Age and growth of the brown meagre Sciaena umbra (Sciaenidae) collected (n = 532) in the north-western Adriatic Sea was studied by means of transverse otolith sections. The maximum age estimated was 19 and 16 years for males and females, respectively. The length at age estimated for each sex indicated that females attain a larger size and grow slightly faster than males. Both marginal increment analysis and edge analysis confirmed that annuli are formed once a year, with opaque zones laid down in summer (June-July). Age readings were very precise, with a percentage agreement of 98% between readers and low values of the index of average percent error (0.9%) and coefficient of variation (1.3%). Von Bertalanffy growth function was fitted to age-length data, and growth parameters were estimated for males (L ∞ = 44.9 cm; k = 0.27, t 0 = −2.17 years) and females (L ∞ = 47.2 cm; k = 0.28, t 0 = −1.82 years). In both sexes of brown meagre, growth rate was high until they attain 2-3 years of age, i.e. at sexual maturity. Most of catches were obtained in late summer-early autumn. On the basis of present data, the sampled population of brown meagre mostly consisted of small fish younger than three years of age (about 90%). In addition, landings of this species in recent years largely decreased. As reported elsewhere in north-western Mediterranean, brown meagre stock in the Adriatic Sea showed clear signs of depletion, thus specific management measures for this species are urgently required.
SUMMARY:Analytical stock assessment of sardine (Sardina pilchardus, Walb.) in the Adriatic Sea from 1975 to 1999 was performed taking into account the occurrence of discarding at sea of sardine caught by the Italian fleet. We have attempted to model the fishermen's behaviour using data collected by an observer on board fishing vessels. This enabled us to estimate the amounts of discards, which were added to the catches landed, collected by ISMAR-CNR Ancona. Discards were calculated for the period 1987-1999, as their values were negligible before 1987. Stock assessment on the entire data series from 1975-1999 was carried out by means of Virtual Population Analysis (VPA). Discarding behaviour differs among ports due to different local customs and market conditions. The quantity added to the annual total catch ranged from 900 tonnes to 4000 tonnes, corresponding to between 2% and 15% of the total corrected catch. VPAs indicated that mid-year sardine stock biomass rose steadily from 400,000 tonnes in 1975 to a peak of 950,000 tonnes in 1984. Subsequently, biomass declined steadily to the more recent values, around 300,000 tonnes. Although discarded quantities were relatively high, their influence on stock assessment was not strong because of the high level of both catch and, in particular, estimated biomass at sea.Keywords: sardine, Adriatic Sea, discards, observer data, regression tree models, stock assessment, population dynamics methods, Virtual Population Analysis (VPA).RESUMEN: EVALUACIÓN DEL ESTOC DE SARDINA DEL MAR ADRIÁTICO (SARDINA PILCHARDUS WALB.), ESTIMANDO LOS DES-CARTES. -Se realizó una evaluación analítica del estock de sardina (Sardina pilchardus, Walb.) del mar Adriático, desde 1975 a 1990, considerando los descartes de sardina realizados por la flota italiana. Se ha intentado modelar el comportamiento de los pescadores utilizando los datos recogidos por un observador a bordo de los barcos de pesca. Ello nos ha permitido estimar las cantidades descartadas y añadirlas posteriormente a los datos de desembarcos recogidos por ISMAR-CNR Ancona. Se calcularon los descartes para el período 1987-1999, ya que los valores eran insignificantes antes de 1987. Se realizó la evaluación del estock de sardina por medio del Análisis de Poblaciones Virtuales (VPA), aplicándolo a toda la serie de datos desde 1975 a 1999. El comportamiento en el descarte varía entre puertos debido a las diferentes costumbres locales y a las condiciones de mercado. La cantidad añadida a la captura total anual varía entre 900 y 4.000 toneladas, que corresponden al 2% y 15% respectivamente, del total de la captura corregida. Los VPAs indican que la biomasa del estock de sardina aumentó de manera constante de 400.000 toneladas en 1975 a un máximo de 950.000 toneladas en 1984. Posteriormente, la biomasa disminuyó de forma continuada hasta alcanzar valores aproximados de 300.000 toneladas en la actualidad. Aunque las cantidades descartadas fueron relativamente altas, su influencia en la evaluación del estock de sardina no parece ser importan...
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