Space-time analyses and association with environmental factors of marine mammal stranding across biogeographic regions of the Philippines

Marine mammal stranding data in the Philippines has been systematically collected and collated since the establishment of the Philippine Marine Mammal Stranding Network (PMMSN) in 2005. While studies on stranding in the country have related the phenomenon to the animal’s biology, ecology, and interaction with human, no study has yet been forwarded to associate stranding with environmental parameters. Recorded stranding events from 2005 to 2016 across biogeographic regions were evaluated for spatiotemporal clustering. There were stranding clusters detected but statistically not significant, indicative of a more varied (e.g., presence of prey) than localized causes (e.g., harmful algal blooms, bacterial outbreak or oil spill). Relationship of stranding with environmental factors such as bathymetry, Chl-a, SST and front were further investigated. The study found that strandings occurred mostly in areas where the 200 m isobath are close to shore. Moreover, high stranding frequency coincided with relatively high Chl-a concentration, low SST and near frontal zones, all of which may indicate strong influence of marine mammal prey. Our GLM model suggested that distance to the 200 m isobath and average Chl-a concentration significantly influenced marine mammal stranding events. However, more than these environmental factors, year the data collected also affected stranding frequency, indicating an increasing awareness towards marine mammal stranding occurrences in the country. This study provides insights on the contribution of environmental factors on stranding patterns which is vital for conservation and management of marine mammal population.

Keywords: Marine mammal stranding, Chl-a, SST, front, GLM