Review of size data from Indian Ocean longline fleets, and its utility for stock assessment.

This report reviews the procedures used to collect and process longline size data for use in IOTC stock assessments. It describes the types of data collected, with a particular focus on data provided by the Japanese, Taiwanese, Korean and Seychelles fleets. It investigates the reliability of size data by comparing spatial and temporal patterns in median size among fleets and time periods. It explores reasons behind sudden changes in the shape of length frequency distributions for the Taiwanese fleet and recommends that stock assessments should in future omit Taiwanese length data but include weight data and observer data. It provides recommendations for analysts preparing size data to include in stock assessments, and proposes future directions for research.