Investigate potential changes in the selectivity of the longline fleet resulting from changes in gear configuration

Project H.1.c - Investigate potential changes in the selectivity of the longline fleet resulting from changes in gear configuration

01 Jan 2019 - 31 Dec 2019

Completed

Program(s) in charge: Stock Assessment Program

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Theme 3. Sustainable fisheries
Goal H. Improve and implement stock assessments, based on the best available science
Target H.1. Undertake the research necessary to develop and conduct at least one benchmark stock assessment for yellowfin and bigeye tunas

Objectives

Evaluate potential changes in targeting on the size composition of the longline catches of bigeye and yellowfin

Background

The current yellowfin stock assessment shows a pattern of residuals for the recent longline length-composition data
Analyses of operational-level longline data from the Japanese fleet have identified possible changes in targeting that may affect the indices of relative abundance and size composition of the catch
The changes in targeting appear to be related to changes in longline gear configuration.
The effect on catch rates and species composition is being investigated in related collaborative research between the IATTC staff and NRIFSF, Japan

Relevance for management

Currently, the longline indices are the main information in the stock assessments of yellowfin and bigeye, therefore unaccounted-for changes in the longline selectivity may compromise management advice

Duration

12 months

Workplan and status

Month 1: match set-by-set gear characteristics and catch data with the sizecomposition data from the Japanese fleet
Months 2-3: analysis of the set-by-set data
Months 5-11: Apply the lessons learnt from the set-by-set data to the aggregated level data used in the stock assessment

External collaborators

NRIFSF, Japan

Deliverables

Presentation for SAC-10, 2019
Procedure to be used in the next full assessment of yellowfin

Updated date: 01 Oct 2020

Progress summary for the reporting period

This project was not funded, but progress was made in the context of Project H.1.d

Challenges and key lessons learnt

Matching the length-frequency and operational data has proved difficult, and is not yet completed

SAC-10 INF-F: Evaluating inconsistencies in the yellowfin abundance indices
Materials for the workshop to improve indices of abundance held under Project H.1.d
SAC-11 INF-L: Comparison of tuna length data collected by observers and fishermen from the Korean longline fleet

Comments

This project was not funded, but progress was made in the context of Project H.1.e