Using Otoliths to Age a Fish with Alternative Male Reproductive Strategies




Townsend, Angus

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Age estimation techniques using sagittal otoliths were performed and evaluated for the plainfin midshipman, Porichtys notatus. Two hundred and twenty-three fish (72 females, 98 guarder males, 23 sneaker males, and 30 juveniles) were collected from intertidal nesting sites in the Strait of Georgia from May to July 2022. Of the techniques tested, simple surface aging and transverse thin sections proved ineffective at enhancing yearly annuli growth rings. However, soaking & surface aging and break & burn were more effective, with 89% and 100% of otoliths, respectively, being able to be aged. Sneaker males were found to be the youngest cohort, followed by females and then guarder males. Using break & burn age estimates and fish measurements, different von Bertalanffy growth functions were constructed for the three reproductive types: females (L∞ = 22 cm, K = 0.24 and t0 = -0.41), guarder males (L∞ = 30 cm, K = 0.15 and t0 = -0.47), and sneaker males (L∞ = 19 cm, K = 0.26 and t0 = -0.43).



midshipman, aging, otolith