The population fluctuates widely due to die-offs and cessation of reproduction during El Niño events, when marine productivity collapses. Irruptions of a sea lion epidemic of unknown causation have occurred during El Niño events, adding to the stress on individuals from starvation. Feral dogs which occasionally prey on sea lions could transmit various diseases to the population, but frequent direct contact between sea lions and domestic dogs in the settlements on San Cristobal, Santa Cruz and Isabela present the greatest danger of disease transmission. The population seems to have declined from a 1978 census until today by an estimated 50% or more (Alava and Salazar 2006) and the reasons for this may partly lie in repeated strong El Niño events but are not clearly understood.
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