Seabird bycatch in Uruguayan longline fisheries

This paper presents: 1) an estimate of the total number of seabirds captured by the Uruguayan pelagic longline fishery in the southwest Atlantic (2003-2012); (2) an analysis of the seabird bycatch data taken by observers onboard on the demersal longline fishery for Patagonian toothfish in the Argentinean-Uruguayan Common Fishing Zone (ZCPAU) and international waters of the southwest Atlantic (2006-2018) and (3) an analysis of the seabird bycatch data from the Uruguayan demersal longline fishery for Atlantic wreckfish (2015-2016). The mean annual bycatch in the pelagic longline fleet ranged between 125 and 844 birds in 2003-2012. Seabird bycatch in the demersal longline fishery for Patagonian toothfish was zero, despite the large fishing effort observed. Most of these vessels operated with a modified traditional Spanish system with Mammals and Birds Excluding Devices (MBED, also known as trotlines). The exception was a single vessel operating in recent years with automatic autoline system, with integrated weighting lines, external weights and a bird scaring line. During 2015-2016, the bird captured per unit effort (BCPUE) in the demersal longline fishery for Atlantic wreckfish was 0.149 birds/1000 hooks. Bycatch was affected by the longline setting time; twenty-two of the 24 birds captured in 2015-2016 were recorded during the first fishing trip of 2015. These birds were captured in two longline sets started few minutes before sunset and one set started few minutes after sunset, during the twilight. After this trip, all longline setting operations started after sunset, except by four longline sets; one of them resulted in the captured of two seabirds. Analyses from the pelagic longline fleet should be considered preliminary but confirms a previous estimate for a shorten period, indicating that bycatch ranged in the order of hundred birds per year. No pelagic longline fishing effort have been deployed within Uruguayan waters from 2013. If this fleet resumes its operation, mitigation measures must be implemented from the beginning. There are current mitigation measures whose applicability and effectiveness have been tested and demonstrated onboard, which would facilitate their rapid implementation. Seabird bycatch in the demersal longline fishery for Patagonian toothfish on the ZCPAU and international waters of the southwest Atlantic is null or negligible. Implemented mitigation measure are considered adequate. The implementation of night setting (after sunset) in the Atlantic wreckfish longline fishery resulted in a dramatic reduction of bycatch. As a precautionary approach, longline setting should be started after nautical dusk and other mitigation measures should be tested to reduce the risk of bycatch to a minimum.