Regional variability in growth and biometrics of yellowfin tuna in Indian waters

Introduction: Yellowfin tuna, Thunnus albacares , a commercially important pelagic species widespread across the Indian Ocean, plays a critical role in Indian fisheries. Understanding regional variation in biometric and demographic parameters is essential for achieving effective stock assessment and fisheries management. This study evaluated regional differences in growth patterns and condition of yellowfin tuna across the Indian Exclusive Economic Zone (EEZ).

Materials and methods: Data of 431 yellowfin tuna were collected from November 2022 to April 2023 from three landing centers. Length, weight, and sex data were used to assess length–weight relationships (LWRs), length and weight frequency distributions, Fulton’s condition factor (K), relative condition factor (Kn), and sex ratio.

Results: Fork length ranged from 48.7 to 185.0 cm across study sites, exhibiting bimodal catch distributions with an intermediate size gap (100 to 128 cm) in mainland landings. All regions displayed negative allometric growth (b = 1.83 − 1.92, R ² ≥ 0.936). Significant regional differences were detected in fork length (H = 8.83, p = 0.012), body weight (H = 7.52, p = 0.023), and condition factor (H = 8.74, p = 0.013), with Kerala catches exhibiting higher mean K (2.64 ± 0.98) than Odisha (2.36 ± 1.03). A strong skew towards males ( p < 0.001) was observed across all regions.

Conclusions: Commercial landings showed significant regional variation in yellowfin tuna size and growth. However, six-month sampling without gear-standardized effort, environmental, or genetic data limits stock-level inference. Observed patterns may reflect potential drivers requiring multi-season and fishery-independent validation.