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Project E.1.a - Evaluate potential improvement of growth model for bigeye in the EPO based on presumed annuli counts from otoliths of large fish

01 Nov 2017 - 01 Nov 2019

Program(s) in charge: Life History and Behavior Group
Evaluate the potential improvement in accuracy of the growth model for bigeye in the EPO resulting from including more age-at-size data for large fish
  • Growth model for bigeye is based on validated counts of daily otolith increments, corroborated by extensive tagging data, but age-at-size data for larger fish (150-200 cm) are lacking
  • High-confidence tagging data for bigeye >150 cm are limited
  • The National Research Institute for Far Seas Fisheries (NRIFSF) of Japan’s collections of otoliths from large bigeye captured in the EPO are now available for evaluating age estimates from counts of presumed annuli
Relevance for management
Improving the accuracy of the bigeye growth model, particularly for larger fish, would help resolve some of the uncertainty regarding the status of the stock, and improve the framework on which management advice is based
24 months; initiated November 2017
Workplan and status
  • Fish Ageing Services (FAS) in Australia counted annuli on 140 pairs of bigeye otoliths from up to 20 fish within each 10 cm length interval between 110 and 200 cm and estimated the ages of the fish
  • FAS age estimates for 110-150 cm fish will be compared to published age-at-size data
  • Growth rates for 150-180 cm fish based on EPO tagging data will be compared with growth rates based on the FAS age estimates.
  • Age estimates from otoliths of 150-200 cm fish will be combined with the existing data set and used in an integrative growth model.
External collaborators
  • Presentation for SPC-OFP bigeye pre-assessment workshop, 2018
  • Potential update of bigeye growth model for use in stock assessments
Updated date: 01 Jun 2019
Progress summary for the reporting period
  • Annual and daily increment counts from 70 otolith pairs, from fish 80-150 cm from the South EPO, were compared.
  • The daily increment counts were compared to decimal ages for 133 fish 112-207 cm from the South EPO.
  • Decimal ages for fish > 150 cm were compared with the integrated growth model for fish from the EPO, including high-confidence tagging data for fish 150-201 cm.
Challenges and key lessons learnt
  • The decimal age estimates based on the 70 otolith pairs are greater for fish 130-150 cm than those based on daily increment counts.
  • Distinguishing annual increments is problematic.
  • For fish 120-150 cm from the South EPO, the decimal age estimates are on average 1.3 years greater than the age at length for fish from the equatorial EPO estimated by the integrated growth model. For fish 150-200 cm from the South EPO, the adjusted annual increment counts estimate age at length 2.4 years greater, on average, than the integrated growth model for the equatorial EPO.
  • These results indicate that the annual age estimates should not be included in a new integrated growth model for bigeye in the EPO.
Schaefer, K., Fuller, D., and Satoh, K. Abstract in Report of the workshop on age and growth of bigeye and yellowfin tunas in the Pacific Ocean, 23-25 January 2019, La Jolla, USA