Operational interactions between the South American sea lion Otaria flavescens and purse seine fishing activities in northern Chile

espanolSe analizan variables temporales, espaciales, ambientales, ecologicas y pesqueras que contribuyen a la variacion del numero de lobos marinos comunes (Otaria flavescens) que interactuan con las faenas de pesca de cerco industrial de la flota que opera en el norte de Chile (18°21'-24°00'S). Observadores cientificos fueron embarcados en buques cerqueros entre febrero 2010 y diciembre 2011. Los datos fueron modelados usando modelos lineales generalizados (MLG) y modelos lineales generalizados mixtos (MLGM). Los resultados muestran que la variabilidad en el numero de lobos marinos atraidos por las operaciones de pesca para alimentarse o intentar hacerlo, se explica por las variables: Hora del lance, Distancia a las colonias de lobos mas cercanas, Temperatura superficial del mar, Especie objetivo del lance, Latitud y Numero de aves marinas en torno a la embarcacion. Luego del analisis detallado de las variables significativas, se puede concluir que los principales mecanismos que estarian actuando sobre la interaccion entre lobos marinos y la operacion de pesca serian: 1) una estrategia utilizada por los otaridos para disminuir el estres por calor en el periodo reproductivo (verano), saliendo al mar en horas de maxima radiacion solar (al mediodia), lo que incrementa notablemente su presencia dentro del cerco en lances realizados a menos de 20 millas nauticas de las colonias y 2) durante periodos calidos, la presencia de ondas Kelvin descendentes disminuiria la disponibilidad de anchoveta (Engraulis ringens) en la zona, lo que provoca que la flota reoriente sus operaciones hacia el jurel (Trachurus murphyi), recurso que generalmente se captura a mayores distancias de la costa y de las colonias, disminuyendo significativamente la interaccion con los lobos marinos. EnglishThis study analyzes temporal, spatial, environmental, ecological and fishing variables that contributed to variations in the number of South American sea lions (Otaria flavescens) that interacted with the industrial purse seine fishing operations in the north of Chile (18°21'-24°00'S). Scientific observers were placed onboard purse seiners vessels between February 2010 and December 2011. Data were modeled using generalized linear models (GLM) and generalized linear mixed models (GLMM). The results show that the variations in the number of sea lions attracted to fishing operations for feeding or attempting to feed on catches, depends on the following variables: Time of haul, Distance to the closest sea lion colony, Sea surface temperature, Target species of the haul, Latitude, and Number of seabirds circling the vessel. After detailed analysis of the significant variables, it can be concluded that the main mechanisms involved in the interaction between the sea lions and the fishing operations were: 1) a strategy used by the sea lions to decrease heat stress during the breeding period (summer) by entering the water when solar radiation is at its peak (around midday), thus notably increasing their presence within the nets during sets that are less than 20 nautical miles from the colonies; and 2) during warm periods the presence of downwelling Kelvin waves decreases the availability of anchovies (Engraulis ringens) in the area. This causes the fleet to change target species and focus on jack mackerel (Trachurus murphyi), which is generally captured further from the coast and the colonies, significantly decreasing the interaction with local sea lions.