Northward habitat expansion of whale shark (Rhincodon typus) in the Western Pacific region

Abstract

Climate change has shifted the global distribution of marine organisms. According to the International Union for Conservation of Nature (IUCN), whale shark (Rhincodon typus) is widely distributed between approximately 30°N and 35°S, with occasional seasonal migration to the north and south. Recently, changes in the spatial distributions of whale shark were detected; the Ishikawa coast near 36.5°N in Japan was recorded as the northernmost limit of the distribution for whale shark in the western Pacific Ocean, but recently, this species has been observed occasionally near 38.4°N in the coastal sea off the east coast of Korea. In this study, using 16 years (2004–2019) of whale shark presence only data in the Indian and Pacific Oceans, we applied both the Gradient Boosting Machines model and the Generalized Additive Model to assess whether the occurrence of whale sharks in Korean waters was an accidental event or whether the suitable spatio-temporal habitat was formed in Korea waters. Environmental predictors in the full model included chlorophyll-a, model-estimated net primary productivity, sea surface temperature, water depth, and distance to shore. Habitat suitability was mainly driven by the spatial variation in bathymetry and sea surface temperature, although these effects differed slightly by season, with overall range expansion. These results provide insight into possible geographic variation of whale shark and the potential suitable habitat of the endangered and vulnerable species for their conservation under a rapidly warming climate.