Andrea Lopez Cazorla

Feeding habits of the juvenile striped weakfish, Cynoscion guatucupa Cuvier 1830, in Bahía Blanca estuary (Argentina): seasonal and ontogenetic changes

The aim of this study was to analyze the feeding habits of the juvenile striped weakfish, Cynoscion guatucupa Cuvier, from Bahía Blanca estuary, Argentina. C. guatucupa is one of the most important regional fishing resources although in the last 10 years landings have greatly decreased. The year class strength of fish as well as stock size and yield are determined during the early life stages. Knowledge about the diet of young C. guatucupa may therefore contribute to our better understanding of the influence that the changes occurring in the biota of the estuary exert on the abundance fluctuations of this species. To this end, we investigated the ontogenetic and seasonal dietary changes of C. guatucupa between 1.00 and 12.99 cm total length (age 0+), and we related them to changes in habitat use and prey selection. Two dietary shifts were found during ontogeny. The first shift, at approximately 4 cm total length, involved a change from demersal-pelagic prey (mysid shrimps) to demersal-benthic prey (Peisos petrunkevitchi Burkenroad). The second shift, at approximately 8 cm total length, involved a progressive increase in ichthyophagy (mainly an increase consumption of the Argentine anchovy Engraulis anchoita Hubbs & Marini). Seasonal dietary changes were also found. They evidenced the changes in the availability of organisms. In autumn, the chaetognath Sagitta friderici Ritter-Zahoni, P. petrunkevitchi, and E. anchoita were the dominant prey items; in winter, the copepod Labidocera fluviatilis Dahl along with S. friderici, mysids, and P. petrunkevitchi constituted the majority of the diet; and, in summer, mysids were the most important prey item consumed. Selectivity data showed that whereas some prey items, such as the copepods Acartia tonsa Dana and Paracalanus parvus (Claus) and S. friderici, were consistently negatively selected by all size classes throughout the year, other prey items, such as fish larvae, mysids, and P. petrunkevitchi,were selected in one season and avoided in another. Additional dietary seasonal differences observed in our research indicate that the limited food supply and the low water temperatures are limiting factors for winter juveniles in BahÕa Blanca estuary. These factors may also directly influence the more-than-10 cm total length seaward migration of large numbers of C. guatucupa that is registered at the end of every autumn.

Demography of feral horses (Equus caballus): a long-term study in Tornquist Park, Argentina

Fil: Scorolli, Alberto Luis. Universidad Nacional del Sur. Departamento de Biologia, Bioquimica y Farmacia; Argentina

Feeding Interrelationships and Comparative Morphology of Two Young Sciaenids Co-occurring in South-western Atlantic Waters

Diet and morphology of the sciaenids striped weakfish, Cynoscion guatucupa, and whitemouth croaker, Micropogonias furnieri, from Bahía Blanca estuary (South America) were studied and compared between March 2000–February 2001. Significant differences in mouth morphometric parameters between striped weakfish and whitemouth croaker were found. Premaxila + maxila length, dentary length, and mouth gape were always larger in the former than in the latter. However, analyses of variance (ANOVA) indicated no differences in the mean maximum size of prey consumed by both species. Schoener’s dietary overlap was generally moderate between the three ontogenetic trophic groups of striped weakfish and whitemouth croaker. High dietary overlap was observed in winter and summer, when both species prey heavily on Peisos petrunkevitchi and mysid shrimps, respectively. In this study, no evidence of food competition was found between young striped weakfish and whitemouth croaker.

Possible predation by the striped weakfish Cynoscion guatucupa on estuary-associated fishes in an Argentinian coastal lagoon

Abstract Cynoscion guatucupa is one of the most important coastal fishery resources of Argentina and Uruguay, with both juveniles and adults being recorded in Mar Chiquita coastal lagoon, a shallow-water estuarine lagoon in Argentina. Cynoscion guatucupa enters and exits the lagoon following tidal cycles, with residence time within the lagoon lasting only for the duration of a tidal cycle. The main objectives of this study were to determine the diet composition of Cynoscion guatucupa captured in the lagoon, and to determine if different size-classes of this species differentially utilize available food resources during their residency within the coastal lagoon. The diet of 511 specimens of C. guatucupa was analysed. The most important prey item in %IRI was Peisos petrunkevitchi, followed by juvenile teleosts including those of Micropogonias furnieri, Odontesthes argentinensis and Mugil platanus. Cynoscion guatucupa enters the lagoon to feed on a variety of invertebrates as well as juvenile teleost fishes. Diet composition showed ontogenetic changes: smaller individuals predominantly consume crustaceans, and as size increases they begin to prey more on teleosts, with the largest fishes specializing on fish. The present study reinforces the role of estuaries for marine fishes as both feeding grounds for juveniles and adults and as refuge areas for juveniles. Furthermore, this study also highlights the importance of food habit studies for understanding the trophic ecology of fishes and estuarine food web dynamics.

