Validation of periodicity of growth band formation in Pacific Sardine (Sardinops sagax) from a captive growth experiment

Pacific Sardine (Sardinops sagax) in the Northeast Pacific Ocean are aged for stock assessments assuming the formation of two otolith growth bands (one opaque and one translucent) a year, but the periodicity of band formation has not been fully validated. To validate our ageing method, we investigated the periodicity of band deposition and somatic and otolith growth rate across a range of temperatures. Live Pacific Sardine (mostly age 0) were collected, marked with oxytetracycline (OTC), and raised in captivity at different temperatures (13 °C, 15 °C, 17 °C, and 21 °C) for up to one year. There was no clear pattern between temperature and somatic growth rate. Otolith growth rate was slower for Pacific Sardine in captivity at 13 °C than at 17 °C. All individuals that were in captivity for one year (n = 21) deposited 2–3 growth bands distal to the OTC mark. Therefore, Pacific Sardine deposited bands in their otoliths at the rate expected for the formation of annuli across ecologically relevant temperatures (13–21 °C) in captivity. Vateritic otoliths were rare but did display an OTC mark at approximately the same distance from the otolith edge as the aragonitic otolith in the pair. The results of this study build upon previous validation research for Pacific Sardine and support the ageing methodology used for this species by all ageing laboratories in the US, Canada, and Mexico.