Numerical Models for Establishing Relationships Between Otolith Morphometrics and Fish Size in Deep-Sea Scorpaenoid and Dactylopterid Fishes

Scorpaenoids and dactylopterids are major bycatch fish groups in the Arabian Sea’s deep-sea shrimp trawl fishery, but their biological characteristics, including otolith morphometry, are poorly understood. This study investigates the relationships between fish sizes (total length and weight) and otolith sizes (length, width, area, perimeter, and weight) of 10 deep-sea scorpaenoid and dactylopterid species using a total of 567 right sagittal otoliths. Significant positive correlations (p < 0.001) were found, and numerical models were developed using linear regression. The r² values for the relationship between otolith variables and fish size were ranged from 0.96 (OL × W, Neomerinthe erostris) to 0.47 (OW × TL, Minous inermis). Models using otolith length (OL) were most effective in predicting fish length for five species viz., Neomerinthe erostris, Setarches guentheri, Dactyloptena orientalis, Snyderina guentheri, and Minous inermis. For other five species, otolith area (OA) provided more accurate predictions. For fish weight prediction, OA was the best predictor for six species viz., Satyrichthys laticeps, Snyderina guentheri, Pterygotrigla macrorhynchus, Pterygotrigla arabica, Minous inermis, and Dactyloptena papilio. Meanwhile, OL showed the highest correlation with fish weight for four species. Otolith weight (OWe) was the best predictor for estimating the total length (r² = 0.94) and weight (r² = 0.90) of Grammoplites suppositus. These models provide novel information on predicting fish size from otoliths for all the given species and aids in future studies to estimate prey biomass for food-web dynamics studies. Moreover, the representative otolith images provided are valuable for taxonomy, paleontology, and ecological studies.