Five-millimetre length bluefin larvae. (Photo: IEO / Fernando de la Gandara)

Oceanographic structures condition bluefin tuna spawning in the Mediterranean

SPAIN
Wednesday, January 16, 2013, 02:10 (GMT + 9)

Spanish scientists discovered that there is a clear relationship between the spawning areas of bluefin tuna in the Mediterranean Sea and the oceanographic structures.

That is one of the main conclusions of a study on the regional scale spatial distribution of spawning areas of three tuna species of major economic importance in the Mediterranean Sea: bluefin, albacore and bullet tuna.

The research was conducted by a team of researchers from the Balearic Oceanography Centre of the Spanish Institute of Oceanography (IEO), in collaboration with the Balearic Islands Coastal Observing and Forecasting System (ICTS SOCIB) and the University of Corvallis, Oregon (US).

Scientists analyzed data obtained from biological and hydrographic oceanographic surveys carried out for five years and found a difference in the factors that influence the distribution of the spawning areas of the three species in the Balearic Sea.

They found that the main spawning areas for bluefin tuna (Thunnus thynnus) are clearly associated with certain oceanographic structures, mainly related to the location of the fronts separating waters of recent Atlantic origin (which go into the Strait of Gibraltar and move up to Balearic Islands) and residents waters, which can vary each year, according to the IEO.

Likewise, they found that the spawning areas of albacore tuna (Thunnus albacares) are also associated with oceanographic structures, but in this case with changes induced by topography that are annually built in the same areas.

Both the blufin and albacore tuna primarily spawn in deep water, unlike the bullet tuna (Auxis rochei), which usually lays eggs in more coastal areas, where adults usually live.

During the investigation, the team also managed to better define the spawning season of these resources:

• Bluefin tuna spawns primarily between mid-June and July;
• Albacore tuna lays eggs later, in late July and early August;
• Bullet tuna has a longer spawning period, from June to August, without so marked peaks.

"The differences in the distribution pattern of the spawning grounds of the three species allow us to elucidate their possible migration routes: from the Atlantic to the Mediterranean Sea for the bluefin, across the Mediterranean for the albacore and from the coastal areas for the bullet tuna," the authors explained.

They also determined that bluefin tuna largely bases itself on environmental signals, so tits spawning habitats may vary depending on the environment. Instead, the spawning habitat of albacore and bullet tuna is primarily conditioned by geography.

This study was developed in the framework of the Larval Ecology and Recruitment Processes of Decapod, Cephalopods and Teleost Fishes project in the Balearic Sea and was funded by the National R&D&i Plan of the Ministry of Economy and Competitiveness.

By Analia Murias
editorial@fis.com
www.fis.com

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