Gordoa, A., Olivar, M. P., Arevalo, R., Viñas, J., Molí, B., and Illas, X. 2009. Determination of Atlantic bluefin tuna (Thunnus thynnus) spawning time within a transport cage in the western Mediterranean. – ICES Journal of Marine Science, 66: 2205–2210. For the first time, tuna spawning in a transport cage being towed from the western Mediterranean spawning ground to a fattening facility off the coast of northeastern Spain was examined during the 2008 fishing season. Daylight and night surface plankton samples were collected using bongo nets located in front of and behind the transport cage. The results for the different time intervals revealed clear and massive nocturnal spawning from 03:00 to 05:00, when the rear bongo was completely jammed with eggs (up to 250 000–300 000 eggs per 1000 m3). Egg size and morphology were consistent with the features of Thunnus thynnus eggs, and identification was confirmed by genetic analysis. Microscopic examination showed the eggs to be in the very early developmental stages. Spawning took place every night over the entire journey. The study showed that neither captivity nor handling/environmental changes along the route inhibited T. thynnus spawning to a very precise biological clock. The study also revealed the diel temporal concurrence of T. thynnus spawning and jellyfish larvae at the sea surface.
SUMMARY: We address the major surface signatures of chlorophyll a in the Catalan Sea within the context of the dynamics of the north-western Mediterranean basin. Monthly composites from MERIS measurements and CHL products for Case 1 waters were analysed from June 2002 to June 2005. Composite images of variability were used to identify surface dynamics. The results showed that coastal and open sea waters were separated by a belt of low variability, a permanent oligotrophic belt that is noticeable with respect to the bloom conditions of the surrounding areas. The width of this Catalan Oligotrophic Belt (COB) located along the continental slope, varied between 17 and 30 km and became blurred in the southernmost area. The chlorophyll a temporal pattern over the shelf showed an almost steady increase from September to March. A similar behaviour but with lower concentrations was observed in oceanic waters. Both temporal patterns showed a disruption during January and/or February that coincided with the well known deep water formation event in the Gulf of Lions. In 2004, the convection was weaker and the offshore temporal trend was not disrupted; however, the opposite was observed in 2005. The spatial chlorophyll a distribution of oceanic waters presented a clear north-south decreasing trend, while the coastal distribution did not show any latitudinal patterns but rather peaks in the areas enriched by river runoff. The observed seasonality was similar to the one published from SeaWiFS data and slightly different from the seasonality shown by CZCS data. Nevertheless, we did not discard the possibility that some of the observed seasonal differences could be a true temporal shift in chlorophyll a production.Keywords: north-western Mediterranean, chlorophyll a, remote sensing, MERIS.RESUMEN: Patrones espacio-temporales de clorofila en el Mediterráneo Noroccidental derivados del sensor MERIS. -En este estudio se examinan los principales patrones en la distribución superficial de la clorofila a en el marco explicativo de la dinámica del Mediterráneo Noroccidental. Para identificar la dinámica en superficie se compusieron imágenes de variabilidad. Los resultados mostraron que entre las aguas costeras y oceánicas se diferenciaba un cinturón de baja variabilidad, permanentemente oligotrófico y visible cuando en las aguas circundantes se producía proliferación algal. La amplitud del Cinturón Oligotrófico del mar Catalán (COB), localizado a lo largo del talud continental, oscilaba entre 17 y 30 km, disipándose en la mitad sur. El patrón temporal de clorofila en la zona de plataforma mostró un claro aumento de septiembre a marzo. Un patrón similar se observó en la concentración superficial en aguas oceánicas. En ambas regiones se observó una interrupción del patrón temporal en enero y/o febrero, coincidiendo con el momento de formación de agua profunda del Golfo de León. En el 2004 el fenómeno de formación de agua profunda fue más débil y el patrón mensual en la región oceánica no sufrió ninguna interrupción, al contrario que en e...
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