchus, which occurred in 45.8% of scats containing cephalopod remains, and represented 58.7% in terms of numerical abundance and 52.0% in mass of cephalopods consumed. The second species most consumed was the myopsid Doryteuthis gahi. The significant higher δ15N values of O. tehuelchus beaks in comparison with those of D. gahi showed that these two species have different trophic levels while occupying similar habitat (δ13C values) in neritic waters of the Patagonian shelf.