Population identification of snapper (Chrysophrys auratus) using body Geometric Morphometrics to inform sustainable fisheries management

The use of morphology to investigate the population structure of fishes is an increasingly used technique in fisheries science. Understanding population structure helps ensure fisheries sustainability and preserves intraspecific biodiversity, which is key to ecosystem functioning. Here, the landmark-based geometric morphometric technique was utilised for the first time on New Zealand snapper (Chrysophrys auratus), a sought-after fish in both recreational and commercial fisheries. Evidence of regional population structure was found, the most pronounced morphological differences being in the head curvature, body depth, eye size, and caudal peduncle width. There were statistically significant differences in body morphology between all but one of the hypothesised populations, with C. auratus individuals correctly allocated to the appropriate populations 86 % of the time. To test optimal population configuration for management areas, several scenarios were run where individual fish were reassigned to different groups, but there was no improvement in allocation success. However, a scenario that excluded fish near the boundaries of current management areas improved allocation success to 99 %. The morphological findings in this study align with other productivity measures for these populations, suggesting that current stocks are comprised of multiple populations. This population structure must be considered at a management level to prevent localised depletions and conserve crucial intraspecific biodiversity.