Effect of nursery ground variability on condition of age 0+ year Merluccius hubbsi

This study examined the southern or Patagonian (41°–55° S) stock of Argentine hake Merluccius hubbsi, the more abundant of the two stocks on the Argentinean continental shelf. Pre-recruits (age 0+ year individuals) of this stock settle and grow in the San Jorge Gulf (45°–47° S, 65° 30′ W), a complex habitat with large spatial variability in environmental features. Relative condition factor, hepatosomatic index, lipid content and fatty-acid composition of muscle and liver, and diet information were combined with physical and biological data to evaluate: how nutritional status of age 0+ year hake varies spatially within the nursery ground; whether changes in condition are related to environmental factors and feeding; whether the indices are interchangeable metrics of condition. Both morphometric and biochemical indices showed dissimilar spatial trends; enhanced liver-based condition coincided with low salinity nutrient rich waters, higher chlorophyll-a values and abundances of Euphausia spp., the preferred prey at most stations, suggesting a bottom-up effect on age 0+ year hake condition. Diminished condition at stations where Thermisto gaudichaudii was the main prey could derive from lower prey quality in terms of energy density and essential fatty acids content. Coastal waters of the gulf would be essential habitats for M. hubbsi pre-recruits. Future monitoring of condition with liver-based indices is encouraged in the gulf, where interannual increasing trends of satellite-derived chlorophyll-a values have been observed, which could have implications for recruitment of the species.Fil: Temperoni, Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Massa, Agueda Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Derisio, Carla María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Martos, Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Marinas; ArgentinaFil: Berghoff, Carla Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Viñas, Maria Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Amphipod-supported food web: Themisto gaudichaudii, a key food resource for fishes in the southern Patagonian Shelf

The trophic role of the hyperiid amphipod Themisto gaudichaudii in the southern Patagonian shelf food web was assessed from the analysis of stomach contents of the local fish assemblage. A total of 461 trawl samples were collected during seven seasonal cruises. A total of 17 out of 38 fish species were found to ingest T. gaudichaudii. This amphipod was a main prey item in five of these species, showing high values of alimentary index: Seriolella porosa (99.9%), Macruronus magellanicus (68.8%), Micromesistius australis (59.1%), Patagonotothen ramsayi (48.6%), and Merluccius hubbsi (10.9%). The contribution of T. gaudichaudii, in weight, to their summer diet was 60%, on average. This contribution was minimal in winter and maximal in summer. Fisheries studies have indicated that these five species, mainly M. magellanicus, account for almost 85% of the fish biomass in the area. Although the remaining 15% did not feed heavily on T. gaudichaudii, they are known to prey on the main hyperiid predators. Our study shows that T. gaudichaudii contributes greatly, both directly and indirectly, to supporting the fish community. We thus proposed that T. gaudichaudii plays a key role as a "wasp-waist" species in the sub-Antarctic region, similar to that of krill in Antarctic waters, channeling the energy flow and enabling a short and efficient food chain.Fil: Padovani, Luciano Nahuel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: Viñas, Maria Delia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata; Argentina. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Sánchez, Felisa. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Mianzan, Hermes Walter. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentin

Temperature conditions in the Argentine chub mackerel (Scomber japonicus) fishing ground: Implications for fishery management

We describe the seasonal migrations of Argentine chub mackerel (Scomber japonicus) into the fishing ground in relation to sea surface temperature conditions and analyse the temperature evolution during the fishing season on the basis of 1955-97 time-series. The upper temperature limit for the presence of schools was around 19°C. At higher values, most schools leave coastal waters (< 50 m) for the shelf. An inverse relationship was observed between catches per unit of effort (CPUE) of the inshore fishery and sea surface temperature. The highest standardized CPUE values corresponded to temperatures lower than 19°C. Above this temperature, the probability of obtaining a standardized CPUE higher than 1 was extremely low, and the standard deviations were minimal. The economic benefit from catches was also analysed through the different months of the fishing season. It was found that the mean benefit corresponding to temperatures lower than 19°C exceeded approximately 15 times that obtained at higher temperatures. A simple fishing strategy was proposed to the commercial fleet in order to improve the economic benefit of the catches. The migratory pattern followed by mackerel during the spawning period was also analysed in relationship to other environmental factors like food availability. Zooplankton composition, size structure and abundance in coastal and shelf waters are described, and their implications for feeding ecology of larvae and adults of the species are discussed.Fil: Perrotta, Ricardo Geronimo. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Viñas, Maria Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Hernández, Daniel R.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Tringali, Leonardo. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentin

