Analysing the natural population growth of a large marine mammal after a depletive harvest

GRANDI, MARÍA FLORENCIA; OCAMPO REINALDO, MATÍAS; GONZÁLEZ, RAÚL A; ROMERO, MARIA ALEJANDRA; SVENDSEN, GUILLERMO M; DANS, SILVANA L; KOEN-ALONSO, MARIANO; GARCÍA, NESTOR A; CRESPO, ENRIQUE A

Scientific Reports

Springer Nature

Año: 2017 vol. 7

An understanding of the underlying processes and comprehensive history of population growth 22 after a harvest-driven depletion is necessary when assessing the long-term effectiveness of 23 management and conservation strategies. The South American sea lion (SASL), Otaria 24 flavescens, is the most conspicuous marine mammal along the South American coasts, where it 25 has been heavily exploited. As a consequence of this exploitation, many of its populations were 26 decimated during the early 20th century but currently show a clear recovery. The aim of this 27 study was to assess SASL population recovery by applying a Bayesian state-space modelling 28 framework. We were particularly interested in understanding how the population responds at low 29 densities, how human-induced mortality interplays with natural mechanisms, and how density30 dependence may regulate population growth. The observed population trajectory of SASL shows 31 a non-linear relationship with density, recovering with a maximum increase rate of 0.055. 32 However, 50 years after hunting cessation, the population still represents only 40% of its pre33 exploitation abundance. Considering that the SASL population in this region represents 34 approximately 72% of the species abundance within the Atlantic Ocean, the present analysis 35 provides insights into the potential mechanisms regulating the dynamics of SASL populations 36 across the global distributional range of the species.