Statistical Characteristics of BPUE (Birds per Unit Effort) of longline fisheries

The Birds per Unit Effort (BPUE), in the context of number of seabirds captured by 1,000 hooks of longlines, seems to have been accepted as a) standard indicator to measure the effectiveness of seabird bycatch mitigation measures, as well as b) an indicator representing the “average” status, or central tendency, of the seabird bycatch occurred in the longline operations.
This document, first, briefly describes an implication of general concept of catch per unit effort (CPUE) and the nature of BPUE data as it stands, and then examines the reliability of two indicators (a and b above) based on BPUE. In this document, the ”BPUE” is referred only to the seabird capture rates standardized with 1,000 hooks of pelagic longline effort, collected through the Japanese Observer Program, while the “CPUE” is referred to a general concept of catch per unit effort, broadly utilized in fisheries assessment and estimation procedures.