TEMPERATURE ENHANCES SWIMMING PERFORMANCE OF INVASIVE SPECIES IN HAWAIIAN STREAMS

Abstract

The effects of climate change, urbanization, and hydrologic modifications on native stream fishes have been well documented; however, the impacts of their effects on invasive species are not as well understood. In the relatively short, high-gradient, and flashy streams of the Hawaiian Islands, continued changes in flow regimes, particularly increased frequency and intensity of floods, and temperature may interact with the swimming performance of invasive species to affect their distribution and abundance patterns within watersheds. Therefore, the objective of this study was to assess the swimming performance of three of the most common invasive species in Hawai‘i: hybridized Molly (Poecilia mexicana X P. formosa X P. sphenops), Green Swordtail (Xiphophorus hellerii), and Blackchin Tilapia (Sarotherodon melanotheron); at three temperature treatments. Individuals were placed in a 10-L recirculating flow tank and subjected to increasing water velocities to measure Uburst and Ucrit at three temperature treatments, 20.0, 26.0, and 32.0°C. Regardless of species, both Uburst and Ucrit increased with increasing temperature suggesting that warming stream temperatures may allow the tested species to establish and maintain populations in higher gradient portions of Hawaiian watersheds despite predicted increases in extreme flow events. Further, inter- and intraspecific differences in morphology, such as body depth, and behavior influenced swimming performance. These critical swimming speeds of non-native fish species will be important factors to model the potential spread and persistence of populations within Hawaiian watersheds, particularly as environmental conditions continue to change due to climate alterations, and allow for a better assessment of control and eradication strategies.