Influence of El Niño Southern Oscillation on the abundance of Zalophus californianus breeding colonies in San Roque and Asunción Islands, Baja California Sur

Abstract

In the northwest of Baja California Sur (B.C.S.) state, two breeding colonies of California sea lion (Zalophus Californianus) are distributed in San Roque and Asunción Islands, susceptible to the Niño Southern Oscillation (ENSO) phenomenon. The total population size of this species is difficult to determine, and has been estimated by different authors since the early 50s. Thus, there is a need to standardize the counting method and create a monitoring, management and conservation plan for the California sea lion and its habitat. In this study, abundance and population structure of Z. Californianus in San Roque and Asunción Islands, Reserva de la Biosfera “El Vizcaíno” (REBIVI), was determined from censuses carried out between 2004 and 2017 as well as its breeding season. The relationship between the ENSO phenomenon and the population abundance was analyzed. It was concluded that Isla Asunción is an important reproductive colony with a general positive growth, while Isla San Roque is an occasional occurrence colony without pups register; the breeding season was defined in the months of June, July and August. During La Niña years, the abundance of the species remains stable, and during El Niño, the abundance declines, when productivity decreases. Based on the results, it is proposed to generate a management plan for the organisms and ecosystem, as well as to establish relevant conservation strategies together with the authorities.