Loligo Gahi Research Articles

Genetic analysis reveals historical and contemporary population dynamics in the longfin squid Doryteuthis gahi: implications for cephalopod management and conservation

AbstractPopulation genetic structure of the Patagonian longfin squid Doryteuthis gahi was assessed across the Falkland Islands, central-southern Chile, and Peru. Microsatellite and mtDNA data partitioned samples into two groups: one consisting of the Peruvian samples, the other comprised the Chilean and Falklands samples, with no sub-structuring within either group. Recurrent demographic independence between groups can be linked to abrupt changes in continental shelf features between the Peruvian and central Chilean sites restricting adult dispersal. Phylogeographic analyses indicate a prolonged period of isolation between the Peruvian and Chilean–Falkland groups which may include divergence in allopatric glacial refugia. Both groups have experienced dissimilar historical population size dynamics with the Peruvian population exhibiting signals of size fluctuations, similar to other species in the area, that align with postglacial changes in the productivity of the Humboldt Current system. Genetic cohesion among central-southern Chilean and Falklands samples supports connectivity across current management boundaries and indicates that phenotypic differences between D. gahi from these areas reflect plastic responses to environmental heterogeneity. The study adds to evidence that loliginid squids typically display connected populations over large geographical areas unless specific oceanographic features restrict gene flow. Recognition of the Peruvian and Chilean–Falklands groups as distinct evolutionary significant units is recommended.

'Superbull' males: what role do they play and what drives their appearance within the Doryteuthis gahi Patagonian Shelf population?

Cephalopod populations exhibit high variability in life history characteristics, such as longevity and size-at-age. The aim of this study was to understand how characteristics of a newly described ‘superbull’ male morph in Doryteuthis gahi populations (Patagonian Shelf) arise and whether there is a selective advantage. At the population level, it is speculated that superbulls provide temporal and spatial connectivity, but individual benefit is less obvious. Age structure and reproductive potential of males was investigated to determine whether superbulls could provide connectivity. Environmental variables affecting size-at-age were explored to ascertain whether morphological differences were primarily phenotypically driven. Superbulls from the autumn spawning cohort were significantly older than the residual population, with added longevity potentially leading to spawning with the following cohort. A reduction in relative testis weight was apparent in superbulls, but spermatophore production remained high. Generalised additive mixed models indicated temperature, location and hatch year had significant effects on size-at-age. Weak correlations between warm El Niño–Southern Oscillation phases and superbull abundance were found. The results suggest that superbulls provide temporal connectivity and arise through phenotypic plasticity, likely providing connectivity as a side effect of body shape and size rather than a genetically selected advantage.

Modeling the potential habitats of dusky, commons and bottlenose dolphins in the Humboldt Current System off Peru: The influence of non-El Niño vs. El Niño 1997-98 conditions and potential prey availability

Odontocete cetaceans are important predators in pelagic ecosystems; however, patterns of spatial and temporal distribution in the marine ecosystem off Peru remain unknown for many species. In this study, we modeled the potential habitats for dusky (Lagenorhynchus obscurus), long-beaked common (Delphinus capensis), bottlenose (Tursiops truncatus) and short-beaked common (Delphinus delphis) dolphins using maximum entropy models to two conditions: non-El Niño and El Niño 97-98. Dolphin sightings positions, fishing net hauls with potential prey data, and oceanographic variables from 24 cruises along the southeast Pacific coast of Peru (03°30′S-18°21′S) between 1997 and 2014 were used to model potential habitats of dolphins and their prey. Our modeling predicts that during non-El Niño conditions, the different dolphin species have a segregated distribution according to the physiography. Dusky and long-beaked common dolphins use mainly habitats over neritic zones segregating partially their spatial distribution while bottlenose and short-beaked common dolphins showed potential habitats mainly over the shelf-break and oceanic waters, respectively. During El Niño 97-98, this physiographic segregation was predicted to be maintained by the models although with northward retraction for bottlenose, long and short-beaked commons dolphins. Accordingly, dusky and long-beaked common dolphin potential habitat overlapped mainly with neritic potential prey species (Peruvian anchovy, Engraulis ringens; silverside, Odonthestes regia regia; red squat lobster, Pleuroncodes monodon; common squids, Doryteuthis gahi and mackerels). Bottlenose and short-beaked common dolphin habitats were predicted to overlap mainly with oceanic potential prey (mackerels; Panama lightfish, Vinciguerria lucetia; myctophids; Humboldt squids, Dosidicus gigas and euphausiids). Our results predict that dolphins use specific physiographic areas throughout the Peruvian marine ecosystem and these habitats did not drastically change during El Niño 97-98.

