Assessing the feeding ecology of three sympatric squids Illex argentinus, Doryteuthis gahi and Onykia ingens off the Patagonian by combining stomach content and stable isotopic analysis

The Ommastrephidae Illex argentinus, the Loliginidae Doryteuthis gahi and the Onychoteuthidae Onikya ingens are squid species coexisting in the south part of the Patagonian Shelf, interacting for similar feeding resources. In the present study, we analyzed the feeding ecology, trophic position and trophic relationships of these three species by combining stomach content and stable isotopic approximations. In particular, stomach content and isotopic analysis were carried out on 20 D. gahi, 20 I. argentinus and 21 O. ingens collected from May 6th and 8th 2013 at depths between 147 and 220 m. The results indicated that the feeding habits of small and larger squids were different in the three species. The two main prey species for small D. gahi individuals were the euphausid Euphausia sp. and the amphipod Eutemisto gaudichaudi, and the main prey for larger D. gahi individuals were a fish and the Munididae Munida subrugosa. The main prey group of small I. argentinus individuals was the amphipod E. gaudichaudi and the myctophid fish, and the main prey for larger size I. argentinus individuals were the paralepididae Arctozenus risso and the Notothenidae Patagonotothen ramsayi, secondly by the squid group. Small O. ingens individuals fed on Micromesistius australis and Notophysis marginata while larger O. ingens individuals fed on Lampanyctus australis and Notoscopelus sp. D. gahi showed higher δ15N values than the other two species and small and larger D. gahi individuals showed similar isotopic values. The δ15N values of I. argentinus and O. ingens were higher for larger individuals. Finally, D. gahi differed in its δ13C values from I. argentinus and O. ingens and the less depleted δ13C values were found in the larger in D. gahi individuals. The results indicate that the three squid species preyed on organisms with similar trophic position, but due to their voracity and their active predation on similar trophic resources, small size individuals segregate their trophic niche from the larger ones. It is important to note that the δ13C values revealed that larger D. gahi individuals had a different distribution in the water column, which probably is a response of the reproductive activity of mature squid near to the surface water.Universidad Nacional Autónoma de Méxic

Feeding habits and trophic interactions of Doryteuthis gahi, Illex argentinus and Onykia ingens in the marine ecosystem off the Patagonian Shelf

The stomach contents of three squids: 57 Doryteuthis gahi with mantle length (ML) ranging from 7.0 to 37.0 cm, 75 Illex argentinus (21.0–32.8 cm) and 116 Onykia ingens (19.9–39.3 cm) from commercial catches on the outer Patagonian shelf grounds during autumn (March and April 2012) were examined to describe their diet and compare their trophic spectrum. D. gahi preyed on 12 different items, I. argentinus on 20 and O. ingens on 29. Prey diversity increased with the sizes of the squids. Along growth, D. gahi shifted from crustaceans, mainly euphausiids to fish (Salilota australis) and squid (D. gahi and Histioteuthis sp.). Small to mid-sized I. argentinus and O. ingens consumed mostly two fish, two squid species D. gahi and Histioteuthis atlantica, two crustaceans Munida gregaria and Munida subrugosa and the Chaetognatha Sagitta elegans. All the three species show a high prey overlapping at similar sizes: Squid of smaller size (5–15 cm ML) fed mainly on crustaceans: D. gahi on euphausiids and squat lobsters (Munididae). Mid-sized squid fed mainly on fish, most frequently Gymnoscopelus sp. and S. australis, and larger I. argentinus and O. ingens fed mostly on squids, including cannibalism. The overlapping of the diet of similar sized squid was large suggesting all preys are abundant species in autumn in the water column in the Patagonian Shelf.Versión del editor

Relaciones tróficas entre el calamar gigante DosidDicus gigas y el pez luminoso Vinciguerria lucetia en el sistema de la corriente de Humboldt de Perú

