Modelización de hábitats y poblaciones para la conservación de las aves marinas - habitat and population modelling for the conservation of seabirds

Abstract

ABSTRACT This PhD thesis aims to advance the knowledge about the ecology of seabird species in relation to their spatial distribution and their population trends within the framework of the marine protected areas. The results and conclusions obtained in this study seek to provide new information and real solutions to improve the conservation status of the sea. At the same time, they aspire to be practical tools that can be used by managers or researchers in making decisions concerning the protection, conservation and management of the marine environment. To this end, different spatial modelling techniques (kernel density analysis and generalised models) and demographic analysis (system dynamics models) have been applied to a long-term data series of bioindicator species of the marine environment (seabirds) within the framework of two marine protected areas: The Special Protection Area for Birds (SPA) Marine Area of the Gulf of Cádiz (Spain) and the Marine Area of the Berlengas Archipelago (Portugal). The results obtained show that the key area for the Balearic shearwater in the Gulf of Cádiz is located in shallow waters between the mouth of the Guadalquivir River and the marine area located off the Bay of Cádiz, and therefore, the delimitation of the current SPA covers less than 40% of this key area. Against this background, it is necessary to extend this marine protected area to the southeast of its current position to cover the entire key area identified for the species. In addition, the results highlight the need to use robust data over a long time period to consistently identify marine protected areas. In the second chapter, it is shown that abiotic variables, such as bathymetry or the distance to the Guadalquivir River, have turned out to be better predictors of the essential habitat of the Balearic shearwater compared to biotic factors, such as chlorophyll concentration. These results differ from those found by other authors in other areas of the species and indicate that in highly dynamic oceanic environments the spatio-temporal lag between primary production and consumers can alter the foreseeable direct relationships. In the third chapter, the distribution of the main species of seabirds in the Gulf of Cádiz is related to the food they consume. The results of the best models indicate that, for the main species, the distribution of seabirds is correlated and highly overlapped with that of small pelagic fish, their natural prey. In particular, the distribution of priority species, such as the Balearic shearwater, is determined by the presence of medium-sized anchovies and sardines in the Gulf of Cádiz. Other species do not show these correlations, which could indicate that they exploit other resources than the prey species studied. In the last chapter, it is demonstrated how the application of systems dynamics models to the Shag population in the Berlengas Archipelago SPA offers a very effective decision- making tool in the management of marine protected areas. In this sense, the simulations indicate invasive species such as rats and mortality associated with accidental capture due to fishing activity as the main threats to the Shag. Without applying any management measures, Shag population would decline by 7% in the Berlengas Islands in the next decade. However, this relict population could increase significantly if the archipelago is kept free of invasive carnivores and mitigation measures are applied to reduce bycatch. In the research carried out for this thesis, the usefulness of applying statistical models to the study of marine predator species as ecological indicators is demonstrated. In this case, the conservation of seabirds and the marine protected areas in the study area are essential for effective conservation and management of the marine ecosystem. Proof of this is the recent proposal to expand the Marine Area of the Gulf of Cádiz SPA, based on the results of this doctoral thesis, which has been accepted by the Ministry for the Ecological Transition and the Demographic Challenge within the framework of the LIFE-IP INTEMARES project.