Vital rates of sardine and anchovy larvae: trying to shed new light on early life history dynamics

Abstract

Laboratory experiments to study the vital rates of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) larvae in relation to differences in several key physical and biological factors considered most important for regulating their growth and survival, are being carried out in the framework of the project VITAL, financed by the Portuguese Foundation for Science and Technology (PTDC/MAR/111304/2009). The experiments aim at obtaining parameters such as the physiological tolerance limits of temperature, salinity and food availability for larvae survival and their influence on larval growth and ingestion rates. The nutritional condition of larvae reared in the laboratory is being monitored and compared with larvae collected in the wild, validating combined techniques (fatty acids and RNA/DNA). The quantitative estimates of the vital rates for the larvae of these fish species under controlled laboratory conditions will be used for parameterize an individual-based model to couple to a hydrodynamic model developed for the western Portuguese coast. Efforts to build models describing environmental regulation of small pelagic fish species (e.g., to examine links between climate and recruitment) are currently hampered by a lack of data such as the vital rates of the larval phase, to which we hope to contribute with our research. In this talk, we will present a synopsis of the results obtained so far for sardines, from adult fish collection and spawning initiation to the experiments of growth rates of sardine larvae under different prey regimes. Nearly 300 adult sardines were acclimated to a tank of the Oceanrio de Lisboa and since 2010 have spawned viable eggs for more than 200 days. Although there were no significant differences in egg size, the mean size of sardine larvae at hatch was significantly different amongst experiments (2.8 - 4.8 mm). Interestingly, in those experiments which had, on average, smaller larvae at hatch, the growth during the first week of life appeared to be higher than in experiments with larger larvae; early growth was significantly related to size-at-hatch until 9 dph, 5 days beyond the exogenous feeding initiation. The growth and survival for the remaining period of exogenous feeding was affected by food type and concentration. Highest growth and nutritional condition (RNA/DNA) of sardine larvae, growing up to 75 dph, were obtained using high concentrations of a mixed diet, combining Gymnodinium sp., rotifers and Acartia grani nauplii. This diet guaranteed higher growth and survival than a diet based on wild plankton