Reprint of Using statolith elemental signatures to confirm ontogenetic migrations of the squid Doryteuthis gahi around the Falkland Islands (Southwest Atlantic)

The Patagonian long-finned squid Doryteuthis gahi is an abundant commercial species within Falkland Island waters. The population consists of two temporally distinct spawning cohorts, inferred to have markedly different patterns of migration and timings of ontogenetic events. Ontogenetic migrations of each cohort were confirmed by analysis of the chemical composition of statoliths collected from both cohorts in two consecutive years. Trace element concentrations were quantified using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), to determine temporal and cohort-specific variation. Individual ablation craters, ablated in a transect from the nucleus to the rostrum edge, were aged to produce high-resolution elemental chronologies. Generalized additive mixed models (GAMM) indicated that cohort and life history stage had a significant effect on Sr/Ca and Ba/Ca ratios. Sr/Ca and Ba/Ca ratios were both negatively correlated with near-bottom water temperature, with Ba/Ca also potentially correlated to depth. Statolith elemental chronologies have useful applications as natural tags, discriminating between spawning cohorts.

Using statolith elemental signatures to confirm ontogenetic migrations of the squid Doryteuthis gahi around the Falkland Islands (Southwest Atlantic)

Abstract The Patagonian long-finned squid Doryteuthis gahi is an abundant commercial species within Falkland Island waters. The population consists of two temporally distinct spawning cohorts, inferred to have markedly different patterns of migration and timings of ontogenetic events. Ontogenetic migrations of each cohort were confirmed by analysis of the chemical composition of statoliths collected from both cohorts in two consecutive years. Trace element concentrations were quantified using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), to determine temporal and cohort-specific variation. Individual ablation craters, ablated in a transect from the nucleus to the rostrum edge, were aged to produce high-resolution elemental chronologies. Generalized additive mixed models (GAMM) indicated that cohort and life history stage had a significant effect on Sr/Ca and Ba/Ca ratios. Sr/Ca and Ba/Ca ratios were both negatively correlated with near-bottom water temperature, with Ba/Ca also potentially correlated to depth. Statolith elemental chronologies have useful applications as natural tags, discriminating between spawning cohorts.

Trophic ecology of the smooth hammerhead shark (Sphyrna zygaena) off the coast of northern Peru

The smooth hammerhead (Sphyrna zygaena) is the third most captured shark species in Peru, a nation with one of the largest shark fisheries in the Pacific Ocean. We sought to better understand the trophic ecology of this shark in northern Peru by analyzing stomach contents. From 2013 through 2015, we collected 485 samples of gut contents from sharks measuring 53-294 cm in total length. Our results show that the smooth hammerhead is a top predator with a diet dominated by jumbo flying squid (Dosidicus gigas) and the Patagonian squid (Doryteuthis (Amerigo) gahi). Smooth hammerheads displayed different diets with different body size, and this finding indicates that sharks change their distribution and habitat during development. This study represents the most comprehensive investigation to date of the trophic ecology of smooth hammerhead in waters off Peru. We propose that these waters represent an important eastern Pacific Ocean feeding ground for smooth hammerhead. Because this species is commercially important and also preys upon other commercial species, these findings could contribute to the design and implementation of plans for ecosystembased fisheries management.

