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

Doc Number: WG-EMM-14/39
Author(s): M.E. Goebel and C.S. Reiss (USA)
Submitted By: Mr Doug Cooper (CCAMLR Secretariat)

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Abstract: 

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.      

This page was last modified on 23 Jun 2014

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