Corroboration of age estimation of megrim (Lepidorhombus whiffiagonis) in northern Iberian waters by cohort tracking.

Abstract

To confirm the consistency of the age interpretation by validation studies is essential for providing accurate age estimates to the stock assessment process using age-structured models. The Atlantic Iberian megrim (Lepidorhombus whiffiagonis) stock is annually assessed by age-structured models in ICES, and specimens are routinely aged by IEO expert readers for this purpose. A total of 8845 otoliths of this stock were aged from 23 annual groundfish surveys carried out in north and northwestern Iberian waters (ICES Div. VIIIc, IXa) and following internationally standardized protocols. Yearly age-length-keys were built using the respective age estimates and applied to the length distribution of each survey, thus obtaining a matrix of abundance indices by age and year. Similar mean lengths are obtained for each age group along the time series. The annual age estimation of L. whiffiagonis is here indirectly validated by tracking cohort abundance indices in the surveys. Strong and weak cohorts are well tracked along the most of their age classes, and the correlations between age abundance indices are statistically significant up to the age 5, which represent around 94% of the total number of this species caught in the surveys. The von Bertalanffy growth parameters for the time-series are estimated (L∞: 56; k: 0.12; t0: -1.88) and the results are compared with previous studies