Assessment of anthropogenic threats to marine megafauna in Thailand

Abstract

Thailand is ranked among the top 20 nations in the world for capture fisheries production and is a popular destination for marine tourism providing the main sources of income and livelihoods for Thai coastal communities. However, rapid human population growth, migration and development of coastal areas have led to increased pressures from small-scale fisheries (SSF) and tourism focussing on marine megafauna (marine mammals, sea turtles and elasmobranchs) in coastal waters of Thailand. To date, effects of anthropogenic activities on marine megafauna in Thailand are poorly understood due to lack of research effort, effective assessment, monitoring and management. This thesis represents the first comprehensive evaluation of anthropogenic threats to marine megafauna in Thailand and includes a catch assessment of SSF using a questionnaire survey with fishers and an assessment of the effects of boat-based dolphin-watching tourism on Indo Pacific humpback dolphin (Sousa chinensis) behaviour using passive acoustic monitoring (PAM) combined with shore-based observations. The thesis focuses on three odontocete species: Indo-Pacific humpback dolphin, Irrawaddy dolphin (Orcaella brevirostris) and Indo-Pacific finless porpoise (Neophocaena phocaenoides); resident off Don Sak, Surat Thani and Khanom, Nakhon Si Thammarat in the central-western Gulf of Thailand, where the species are subjected to multiple anthropogenic threats including fisheries and marine tourism. The research provides the first independent investigation of odontocete occurrence and foraging occurrence using PAM and a new estimation of the abundance of Indo-Pacific humpback dolphins based on capture-recapture analysis of photo-identification data collected during boat-based surveys. The thesis results reveal that the level of marine megafauna catch in Thai SSF is of concern and likely unsustainable for some of the documented species and highlights the need for further investigation. PAM indicated relatively high acoustic activity of odontocetes in the central- western Gulf of Thailand, and in particular off Laem Thuat Pier, Don Sak, Surat Thani. Further, the results showed that the dolphin-watching tourism significantly affected the short-term behaviours of Indo-Pacific humpback dolphins at levels that may result in long-term negative impacts on both individual and population levels. Odontocete populations in the central western Gulf of Thailand are threatened by a combination of human threats including fisheries catch, coastal construction, vessel traffic and tourisms. This thesis highlights the urgent need for better understanding and mitigation of the effects of these anthropogenic activities on marine megafauna in Thailand through further research, conservation and management. The results of the thesis provide an initial evidence base for initiation of conservation and management actions to safeguard the health of marine megafauna species in Thailand and odontocete populations in the central-western Gulf of Thailand and the ecosystem services they provide.