Habitat use and trophic ecology of the introduced snapper Lutjanus kasmira and native goatfishes in Hawai'i

There have been persistent concerns among the fishing community in Hawai'i that the introduced snapper Lutjanus kasmira has caused declines in populations of native shallow-water fishery species. L. kasmira has purportedly caused these declines through predation on juveniles and/or competition with adults for food or shelter. Because goatfishes were commonly cited as having been adversely affected by the introduced snapper, the present investigation compared habitat use and trophic ecology of L. kasmira and three native species of goatfish (Mulloidichthys flavolineatus, M. vanicolensis and Parupeneus multifasciatus). Studies of small-scale habitat use indicated that L. kasmira can displace resting schools of M. vanicolensis farther from shelter. However, clear detrimental effects of this displacement have not been quantified, and any such effects would likely be limited to locations where these species co-occur at high densities. Acoustic telemetry and research fishing found that larger-scale habitat use patterns of L. kasmira and goatfishes would be unlikely to drive competition for food. Areas used by Mulloidichthys spp. for nocturnal feeding were generally deeper sandy habitats, while those used by L. kasmira were shallower and closer to the reef. P. multifasciatus always stayed relatively close to the reef but fed during the day. Fish were collected for dietary analysis off the south shore and Kane'ohe Bay of O'ahu, and off the west shore of the Island of Hawai'i. Archived diet data from the Northwestern Hawaiian Islands and Puako Bay on the Island of Hawai'i were also incorporated into dietary analyses. Although there was some similarity in types of prey consumed by L. kasmira and P. multifasciatus, there was no evidence that abundance of L. kasmira affected the diet or biological condition of P. multifasciatus or any other species in the study. Additionally, no fish (e.g. P. porphyreus, Zebrasoma flavescens) or invertebrate (Ranina ranina, Octopus cyanea) species that were important to local fisheries were identified in L. kasmira guts. Given the lack of evidence of strong ecological interactions between L. kasmira and other species in this study, fears that the introduced snapper has had a detrimental impact on commercially important native species in Hawai'i appear to be unfounded.