Browsing by Author "Peliz, A."
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- Are sardine larvae caught off northern Portugal in winter starving? An approach examining nutritional conditionsPublication . Chicharo, Maria Alexandra; Esteves, E.; Santos, A. Miguel P.; Santos, Antonina dos; Peliz, A.; Re, P.Recently, winter upwelling events off western Iberia have become more frequent. This may affect the production and survival of sardines egss and larvae through increased offshore transport. By analysis of RNA: DNA ratios, we investigated the impact of winter upwelling events on the larval conditions of Sardina pilchardus larvaeas a function of oceanographic conditions and food availability. Larvae were collected on a research cruise off northern Portugal in February 2000. Environmental parameters such as wind, water temperature, salinity microzooplankton biomass and daily egg production of the calanoid copepod Calanus helgolandicus also measured. The mean RNA:DNA ratios wererelatively high, indicating that almost all larvae collected were good condition. This was in agreement with the high microzooplankton biomass and high daily egg production of the copepod C. helgolandicus recorded during the same period. No adverse effects of upwelling causing offshore transport of larvae into poor feeding areas could be demonstrated because of the presence of a stratified warm plume with consequent high food production.
- Assessing the impact of environmental forcing on the condition of anchovy larvae in the Cadiz Gulf using nucleic acid and fatty acid-derived indicesPublication . Teodosio, Maria; Garrido, Susana; Peters, J.; Miguel de Sousa Leitão, Francisco; Re, P.; Peliz, A.; Santos, A.M.P.Understanding the environmental processes affecting fish larvae survival is critical for population dynamics,"conservation purposes and to ecosystem-based fishery management. Using anchovies (Engraulis encrasicolus) of the Cadiz Gulf as a study case and considering the "Ocean Triad" hypothesis, we investigate the larval ecophysiological status and potential survival in relation to oceanographic variables. Therefore, this study aims to describe the nutritional condition of anchovy larvae during spawning season (peak in summer) through nucleic acid- and fatty acid (FA)-derived indices and to analyze the effects of the major environmental parameters (Depth, Temperature, Salinity, Plankton biomass) on anchovy survival potential at early phases. Fish larvae were collected in August from 30 m to 400 m depth at 35 stations off the southern Iberian coast. A previous upwelling event influenced the oceanographic conditions of the more western stations off Cape Sao Vicente (CSV). Along the coast, the water became warmer from west to the east through Cape Santa Maria (CSM) ending at Guadiana estuary, where easterly winds originated the development of a counter current. The standardized RNA/ DNA (sRD) of anchovy larvae decreased throughout larval ontogeny, reflecting a reduction of growth during the development. Essential FA concentrations also decreased, but docosahexaenoic acid (DHA) in particular was highly conserved even after the reduction of total FA concentration in anchovy larvae related to the onset of swimming abilities (post-flexion phase). The oceanographic conditions (west upwelling, east counter current, and stratification) led to a nearshore aggregation of plankton and anchovy larvae with good ecophysiological conditions in the central area of the southern coast, where an optimal range of temperature and chlorophyll, as an indirect food proxy for anchovy larval development, were registered. The study proves that the oceanographic conditions of the study area are putative drivers of the ecophysiological condition of anchovy larvae to guarantee potential survival, supporting the "Ocean Triad" hypothesis with major repercussions for recruitment and population dynamics.
- Physical-biological interactions in the life history of small pelagic fish in the Western Iberia Upwelling EcosystemPublication . Santos, A. Miguel P.; Chicharo, Maria Alexandra Teodosio; Santos, Antonina dos; Moita, Teresa; Oliveira, P. B.; Peliz, A.; Re, P.This paper reviews relevant investigations conducted in the Western Iberia Upwelling Ecosystem (WIUE) on the dynamics of small pelagic fish (SPF), its relationship to climate changes and processes related to the ‘ocean triad’ (enrichment, concentration, transport/retention). In the last decades, a decline in the productivity of several SPF species (e.g., sardine and horse mackerel) was observed in the WIUE, which is partially explained by environmental variability (e.g., changes in coastal upwelling). The main mechanism proposed to explain this decline is the increased frequency and intensity of upwelling events during the spawning season (winter) of these species, which is typically a period when convergence conditions prevail. Thus, this ‘anomalous’ situation promotes egg and larval dispersal away from the favourable coastal habitat (the shelf) and consequently has a negative impact on their survival and recruitment. However, the variability of local features like the Western Iberia Buoyant Plume (WIBP) and the Iberian Poleward Current (IPC) introduce important fluctuations in the transport patterns of the region, and could modulate the impact of these winter upwelling events in the survival of larvae. The retention on the shelf of larval sardine along convergence zones formed by the interaction of these two features plays an important role in their survival. Furthermore, the WIBP is a suitable environment for the growth of phytoplankton and for larval fish survival. From these findings it is clear that simplified Ekman transport models could not explain larval fish transport/retention patterns in this region and more realistic biophysical models should be used to simulate the local oceanographic conditions to understand larval dynamics and the success of recruitment of SPF in the Western Iberia.