Pisces, Anegada Bay protected area, Buenos Aires province, Argentina

We provide the first list of marine fish from Anegada Bay, a coastal protected area in Buenos Aires Province. Fish records were obtained from gillnets and recreational fishery captures. Thirty seven species belonging to 29 families and 18 orders were identified. The most numerous order was Perciformes with eight families and 10 species. Odontesthes argentinensis, Micropogonias furnieri, Cynoscion guatucupa and Mustelus schmitti were verified in all sampling sites and the last two were the most represented either in the experimental fishing and recreational captures. Presence of Lagocephalus laevigatus extended the so far known range distribution of this fish species, representing the southernmost records in Argentinean coastal waters. The fish fauna composition from Anegada Bay could be considered as from a transitional zone.

Ontogenetic changes in the feeding strategy of Lepidonotothen nudifrons (Pisces, Nototheniidae) off the South Shetland Islands and the Antarctic Peninsula

ABSTRACT The diet and feeding strategy of Lepidonotothen nudifrons off the South Shetland Islands and the Antarctic Peninsula, as well as their variation in relation to ontogenetic stage (juvenile–adult) and sampling area, were determined by stomach contents analysis. Additionally, the trophic level of this species was estimated to determine its position within the Antarctic food web. Out of 247 specimens with prey in their stomachs, 144 were caught near the South Shetland Islands and 103 off the Antarctic Peninsula. Ontogenetic changes in the trophic ecology of L. nudifrons were observed in both areas and were mainly related to a decrease of copepods and an increase of euphausiids in the diet. The diet of juveniles from the South Shetland Islands was characterized by the dominance of calanoid copepods, followed by isopods and amphipods, whereas diet off the Antarctic Peninsula was dominated by amphipods and cyclopoid copepods. The diet in adults was dominated by amphipods and euphausiids in both areas. The specialization of individual predators on different prey types was observed when considering the whole population of L. nudifrons, but when ontogenetic stages were considered separately it showed a more mixed feeding strategy, with different dominant prey for each class. Although the trophic level increased with fish size, L. nudifrons can be classified as secondary consumer throughout its lifespan.

Relationship between ecomorphology and trophic segregation in four closely related sympatric fish species (Teleostei, Sciaenidae)

This study explores the relationship between ecomorphology and trophic segregation in four closely related sympatric fish species (Teleostei, Sciaenidae) that are known to differ in their trophic habits. Only adult specimens were analyzed: 103 Cynoscion guatucupa, 77 Pogonias cromis, 61 Micropogonias furnieri, and 48 Menticirrhus americanus. The four species presented divergent ecomorphological traits related to swimming agility, prey spotting and capture, and the potential size of prey they were able to swallow. Results suggest that these sciaenid species can partition the food resources, even though they completely overlap in space. Differences in their ecomorphological traits appear to correlate closely with the diet and consequently could explain the trophic differentiation observed. Arguably, these ecomorphological differences play a significant role in the coexistence of the adults of these sympatric fish species.

Distribution and human health risk assessment of PAHs in four fish species from a SW Atlantic estuary

The aim of this study is to assess—for the first time—the concentration of the 16 polycyclic aromatic hydrocarbons (PAHs) in the muscle tissues of four fish species (Micropogonias furnieri, Cynoscion guatucupa, Ramnogaster arcuata, and Mustelus schmitti) from Bahía Blanca estuary, Argentina and to evaluate their sources, distribution, and the human health risks implicated. Considering the four species under study, mean total PAH concentrations showed the following decreasing accumulation trend: M. schmitti, R. arcuata, C. guatucupa, and M. furnieri. Low molecular weight PAHs, such as naphthalene and phenanthrene, were generally predominant, displaying properties of PAH mixtures generated from petrogenic pollution. Of the four fish species analyzed, M. furnieri was the only one that did not raise any human consumption warning. In the case of the other species, exceeding values were found above the safety human consumption guidelines. Nevertheless, the screening criteria for carcinogenic PAHs proposed by the USEPA indicated a good quality status for these fish species.