Bluefin tuna SOCIB-IEO cruise in the southern waters of the Balearic Islands
As part of the BLUEFIN Project, which is taking place between 2011 and 2014 under the specific collaboration agreement signed to this effect between the Spanish Institute of Oceanography and Coastal Observing System of the Balearic Islands, IEO and SOCIB researchers set off on the Bluefin 0613 cruise aboard the R/V SOCIB. The overall objective was to obtain in situ data, by launching surface drifters and performing selective larvae fishing, for the parameterization and validation of predictive models to locate spawning areas and larval survival of bluefin tuna in the Balearic Sea. Thus, the specific objectives of this campaign were:
- Determine the influence of hydrographic scenario in the structure, distribution and condition of larval populations of Atlantic bluefin tuna in the Balearic Sea.
- Evaluate the reliability of the models developed and spawning habitat for the species, including early versions of the operating model.
- Define the trophic ecology of larvae and post-larvae of Atlantic bluefin tuna in the Balearic Sea.
- Calculate a Larval Index for estimating spawning stock biomass.
- Get calibration coefficients for standardizing the results obtained in samples of tuna larvae with different types of fishing nets and methodologies.
- To determine the environmental influence on the vertical structure of tuna larvae populations.
In the first phase, developed between June 20th and July 7th, the scientific team took out a systematic planktonic sampling of 120 stations using Bongo 90/60/20 nets, as well as hydrographic profiles and water sampling with a CTD rosette equipped with Niskin bottles. On a second phase the cruise sought to locate, measure and monitor the development, through intensive sampling during the diurnal cycle, a high-density spot of Atlantic bluefin tuna larvae and locate the presence of post-larvae areas, carrying out intensive icthyoplankton hauls.
The objectives for the campaign have been covered at a good pace and the first data obtained allow to advance that this year is an anomalous year regarding the number of summer campaigns in the same area since 2001, since the surface water temperature is about two degrees lower than usual for this season. The hydrographic scenario has also different characteristics due to a strong blocking of the circulation in the Ibiza Channel due to the presence of resident surface waters eddies, which make that Atlantic surface waters do not reach the southern part of Ibiza and Formentera, as often happens at this time, but flow around the islands to the south of Cabrera archipelago. All this factors seems to have directly influenced the spatio-temporal patterns of bluefin tuna spawning area in the Balearic Islands.
These results will contribute to achieve the project's strategic objective: to provide scientific information relevant to the design and implementation of management systems to optimize the exploitation of Atlantic Bluefin tuna stock, so as to promote and maintain a good state of the populations.
