(17-11-10) Scientists of the IEO have begun a campaign to match and tag swordfish with electronic systems to improve our knowledge about the species, understand their daily behaviour and contribute to the sustainable management of this fishery resource.

    On Tuesday November 9 a group of scientists of the oceanographic centres of the IEO in A Coruña and the Canary Islands began a marketing campaign whose main goal is to put 15 electronic tags to swordfish specimens. Those tags will send valuable information via satellite.

    The main purposes are to verify the daily behaviour of the swordfish regarding geographical position, temperature and depth, as well as their mortality rates after being tagged and rates of mixing of the different Atlantic stocks.

    In short, it is to improve the knowledge about their individual behaviour to integrate it in the process of assessment and ordering of the Atlantic populations within the framework of the ICCAT.

    The vessel used for this activity is a commercial longline fishing vessel of surface, based on Galicia, which has given all the facilities to scientists for the activity. During the commercial fishing operations scientists will work with swordfish alive that have the right conditions to be marked and then released guaranteed their survival.

    Once the pop-up tags are put on the specimens, these tags will automatically be released from the animals in about 12 months at maximum, after having registered continuously and having emitted stored information about their behaviour.

    The data, received via satellite, will be analyzed by the scientific staff of the IEO in the centres in A Coruña and Tenerife and it is expected that the first results will be in one year approximately.

    During this campaign they will also tag great pelagic species, such as sharks, billfish and other. All these activities can be considered highly profitable given the little investment and the interesting expected scientific results.

OTHER PREVIOUS EXPERIENCES

    Tag activities on tuna and similar species, and mainly on swordfish and associated species, have huge difficulties to be done, thus they have been restricted in many cases to opportunist activities, due to the lack of resources to rent commercial vessels. Oceanographic vessels is little appropriate for these fishing activities.

    However, despite the limitations, conventional and electronic activities have been done in the last decades, which have offered very interesting results at international scientific forums.

    In spite of the scarcity of resources, especially from two specific projects supported from the EU in the last decade, stock and blending hypothesis have been supported, hypothesis that would hardly arguable exclusively from tagging data by Western Atlantic countries.

    Besides the conventional tagging, the IEO has recently begun pop-up electronic tagging experiences on swordfish, since the electronic-file implanting tags are not viable to this species.

    Despite additional difficulties in tagging swordfish regarding other tuna or large pelagic, during the last years the IEO has carried out preliminary experiences in the Pacific Ocean (Abascal et al. 2009; Abascal et al., submmitted) and recently in the NE Atlantic through the IEO campaign of the acronym SWOTAG2008, whose results are being prepared right now.

    The first tentative in western Pacific and the second experience along with scientists of the CSIRO of Australia in Easter Pacific were very interesting regarding the obtained data. The campaign SWOTAG2008 in North-Central-Western Atlantic has allowed very interesting data that are being studied right now. However, the absence of tagging activities in NE Atlantic limits to draw conclusions on a global level of the entire North Atlantic.

    The campaign SWOTAG2010, which is begun now, wants to minimize these deficiencies in knowledge and to plan this sort of electronic tagging activities of this species for the first time in subtropical NE Atlantic.

ADDITIONAL INFORMATION ABOUT TAGGING

    Due to special characteristics of large pelagic, scientific research campaigns cannot be done, such as the acoustic or trawling campaigns carried out routinely for small pelagic and demersal species.

    Tagging this species has been one of the main sources of biologic and behaviour information, very useful to evaluate stocks, providing information on parameters related to growth, natural mortality and fishing, fisheries interactions, mixing with other stocks, etc.

    In the last years, the development of electronic tagging techniques has allowed to get a lot of information on individual behaviour and habitat preferences of different species, completely independent of the fisheries.

    In the campaign SWOTAG2010 they are intended mainly to tag as much as 15 specimens of swordfish with pop-up file-satellite tags. These tags are joined by a special monofilament plastic anchor that is inserted into the dorsal musculature of the fish with the help of a pole.

    The tags are programmed to file information bout depth, temperature and light level at intervals of 10 seconds in case the tag is recaptured. On the contrary, tags are programmed to come off by themselves one year after the tagging.

    Once this happens they will transmit the information summarized through a satellite ARGOS system, so there is no need to catch the fish again. That information consists mainly in histograms about the frequency of time at predefined intervals of depth, temperature and light curves.

    Based on previous experience, it is expected to get much information about the habitat preferences of swordfish in the North East Atlantic. This information can be used to predict individual behaviour and the vulnerability of the species regarding oceanographic conditions and make standardizations of the fishing effort.

    Another immediate result is the study of population structure, migration and the relationship between biological regions. The estimation of the routes the fish cover is done through recorded light levels: as a first step, the surface light is estimated from untreated light data and depth entries.

    Once they have the surface light curve, they can estimate time of sunrise and sunset, as the tugs incorporate an internal clock and, through them, a first estimation of location can be made. These locations are corrected later through a Kalman filter, comparing the data registered with bathymetry databases and sea surface temperature images got via satellite.

Text: M. Lozano / N de P