Tropical seabirds as indicators of Human stressors and as tools for marine spatial planning in the Tropical Atlantic

Abstract

Anthropogenic pressures on the marine environment have long impacted the marine ecosystems and its associated species. All over the world, seabird populations are affected by these pressures, with significant population declines on all taxa. To attenuate these populational declines and ensure associated ecosystem conservation, researchers use tracking devices to identify areas of important seabird conservation, while distinguishing areas of high human pressure where urgent management is needed. Thus, in this thesis I used fishermen perceptions and vessel tracking with species distributions to identify species that are more prone to fishery bycatch, while using seabird multi-species tracking data to designate areas of marine conservation (Key Birds and Biodiversity Areas – KBA) inside the Cabo Verde islands Exclusive Economic Zone (EEZ). Main results of this thesis are: (1) the debate of the current knowledge on the identification of indicator species and biodiversity hotspots which are important for marine spatial planning and design of Marine Protected Areas (MPAs) (Chapter 1); (2) fishermen’s’ observations indicated Cabo Verde shearwaters as having the highest risk of bycatch in the Cabo Verde fisheries, associated with artisanal handlines, closely followed by brown boobies and red-billed tropicbirds. Additionally, while fish-landing changes occurred due to variables affecting the marine food web, shearwater chick development was also correlated with changes in fish-landings influenced by prey availability in the ocean (Chapter 2); (3) confirming fishermen’s reports, overlap and foraging response-changes to fishing vessels’ proximity was higher for Cape Verde shearwaters often attending artisanal boats using handlines, while brown boobies attended more industrial vessels and red-billed tropicbirds and red-footed boobies had low response to fisheries’ effort and distribution (Chapter 3); (4) Boobies exhibit plasticity in their foraging ecology, adapting to different circumstances of environmental conditions and competitors, while breeding stage and presence of marine physical features play an important role in their foraging decisions. Interesting ecological outcome was related with the spatial, behavioural and trophic segregation of female brown boobies in relation to male brown boobies and male and female red-footed boobies, when the two species co-exist in sympatry (Chapter 4); (5) current MPA network in the archipelago is not sufficient for species conservation, requiring large area expansion. However, key areas identified are very coastal and mainly require national management of seasonal MPA implementation with an emphasis on local community involvement and active management. Added bycatch and vessel collision mitigation measures are recommended to decrease direct fishing pressure impacts on the seabird community of the Cabo Verde archipelago (Chapter 5); and finally (6) this study shows that the use of species distributions to identify breeding, feeding and congregating sites, while overlapping with fishing pressure on the surroundings of their breeding sites is extremely valuable to ensure MPA design, management, and effectiveness for species protection. As such, areas should be large enough to embrace all the important features to ensure conservation, while considering temporal and spatial changes between and within species and ensuring effective and active regulations to minimize the impact of any existing anthropogenic threats. Overall, this thesis confirms interactions of Cape Verde shearwater and other species with fisheries inside de archipelago of Cabo Verde, how coastal species foraging behaviours are influenced by environmental variability in a tropical region and informs marine spatial planning for the nation’s EEZ against existing protected areas, highlighting the need to revaluate these areas also taking into consideration both socio-economic and and-ecological aspects of updating the network of MPAs within the Cabo Verde archipelago.