Assessing the potential for successful translocation and co-management of two endangered aquatic species

Translocation programmes for endangered species typically focus on a single species, but in areas where little native habitat remains, it may be necessary to translocate multiple species to the same sites. Interactions between translocated species, such as predation and competition, are among the factors that need to be considered when planning multispecies translocations. Translocation sites for aquatic species are particularly scarce in southern California, where a limited number of sites exist for historically co-occurring endangered mountain yellow-legged frogs Rana muscosa and unarmoured three-spine sticklebacks Gasterosteus aculeatus williamsoni. To determine how these species would interact if translocated to the same sites, we carried out experiments ex situ with R. muscosa tadpoles and a surrogate subspecies of stickleback (G. a. microcephalus). We found that (1) adult sticklebacks preyed on hatchling tadpoles but did not consume R. muscosa eggs or large tadpoles; (2) tadpoles did not consume stickleback eggs or disturb sticklebacks nests; and (3) both species' microhabitat use shifted slightly when the other was present. Our results suggest that these species can likely be co-managed successfully, if measures are taken to curb stickleback predation on tadpoles until the R. muscosa population is well established. Using ex situ studies to evaluate species interactions prior to translocation is an approach that could prove useful in other species recovery programmes. Multispecies translocations could make better use of available resources when habitat is limited and promote ecosystem recovery by re-establishing interactions among native species.