Translocation prevents the extirpation of a threatened minnow during ongoing drought and nonnative species invasions

Abstract

Stream habitats and disturbance regimes are rapidly changing, leading to cascading effects on native and nonnative fish communities. Managers face the ongoing and daunting challenge of trying to maintain or recover native fish populations as habitat is dried or nonnative species invade. This reduction of suitable habitat has led to species distribution declines and an overall lack of success in many native fish management activities. Our study aimed at exploring the potential success in managing a heavily depleted native fish species by attempting to reestablish extirpated populations. We first examined how the distribution of a threatened minnow has declined from its historical to its contemporary range, then we examined if numerous translocation events during increasing pressures of nonnative invasions and ongoing multi- decadal drought could successfully expand their distribution. Lastly, we assessed if nonnative mechanical removals were effective in newly invaded streams. Little Colorado Spinedace Lepidomeda vittata distribution was reduced to only two remaining populations from the 1960s through the early 2000s. Translocations started in 2001 and despite the negative effects of drought and species invasions the efforts were largely successful (8 of 9 streams), likely because managers conducted multiple translocation events and targeted perennial reaches where nonnative aquatic predators were not present. When translocated streams were invaded by nonnative fish, multi-pass mechanical removal efforts proved to be highly effective (removal rates of invaded populations: 98.1-100%). We demonstrate that translocation and mechanical removal efforts in small streams can be a pivotal tool in managing native fish species even if sufficient habitat is scarce on the landscape; however, these efforts will likely require constant and long-term commitments to maintain species throughout their native ranges.