The Fecal DNA Metabarcoding and Feeding Photos Reveal Prey of Eden’s Whales (Balaenoptera edeni edeni) in China

A stable population of Eden’s whales (Balaenoptera edeni edeni) inhabits the Beibu Gulf, southern China, but its diet remains poorly understood. We integrated fecal DNA metabarcoding, photographic identification, and fishery-market surveys to investigate prey composition around Weizhou Island, China. Sixteen fecal samples collected between 2021 and 2026 were analyzed using COI, while eight were additionally analyzed using 12S MiFish and 18S V4 markers. The 12S marker detected 41 fish-associated taxa, including small nearshore schooling fishes such as Ilisha, Nematalosa, Thryssa, and Sardinella. Surface and underwater photographs of feeding events supported two candidate prey taxa, with individuals morphologically consistent with Sardinella albella and Alepes djedaba. Comparisons between whale fecal DNA and seawater eDNA showed that several taxa had higher relative representation in fecal libraries than in seawater controls. Fishery-market surveys recorded 19 fish taxa from Weizhou Island and supplementary surveys in Dapeng Bay, among which eight taxa were not detected in the fecal DNA dataset and treated as market-only records of potential prey availability rather than direct molecular evidence of whale consumption. COI and 18S markers also recovered copepods, hydrozoans, bivalves, gelatinous organisms, and microalgae, which were interpreted cautiously as potential co-ingested, environmental, or broader food-web-associated signals rather than necessarily direct prey. Overall, the molecular, photographic, and fishery-based evidence consistently indicated that small nearshore schooling fishes represent the most robust candidate prey group. Spatial analyses using AquaMaps-derived distribution probability grids showed that candidate prey-associated taxa are mainly concentrated in coastal and shelf-associated ecosystems. This study provides the first multi-evidence assessment of prey composition in Eden’s whales in Chinese waters and highlights the value of integrating fecal DNA metabarcoding with field-based visual evidence for studying the diet of coastal baleen whales.