Adjusting time-of-day and depth of fishing provides an economically viable solution to seabird bycatch in an albacore tuna longline fishery

Abstract

Marine megafauna exposed to fisheries bycatch belong to some of the most threatened taxonomic groups and include apex and mesopredators that contribute to ecosystem regulation. Fisheries bycatch is a major threat to the conservation of albatrosses, large petrels and other pelagic seabirds. Using data sourced from a fisheries electronic monitoring system, we assessed the effects of the time-of-day and relative depth of fishing on seabird and target species catch rates for a Pacific Ocean pelagic longline fishery that targets albacore tuna with an apparently high albatross bycatch rate. Using a Bayesian inference workflow with a spatially-explicit generalized additive mixed model for albacore tuna and generalized linear mixed regression models both for combined albatrosses and combined seabirds, we found that time-of-day and fishing depth did not significantly affect the target species catch rate while night-time deep setting had > 99% lower albatross and total seabird catch rates compared to both deep and shallow partial day-time sets. This provides the first evidence that night-time setting in combination with fishing deep reduces seabird catch risk and may be commercially viable in this and similar albacore tuna longline fisheries. Findings support evidence-informed interventions to reduce the mortality of threatened seabird bycatch species in pelagic longline fisheries.

Nanopore environmental DNA sequencing of catch water for estimating species composition in demersal bottom trawl fisheries

“…With such information, best practices and adaptive fishing patterns can be promoted to reduce and prevent certain bycatch, ultimately minimizing fishing‐related mortality and safeguarding vulnerable and endangered populations. For instance, in pelagic longline fisheries, data obtained from electronic monitoring programs provided the basis to inform management strategies, such as modifying the time of day and fishing depth, aimed at diminishing the mortality of threatened seabirds as bycatch species (Gilman et al., 2023). Similarly, eDNA analysis can provide insights into the spatio‐temporal patterns of bycatch species in demersal fisheries, promoting more effective evidence for bycatch avoidance and aiding in the monitoring of mitigation measures.…”