Environmental influences on the recruitment process inferred from otolith stable isotopes in Merluccius merluccius off the Balearic Islands

Oxygen (δ18O) and carbon (δ13C) isotope ratios in sagittal otoliths were analysed in recruits and juveniles of European hake Merluccius merluccius L. caught in the northwest (Sóller, SO) and south (Cabrera, CA) of the Island of Mallorca (western Mediterranean) over 2 consecutive years (2003 and 2004). The analytical method used allowed data to be gathered on both environmen-tal and trophic conditions experienced by fish during the pelagic early life stages (registered in the composition of the inner part of the otolith, core area) and the demersal aggregations of recruits (at the otolith edge). Results on the seasonal variation of oxygen isotope signatures at the edge of fish otoliths captured in SO and CA indicated different vertical migration behaviours of hake between the bottom and the thermocline. δ13C showed a clear ontogenetic pattern between the core area and the edge, confirming the differences in diet from the early stages to post-recruits. The seasonal analysis of δ13C data from the otolith edge indicated that fish from the early stages in June 2003 encountered poorer trophic resources, which resulted in poor fish condition and subsequent poorer recruitment. The estimated temperature from the core area of otoliths showed lower temperature regimes in the 2002 hatching season compared to the 2003 hatching season, which could be a possible explanation for the observed differences in success of subsequent recruitment. © Inter-Research 2008.Peer Reviewe

Can we model otolith growth and opacity patterns as a response to environmental factors and fish metabolism ? A DEB-based framework

This report presents a conceptual and numerical model of the formation of fish otoliths within a DEB-based (Dynamic Enerby Budget) framework. The proposed model relies on two mains assumptions: 1. The precipitation of the calcium carbonate in the endolymph is controlled by organic precursors; 2. The activity of these organic precursors can be modelled as a DEB product, i.e. as a function of metabolic fluxes, such as somatic growth and maintenance fluxes; 3. The existence of a temperature-driven effect on the dynamics of the precipitation of calcium carbonate for given conditions in the activities of ionic precursors; From these assumptions, a DEB-based otolith model is described relating the dynamics of the otolith growth and opacity to temperature and feeding conditions. An extension to the simulation of otolith images is presented. This model is shown to conform to a number of well-known facts on otolith. Besides, comparisons between model simulations and real otolith patterns are reported for different cases: otolith data from rearing experiments and otolith patterns from two different cod stocks, namely Barents sea cod and North Sea cod. This example illustrates the great potential of the proposed approach