Feeding ecology of the green turtle Chelonia mydas in northern Peru

Diet and food preferences of the green turtle Chelonia mydas were analyzed based on digestive tract contents of dead specimens caught incidentally by an artisanal gillnet fishery in Sechura Bay, northern Peru. We examined 27 digestive tracts and identified 35 prey items. The sampled turtles were all juveniles (CCL = 53.7 ± 1.2 cm, range 40.5-67.0 cm). The prey items were grouped into six categories: algae, cnidarians, mollusks, arthropods, chordates and garbage/anthropogenic debris. The items with the highest Frequency of Occurrence values (% FO) were: Caulerpa filiformis (77.8%), Loligo gahi (eggs) (51.9%) and Rhodymenia corallina (44.4%). By weight (% W), the most important items, were L. gahi (eggs) (33.3%), Stomolophus sp. (7.3%) and Aphos porosus (6.5%). According to the Preponderance Index (%IP), the preponderant item was L. gahi (eggs) with 6.1% and 61.2% during winter-spring and summer-autumn, respectively. According to the Resultant Weight index (Rw) of wet items, the most important items were: C. filiformis (13.1%), L. gahi (eggs) (10.5%), R. corallina (7.4%), plastic (7.5%), Gigartina chamissoi (5.1%). Garbage/anthropogenic debris was common in the digestive tracts analyzed. Plastic items had a frequency of occurrence of 44.4%. A greater diversity of food items was observed during summer and autumn. This study shows that juvenile C. mydas forage on a variety of resources. We recommend that conservation plans, land use planning and future management plans in the Sechura Bay include green turtles as a sentinel species for monitoring biodiversity of marine resources and the degree of pollution in the Bay.

Jack of all prey, master of some: Influence of habitat on the feeding ecology of a diving marine predator

Marine species occupy broad geographical ranges that encompass varied habitats. Accordingly, resource availability is likely to differ across a species range and, in-turn, this may influence the degree of dietary specialization. Gentoo penguins Pygoscelis papua are generalist predators occupying a range of habitats with a large breeding range extending from Antarctica to temperate environments. Using the most extensive stomach content data set on gentoo penguins this study investigated their feeding ecology at the Falkland Islands (52°S, 59.5°W), the world’s largest population. Sampling occured in consecutive breeding seasons (2011–2013), across multiple foraging habitats utilizing stomach content data and carbon and nitrogen stable isotope values of feathers. The first species specific description of diet at this scale for the Falklands revealed six key prey items for the birds: rock cod (Patagonotothen spp.), lobster krill (Munida spp.), Falkland herring (Sprattus fuegensis), Patagonian squid (Doryteuthis gahi), juvenile fish (likely all nototheniids), and southern blue whiting (Micromesistius australis). Niche width, relating to both stomach content and stable isotope data related to the surrounding bathymetry. Birds from colonies close to gently sloping, shallow waters, fed primarily on benthic prey and had larger niche widths. The opposite was observed at a colony surrounded by steeply sloping, deeper waters. Therefore, gentoo penguins at the population level at the Falklands are indeed generalists, however, at individual colonies some specialization occurred to take advantage of locally available prey, resulting in these birds being classified as Type B generalists. Hence, future studies must account for this intra-colony variation when assessing for factors such as inter-specific competition or overlap with anthropogenic activities.

Differences in the trophic niche along the gladius of the squids Illex argentinus and Doryteuthis gahi based on their isotopic values

The squids Doryteuthis gahi and Illex argentinus coexist in the Patagonian shelf and other oceanic waters of the South Atlantic Ocean. Both species perform movements to and from shallow waters related to their ontogenetic growth. To examine changes in the trophic habitats in both species and across the ontogeny, we analyzed the stable isotopic values of δ13C and δ15N in their gladii. Based on sections of the gladii, we compared the trophic niche in three stages (adult [the newest section], juvenile [middle section], and a near-birth section [near the conus]). δ13C and δ15N values differed significantly between the two species and between gladius segments, revealing interspecific and ontogenetic differences in the trophic niche width. In particular, differences between segments of the gladius concurred with the ontogenetic and spawning migrations of these squids, in the Patagonian Shelf.

Pelagic or benthic prey? Combining trophic analyses to infer the diet of a breeding South American seabird, the Red-legged Cormorant, Phalacrocorax gaimardi

The available information about the feeding habits and preferences of the Red-legged Cormorant (Phalacrocorax gaimardi) generally suggests that this near-threatened South American cormorant is a sedentary benthic forager that also incorporates pelagic prey in its diet. In order to describe the dietary composition and assess the importance of certain prey types (pelagic vs benthic), we studied the diet of this cormorant on the Argentine Atlantic coast during four breeding seasons, using a combined technique of conventional diet assessment (pellets) and stable isotope analysis. Our results show that the Red-legged Cormorant forages mainly on pelagic and demersal—pelagic prey. Results of both techniques showed the main prey to be the Patagonian Sprat, a small high-energy-content pelagic forage fish, and the Patagonian Squid, a low-energy-content demersal—pelagic invertebrate. We also found an overall low prey diversity and important interannual variation for the main prey types, as well as variation between the different breeding stages. This study therefore contributes new and unambiguous information about the Red-legged Cormorant's use of trophic resources and suggests that the combination of a conventional technique with stable isotope analysis provides a solid framework for this seabird diet assessment.

