Otolith Shape Variation Reveals a Preliminary and Novel Stock Structure Signal of Yellowtail Kingfish ( Seriola lalandi lalandi ) in Aotearoa New Zealand

Accurate stock delineation is essential for sustainable fisheries management, yet remains challenging in highly mobile marine species where conventional markers may lack resolution. Here, we present the first evaluation of sagittal otolith shape variation in Yellowtail kingfish ( Seriola lalandi lalandi ) across five sampling regions in Aotearoa New Zealand, using wavelet‐based contour descriptors and traditional shape indices to test for spatial structuring among sampling regions ( n = 112 individuals), assessed via Canonical Analysis of Principal Coordinates (CAP) and permutation‐based PERMANOVA. Wavelet descriptors revealed statistically significant differences in otolith shape between Auckland west and all other sampled regions—a finding of particular relevance given the species' recent and ongoing southward range expansion, and the absence of previously documented stock‐level differentiation in this area. No significant differences were detected among southern regions. However, the proportion of variance explained was modest (CAP R 2 = 7.1%), indicating that the observed differences represent a preliminary signal of spatial structuring rather than confirmed stock boundaries. These results provide a baseline for future multi‐marker investigations to clarify the mechanisms driving the observed morphological differentiation and inform adaptive management of a range‐shifting species.