Calibration and validation of an algorithm for remote sensing of turbidity over La Plata river estuary, Argentina

The La Plata River, located at 35°S on the Atlantic coast, is one of the largest waterways of South America. It carries a large amount of suspended particulate and dissolved organic matter, and is considered among the most turbid waters of the world. Very high values of total suspended matter have been reported in this region, with mean values ranging from 100 to 300 g m-3 and extreme concentrations up to 400 g m-3. Satellite sensors have shown to be the best tools available to map river plumes and to study their influence on the adjacent ocean. However, global algorithms for remotely estimating sediment concentration are not currently available. Moreover, such high sediment loads represent a challenge to atmospheric correction algorithms which usually rely on the assumption of zero water-leaving reflectance in the near infrared or short wave infrared part of the spectrum (black pixel assumption). In the extremely turbid waters of La Plata Estuary such assumptions are not valid. A two band algorithm to estimate turbidity using near infrared and the short wave infrared bands (858 nm and 1240 nm) of the MODIS-Aqua sensor is presented. The model is calibrated using in situ reflectance and turbidity measurements from turbid waters of the Southern North Sea and Scheldt River (Belgium) and then applied to MODIS imagery of La Plata River estuary (Argentina). A good correlation was found between modelled and in situ turbidity values when the algorithm was applied to concurrent MODIS imagery. Moreover, satellite-derived turbidity maps show a spatial distribution of sediment consistent with patterns and characteristic features of the estuary

Spawning and fecundity of the white croaker Micropogonias furnieri Desma rest, 1823 of the Rio de la Plata estuary, Argentina

Se estima la fecundidad parcial y relativa de la corvina rubia Micropogonias furnieri Desmarest, 1823 del Río de la Plata, se calcula su frecuencia reproductiva y se analizan los movimientos de los grupos desovantes durante la reproducción. El estudio se realizó en la zona común de pesca argentino-uruguaya (Atlántico sudoccidental, 34°-39° 30'S) durante el mes de noviembre. Se utilizaron 373 hembras para el análisis histológico de los ovarios, de las que se seleccionaron 31 ejemplares en estadio de hidratación ovocitaria para la determinación de la fecundidad a partir del conteo de ovoritos hidratados por el método gravimétrico. La frecuencia reproductiva se estimó calculando el porcentaje de hembras con folículos postovulatorios en las muestras. El desove de la corvina rubia se concentra en el sector interno del estuario del Río de la Plata en coincidencia con el frente salino de fondo. En el resto del estuario las hembras se encuentran activas, en fase de recuperación gonadal, desplazándose posteriormente hacia el sector interno, donde completan la maduración y desovan. La frecuencia reproductiva promedio fue de 12 días; la fecundidad parcial varió entre 50 000 y 750 000 ovocitos para un rango de tallas entre 31 cm y 62 cm de longitud total, observándose un ajuste de tipo potencial en relación con la longitud total y un ajuste lineal en relación con el peso total (libre de ovamos). La fecundidad relativa presentó un valor promedio de 232 ovocitos por gramo de hembra (libre de ovarios), encontrándose una relación positiva con la talla de los ejemplares.Relative fecundity, batch fecundity and spawning frequency of white croaker Micropogonias furnieri Desmarest, 1823 of the Rio de la Plata estuary were estimated. Displacements of the spawning groups during the reproductive season were also analysed. The study was carried out in the Argentine-Uruguayan Common Fishing Zone (South-west Atlantic, 34°-39° 3O'S), during November For the histological analysis of ovaries, 373 females were sampled. Thirty-one individuals with hydrated ovaries were selected for the fecundity estimates. The number of hydrated oocytes was determined with the gravimetric method, and the spawning frequency was estimated from the daily proportion of females with postovulatory follicles. Micropogonias furnieri spawns in the inner zone of the Rio de la Plata estuary, in coincidence with the bottom saline front. In the rest of the estuary, the individuals remain in the partially spent stage, moving afterwards to the inner sector where they reach maturity, and spawn. Mean spawning frequency was 12 days, and batch fecundity ranged between 50000 to 750 000 oocytes for females between 31-62 cm, total length. The relationship of batch fecundity vs total length presented a better fit to the potential model, while the regression batch fecundity vs total weight (ovary-free) was lineal. The mean relative fecundity was 232 oocytes per female gram (ovary-free), showing a positive relationship with total length.Instituto Español de Oceanografí

Bycatch of franciscana dolphins Pontoporia blainvillei and the dynamic of artisanal fisheries in the species' southernmost area of distribution

Na Argentina, a toninha é um dos cetáceos mais vulneráveis devido às capturas por rede de pesca artesanal. O presente estudo teve como objetivo estimar as capturas acidentais no sul da província de Buenos Aires, através de entrevistas aos capitães de barcos de pesca artesanal, entre os anos 2006-2009. As capturas foram reportadas para redes de emalhe e de camarão; com as mais altas frequências entre outubro e fevereiro, a 5 km da costa e 10-20 m de profundidade. A mortalidade acidental média anual estimada foi de 107 golfinhos (IC 95% = 87-129), 92 em redes de emalhe (IC 95% = 73-112) e 15 em redes de camarão (IC 95% = 8-25), com uma captura de 0,029 golfinhos/km de rede de emalhe (IC 95% = 0,023-0,036) e 0,024/rede de camarão (IC 95% = 0,012-0,035). As flutuações anuais responderam principalmente às diferenças nos dias de pesca. Considerando o último levantamento estimativo feito para o norte costeiro da província, estima-se uma mortalidade entre 360-539 golfinhos/ano em toda a província de Buenos Aires. Esses valores correspondem de 2,5-3,7% da abundância populacional da Argentina; o que traria como consequência um declínio populacional da espécie, tornando-se fundamental encontrar alternativas de pesca para a área.In Argentina, the franciscana dolphin is one of the most vulnerable cetaceans regularly entangled in coastal artisanal fishery nets. The aim of this paper is to estimate the species' incidental mortality on the Southern coast of Buenos Aires province through interviews with the captains of artisanal fishing vessels, in the period 2006-2009. Franciscana bycatch was reported for gillnets and shrimper gear all year round but it occurred more frequently between October and February, at 5 km offshore and 10-20 m depth. The estimated mean annual incidental mortality was 107 dolphins (CI 95% = 87-129), 92 caught in gillnets (CI 95% = 73-112) and 15 in shrimpers' gear (CI 95% = 8-25) with a capture per unit effort of 0.029 dolphins per km of gillnet (CI 95% = 0.023-0.036) and 0.022 per shrimpe r's net (CI 95% = 0.012-0.035). Annual fluctuations were due to differences in the number of gillnetting fishing days. If mortality estimates for the Northern coast are also taken into account, values attain a maximum of 360-539 dolphins bycaught in the entire Buenos Aires province, representing 2.5-3.7% of the species' abundance in Argentina. This will inevitably lead to the decline of franciscana dolphin populations in the near future unless alternative fishing grounds are identified and alternative gearadopted

Flota costera argentina: antecedentes y situación actual

Historic records of the coastal fleet, their evolution and present situation were analyzed. Coastal fishing was characterized and, according to ecologic and environmental parameters, divided into bonaerense and patagonic areas. Fleets participation in the coastal fisheries of the Province of Buenos Aires and characteristics of coastal fishing fleets of the different argentinian harbors were analyze