Age and growth of four spot megrim (Lepidorhombus boscii) in northern Iberian waters corroborated by cohort tracking

Age and growth are key biological aspects for the age-structured assessment of exploited fish populations. Confirming the consistency of fish age interpretation by validation/corroboration studies is essential for providing accurate age estimates to the stock assessment process. The Atlantic Iberian stock of four-spot-megrim (Lepidorhombus boscii), an important exploited demersal fish, is annually assessed by age-structured models in ICES, and specimens are routinely aged by IEO expert readers for this purpose. A total of 11,741 otoliths of this stock were aged from 23 annual groundfish surveys carried out in Cantabrian Sea and Galician waters (ICES Div. VIIIc, IXa) and following internationally standardized protocols. Annual 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 most of the time-series. The von Bertalanffy growth parameters for the time-series are estimated (L∞: 49.0; k: 0.13; t0: 1.13) and the results are compared with previous studies. The annual growth pattern estimated for L. boscii is here corroborated by tracking cohort abundance indices in the surveys. The current otolith age estimation criterion used and the resulting age estimates obtained by the age readers can be considered valid. Strong and weak cohorts are well tracked along most of their age classes, and the correlations between age abundance indices are statistically significant up to the age 6, which represent around 95% of the total number of this species caught in the surveys. The findings here presented on the age of L. boscii and its corroboration can help to reduce the uncertainty in the estimation of its demographic structure and hence, ultimately, it will be important for a better understanding of its relevance in the functioning of the benthic community of the shelf.Versión del edito

Hake recruitment in the southern stock (ICES divisions Vlllc and IXa).

Spatial distribution and year class strength for hake in the Southern stock (ICES Oivisions Vlllc and IXa) are analysed from historical series from spanish bottom trawl surveys (1980-1990). A nursery ground in the continental shelf of the northern coast of the Iberian peninsula is compared with the recruitment in adjacent areas (Portuguese and French waters)

Age determination procedures for benthic fish in Spanish Institute of Oceanography (IEO)

This handbook presents a summary of the age estimation procedures used in the Spanish Institute of Oceanography (IEO) for some of the main commercial benthic species of fish for the Spanish fleet: megrim (Lepidorhombus whiffiagonis), four spot megrim (Lepidorhombus boscii), white anglerfish (Lophius piscatorius), black anglerfish (Lophius budegassa). It provides information about the sampling program, the morphology of hard parts (otoliths and illicia), their extraction, preparation, and the age estimation criteria. A summary of information related to the accuracy, validation and corroboration of age of each species is also presented, as well as that related to the precision, quality control and verification of age

Four spot megrim (Lepidorhombus boscii) weight-length and weight-weight relationships in northern Iberian waters (stock 8.c, 9.a)

Total weight-length, gutted weight-length and total weight-gutted weight relationships were fitted for the Iberian Atlantic stock of four spot megrim (Lepidorhombus boscii) and their temporal variations were analyzed. The large sample size, size range and timeseries available allowed obtaining robust somatic parameters of combined sexes for the total weight-length relationships (a=0.0043, b=3.2008), for the gutted weight-length relationships (a=0.0055, b=3.1139), and the weight conversion factors (1.062). They are considered to best fit the current biometric relationships and most appropriate to be used in the stock assessment of the status of the stock and they contribute to a deeper knowledge of the life history traits of this species

Megrim (Lepidorhombus whiffiagonis) weight-length relationships in the northern Bay of Biscay and Celtic Sea

The weight-length relationships are of a great interest in fish biology, stock assessment and fishery management, by predicting weight from length information and allowing to estimate the stock biomass. Weight-length relationships of megrim (Lepidorhombus whiffiagonis), an economically relevant flatfish species, are studied for two decades (2001 to 2019) in northern Bay of Biscay and Celtic Sea (ICES stock Div. 7.b-k, 8.abd), two important European fishing areas. More than 22000 specimens collected from commercial landings by AZTI and IEO were sampled. Total fish length, total weight and commercial gutted weight were obtained. Four five-year periods (quinquennium) (2000-04; 2005-09; 2010-14; 2015-19) were defined in the studied time-series. Both the large sample size and time-series available, as well as the collaboration between both institutions collecting complementary information from this stock, allowed obtaining robust somatic parameters and analyzing their temporal variations. A weight-length relationship model was fitted and the quinquennium and semester factors, which are of interest biologically and for assessment purposes, and their interactions were significant in the preliminary model. The weight-length relationships, both for total and gutted weight and for the combined sexes of the most recent quinquennium are presented in this work and considered the most suitable to be used in the oncoming annual assessment process of the status of this stock in northern Bay of Biscay and Celtic Sea in ICES

Age estimation of megrim (Lepidorhombus whiffiagonis) corroborated by cohort tracking in northern Iberian waters

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

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

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