Linking Predator-Prey Dynamics: Spatiotemporal Trends in Marine Predation Around Shetland

Understanding the drivers of population dynamics is a fundamental question in both pure and applied ecology. For marine top predators quantifying the role that prey availability plays is critical in evaluating the potential impacts of current and planned human activities, and thus for environmentally sustainable management of the ecosystem. However, such research has been limited by a lack of prey data at an appropriate resolution, resulting in researchers primarily having to rely on coarse resolution prey data (International Council for the Exploration of the Sea; datras.ices.dk) or environmental covariates as proxies for prey availability. Such a lack of data has also hampered effective management of inshore fish stocks. Shetland benefits from a set of datasets (all available for this project), unique in the UK, that would allow exploration of the spatiotemporal relationship within and between top predators and fish. Moreover, Shetland is an area of conservation and management interest; it hosts significant fish diversity and populations of predator species while supporting high and increasing levels of marine resource acquisition. Shetland has a dedicated inshore fish survey (annual from 2011; SUHI). In addition, there are historic sandeel data (1974-1999). For seabirds, there are breeding abundance data, and a monthly beached bird survey measuring seabird corpse and oil pollution rates, from around Shetland for over four decades (SOTEAG, Seabird Monitoring Program & RSPB), resulting in one of the UK's most comprehensive datasets on seabird abundance. These data are augmented by extensive tracking datasets (seven species; RSPB). Furthermore, SMRU hold data on seal haulout abundance, diet and tracking data. These data show stark species and regional variation across Shetland in trends in abundance of fish, seabirds and seals. For example, the Shetland harbour seal population fell by ~ 40% between 2001 and 2015 with stable abundance prior to and following that fall. However, the areas encompassing the two (harbour seal) SACs show contrasting trend; the Yell Sound trend mirrors the Shetland-wide trend but southeast Shetland (includes Mousa SAC), has shown a continuing decline since the early 1990s. There is a lack of studies of long-term population trends across multiple species and trophic levels. Comparative analyses of trends of top predators can elucidate the drivers of change. Indeed, populations of species with a limited foraging plasticity are more sensitive to reduced prey availability.