Ontogenetic and seasonal shifts in diets of sharptail mola Masturus lanceolatus in waters off Taiwan

Abstract

Sharptail mola Masturus lanceolatus share a circumglobal distribution with ocean sunfish Mola mola and are typically regarded as gelatinous plankton feeders. Both species are frequently captured as bycatch in the same areas, but sharptail mola are often targeted and heavily harvested in certain regions. However, the diet of sharptail mola remains poorly described. We examined the foraging habits and trophic dynamics of sharptail mola from waters off eastern Taiwan using stomach content analysis (SCA; n = 162), bulk tissue stable isotope analysis (SIA; n = 213), and compound-specific isotope analysis of amino acids (CSIA-AA; n = 10). Results demonstrated that sharptail mola mainly consumed tunicates, with lower dietary proportions of diverse prey from epi- and mesopelagic, coastal, and benthic habitats. The diet of sharptail mola changed significantly with size; small mola (<80 cm) had lower δ15N and δ13C values and fed on more pteropods and Salpidae, while large mola (>80 cm) fed on more Pyrosoma spp., cephalopods, and benthic organisms living on sandy substrates, with larger individuals having correspondingly higher isotope values and trophic positions. Diet compositions and δ13C values also showed seasonal variations across body size, suggesting that sharptail mola might undergo seasonal migrations with changing availability of food resources. The results provide insights into the trophic dynamics of sharptail mola and suggest that their foraging behavior varies across life-history stages and seasons.