Which are the main threats affecting the marine megafauna in the Bay of Biscay?

Abstract

The marine environment faces an increasing number of threats, mainly driven by anthropogenic activities, that are causing growing impacts on marine species and processes. In Europe, the EU Marine Strategy Framework Directive (MSFD) aims to achieve or maintain Good Environmental Status (GES) of the European waters by 2020. The Directive specifically refers to biodiversity with the first of the eleven qualitative descriptors (proposed to help describe what GES should look like) being Biodiversily is maintained. For this descriptor, the status of several functional groups, including marine megafauna species, need to be assessed using criteria such as population size and condition, and mortality due to bycatch in fishing gear, that compare current values against agreed thresholds. To contribute to this process, we performed an assessment of the threats affecting the marine megafauna community (i.e. seabirds and cetaceans) in the Bay of Biscay synthesizing the available evidences and identifying the main threats affecting the marine megafauna to help prioritise the required management and conservation actions. We analysed 4,023 admissions of seabirds recorded during 2004-2016 from four Wildlife Rehabilitation Centres to obtain an initial quantitative assessment of the pressures exerted on seabirds. The main marine threats identified in the Spanish North Atlantic sub-region were cachexia (52.3\%), exposure to crude oil (10\%) and interaction with fishing gears (5.3\%). When considering all threats together, the common guillemot, the yellow-legged gull, the northern gannet, the great cormorant and the razorbill were the main affected species. In addition, we summarised the available information to perform an updated qualitative assessment of the severity of the threats faced by seabirds and cetaceans. The qualitative assessment showed that cetaceans are especially vulnerable to bycatch, vessel collision, and pollution-related threats, whilst seabirds are particularly sensitive to oil spills, bycatch and marine litter. This type of assessment studies can aid in the identification of priority areas and/or species where management measures should be applied to ensure that the ultimate goal of the MSFD, sustainable conservation of the marine environment, is reached.