Trophic Niche Differentiation and Foraging Plasticity of Long-Finned Pilot Whales (Globicephala melas edwardii) in Tasmanian Waters : Insights from Isotopic Analysis

Christine Jackson ^1* Rosemary Gales ² Yves Cherel ³ George Jackson ⁴ Patti Virtue ⁵

• ¹ Loma Linda University, Loma Linda, United States
• ² department of natural resources and environment Tasmania, Hobart, Australia
• ³ UMR7372 Centre d'études biologiques de Chizé (CEBC), Villiers En Bois, Poitou-Charentes, France
• ⁴ School of Medicine, Loma Linda University, Loma Linda, California, United States
• ⁵ Institute for Marine and Antarctic Studies, College of Sciences and Engineering, University of Tasmania, Hobart, Tasmania, Australia

Understanding the foraging preference of cetaceans is crucial for assessing their role as apex 50 predators and indicators of marine ecosystem health. Using stable isotope analysis, we 51 investigated trophic niche differentiation and foraging plasticity in 141 long-finned pilot whales 52 (Globicephala melas edwardii) that stranded along the Tasmanian coast at three locations 53 (Marion Bay, King Island, and Maria Island). Stranding location accounted for most of the 54 variability in skin isotopic values (δ 13 C: -17.9 ± 0.2 ‰ to -16.9 ± 0.2 ‰, Principal Coordinate 1 55 = 89%), likely reflecting differences in foraging habitats. In addition, isotopic niche overlap 56 ranged from minimal (0-10% between Marion Bay and Maria Island) to moderate (between 57Marion Bay and King Island, and King Island and Maria Island). While sex related differences in 58 isotopic niche space were minimal overall, there was some variability in the core niche space 59 between males and females at Maria Island. Dietary proportions from our mixing model support 60 a predominantly cephalopod diet for pilot whales in Tasmanian waters (91%, CI: 63-90%), with 61 greater contributions from offshore dietary sources (68%, CI: 25-95%). The dietary variability 62 across the three strandings highlights the foraging plasticity of pilot whales, which despite their 63 preferences for a wide range of oceanic cephalopods, can adopt a more generalist feeding 64 strategy when necessary. These findings provide valuable insights into the ecological role and 65 adaptability of pilot whales in Tasmanian waters, highlighting the importance of monitoring apex 66 predators to inform conservation and ecosystem management strategies in dynamic marine 67 ecosystems.