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

Abstract

© 2015, Universidad de Valparaiso. All rights reserved.This study analyzes temporal, spatial, environmental, ecological and fishing variables that contr ibuted 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.