Stock assessment of sardine (<i>Sardina pilchardus</i>, Walb.) in the Adriatic Sea with an estimate of discards

Abstract

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...

Application of a bioeconomic model for supporting the management process of the small pelagic fishery in the Veneto Region, northern Adriatic Sea, Italy

“…Discarding does not occur in relevant quantities, as declared by the operators and confirmed in Santojanni et al (2005), so fishing mortality due to discards was not included in the model.…”

“…Fishing for other pelagics and also "white fish" (Sparidae, Mugilidae, Merlangus merlangus, etc.) takes place occasionally and opportunistically, but it is considered rather rare (Santojanni et al, 2005). The bioeconomic model called MEFISTO is a multispecies, multifleet and multigear simulation model described in detail in Lleonart et al (1999Lleonart et al ( , 2003.…”

“…Small pelagic fisheries play significant economic and social roles in the total value of catches and the number of fishermen employed within the industry. These two small pelagic species have shown important fluctuations in abundance over the last 30 years in the northern and central Adriatic Sea (area 17 of the General Fisheries Commission for the Mediterranean), with a near-collapse of the anchovy stock in the late 1980s (Santojanni et al, 2003;2007a) and a steady decline of the sardine stock in recent years (Santojanni et al, 2005;2007b). Although large fluctuations of small pelagics stocks are well-known and environmentally-driven in many cases (Patterson, 1992;Cushing, 1996), in the case of anchovy and sardine of the northern and central Adriatic, the values of fishing mortality were outside precautionary levels, coinciding with the periods of near-collapse of stocks (Santojanni et al, 2007a, b).…”

Regional management of multi-species fisheries on the basis of shared stocks and property rights: a Mediterranean case

“…Landings of purse seiners are usually of better quality (fishes are less damaged) and can get a higher price than the landings of trawlers. Discarding by the Adriatic small pelagic fishery has been investigated very little; Santojanni et al (2005) concluded that moderate discarding of sardine can be found in specific geographic zones when the length of the fish is smaller than the market requirements. However, they described fishermen behaviour before the year 2000.…”

An observing system for the collection of fishery and oceanographic data

“…After FOS data were collated, the next step consisted in estimating an index of relative fish abundance. To do this we followed the classical method based on the use of catch and effort data (Richards and Schnute, 1992;Goñi et al, 1999;Campbell, 2004;Santojanni et al, 2005). MFSTEP satellite and model products were selected and used as explanatory variables.…”