Investigating foraging associations between seabirds and top marine predators

Seabirds play a fundamental role in oceanic and coastal ecosystems, through top-down control of food-webs and as a vector between marine and terrestrial nutrient cycles. Seabirds feed primarily on pelagic forage species consuming over 7% of the ocean's productivity [70 million tonnes]. Previous work has identified how prey fluctuation has population-level consequences for seabirds. Many seabird taxa are commensal foragers with subsurface and pelagic sub-surface predators such as tuna, sharks and dolphins (hereafter, predators), many species of which are depleted by fisheries and of conservation concern.

For example, roughly 50% of seabird foraging of the coast of Devon and Cornwall is associated with predators (Fig 1). However, the implication of predator depletion (or recovery) for seabirds is poorly understood. Predators chase prey to the surface, making them available to seabirds so predator occurrence is therefore a hypothesised driver of seabird foraging success and therefore population growth. Alternatively, seabirds could be in direct competition with predators, and – hypothetically - benefit from their removal by fisheries. A challenge to solving this debate is a lack of investigation in predator-seabird interactions across a range of spatio-temporal scales. A more comprehensive understanding of the behavioural associations between subsurface top predators (eg cetaceans, sharks, and tuna) and seabirds will yield predictive power over change in our pelagic ecosystems resulting from processes such as climate change and evolving conservation management strategy. Moreover, the project will highlight the functional consequence of subsurface predator range expansions and population recovery, with direct and specific relevance the Devon and Cornish coast where tunas and certain dolphin species are increasingly common (Fig 2).

This project will explore the ecological association between seabirds and predators across multiple temporal and spatial scales, through four objectives (O). First, the candidate will investigate the biogeography of seabird foraging behaviour and by extension, their dependence on facilitated foraging, using a georeferenced, global dataset on diving depth and foraging mode for 162 species of seabirds (O1). Next, by combining existing and new data from seabird visual-surveys and pelagic baited remote underwater video systems [BRUVS] the candidate will investigate the spatial and temporal association of prey, predators and seabirds in a pristine tropical system (O2). The candidate will use existing and new visual survey data (8 years) collected from the University sailing yacht Take-the-Helm, to investigate seabird assemblage variability- and their foraging behaviour – associated with tunas, and dolphins (O3). Finally, the candidate will combine novel visual- and echosounder surveys onboard the RV Falcon Spirit to establish the fine scale association and the mechanistic relationship between prey abundance, predator occurrence, and seabird foraging success.

This project will encompass several key analytical approaches for measuring animal distribution and abundance and their associative relationships, including the following techniques: Visual survey techniques, Distance sampling methods for analysing line transect visual surveys for seabirds and cetaceans. Echosounder and BRUVS analysis for estimate prey and predator distribution, including in-person training in Echoview in how to process echosounder datasets. Distribution and habitat modelling, how to conduct model-based distribution and habitat assessment using visual and acoustic dedicated survey data. Habitat and distribution modelling: training in density-surface modelling, and other relevant modelling techniques in R. The training will include transferable scientific skills including remote sensed data acquisition, and training in the use of analytical packages including; ArcGIS/QGIS, R, Python, Echoview, Raven, MATLAB, MaxEnt.