Time Will Tell: Linking Otolith Geochemistry to Growth Ring Formation in White Hake (Urophycis tenuis).

LaFreniere, Benjamin¹*, Briony Donahue², Rebecca Peters², Dr. Alicia Cruz-Uribe³, Dr. Nate Miller⁴, Dr. Richard McBride⁵, Dr. John Mohan¹, ¹University of New England, ²Maine Department of Marine Resources, ³University of Maine, ⁴The University of Texas at Austin, ⁵Northeast Fisheries Science Center

White Hake (Urophycis tenuis) are a common groundfish distributed throughout the Gulf of Maine. Like other species of groundfish in the North Atlantic, both historical overfishing and climate change are hypothesized to be the main contributors to slow recovery from a historically overfished stock. For most marine species that are commercially harvested, age and growth patterns are well documented and intended to be validated, allowing for age-based stock assessment and management practices. Reported to live up to ~20 years, White Hake age estimation based on visual otolith growth ring enumeration is challenging due to unclear annuli identification, with reports of both false and weak annuli, leading to uncertainty in the biological and abiotic mechanisms driving annuli formation. We compare traditional visual age and growth techniques using sectioned otoliths to cycles of elemental concentrations measured by laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS). We test the hypothesis that annual oscillations in both environmental conditions and internal physiology influence elemental uptake during otolith mineralization. Of the investigated trace elements (Mg, Mn, Sr, Ba), both Mn and Ba incorporation into White Hake otolith layers show promising correlations to visual annuli, offering an additional tool to enhance annuli identification and increase the precision of aging this species. These results further demonstrate that otolith geochemistry can improve the accuracy and precision of fish age estimation.