9 pages, 4 figures, 3 tables[EN] Acoustic surveys for assessing the biomass and distribution of the jumbo squid (Dosidicus gigas) and the lightfish (Vinciguerria lucetia) were carried out in the Humboldt Current System of Peru in 2007 and 2008. At the same time, 937 jumbo squid were caught and their stomach contents analyzed. The diet of the jumbo squid was dominated by mesopelagic fish. The first component of their fish diet was V. lucetia and the second component was the myctophid fish Diogenichthys laternatus. Acoustic biomass estimates of these species show that V. lucetia is an important component in aggregative structures in the Humboldt Current System of Peru and its distribution and movements are closely related to the migratory movements of the jumbo squid. The trophic relationship observed between D. gigas and V. lucetia promotes an increase in jumbo squid biomass and, has a positive trophic effect on the ocean ecosystem[ES] La biomasa de calamar gigante Dosidicus gigas y el pez mesopelágico Vinciguerria lucetia se obtuvo a partir de detección acústica en la Corriente de Humboldt de Perú durante 2007 y 2008. Simultáneamente, 937 calamares fueron capturados y se les analizó el contenido estomacal. La dieta de D. gigas estuvo dominada por peces, siendo V. lucetia el principal componente y en segundo lugar el mictófido Diogenichthys laturnatus. A partir de la evaluación de la biomasa de ambas especies, estimada por el método acústico, se observó que V. lucetia es uno de los principales componentes en el sistema de la Corriente de Humboldt de Perú y sus patrones de distribución y movimientos espacio-temporal están fuertemente relacionados a los desplazamientos migratorios del calamar. Estas relaciones tróficas promueven un incremento de la biomasa de D. gigas que es resultado de un patrón similar en V. lucetia, lo que propicia un efecto trófico positivo en el ecosistema oceánicoThis article is partly based on the PhD thesis in Marine Science of Rigoberto Rosas Luis. His doctoral degree is supported by CONACyT (Consejo Nacional de Ciencia y Tecnología, México).Peer reviewe

Constraining the magnitude of the Chiral Magnetic Effect with Event Shape Engineering in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76$ TeV

In ultrarelativistic heavy-ion collisions, the event-by-event variation of the elliptic flow $v_2$ reflects fluctuations in the shape of the initial state of the system. This allows to select events with the same centrality but different initial geometry. This selection technique, Event Shape Engineering, has been used in the analysis of charge-dependent two- and three-particle correlations in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}} =2.76$ TeV. The two-particle correlator $\langle \cos(\varphi_\alpha - \varphi_\beta) \rangle$, calculated for different combinations of charges $\alpha$ and $\beta$, is almost independent of $v_2$ (for a given centrality), while the three-particle correlator $\langle \cos(\varphi_\alpha + \varphi_\beta - 2\Psi_2) \rangle$ scales almost linearly both with the event $v_2$ and charged-particle pseudorapidity density. The charge dependence of the three-particle correlator is often interpreted as evidence for the Chiral Magnetic Effect (CME), a parity violating effect of the strong interaction. However, its measured dependence on $v_2$ points to a large non-CME contribution to the correlator. Comparing the results with Monte Carlo calculations including a magnetic field due to the spectators, the upper limit of the CME signal contribution to the three-particle correlator in the 10-50% centrality interval is found to be 26-33% at 95% confidence level

Constraining the magnitude of the chiral magnetic effect with event shape engineering in Pb–Pb collisions at √sNN=2.76 TeV

In ultrarelativistic heavy-ion collisions, the event-by-event variation of the elliptic flow v2 reflects fluctuations in the shape of the initial state of the system. This allows to select events with the same centrality but different initial geometry. This selection technique, Event Shape Engineering, has been used in the analysis of charge-dependent two- and three-particle correlations in Pb–Pb collisions at √sNN=2.76 TeV. The two-particle correlator 〈cos⁡(φα−φβ)〉, calculated for different combinations of charges α and β, is almost independent of v2 (for a given centrality), while the three-particle correlator 〈cos⁡(φα+φβ−2Ψ2)〉 scales almost linearly both with the event v2 and charged-particle pseudorapidity density. The charge dependence of the three-particle correlator is often interpreted as evidence for the Chiral Magnetic Effect (CME), a parity violating effect of the strong interaction. However, its measured dependence on v2 points to a large non-CME contribution to the correlator. Comparing the results with Monte Carlo calculations including a magnetic field due to the spectators, the upper limit of the CME signal contribution to the three-particle correlator in the 10–50% centrality interval is found to be 26–33% at 95% confidence level