A review of the data availability, model configuration and catch estimation for the 2017 blue shark (Prionace Glauca) stock assessment in the Indian Ocean.

This paper presents a review of the 2017 stock assessment of blue shark in the Indian Ocean using Stock Synthesis (version 3.24f http://nft.nefsc.noaa.gov/Download.html). This paper is largely based on the assessment document (IOTC–2017–WPEB13–33 Rev_1), as well as the catch estimation document (IOTC-2017-WPEB13-23). The blue shark assessment model is an age structured (25 years), spatially aggregated (1 region) and two sex model. The catch, effort, and size composition of catch, are grouped into 8 fisheries covering the time period from 1950 through 2015. Seven indices of abundance, all from longline fisheries, were available as well as three alternative time series of total catch. The base case model is parameterized using indices of abundance from the Portugal (2000-2015), Reunion (2007-2015) and the Japanese late (1992-2015) series, along with estimates of catch generated via a generalized additive model. The estimated abundance trend is decreasing throughout the time frame of the model, and spawning stock abundance has decreased to approximately 1.503 times SSBMSY, (80% CI is 1.33-1.63). The fishing mortality has increased steadily over the model time frame with F2015/FMSY= 0.904 (80% CI =0.68 to 1.13).