Shifts in the feeding ecology of the endemic and Endangered Sardinella tawilis in Lake Taal, Philippines

Understanding fish feeding ecology may provide key ecological information for fisheries conservation and management. In Lake Taal, Philippines, the Endangered status of the endemic Sardinella tawilis , the world’s only freshwater Sardinella species, underscores the threats and vulnerability of its remaining population due to the recent eruption of Taal Volcano and ongoing anthropogenic pressures. In this study, we examined possible shifts in the feeding ecology of S. tawilis by assessing its trophic position through the evaluation of the pelagic food web structure in Lake Taal and analyzing changes in its prey preferences, diet composition, morphometrics, and gonadal maturity between 2 collection periods: pre- and post-eruption of Taal Volcano. Stable isotope analysis (SIA) quantitatively confirmed that S. tawilis primarily feeds on zooplankton due to its size-selective zooplanktivorous feeding behavior. This was further confirmed by gut content analysis (GCA) revealing the dominance of copepods and cladocerans in its diet. Temporal comparison of diet composition and the selectivity index indicated a shift in the most preferred prey item from calanoids to cyclopoid copepods and a noticeable increased preference for Moina micrura , Ceriodaphnia cornuta , and Bosmina fatalis . However, morphometry and gonadal maturity showed no significant differences between the collection periods. Together, these findings provide a 15 yr update on the feeding ecology of S. tawilis , and demonstrate the capacity of combined SIA and GCA to elucidate trophic interactions. These could aid stakeholders and policymakers in creating ecosystem-based conservation and management strategies to aid recovery of this Endangered species.