Collective Volume of Scientifics Papers ICCAT, vol.78, no.3, pp.938-952, 2021 (Journal Indexed in ESCI)
A calibration exercise was carried out with the objective of ensuring that age readings provided
by the Fish Ageing Services laboratory (FAS) follow the ICCAT reviewed reading protocol.
There were found differences in band counts between ICCAT expert readers and FAS readings.
These differences start from specimens with more than 10 bands and are more pronounced for
older specimens. The results of the present calibration are very similar to those of the previous
one. These differences in readings appear to be due to the fact that FAS uses the entire section
of the otolith to count annual bands, whereas ICCAT readers focus on the inner part of the
ventral arm. Analyses conducted to establish which reading is more appropriate: growth
function estimation and cohort follow-up analysis, seem to indicate that ICCAT readers are more
accurate than FAS readers. We suggest applying a correction vector to otoliths read by FAS and
with more than 10 annual bands, in order to incorporate the FAS readings into the GBYP age
database. This ageing bias vector has been obtained from the current and previous calibrations.