The utility of otolith-based methods for discriminating stock structure of the fishery important monacanthid, Nelusetta ayraud, over an intermediate scale

Connectivity and population structure of exploited fish species are critical to understand for effective assessment and management at appropriate spatial scales. We provide a first look at connectivity and population structure of a fishery-important monacanthid, Nelusetta ayraud, using otolith-based methods to compare among three locations (220-540 km apart) along the coast of New South Wales (NSW), Australia. Otolith elemental signatures sampled with laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) revealed differences between two of the three locations during a recent period before capture, as well as differences between the two times examined, although spatial differences were consistent across these times. In contrast, elemental signatures in the juvenile core of the otolith did not differ among locations. Sr:Ca increased linearly with age, and Ba:Ca initially increased to age 1+ before declining in older age classes, consistent with previous observations of an ontogenetic movement into deeper offshore waters for N. ayraud. No differences in otolith shape were detected among locations using Elliptical Fourier Analysis. Our findings suggest there may be spatial structuring of the N. ayraud stock over an intermediate scale (100s km) within NSW, which will inform the design of a larger nation-wide investigation.