Conservation trade-offs: island introduction of a threatened predator suppresses invasive mesopredators but eliminates a seabird colony

Offshore islands are ideal for establishing insurance populations of endangered species as they often lackthreatening processes found on mainlands. However, introductions of endangered predators can have complexeffects on island species. The Tasmanian devil (Sarcophilus harrisii) was introduced to Maria Island in Tasmania,Australia in 2012 to establish an insurance population separate from a novel disease causing declines throughoutits native range. Maria Island has small breeding colonies of the short-tailed shearwater (Puffinus tenuirostris) thatare preyed on by an invasive mesopredator (feral cat, Felis catus) and an introduced native omnivore (commonbrushtail possum, Trichosurus vulpecula). We tested whether the introduction of devils increased predationpressure on shearwaters or reduced it by suppressing cat and possum activity. We measured predator activity onshearwater colonies, and surveyed burrow occupancy of shearwater adults and chicks, from 2013 to 2016; wealso monitored shearwaters at a colony on a nearby island without terrestrial predators for comparison.Increasing devil activity was associated with decreasing total predator activity at shearwater colonies on MariaIsland due to declines in possum and cat activity, evidently caused by predation on possums by devils, andcompetition with cats. However, shearwater colonies continued to decline, reaching zero occupancy within fouryears of devil introduction. Because of their larger size and ability to dig, devils had greater impacts on nestingshearwaters than either cats or possums. Conservation translocations of endangered predators must considertrade-offs between their protection and potential impacts on non-threatened native prey species