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Project H.1.d-2 - Improve indices of abundance based on longline data (Extension)

01 Jan 2020 - 31 Dec 2022

Program(s) in charge: Stock Assessment Program
  • Improve the yellowfin and bigeye indices of relative abundance from longline data
  • Determine methods to identify targeting in longline fisheries
  • Develop spatio-temporal models for creating indices of relative abundance from longline data
  • Develop appropriate longline length-composition data for the index of abundance and for the catch
  • Continue the ongoing collaborative work
  • Indices of relative abundance derived from longline CPUE data are the most important piece of information in the bigeye and yellowfin stock assessments
  • Only the Japanese data are currently used to create these indices
  • The characteristics, tactics, and spatial distribution of the fishery have changed over time
  • The same length-composition data are used for the index and for the catch, but these could differ 
  • Collaborative research and a workshop in 2019 have substantially progressed the work towards achieving the objectives.
  • New methods, such as spatio-temporal modelling, have been developed and are used in the creation of the indices 
  • Additional research is needed to address changes in target species and factors that may change catchability so better indices of abundance by size class can be estimated  
  • Access to operational-level data for longer time periods is essential for advancing the research. Several CPCs have granted such access to the staff under bilateral MoUs renewable.
  • The staff is recommending changes in the data submission to facilitate the research on longline data 
  • Research conducted to resolve issues in using the longline CPUE and composition data needs to be presented and discussed with scientists of the relevant CPCs
Relevance for management
The indices have direct impact on the stock assessment and any improvements in the indices will directly improve the management advice for bigeye and yellowfin
Winter 2022
Workplan and status
  • 2020-2022: work with CPC scientists to progress longline research
  • Winter 2022: workshop preparation.
  • Spring/Summer 2022: one-week workshop to discuss the results of the research conducted to resolve issues in using the longline CPUE data, write workplan to finish the work.
  • Summer/Fall 2022: write workshop report, manuscript on longline indices of abundance
External collaborators
  • CPCs involved in the longline fishery, mainly China, Japan, Korea, Chinese Taipei
  • Invited speakers
  • Workshop report
  • Indices of relative abundance
  • Length compositions
  • Project report to SAC-14, 2023
Updated date: 01 May 2023
Progress summary for the reporting period
Research on spatiotemporal models was conducted using aggregated data shared by Japan through MOU. The index for bigeye tuna was improved.
Through collaboration with Japan and Korea, indices for South EPO swordfish using spatiotemporal models were obtained, in preparation for the 2022 stock assessment.
Challenges and key lessons learnt
The project was not funded, the workshop did not take place. However, discussion with CPCs, mainly Japan and Spain, took place, facilitated by visits of one staff member to the Centro Español de Oceanografía (Madrid) and National Far-Sea lab (Yokohama) while on trips for other meetings. Collaborative work was agreed, and a new MOU with Japan was discussed. Discussions with other scientists took place in several venues, and the need for a wider discussion on use of longline data for indices of abundance is widespread across RFMOs. The same fleets fish in different oceans and for different species. The need for guidelines on good practices on how to use longline data and how to standardized it to represent the stocks is urgent. Several recent assessments were almost jeopardized due to longline indices of abundance issues. The IATTC staff would like to initiate a dialog across scientists and scientific providers working on different RFMOs on this topic.
The staff also organized a workshop focused on industrial longline to discuss the recommendations to change the data reporting resolution, with the aim of improving the data reporting of longline logbooks (WSDAT-01)
SAC-14-15 SWO assessment
  • The staff is requesting for funding again this year. The objectives would be broader to encompasses tuna, billfish and sharks and focus on discussing good practices when constructing indices of abundance using longline data.
  • The staff will start collaborative work with Japan to analyze the logbook data, which will initiate after SAC-14 with a 2 month visit of a Japanese scientist.