Quantifying the Current and Future Risk of Invasiveness of the Non-native Fishes in Ramsar-listed Lake Naujan, Philippines

The number of non-native fish species introduced into the Philippines has steadily increased over the last decades, similar to other Southeast Asian countries. This trend of non-native species introductions is of high concern for the conservation of the native aquatic biota of the country, as invasive fishes are known to be responsible for a wide range of detrimental effects. In this study, the 13 non-native freshwater fish species recently reported for Ramsar-listed Lake Naujan (Province of Oriental Mindoro) were screened for their invasiveness risk under current and predicted climate change scenarios. Of the screened species, 23.1% and 61.5% were ranked as high risk under current and future climate conditions, respectively. The higher-risk species were redbelly tilapia Coptodon zillii, Nile tilapia Oreochromis niloticus, and guppy Poecilia reticulata. These findings indicate a high likelihood that the already threatened aquatic biota of Lake Naujan will be further affected by the presence of the resident non-native fish species in the near future. Recommendations include: (i) implementation of an introduction vector and pathway analysis; (ii) establishment of a comprehensive list or database of potentially invasive or prohibited species; (iii) continuous monitoring and surveillance of fish activities in the lake; and (iv) implementation of a comprehensive, government-led information, education and communication campaign. The outcomes of this study are also meant to serve as a foundation for the development of shared regulations to control the international trade of non-native fish species not only in the Philippines but also among southeast Asian countries.