Assessing the Uncertainty of Total Seabird Bycatch Estimates Synthesized from Multiple Sources with a Scenario Analysis from the Western and Central Pacific

Simple Summary Each year, billions of seabirds undertake extensive migrations, connecting remote regions of the world, potentially synchronizing population fluctuations among distant areas. This connectedness has implications for the uncertainty calculations of the total seabird bycatch estimate at a regional/global scale synthesized from individual assessments conducted at a local scale. Globally, fisheries bycatch poses an environmental problem in fishery management, and estimating the uncertainty associated with a regional/global seabird bycatch estimate is important, because it characterizes the accuracy and reliability of the fisheries' impact on the seabird populations. In this study, we focus on the estimation of the variability of total seabird bycatch, synthesized from multiple sources. In addition to a theoretical exploration, we also provide a hypothetical scenario analysis based on data from the Western and Central Pacific Fisheries Commission convention area. The results show that the assumptions on the correlation between different areas has a big impact on the uncertainty estimates, especially when the number of areas to synthesize is large, and simplifying assumptions failed to capture the complex dynamics of seabird bycatch rates among different areas. It is recommended to empirically estimate the correlation of bycatch rates between each pair of sources when time series of bycatch rates are available.Abstract Each year, billions of seabirds undertake migrations, connecting remote regions of the world, potentially synchronizing population fluctuations among distant areas. This connectedness has implications for the uncertainty calculations of the total seabird bycatch estimate at a regional/global scale. Globally, fisheries bycatch poses a major problem in fishery management, and estimating the uncertainty associated with a regional/global seabird bycatch estimate is important because it characterizes the accuracy and reliability of the fisheries' impact on the seabird populations. In this study, we evaluate different assumptions underlying the estimation of the variability of the total seabird bycatch at a regional/global scale based on local assessment reports. In addition to theoretical analysis, we also simulate multiple spatially distant separately managed areas with relatively low levels of observer coverage, based on bycatch data from the Western and Central Pacific Fisheries Commission convention area. The results show that assuming a completely synchronized variation produced the most conservative uncertainty estimate and it also missed an opportunity to improve the precision. Simplified correlation structures also failed to capture the complex dynamics of bycatch rates among spatially distant areas. It is recommended to empirically estimate the correlation of bycatch rates between each pair of sources based on bycatch rate time series.