The mortality of seabirds in fisheries has had a serious negative impact on many seabird populations, yet the extent of fishery-derived seabird mortality in pelagic longline fisheries, remains poorly understood. In this study, we analyze fishing effort and catch data of the Taiwanese distant-water longline tuna fleet -the largest fleet in the Atlantic Ocean. These data collected by fishery observers over a 5-year span include 61 trips involving 6181 observed sets of over 20 million hooks, where 198 seabirds were caught (23 of which were released alive). Most birds were caught in the South Atlantic, with estimated seabird bycatch rates ranging from 0.026 birds per thousand hooks in the southwest Atlantic to 0.063 birds per thousand hooks in the southeast Atlantic. Black-browed, Atlantic yellow-nosed, and wandering albatrosses, as well as spectacled and southern giant petrels, were the most frequently caught species. Seabird bycatch hotspots were identified at 20°-40°S/10°W-15°E and 35°-45°S/45°-55°W. In the South Atlantic Ocean, generalized additive models indicated that fishing location and the number of birds sighted significantly influenced seabird bycatch rates. Extrapolating these spatially and temporally explicit seabird bycatch rates to the fishing effort data of other distant-water longline fleets and extrapolating the bycatch rates reported in the literature to the reported fishing effort of coastal nation fleets, we estimate the total seabird incidental mortality from pelagic longline fishing in the southern Atlantic Ocean to be between 3446 and 6083 birds per year from 2004 to 2008. These findings support proposals calling for the required use of best-practice mitigation measures by all pelagic longline vessels operating in seabird bycatch hotspots in the South Atlantic Ocean. International cooperation on research and data sharing is critical to ensure the sustainability of seabird populations and fisheries.

Seabird bycatch by the longline fisheries of the Pacific Ocean is a major conservation concern. However, relatively few studies have examined the impacts of distant water longline fishing on the high seas due to the difficulty associated with deploying observers. Our study addresses this data gap by analyzing data from 2666 Taiwanese scientific observation data sets from 2002 to 2007 to calculate the seabird bycatch rate and to estimate the mortality of seabirds as a result of fishing activities by the entire fleet. A total of 379 seabirds were caught and 88% were albatross. A negative binomial distribution was used to represent the observed data based on spatial and temporal stratification, which yielded bycatch rates that ranged from 0.0003 to 0.2213 birds per 1000 hooks. The bycatch rates were highest in the areas between 25-451N and 1651E-1601W between October and March and the areas between 25-351S and 1701E-1651W between April and September. Using the observed data for bycatch rates and total fishing effort, the estimated number of seabird deaths caused by the Taiwanese fleet ranged from 1120 to 4290 birds annually. Increasing the observer coverage of specific fleets and areas, prioritizing observer programs and combined with international cooperation in research, would improve bycatch calculations. Seabird conservation efforts can be improved by monitoring fishing effort and the mandatory implementation of multiple mitigation measures.

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The authors were recently made aware of some confusion regarding Figure 4 in this publication.In Figure 4, the authors provide two groups images of NCL and MMP7 from the same mice but consecutive sections. However, the labeling has led some readers to incorrectly conclude that images of NCL and MMP7 are from two different mice. Please see a relabeled image and new figure legend for clarification.The authors wish to apologize to the readers and publisher for any confusion.

Read the Feature Paper: Estimates of seabird incidental catch by pelagic longline fisheries in the South Atlantic OceanCommentaries on this Feature Paper: Finding the missing pieces: working to solve the fisheries bycatch puzzle; Next step for reducing seabird bycatch; Requisite improvements to the estimation of seabird by‐catch in pelagic longline fisheries