A predator-based approach to conflicts and interactions between pinnipeds, salmon aquaculture and fisheries in the Northwest Patagonia
Abstract
Predation by the Southern sea lion Otaria byronia is a central factor in socio-ecological conflicts involving fisheries and salmon aquaculture in southern Chile. While most efforts have been aimed at estimating fishery and aquaculture losses, we focus here on estimating the prey supply needed to sustain the current population of O. byronia in the Northwest Patagonian Fjords System (NWPFS). Integrating updated population abundance, life stage-sex composition, diet data, and bioenergetics modeling, we estimated an average daily consumption of 4.8 kg per sea lion—considerably lower than previous figures often cited in public discourse. Annual consumption of southern hake Merluccius australis by O. byronia was estimated at approximately 3,900 metric tons, corresponding to 82% of the median local fishery landings over the past two decades. This substantial overlap highlights potential competition for this heavily exploited resource. In contrast, predation on Patagonian sprat Sprattus fuegensis was negligible in biomass and fishery terms. The annual consumption of escaped salmonids was estimated at 728 tons, underscoring the role of O. byronia as a biological control of these invasive populations. Conversely, consumption of caged salmonids was minimal (~142 tons annually), challenging salmon producers’ claims of significant losses due to sea lions. These findings highlight the urgent need to shift the prevalent fisheries management mindset from a narrow, monospecific focus on target species toward a broader, ecosystem-based approach. This shift implies, in practice, incorporating O. byronia’s trophic demand into quota estimation processes to ensure sustainable management of shared resources like southern hake. Only by recognizing and accounting for the ecological role and energetic needs of this top predator can management strategies effectively balance conservation objectives with fishery yields, reducing conflicts and promoting long-term ecosystem resilience.