Assessing Potential of Pearl Oyster, Pteria penguin , Spat Collection to Support Mabé Pearl Production in Tonga

ABSTRACT Reliable spat supply remains a key constraint for Mabé pearl farmers in the Pacific island nation of Tonga. This study evaluated the effect of deployment depth on Pteria penguin (Röding, 1798) spat recruitment and final shell size across seven sites in Vava'u, Kingdom of Tonga. Spat collectors were deployed at depths of 6 and 12 m for 12 months between October 2023 and October 2024, and all spat recruited were counted and measured. A total of 767 spat were recovered across the seven sites; recruitment occurred at all sites, although Utulei E had zero spat at 6 m. Spat abundance was consistently higher at 12 m across sites, with a mean increase of 44.1 individuals per site, although the paired comparison did not reach statistical significance ( t = 2.30, p = 0.061). Shell size was significantly smaller at 12 m ( β = −0.367, p < 0.001), suggesting that early growth rates may be influenced by deeper deployment depths. Results are indicative of a depth‐associated trade‐off between recruitment and early shell length. These findings have been adopted by the Tongan Ministry of Fisheries, with 12 m now adopted as the standard deployment depth for spat collectors targeting P. penguin . This study provides field‐based evidence to inform and optimise spat collection practices for P. penguin mariculture in Tonga, supporting further sector development.