Assessing the trophic ecology of three sympatric squid in the marine ecosystem off the Patagonian Shelf by combining stomach content and stable isotopic analyses

ABSTRACTSquid species are important components of the Southern Atlantic Ocean ecosystems, as they prey on a wide range of crustaceans, fish and cephalopods. As a result of this trophic interaction and their high abundance, they are considered reliable indicators of energy transfer and biomass in the food web. We identified Illex argentinus, Doryteuthis gahi and Onykia ingens as the most important squid species interacting on the Patagonian shelf, and used isotope analysis and stomach content identification to assess the feeding ecology and interaction of these squids in the ecosystem. Our results describe trophic interactions by direct predation of O. ingens and I. argentinus on D. gahi, and a trophic overlap of the three squid, and indicate a higher trophic level and differences in the foraging areas for mature and maturing D. gahi inferred through δ15N and δ13C concentrations. These differences were related to the segregation and different habitat of large mature D. gahi and suggest a food enrichment of C and N based on feeding sources other than those used by small maturing D. gahi and I. argentinus and O. ingens.

Cephalopods of Pacific Latin America

Cephalopod fisheries have experienced outstanding growth in Latin America during the last quarter century, increasing from 0.5% to 7% of total Latin American landings since 1990. Its waters account today for a third of world cephalopod catches, with about two-thirds of this total being landed by Latin American countries and the remainder by East Asian countries. The ommastrephid squids Dosidicus gigas and Illex argentinus have led catches worldwide, while Doryteuthis gahi is the most important loliginid. Mexico, Peru, Chile, Argentina and the Falkland Islands (Malvinas) account for 98% of landings in the region. Pacific waters account for 60% of cephalopod landings in Latin America. Mexico, Peru and Chile account for virtually all landings from the Pacific. This has been largely achieved through switching the targets of national fishing fleets to squid. There are a variety of directed fisheries for octopus, some of which raise concerns about sustainability. Most landings are exported to East Asia and Europe, but local cephalopod supply has increased. Aquaculture research on octopus in Chile is experiencing a mayor advance with international impact.Cephalopod research in Latin America is progressing in response developments in the fishing industry, especially in Mexico, Peru, and Chile. Nevertheless, cephalopod consumption is still relatively low and fisheries in these countries all depend strongly on foreign markets. In the smaller countries of Central America, as well as Colombia and Ecuador, cephalopods remain negligible as a marine resource.

Temporal variation in the diet of gentoo penguins at the Falkland Islands

Knowledge of diet is critical in interpreting the ecological roles of marine top predators and provides information towards their conservation and management. The Falkland Islands hold the largest number of breeding gentoo penguins. Yet knowledge of gentoo penguin diet at the Falklands is limited to either broad taxonomic divisions of prey items or dietary samples collected only on a single day. This study is the first to investigate gentoo penguin diet at Cow Bay, Falklands, to the species level, over repeated sampling intervals during the breeding period. Through stomach content analysis, we determined diet over a large temporal scale (2002/2003/2004–2011/2012/2013) and between the guard and creche periods of chick rearing. The principle prey item by reconstituted mass was rock cod fish Patagonotothen spp., for all periods (47–78 %) except that of the 2012/2013 creche period (19 %) when Falkland herring Sprattus fugensis made up the bulk of the diet (52 %). Of the cephalopods recovered, Patagonian squid Doryteuthis gahi was prominent (1–24 %), while crustaceans contributed negligibly to gentoo penguin diet. Our findings revealed that gentoo penguins breeding at the Falkland Islands were primarily demersal foragers with an ability for pelagic feeding. Diet choice appears to reflect prey availability.

