Enhancing insights into foraging specialization in the world’s largest fish using a multi-tissue, multi-isotope approach

Intra-species variability in foraging strategies may be common, which has significant implications for efforts to understand and manage enigmatic species like the whale shark Rhincodon typus. The ecological relevance of differences in tissue isotopes within and between individuals in the context of foraging however depends on understanding tissue turnover times and carbon (Δ13C) and nitrogen (Δ15N) discrimination, which can vary with physiology, metabolism and diet quality. Here we examine isotope dynamics in captive R. typus as a basis for enhanced ecological insights into wild populations of the world’s largest fish and other enigmatic species. A variable diet, principally consisting of two krill (Euphausia pacifica and E. superba) provided an average of 48 MJ d-1 (± 20 S.D.), or 2.7 times (± 1.3) basal metabolic requirements. On this diet, in agreement with allometric relationships, large body sizes (3,000 to 4,000 kg) were matched by slow plasma and cartilage turnover rates (empiri...