Pacific Islands Fisheries Science Center (U.S.)

A base-case model in Stock Synthesis 3.30 for North Pacific Swordfish (Xiphias gladius) is described. The base-case model covers 1975-2016 for the Western Central North Pacific Ocean (WCNPO) region as determined by the Billfish Working Group at the January 2018 working group meeting. It includes all the data available for the WCNPO region as of the January Billfish WG data preparatory meeting with the exception of two WCNPO indices which are not included in the likelihood estimation. It includes data from three International Scientific Committee for the Conservation of Tuna and Tuna-like Species (ISC) countries and from other countries in aggregate from the Western Central Pacific Fisheries Commission (WCPFC) and Inter-American Tropical Tuna Commission (IATTC). Two alternative models are also described. Alternative model one was the base-case model with the inclusion of the remaining two WCNPO indices in the likelihood estimation, used to evaluate how they may have impacted model results. Alternative model two was the base-case model plus two environmental indices for recruitment. These indices are the Southern Oscillation Index from 1952-2016, which has been shown to correlate with swordfish recruitment deviations, and an index of estimated phytoplankton biomass from 2002-2016, which has been shown to correlate with bigeye tuna recruitment. The final base-case model converged, but additional work is required to improve the fit to the CPUE and length composition data. Initial results suggest the WCNPO swordfish stock is being fished below FMSY and spawning stock biomass is above SSBMSY.

http://doi.org/10.7289/V5/WP-PIFSC-18-005

Working Paper