This paper proposes a vector sensor measurement model and the related Bartlett estimator based on particle velocity measurements for generic parameter estimation, illustrating the advantages of the Vector Sensor Array ͑VSA͒. A reliable estimate of the seabed properties such as sediment compressional speed, density and compressional attenuation based on matched-field inversion ͑MFI͒ techniques can be achieved using a small aperture VSA. It is shown that VSAs improve the resolution of seabed parameter estimation when compared with pressure sensor arrays with the same number of sensors. The data considered herein was acquired by a four-element VSA in the 8-14 kHz band, during the Makai Experiment in 2005. The results obtained with the MFI technique are compared with those obtained with a method proposed by C. Harrison, which determines the bottom reflection loss as the ratio between the upward and downward beam responses. The results show a good agreement and are in line with the historical information for the area. The particle velocity information provided by the VSA increases significantly the resolution of seabed parameter estimation and in some cases reliable results are obtained using only the vertical component of the particle velocity.

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The life cycle of the red swamp cray sh, Procambarus clarkii from a shallow lagoon in the Aveiro region was studied for 14 months. Analysis of the size frequency distribution and growth provided evidence for an extended recruitment period with a peak in autumn (October/November). Females clearly outnumbered males and the average sex-ratio (males/females) was 0.36. The values for the Von Bertalanffy growth parameters were L 1 D 62:01 mm, K D 0.23, and t 0 D 0:11 month. The high abundance of this species and the extended recruitment period, support the need for a proper management and exploitation of this biological resource. RESUMO O ciclo de vida do lagostim-vermelho-da-Louisiana Procambarus clarkii da ria de Aveiro foi estudado ao longo de 14 meses. A análise da distribuição das frequências de tamanho e de crescimento mostrou um período de recrutamento extenso com um máximo no Outono (Outubro/Novembro). As fêmeas ocorreram com maior abundância que os machos, o que se traduziu numa proporção de sexos (machos/fêmeas) de 0,36. Os valores calculados para os parâmetros de crescimento de Von Bertalanffy foram L 1 D 62,01 mm, K D 0,23 e t 0 D 0,11 mês. A elevada abundância desta espécie e o largo período de recrutamento apontam para a necessidade de uma adequada gestão e exploração deste recurso biológico.

For 2 years, the flatfish community of Minho estuary (Northwest of Iberian Peninsula) was surveyed monthly with a beam trawl. Flounder, Platichthys flesus, was the most representative species contributing the most (74%) to the total flatfish abundance and was the only species occurring throughout the sampling period and along the entire salinity gradient. The majority of flounder sampled consisted of 0-and 1-year group individuals. In both years, a peak in abundance was recorded in late spring-summer months (from May to August) which coincided with seasonal settlement events. Higher densities of newlysettled flounder were obtained in the most upstream site, located in the tidal freshwater wetland, indicating that this area is an important nursery area. Of the environmental variables tested, temperature and salinity were the best predictors for 0-year group abundance explaining around 30% of the variability, whereas sediment was also important when considering all age groups together. This study supports the generally prevalent idea that estuaries act as nurseries for the early life stages of flounder, with particular relevance to the tidal freshwater estuarine wetlands.