Behavioral responses of Irrawaddy dolphins, Orcaella brevirostris (Owen in Grey, 1866) to fishing boats in a globally important marine mammal area in central Philippines

Authors:
Machir Glib Lirazan¹, Ericson Vince Ray Yulo^1,2, Maria Therese Kathleen Martir¹, Regie Antonette Salvilla¹, Jessica Oñate-Pacalioga^1,3, Manuel Eduardo de la Paz^1,4*
1Natural Sciences Department, University of St. La Salle, Bacolod City, Negros Occidental, Philippines
²Provincial Environment and Natural Resources Office, Bacolod City, Negros Occidental, Philippines
³Institute of Environmental and Marine Sciences, Silliman University, Dumaguete City, Negros Oriental, Philippines
⁴Laboratory of the Biology of Aquatic Resources, Graduate School of Integrated Sciences for Life, Hiroshima University, Hiroshima, Japan

*Correspondence: makoy28_delapaz@yahoo.com

ABSTRACT
The Irrawaddy dolphins, Orcaella brevirostris (Owen in Grey 1866) of Guimaras Strait, Philippines, have been known to utilize a core habitat within a coastal area surrounding the Bago River estuary in Negros Occidental. The dolphins’ close dependence on coastal waters often makes unavoidable direct interaction with human communities. Daily human activities in the coastal areas can pose serious threats to the dolphins, including high risk of entanglement in fishing nets, pollution, and disturbances caused by fishing boats and larger vessels. This study determined the behavior of dolphins toward different kinds of boats present in Bago-Pulupandan coastal waters. Factors identified to affect dolphin behavior towards boats include boat type (motorized or not), size, and distance from dolphins. Dolphin behavior towards boats were categorized as either positive, negative, or neutral. Results showed that the dolphins mostly exhibited neutral behavior towards boats, regardless of state and boat type. The dolphins’ passive behavior around vessels may make them more vulnerable to boat strikes, especially from speeding motorized boats. Recommendations include strict regulation of boat speed and traffic within their core habitat to minimize injuries, net entanglement, and avoid mortality.
Keywords: behavioral responses, boat traffic, fishing gears, habituation, Guimaras Strait