Environmental impacts on recruitment migrations of Patagonian longfin squid (Doryteuthis gahi) in the Falkland Islands with reference to stock assessment

Doryteuthis gahi squid stocks in the Falkland Islands are assessed by depletion models which may include in-season recruitment pulses. Occurrences of in-season recruitment pulses are inferred by sharp peaks in CPUE, but this ad hoc approach does not distinguish between true recruitments into the fishery and aggregations of squid already in situ. Data were therefore investigated from 13 fishing seasons in which true recruitments could be identified by changes in D. gahi size distributions, and related to environmental variables of sea wind, sea surface temperature, and geostrophic currents. Changes in size distributions showed 30% of CPUE peaks to be true recruitments. Recruitment peaks followed a significant parabolic relationship between east-west and north-south sea wind vectors. Recruitment peaks occurring under west sea winds were characterized by a positive correlation between west and north wind speeds. Recruitment peaks occurring under east sea winds were characterized by a positive correlation between east and north wind speeds. The wind speed criteria were used to classify CPUE peaks in all D. gahi fishing seasons from 2002 to 2012. Among winter seasons, D. gahi abundance estimates correlated best with CPUE when depletion models included all recruitment peaks. Among summer seasons, which are shorter, abundance estimates correlated best with CPUE when depletion models included only the last overall peak. We hypothesize that identifying recruitment peaks improves the accuracy of depletion models, but time series must be sufficiently long for multi-peak models to fit optimally.

Paralarvae of cephalopods in channels and fjords of the southern tip of Chile (46–53°S)

Cephalopods are common in Chilean waters; however, there is little information on the distribution and abundance of their early life stages. In the austral spring seasons of 2008 and 2009 zooplankton samples were collected during two oceanographic cruises (CIMAR 14, CIMAR 15) in Patagonian fjords and channels of southern Chile between 46°S and 53°S. Zooplankton sampling was conducted at 82 stations with Bongo (60cm diameter, 300μm mesh size) and Tucker (1m2 diameter, 300μm mesh size) trawl nets. The paralarvae were preliminarily identified by morphology and pigment patterns. Subsequently, their identity was confirmed through mitochondrial DNA (16S rRNA and COIII) analysis comparing them with the common adult octopus species from Chile which also have planktonic paralarvae (Octopus mimus, R. fontaniana and Enteroctopus megalocyathus) by phylogenetic analysis. We obtained 12 octopus and 1 squid paralarvae in 2008 and 16 octopus and 1 squid paralarvae in 2009. The paralarvae were caught exclusively in areas with higher oceanic influence and were absent in areas with greater freshwater discharge and/or ice melting. Southern Chile is characterized by geomorphological discontinuity due to fragmentation of the south coast starting at 41°30‘S, where there is a large freshwater influence in estuaries promoting fjord-like characteristics. Thus, it is not surprising that cephalopod paralarvae were not found in such places, because they are stenohaline. Both morphometric and molecular data confirmed that 26 paralarvae belonged to R. fontaniana; one paralarva was identified as Enteroctopus megalocyahtus; Doryteuthis gahi and Onychoteuthidae were also collected. Our results expand the known range of cephalopod paralarvae to areas where they have never have been reported in the southern tip of Chile. The presence of paralarvae in these fjords supports the hypothesis of their use as spawning grounds for many species of squid and octopus of different families.

Population dynamics of the squids Dosidicus gigas (Oegopsida: Ommastrephidae) and Doryteuthis gahi (Myopsida: Loliginidae) in northern Peru

Pelagic squids of continental shelf ecosystems mostly include oceanic and migratory species of the family Ommastrephidae and neritic species of the family Loliginidae. These two families have contrasting life history strategies; ommastrephids spawn in the open ocean and are thought to have a high dispersal potential, while loliginids spawn on the bottom and are likely to have a low dispersal potential. Consequently, these squid species should display different patterns in their population dynamics, which can be inferred through commercial catches. To study the population dynamics of the Ommastrephidae and the Loliginidae families, monthly time series catches of Dosidicus gigas and Doryteuthis gahi were used. These artisanal fishery catches were made in northern Peru from 1999 to 2010. They were standardized to construct autocorrelation functions so that the relationship between catch dynamics and short-term environmental change (thermal anomalies of sea surface temperature were used as a proxy) could be studied. The results revealed that increases in catches of D. gigas and D. gahi are not related to thermal anomalies, but rather a pattern of drastic fluctuations in D. gahi catch sizes are seen. In, both species, temporal relationships indicate that the annual growth rate and changes in abundance can modelled as a function of the catch density observed in previous years. We propose that these population differences result from the contrasting life history strategies and differential habitat use of these two squid species.

