Karim SotoAlumni
MSc 2004

Supervisor
Dr Andrew Trites

Thesis
The effects of prey abundance on the diet, maternal attendance and pup mortality of the South American sea lion (Otaria flavescens) in Peru

The Peruvian upwelling system is one of the most unpredictable but productive marine ecosystems in the world that is regularly affected by El Nino and La Nina events. As a consequence, South American sea lions (Otaria flavescens) inhabiting the Peruvian coast face stochastic fluctuations in the abundance and distribution of their prey. The goal of my study was to determine the effects of marine environmental changes on the reproductive success of South American sea lions in Peru on the Ballestas Islands during the 1997-2002 breeding seasons.

I also wanted to assess whether changes in diet and maternal behaviour during this time were proxies of major changes in the abundance of marine resources. South American sea lions consumed primarily anchovy and squat lobster during the 1999- 2001 La Nina, but consumed a greater diversity of prey when abundance was low during the 1997-1998 El Nino.

Lactating females also modified the length of time they spent at sea and onshore in response to changes in the abundance of prey. Low abundances and quality of prey during El Nino caused females to continue foraging for longer periods. This resulted in greater times between nursing episodes, and ultimately led to the starvation of pups. In contrast, during the 1999-2001 La Nina, females spent shorter times at sea and longer times onshore as prey became more abundant.

Pup production and mortality were also directly related to the abundance of prey. Pup mortality reached 100% during El Nino and remained high during the favourable conditions of La Nina due to the short-term effects that El Nino had on population dynamics and subsequent maternal behaviour.

Abortions were also higher during El Nino compared to other years, while numbers of pups bom were significantly reduced during and after El Nino due to the death of a high proportion of the adult population. My study suggests that South American sea lions in Peru are highly vulnerable to extreme changes in prey abundance. It also demonstrates that sea lion reproductive parameters, maternal attendance, and diet are strongly related to marine environmental conditions and annual variations in prey abundance. As a result, South American sea lions appear to be good indicators of stochastic changes in the distribution and abundance of marine resources in the Peruvian upwelling ecosystem.

Publications

The effects of prey abundance on the diet, maternal attendance and pup mortality of the South American sea lion (Otaria flavescens) in Peru. Soto, Karim. 2004. Masters Thesis, University of British Columbia. 73 pages (PDF)

Changes in diet and maternal attendance of a South American sea lions indicate changes in the marine environment and the abundance of prey. Soto, K., A.W. Trites, and M. Arias-Schreiber. 2006.  (PDF)

The effects of prey availability on pup mortality and the timing of birth of South American sea lions (Otaria flavescens) in Peru. Soto, K., A.W. Trites, and M. Arias-Schreiber. 2004. Journal of Zoology 264:419-428. (PDF)