Piscivorous bird assemblages at functional rather than species level better predict predation risk on open culture fish ponds within enhanced fertilization treatment regime

This study explored how increased water turbidity in open-aquaculture ponds as a result of enhanced fertilization influences piscivorous bird assemblages and predation pressure on fish. Fertilization treatments were applied to 24 earth-bottom ponds, and bird assemblages, visitation frequencies, diversities and predation rate responses were compared at species richness and across four functional group scales during six months. Bird visitation frequency, species richness and functional diversity increased around unfertilized ponds, especially for large wading birds. Fertilization and bird species richness were each negatively related to bird predation rate, whereas functional diversity was positively associated with predation rate regardless of pond fertilization. Furthermore, predation rate reduced in response to pairwise interactive effects of fertilization and functional group identity, but increased with fertilization’s respective interaction with functional diversity and visitation frequency. Contrastingly, species richness showed no interactive effect with fertilization or visitation rate. Thus, in applying enhanced pond water fertilization as a mitigation measure for controlling and tracking damage impact caused by piscivorous birds, it is potentially more beneficial to adopt a bird functional rather than species-based approach, given the observed higher sensitivity of functional diversity in predicting predation rates. The findings present novel, farmer-centered and affordable strategies for piscivorous problem-bird control toward sustainable aquaculture.