Intra- and interannual variation in the diet of the Magellanic penguin (Spheniscus magellanicus) at Martillo Island, Beagle Channel

Knowledge of seabirds’ diet at each breeding site and its temporal variation is key to understanding and evaluating how changes in marine resources affect each seabird population. In this study, we determined the diet of Magellanic penguins (MP, Spheniscus magellanicus) at Martillo Island, accounting for sex, breeding stage and year. We analyzed a total of 144 stomach contents during three consecutive breeding seasons (2006–2007, 2007–2008 and 2008–2009) and stages (incubation, early and late chick-rearing). MP fed mainly on fuegian sprat (Sprattus fuegensis), which represented 75 % of the biomass consumed by birds during the entire study. The next important prey was squat lobster (Munida gregaria), followed by Patagonian squid (Loligo gahi). Both sexes consumed similar prey items. We observed variation in diet relative composition among breeding years and stages. Fuegian sprat consumption decreased throughout the years whereas squat lobster increased. Penguins consumed a higher proportion of squat lobster and Patagonian squid during the incubation stage than in the chick-rearing stages, whereas fuegian sprat was almost the only prey item consumed during the late chick-rearing stage. MPs show certain flexibility in the use of resources probably as a response to changes in prey populations. Variability in the diet among different reproductive stages could be related to changes in the distribution and abundance of their main prey near the colony during the breeding season together with changes in the energy requirements of seabirds.

Commercial squids: Characterization, assessment of potential health benefits/risks and discrimination based on mineral, lipid and vitamin E concentrations

The most consumed squid species worldwide were characterized regarding their concentrations of minerals, fatty acids, cholesterol and vitamin E. Interspecific comparisons were assessed among species and geographical origin. The health benefits derived from squid consumption were assessed based on daily minerals intake and on nutritional lipid quality indexes. Squids contribute significantly to daily intake of several macro (Na, K, Mg and P) and micronutrients (Cu, Zn and Ni). Despite their low fat concentration, they are rich in long-chain omega-3 fatty acids, particularly docosahexaenoic (DHA) and eicosapentanoic (EPA) acids, with highly favorable ω-3/ω-6 ratios (from 5.7 to 17.7), reducing the significance of their high cholesterol concentration (140–549mg/100g ww). Assessment of potential health risks based on minerals intake, non-carcinogenic and carcinogenic risks indicated that Loligo gahi (from Atlantic Ocean), Loligo opalescens (from Pacific Ocean) and Loligo duvaucelii (from Indic Ocean) should be eaten with moderation due to the high concentrations of Cu and/or Cd. Canonical discriminant analysis identified the major fatty acids (C14:0, C18:0, C18:1, C18:3ω-3, C20:4ω-6 and C22:5ω-6), P, K, Cu and vitamin E as chemical discriminators for the selected species. These elements and compounds exhibited the potential to prove authenticity of the commercially relevant squid species.

Egg masses of the Patagonian squidDoryteuthis (Amerigo) gahiattached to giant kelp (Macrocystis pyrifera) in the sub-Antarctic ecoregion

Egg masses of the Patagonian squid Doryteuthis (Amerigo) gahi attached to giant kelp (Macrocystis pyrifera) in the Magellanic channels of the sub-Antarctic ecoregion in southern South America is documented for the first time. Of seven egg masses observed between 2008 and 2011, one was taken to the laboratory to be analysed and photographed. Comprising long transparent capsules containing eggs, the masses were strongly attached to the stipes of M. pyrifera. This macroalgae is a potentially important economic resource due to its multiple industrial uses; this study shows that it also serves an important ecological role as a spawning substrate for D. gahi.Keywords: Doryteuthis; egg masses; giant kelp; Patagonian squid; sub-Antarctic ecoregion(Published: 5 November 2014)Citation: Polar Research 2014, 33, 21636, http://dx.doi.org/10.3402/polar.v33.21636

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 37.0cm, 75 Illex argentinus (21.0–32.8cm) and 116 Onykia ingens (19.9–39.3cm) 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 (5–15cm 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.