Abstract

Bycatch of marine mammals in fisheries is a critical conservation issue worldwide, and Chile is no exception. Pinnipeds such as the South American sea lion (Otaria byronia, SASL) frequently encounter fishing gear along the Chilean coast. Despite widespread evidence of these interactions, few studies have spatially assessed SASL bycatch risk across multiple fisheries for this species. This study applies the Bycatch Risk Assessment (ByRA) toolbox, a GIS-based model, to evaluate and compare the risk of SASL bycatch across nine Chilean purse-seine and trawl gear fisheries based on data from on-board scientific observer logs from 2015 to 2019. Our findings identify trawl fisheries, particularly those targeting southern hake (Merluccius australis), as posing the highest bycatch risk, especially during the non- reproductive season when SASL exhibit broader spatial distribution. Purse-seine fisheries presented lower risk overall, with the industrial northern fleet showing the highest relative risk. Spatial patterns revealed that risk is concentrated in nearshore areas, where the overlap between the distribution of SASL and fishing activity is the greatest. These results provide a robust, spatially explicit foundation for prioritizing mitigation measures, including the mandatory use of exclusion devices and seasonal restrictions. Our approach underscores the potential mitigation provided by evidence-based management of marine mammal bycatch in Chile and contributes information toward the assessment of compliance with domestic and international regulations.