Evaluation of otolith microstructures for ageing of larval white sturgeon

Abstract

Sturgeon populations are endangered worldwide, mainly due to habitat degradation and overexploitation causing recruitment failure. Understanding of early development, survival and growth in sturgeon is limited by a lack of a validated method to directly estimate larval age. In a laboratory calibration study, we reared white sturgeon (Acipenser transmontanus) larvae from hatch for 3 weeks at 12 and 16 °C and two feeding regimes (fed and unfed) to determine the usefulness of their vateritic microotoconia for larval ageing and the influence of environmental factors on ring structure and size. By marking the otoliths twice at known ages with Alizarin Red S, we were able to confirm the presence of daily rings in the largest microotoconia and the feasibility of ageing larval sturgeon using otoliths. Three observers blind to age and treatment assessed larval age from daily rings with an overall precision of 67%–82% and 30%–70% accuracy, dependent on larval age. Neither temperature nor feeding had a significant effect on ring width or readability. Thus, ageing sturgeon larvae using otolith microstructures is a promising tool for sturgeon conservation efforts.