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Cooler Water Temperatures Delays Spawning Med Bluefin

Low water temperatures could have delayed the spawning stage of bluefin in the waters of the Balearic Sea this year, according to Spanish scientists.

A study that will run until 2014 is conducted by researchers and technicians from oceanographic centers in Balearic Islands and in Malaga of the Spanish Oceanographic Institute (IEO) and of the Coastal Observing System of the Balearic Islands (Socib), as part of the BlueFin project annual season. The team aims to record oceanographic parameters and obtain water samples and those of various types of plankton that are adequate and sufficient for parameterization and validation of models to predict the location of spawning areas and tuna larval survival rate.

It is thought that this will allow for the application of management systems that may optimize the capture of bluefin tuna and the health of its stocks.

The researchers hope to locate, measure and monitor developments through intensive sampling along the daily cycle of at least one high density Atlantic bluefin tuna larvae set, while also trying to locate the regions where post-larvae can be found. 

The specific objectives of the survey are:
• To determine the influence of the hydrographic scenario on the Atlantic bluefin tuna larvae stock structure, distribution and status in the Balearic Sea;
• To assess the reliability of the spawning habitat models that have already been developed for the species, including early versions of the operating model;
• To define the trophic ecology of Atlantic bluefin tuna larvae and post larvae in the Balearic Sea, considering both its direct or indirect relationship with other planktonic groups such as the interactions among the tuna larvae of the different species and sizes;
• To calculate a larval index for estimating the reproducer stock biomass;
• To get calibration coefficients for standardizing the results obtained in quantitative sampling of tuna larvae with different types of fishing nets and methodologies;
• To determine the environmental influence on the vertical structure of tuna larval stocks.

It was found that this year water temperatures are around two degrees lower than usual for this time.

The hydrographic scenario also has different characteristics: due to a strong blocking of the circulation in the Ibiza Channel, the Atlantic surface waters do not reach the south of the Pitiusas Islands as it often happens at this time but they go around the islands in the south and head for the Cabrera zone.

These circumstances seem to have had a direct impact on the spatiotemporal distribution of bluefin tuna spawning in the Belaric waters.