A semi-automated method for daily age estimation in larval populations by discriminant function models

Discriminant analysis including the best age-correlated variables selected by SMLR’s to construct a predictive model based on somatic and otolith biometry was applied. Age of anchovy larvae ranging from 10 to 12 mm collected along Western Mediterranean coasts during MEDIAS209 survey were estimated by otolith microstructure analysis and compared with the number of daily increments estimated by the model. The model compound by Perimeter2 + Area2 was able to estimate correctly the age of the otoliths in 75% of the cases assuming ±1 day of error increasing to 90% assuming ±2 days of error with mean values of APE (3.33%) and CV (4.71%) systematically low. The results indicate the precision of the increment estimates. Moreover, no differences between the estimated ages from direct readings and those estimated by the model were observed. The proposed method implies a reduction in the subjectivity factor and the cost/benefit ratio for ageing studies in fish larvae.Postprint1,586

Climate-induced environmental conditions influencing interannual variability of Mediterranean bluefin (Thunnus thynnus) larval growth

Daily growth variability of bluefin (Thunnus thynnus) larvae sampled in their Balearic Sea spawning grounds during the 2003–2005 spawning seasons was examined. Multi-factorial ANOVA was applied to study the effects of environmental variables, such as temperature at 10 m depth (T10), microzooplankton dry weight (MDW) and protein/dry weight ratio (PROT/ MDW) on larval growth. The 2003 bluefin tuna (BFT) larval cohort showed the fastest growth, recognizable from enhanced otolith and somatic mass increment compared to the 2004–2005 larval cohorts. The 2003 BFT larvae showed greater recent growth than the 2004–2005 BFT cohorts, which decreased in the last stages of development. Growth differences between the 2004 and 2005 larval cohorts were not significant. The environmental conditions between 2003 and 2004–2005 were highly contrasting as a result of the 2003 warming anomaly. Somatic and otolith growth rates (OGR) were significantly related to T10 and MDW, as well as to the PROT/MDW ratios. Nonetheless, the effect of T10 on OGR depended on the relative high (H) or low (L) levels of MDW and PROT/DW. Higher OGR was observed when T10 was high, MDW was low and PROT/DW was high. This environmental scenario conditions were met during 2003, which recorded the highest surface temperature and low planktonic biomass. Somatic growth,expressed as larval DW growth increase (DWGR), showed three-factor significant interactions with T10*MDW*PROT/MDW, in which the two-way interactions of MDW*PROT/MDW showed differences in the function of T10 levels.Postprin

Spawning frequency of Sardina pilchardus, (Walb.) off the Spanish North Atlantic coast in 1997

This paper presents the spawning fraction and spawning frequency estimates of Sardina pilchardus off the North Atlantic Spanish coast in March 1997 using the Postovulatory Follicle Method. The fraction of mature female sardine with less than 48-h-old postovulatory follicles averaged 0.18 (standard deviation = 0.08), indicating that the mean interval between each spawning was approximately six days along the eastern Cantabrian coast. This spawning fraction estimate is higher than those estimated for the western Cantabrian and Galicia coasts as could be expected from the differential distribution of sardine by age with an increment towards the east; and it is slightly lower than in previous years due to changes in the species distribution pattern by age.Versión del editor1,586