Data from: 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 (empirically derived
as 9 months and 3 years, respectively), which provide tissue-specific
limits on the time-scales over which we can isotopically detect changes in
diet in this species. Average diet-to-tissue discrimination showed
significant variation between tissues (plasma and cartilage), and among
growing and fasting individuals (Δ13C range: 1.5 – 5.5 ‰; Δ15N range: −0.1
– 2.9 ‰). Assimilation rates increased with temperature and were higher
for the smaller E. pacifica (15 ± 2 mm) than E. superba (48 ± 2 mm).
Growth significantly lowered both Δ15Nplasma and Δ15Ncartilage, with
inappetence markedly reducing Δ15Nplasma and Δ13Cplasma, as well as
significantly altering blood biochemistry. Captive findings facilitated
the first robust multi-tissue growth- and nutrition-corrected isotope
analysis of a wild R. typus population, suggesting individual foraging
specialization on low trophic level mid-ocean or coastal prey. Long-term
fasting during ocean-basin scale migrations may be common and such
metabolic effects should be carefully quantified when isotopically
assessing intra-species foraging differences. The
metabolically-constrained multi-tissue, multi-isotope approach described
can facilitate ecological insights that are indispensable for effective
conservation and management of globally threatened, but poorly understood,
species by identifying differences in key foraging areas and target prey
within and between individuals.