2 alumnos del Máster de Ecología Marina de la UIB defienden su tesis de máster

Dos alumnos del Máster de Ecología Marina de la UIB defienden su tesis de máster en el Centro Oceanográfico de Baleares

Hoy, 29 de julio de 2015, los alumnos del Máster de Ecología Marina de la Universitat de les Illes Balears, Laura Oliver y Vicenç Moltó, han defendido sus respectivas tesis de máster en la sede del Centro Oceanográfico de Baleares. A continuación se presentan los abstracts de cada una de las defensas.

• Comparación de dos métodos no invasivos para la caracterización de comunidades profundas : ROV vs SUB. Laura Oliver.

  

  Abstract: Marine ecosystems are in constant degradation and in order to relieve the loss of the habitats multiple regulations and proposals have been enforced by the law. The characterization of the deepest habitats has been the first link to follow for having a good arrangement, and video systems have been the most effective method to evaluate the good environmental conditions. Currently the application of these methods is based in two systems: remotely operated vehicles (ROV) and the use of autonomous underwater vehicles (AUV). The aim of this study is to compare the two methods for a subsequent analysis about the deep benthonic communities. One of the key points of this research is to set up on the high capacity of georeferenced underwater transects by Tracklink systems. This project has been focused on comparing abundances, density and size structure of habitat forming macrospecies from transects spatially located in the same position. The goal of the former comparison is to assess whether there are differences between the two methods. Surprisingly there have been significant variances within the two processes, although transects were geographically in the same position. Two possible hypothesis have been revealed: the first one unfolds that the positioning systems are not accurate enough to carry out a long term monitoring of deep populations; and the second one discloses that both methods have highly divergent characteristics for the evaluation of structural benthic communities.

• Tracking a high density bluefin tuna larval patch: development of methodologies to calculate daily mortality and growth rates. Vicenç Moltó.

  

  Abstract: The Atlantic bluefin tuna (Thunnus thynnus) is a highly migratory species whose Eastern stock enters in the Mediterranean at the end of spring to spawn, being the waters around Balearic Islands one of their main spawning grounds. The breeders of this stock were heavily fished for decades, mainly from the seventies, due to their high market price, which produced a sharp decrease of the spawning stock biomass. Despite strict protective measures established from 2007 have resulted in an apparent recovery of the stock in the last years, the available fishery-dependent data are not enough for obtaining accurate evaluations of the real state of the stock. Thus, fishery independent indices, as for example larval indices, are required to improve stock evaluations. Within this context, this study aims for a better parameterization of the algorithms used for larval index calculation. Specifically, we have focused on determining daily mortality and growth rates, developing tools for obtaining more precise estimations of these ecological parameters. In order to do so, a high density bluefin tuna larval patch was tracked with a Lagrangian drifter and sampled intensively during 52h approx. There were good correlations between geostrophic currents, the drift of the buoy and the position of the patch, which allowed its characterization and the estimation of growth rates and daily mortality rates for the different subcohorts sampled within the patch. Growth rates ranged between 0.40 and 0.65 mm/day approx., which are in accordance with growth rates obtained for other tuna species. Daily mortality rates were estimated to be 0.78 and 0.86 day -1 for the smaller and larger subcohorts of the patch, respectively. However, other parameters such as dispersion and catchability variations along ontogeny should be taken into account for more accurate estimations. In addition, this type of studies should be carried out on different cohorts along the spawning season and covering the whole larval sizes range, in order to get mean values of these parameters, which would constitute the next steps of this line of research.