Diet and reproduction in the white-spotted eagle ray Aetobatus narinari from Queensland, Australia and the Penghu Islands, Taiwan

Abstract

Aetobatus narinari, a circumglobal batoid, is subjected to increasing fishing pressures, especially throughout South-east Asia. However, its management and protection is complicated by the lack of relevant life history information. It appears to be a late-maturing, long-lived stingray with a size-at-maturity of ∼130 and >150 cm in ventral disc width for males and females respectively. Like other myliobatids, A. narinari is a matrotrophic viviparous species exhibiting lipid histotrophy as indicated by trophonemata. Only the left ovary and uterus are functional. The presence of mature sperm in the testes, collecting ducts, epididymis and ductus deferens coincided with the estimated time of parturition and mating. Catches indicated an unbiased sex ratio. Aetobatus narinari is a hard-prey specialist that feeds mainly on gastropods, molluscs and hermit crabs (Diogenidae). Molluscs comprised numerically and gravimetrically the most important prey group (Index of Relative Importance (IRI): 85.9% in Australia, 99.9% in Taiwan) and were observed in 83.3% and 100% of stomachs containing food from Australia and Taiwan respectively. Minor dietary shifts from a gastropod–crustacean to a more gastropod–bivalve based diet occurred as body size increased. This study provides vital biological data for the effective management and conservation of A. narinari.