Food web properties in degraded stream communities may increase their resistance and resilience to the successful reinvasion of desired taxa after physical restoration, resulting in restoration failure. Degraded stream communities in New Zealand are often dominated by protected prey, such as freshwater snails, which are less vulnerable to predation than desired taxa such as mayflies. Therefore, recolonizing vulnerable taxa may be preferentially preyed on, limiting restoration success. Moreover, vulnerable prey may modify behaviours in the presence of protected prey e.g. changing feeding behaviour, leading to long term decreased prey fitness in these organisms. Using stream mesocosms, we investigated how differences in prey vulnerability to predation could impact restoration success. Different densities of protected snails, Potamoprygus antipodarum and vulnerable mayfly larvae, Deleatidium spp. were added to stream mesocosms alongside a predatory fish, upland bully, for 24 hours. We calculated consumption-based interaction strengths, and also observed prey behaviour. Interaction strengths were stronger between Deleatidium and fish when fewer Deleatidium were present, and less total prey biomass was consumed when higher relative densities of protected prey to vulnerable prey were present. A minimum density of Deleatidium may therefore be required to re-establish in degraded communities containing fish. High densities of snails modified Deleatidium behaviour so they appeared less on surfaces, which could lead to long term fitness reductions. These decreased levels of fitness could lead to reduced colonization success of vulnerable biota, preventing the biotic restoration of abiotically restored streams. Therefore, the degraded community structure should be considered in stream restoration planning.