Changes in growth of the Naru eagle ray Aetobatus narutobiei in Ariake Bay, based on over two decades of monitoring under fishing pressure

Intensive fishing has altered the growth of both target and non-target teleost fish. However, the effects of intensive fishing on elasmobranchs remain poorly understood. The Naru eagle ray Aetobatus narutobiei is a species endemic to East Asia that primarily inhabits Ariake Bay, Japan. Since 2001, a predator control program has been implemented to protect economically valuable bivalves, which has led to a significant decline in the population of this species. Understanding its age and growth parameters is crucial for accurate assessment and sustainable management. This study analyzed 864 vertebral samples (389 males and 475 females) collected during three phases—the Initial Phase (2001–2005), Development Phase I (2013–2018), and Development Phase II (2019–2024)—to estimate age and growth using four candidate models. Model selection based on AIC c indicated that the von Bertalanffy growth function provided the most precise description of the species’ growth in terms of fitting to the observed age-disc width data. The maximum observed age during the sampling period was 18 years for males and 30 years for females. The likelihood ratio test indicated significant differences in the growth curves between the Initial Phase and Development Phases in both sexes. The asymptotic disc width ( DW ∞ ) decreased over time, while the growth coefficient ( k ) increased, indicating growth acceleration. Although the primary factors driving growth changes remain unclear, reduced intraspecific competition due to population decline may be a more direct and critical factor than elevated seawater temperature. This study enhances our understanding of the biology of A. narutobiei and provides a critical foundation for future stock assessments. • Investigated the age and growth parameters of the Naru eagle ray. • Evaluated temporal shifts in growth parameters under long-term predator control. • Analyzed 864 vertebral samples over two main phases (2001–2005 and 2013–2024). • Findings suggest temporal shifts in the growth of this species. • First study to document growth changes in a ray population following a population decline.