Association between porpoise presence and fish choruses:implications for feeding strategies and ecosystem-based conservation of the East Asian finless porpoise

The associations between feeding activities and environmental variables inform animal feeding tactics that max-imize energetic gains by minimizing energy costs while maximizing feeding success.Relevant studies in aquatic animals,particularly marine mammals,are scarce due to difficulties in the observation of feeding behaviors in aquatic environments.This data scarcity concurrently hinders ecosystem-basedfishery management in the context of small toothed-cetacean conservation.In the present study,a passive acoustic monitoring station was deployed in an East Asianfinless porpoise habitat in Laizhou Bay to investigate potential relationships between East Asianfinless porpoises and their prey.The data revealed that porpoises were acoustically present nearly every day during the survey period.Porpoise detection rates differed between spring and autumn in concert with activities offish choruses.During spring,fish choruses were present throughout the afternoon,and this was the time when porpoise vocalizations were the most frequently detected.During autumn,whenfish choruses were absent,porpoise detec-tion rates decreased,and diurnal patterns were not detected.The close association betweenfish choruses andfin-less porpoise activities implies an“eavesdropping”feeding strategy to maximize energetic gains,similar to other toothed cetaceans that are known to engage similar feeding strategies.Underwater noise pollution,particularly those maskingfish choruses,could interruptfinless porpoises’feeding success.Fisheries competing soniferousfishes withfinless porpoise could impactfinless porpoise viability through ecosystem disruption,in addition tofishing gear entanglement.

The effects of prey depletion on dietary niches of sympatric apex predators in Southeast Asia

Resource depletion exerts opposing pressures on co-occurring consumers to expand diets while limiting overlap with competitors.Using foraging theory as a framework,we tested the effects of prey availability on diet spe-cialization and overlap among competing Asian predators:dhole,leopard,and tiger.We used scat analysis from a prey-poor site,combined with a quantitative synthesis of 40 other diet studies,to determine biomass of different prey types consumed by each predator.We then assessed diet composition in relation to prey density,and compared diet breadth and overlap between prey-poor and prey-rich sites.In prey rich areas,all three predators specialized on energetically profitable medium and large ungulates(>30 kg),resulting in narrow,overlapping niches.Each predator shifted toward less profitable small-bodied prey(≤30 kg)as preferred ungulates declined,whereas con-sumption of preferred ungulates was unrelated to small prey abundance,as predicted by foraging theory.Diet breadths doubled under prey depletion(except leopard),but overlap declined as diets diverged via species-specific traits that facilitated capture of different types of alternative prey.Asia’s apex predators adapt similarly to depletion of mutually preferred ungulates by switching to more numerous but less profitable small prey.Yet they can also partition a depleted prey base through intrinsic niche differences,thereby avoiding competitive exclusion.Our find-ings illuminate the stabilizing properties of adaptive foraging and niche differences in ecological communities,and provide insights into the behavior and resilience of Asia’s endangered apex predators in response to prey depletion in the heavily poached forests of this region.