Large-scale geographic patterns of pelagic copepods in the southwestern South Atlantic

We compiled an extensive dataset of copepod presence/absence data to define ecoregions in the southwestern South Atlantic (33°S–55°S) and to examine their relationships to water mass characteristics. We also investigated the role of mesoscale fronts in determining the boundaries of the ecoregions. Finally, we compared copepod distributions with previously defined biogeographical provinces in the southwestern South Atlantic. The regional copepod community is organized into six assemblages that occupy distinct areas of the shelf, the shelfbreak, and the oceanic realm. These areas are characterized by different water masses. In general, the spatial configuration of the ecoregions matches that of the previously defined regional biogeographic provinces and marine fronts seem to act as boundaries between the ecoregions.Fil: Acha, Eduardo Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Viñas, Maria Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Derisio, Carla María. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Alemany, Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Piola, Alberto Ricardo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Energy density of age-0+ Merluccius hubbsi (Actinopterygii, Merlucciidae) as a food quality proxy for upper level predators

Determinar la densidad energética (DE) de los peces brinda información clave para modelos bioenergéticos de predadores y estudios de tramas tróficas. En la plataforma continental argentina, los prerreclutas del efectivo patagónico de Merluccius hubbsi se concentran en el Golfo San Jorge (45º-47ºS, 65º30’W), donde son alimento de otros peces demersales, aves y mamíferos marinos. La DE de los prerreclutas -derivada de las proteínas y los lípidos almacenados en músculo e hígado- se determinó como un indicador de calidad nutricional, para evaluar la cantidad de energía disponible para sus predadores. La DE (n = 40) varió entre 1,6 y 5,5 kJ g–1 peso húmedo (3,4 ± 0,9), siendo el músculo el tejido que mejor explicó sus variaciones (R2 = 0,99; p < 0,001). En el músculo dominaron las proteínas (92,9 ± 3,2%), mientras que en el hígado se observó un aporte similar de las proteínas (55,5 ± 14,1%) y los lípidos (44,5 ± 14,1%). Los resultados aportan información novedosa, que era escasa para M. hubbsi en la plataforma continental argentina, y son útiles en el marco de modelos de ecología trófica de sus predadores, permitiendo comprender el flujo de energía en la trama trófica del Golfo San Jorge.Assessing the energy density (ED) of forage fish provides key information for top predators bioenergetics’ models and food web studies. In the Argentinean Continental Shelf (ACS), age-0+ year individuals of the Patagonian stock of Merluccius hubbsi concentrate in the San Jorge Gulf (45º-47ºS, 65º30’W), where they constitute an important food source for demersal fish, seabirds and marine mammals species. Age-0+ M. hubbsi ED -deriving from proteins and lipids stored in muscle and liver- was determined as a food quality proxy, to gain insight into the amounts of energy they pass to predators. ED values ranged from 1.6 to 5.5 kJ g– 1 wet weight (3.4 ± 0.9) (n = 40), with muscle explaining most of its variation (R2 = 0.99; p < 0.001). Muscle was dominated by proteins (92.9 ± 3.2%), while a similar contribution of both proteins (55.5 ± 14.1%) and lipids (44.5 ± 14.1%) was observed to the liver. These results provide novel information that was scarce for M. hubbsi in the ACS, particularly for the age-0+ stage. Data will be useful in the context of M. hubbsi predators’ trophic ecology models, to understand how ecosystem shifts influence the structure of the San Jorge Gulf food web.Fil: Temperoni, Brenda. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Massa, Agueda Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentina. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Viñas, Maria Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentina. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentin

First-feeding of hake (Merluccius hubbsi) larvae and prey availability in the North Patagonian spawning area

The diet of Merluccius hubbsi first-feeding larvae was analysed and related to food availability in stratified waters of the Patagonian spawning area. The gut contents of small larvae ranging from 2 to 4 mm SL, collected from five consecutive depth strata (upper 50 m of the water column), were examined. After dissection of the larvae, the prey items were stained with tolouidine blue. The feeding incidence, and the types, sizes and numbers of food particles per larvae were determined. The mean feeding incidence was 64.5 %. Food particles 45 to 136 μm in width constituted the bulk of the prey ingested, which consisted of nauplii and early copepodites of the small copepod species frequently found in the sampling area. The most abundant taxa among the gut contents were Paracalanus parvus. Oithona spp.. Acartia tonsa and members of Pseudocalanidae. The mean number of nauplii per larva was 4.4 times higher than the number of copepodites, but the volumetric ratio between the two groups was 1.4:1. The results of larval gut analysis were related to zooplankton distribution in the field. First-feeding strategies of hake and anchovy larvae growing in the area were compared.Fil: Viñas, Maria Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Santos, Betina. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentin

