Information on fish size structure is essential for assessing population health in both fisheries and conservation management. Due to the high cost of stereo-video equipment, there is a need for simple allometric models that allow accurate body-size estimation. In a recent marine education program, we aimed to enable school children to estimate fish body size without access to stereo-video systems. We therefore developed allometric models linking easily visible morphological traits, as well as pair-wise ratios of those traits, to fork length (FL). Hand measurements were taken from fresh-caught Chrysophrys auratus, a highly targeted commercial and recreational fishery species. Specimens were sampled from three sites spanning the species’ wide latitudinal distribution in Western Australia: Shark Bay (25.5°S), Kalbarri (27.7°S) and Black Point (33.6°S).
Linear regressions demonstrated significant and strong positive allometric relationships between FL and four out of six morphometric traits, with eye-to-anal fin distance (EF) as the strongest single predictor. Eye height (EH) emerged as a particularly important trait, with EH-based pairwise ratios (e.g., EH/EF: R² = 0.681) providing robust predictive power and greater contrast with other morphometrics. These relationships were consistent across regions, which is crucial for this widely distributed species.
These findings support the development of simple allometric models suitable for single-camera and/or community-led monitoring programs, enabling accurate body-size estimation of pink snapper without specialised stereo-video equipment.