Squeezed from both ends: Decline in Antarctic fur seals in the South Shetland Islands driven by both Top–down and Bottom–up processes

Understanding the relative contributions of different sources of mortality and survival in predator populations can improve ecosystem models and management of marine ecosystems.  Within the Antarctic bottom-up processes are widely cited for explaining penguin population declines, whereas for Antarctic fur seals, top-down processes are most cited as the primary driver for declining pup production.  This has led to an under emphasis of the role of bottom-up drivers for controlling fur seal production within the system.  We review the historical data in Antarctic pup production and provide annual pup production estimates from 2002-2012 for Cape Shirreff, Livingston Island.  Age-specific natality rates are provided as an indicator of bottom-up drivers and we contrast these with early season neonate mortality and leopard seal predation rates.  Fur seal pup production has undergone a dramatic declines in the last decade (12.1% per annum since 2002).  Since 1998, natality rate has also declined 14%, largely driven by poor recruitment and an aging population.  However, age-specific natality rate has also declined.  Predation rate has increased 4% per year since 2002.  We discuss the relative roles of bottom-up and top-down contributions to the decline in fur seals.