Food and feeding of Argentine hake (Merluccius hubbsi) larvae in the Patagonian nursery ground

Feeding success during the early life stages of fish is one of the main factors that determines recruitment and stock fluctuations. In the Argentine Sea, the Patagonian stock of Merluccius hubbsi is the most important in biomass, spawning from December to April in the north Patagonian shelf region (43–45°30′). Since previous knowledge about larval feeding of the species in this region is fragmentary, adequate information is required for a complete assessment of its importance in the food web and its effect upon recruitment. Our primary objective was to examine the feeding strategy of M. hubbsi larvae in relation with prey availability in the nursery ground. Feeding incidence was 87%; hake larvae consumed mainly calanoid copepodites <2 mm in size, which were preferred prey upon more available items, and that may be nutritionally beneficial for larvae. Hake larvae were specialist at a population level toward such prey, with a narrow trophic niche. There was a clear trophic diel pattern in the number of prey ingested. Results indicate that the nursery area might be favorable for a successful feeding of hake larvae while they grow and develop. Data provided here are relevant not only to determine trophic interactions in the region but also to identify possible causes of recruitment successFil: Temperoni, Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Viñas, Maria Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentin

Feeding strategy of juvenile (age-0+ year) Argentine hake Merluccius hubbsi in the Patagonian nursery ground

Age-0+ year juvenile Argentine hake Merluccius hubbsi (60–150 mm total length, LT) from San Jorge Gulf, north Patagonian shelf region of the Argentine Sea, had an almost exclusively pelagic diet dominated by the hyperiid amphipod Themisto gaudichaudii and the euphausiid Euphausia lucens. This suggested that final settlement and permanent demersal habitat utilization might not, as previously reported, occur at earlier sizes (c. 20 mm LT). Their feeding strategy involves specialization at a population level towards both the main pelagic prey, indicating a narrow trophic niche. Novel data are provided which contribute to the growing body of information in relation to the age-0+ year transitional stage in demersal fishes and particularly to M. hubbsi recruitment in the Argentine Sea.Fil: Temperoni, Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo; ArgentinaFil: Viñas, Maria Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo; ArgentinaFil: Buratti, Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentin

Enhancing fish diet analysis: equations to reconstruct Themisto gaudichaudii and Euphausia lucens length from partially digested remains

Themisto gaudichaudii and Euphausia lucens are important prey of several fish and squid species of commercial value in the southwest Atlantic Ocean. Although allometric relationships linking size and weight can be used to estimate prey biomass, size is often difficult to obtain as they are usually partly digested. The objective of our work was to provide length length relationships to estimate body size of both crustaceans from their remains in fish stomachs, as a first step to estimate their weight. Measurements were performed on intact specimens collected in the field. Each of the body dimensions analysed (eye height and width for T. gaudichaudii, and carapace length and eye diameter for E. lucens) was significantly related to total length in both species. Thus, they appear to be highly reliable predictors of original size and can potentially aid in the identification of crustacean remains, allowing a more accurate analysis of digested contents.Fil: Temperoni, Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Viñas, Maria Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Hernández, Daniel. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentin

Fatty acids composition as an indicator of food intake in Merluccius hubbsi larvae

Fatty acids (FA) analysis is a well-established approach for qualitatively studying feeding preferences. In the Argentinean Continental Shelf, Argentine hake Merluccius hubbsi supports the major demersal finfish fishery. The Patagonian stock of the species spawns and nurses in austral summer in the north Patagonian shelf (NPS, 43°-45°30′S). Previous studies about larval feeding in the NPS have solely focused on gut contents, indicating selectivity upon calanoid copepods. Hence, our main objective was to apply the FA approach to confirm and/or broaden M. hubbsi larval food selection. Hake larvae and copepod FA profiles overlapped significantly, dominated by the saturated FA 16:0, the monounsaturated FAs 18:1n-9 and 22:1n-9, and the polyunsaturated FA 22:6n-3. Moreover, identified markers typical of bacteria (15:0, 17:0) and dinoflagellates (18:4n-3, 22:6n-3) suggest a microbial input at the base of the NPS food web, with the latter probably acting as an intermediate step between bacteria and hake larvae. Possible direct predation upon protozoans by larvae is postulated, broadening the known trophic spectrum derived from classical diet analyses. The FA approach allowed us to clarify feeding preferences in the NPS, with data being relevant in the context of hake recruitment studies.Fil: Temperoni, Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Massa, Agueda Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Viñas, Maria Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentin