Seabird bycatch in a sardine purse seine fishery

Limited understanding of seabird bycatch in purse seine fisheries has been highlighted as a key information gap in assessments of seabird bycatch in fisheries globally. This study documents the bycatch of breeding flesh-footed shearwaters (Ardenna carneipes) in a sardine purse seine fishery on the southern coast of Western Australia. Fishery-dependent bycatch records from 2009/2010 to 2017/2018 showed a strong peak in the mortality rate per fishing trip during March and April, closely associated with the final stage of chick rearing. Observers during those peak months in 2007, 2008, 2017, and 2018 recorded 171 mortalities during 222 trips at per trip rates (±95% confidence limits) ranging from 0.59 (0.25–1.17) in 2017 to 1.10 (0.56–1.96) in 2007. Zero mortalities were recorded on at least 70% of trips in any year, suggesting infrequent formation of net folds that can trap birds. Total annual mortalities estimated for 2016/2017 and 2017/2018 were 123 (52–251) and 172 (91–302), respectively. Although within a sustainable anthropogenic limit of 495 (369–660) estimated from conservative application of the potential biological removal method, the extent of other anthropogenic mortalities is unknown. Further research on the effect of distance of breeding colonies from fishing operations is required.