Mª Ángeles Peña asiste al WGFAST del ICES

Una investigadora del Centro Oceanográfico de Baleares del IEO asiste a la reunión anual organizada por el ICES "Working Group on Fisheries Acoustics Science and Technology" que se ha celebrado en San Sebastián (España) entre los días 16 a 19 de abril de 2013.

El Grupo WGFAST del ICES se centra en el desarrollo y aplicación de la ciencia y la tecnología (equipos acústicos y otros sensores) que se utilizan para observar el medio ambiente marino.

En respuesta al plan estratégico del ICES 2009-2013, WGFAST trabaja en la contribución de los métodos acústicos y complementarios a los objetivos de un enfoque ecosistémico con observaciones bentónicas y pelágicas para mejorar la evaluación y gestión de los recursos marinos vivos, los mecanismos de comprensión y los procesos de cambio y estabilidad y parametrizar y evaluar modelos de estructura y función del ecosistema. Se abordan cuatro categorías principales de trabajo: 1) Aplicación de los métodos acústicos para caracterizar los ecosistemas. 2) Propiedades acústicas de los organismos marinos. 3) Comportamiento y 4) Tecnologías emergentes, metodologías y protocolos.

Durante la reunión Mª Ángeles Peña presentó las dos comunicaciones de las que es primera autora, de las tres presentadas en el marco de los proyectos JUVENA y MAFIA.

• Acoustic properties of juvenile anchovy (Engraulis encrasicolus) in the Bay of Biscay. Marian Peña and Enrique Nogueira.

  Abstract: Since 2006 the Spanish Institute of Oceanography performs an autumn survey target-ing juvenile anchovy (Engraulis encrasicolus) in the Bay of Biscay. Data from a Simrad EK60 with five frequencies (18, 38, 70, 120, and 200 kHz) from the 2009 survey is employed for a multifrequency analysis of the anchovy backscattering. Differences with sizes and depth are evaluated. Four simple backscattering models accounting for depth, tilt angle, swimbladder and body physiology are developed, and com-pared with observed values by means of an unsupervised neural network, the Self-Organizing Map. A revision of the inversion method is considered for the inference of anchovy sizes; several metrics and optimizers are compared and discussed. Tech-niques to facilitate convergence and frequency weighting are explored.

• Analysis of the acoustic discrimination of krill. Marian Peña, Lucio Calise and Enrique Nogueira.

  Abstract: Acoustic discrimination of different species is often performed by comparison of the frequency response or dB difference of all the available frequencies with respect to the 38 kHz response. For krill species is common to discriminate based exclusively in the difference between the 120 and 38 kHz frequencies. More recent papers warn on the variation of this pair of frequencies difference with length. After a revision of the literature, we investigate the variability of this difference with orientation, physiology, and length, employing the state of the art model for this species, the Stochastic Distorted Wave Born Approximation. Two scenarios of mixed species are simulated (krill and mesopelagic fish, krill and juvenile anchovy), and their discrimination examined with an unsupervised organizing map in order to evaluate the number and frequencies necessaries, considering the usual working frequencies.

• Spatial dynamics and shoal behavior of juvenile anchovy (Engraulis encrasicolus) in the Bay of Biscay. Guillermo Boyra, Enrique Nogueira and Marian Peña.

  Abstract: In the year 2009, two consecutive acoustic surveys targeting juvenile anchovy were carried out with a delay of about three weeks in the Bay of Biscay. In total, about 45 sampling days under stable meteorological and hydrographical conditions between early September and mid October, made possible to monitor the changes on spatial distribution and shoal aggregation patterns of this species. In the first survey, juveniles were seen spread over a large area on the oceanic and slope waters, while in the second one, three weeks later, the spatial distribution moved towards the coast but without entering the continental shelf, thus compressing into a narrower band parallel to the shelf break. Also, the vertical distribution was seen to change by increasing its mean depth. On the other hand other behavioral changes were also observed. The shoal aggregation patterns changed from diffuse and small near surface aggregations to increasingly denser and larger schools that appeared more reactive to the vessels. Towards the end of the sampled period, anchovy juveniles and adults were found mixed together in some locations of the outer French shelf.