MEPS 748:163-174 (2024)  -  DOI: https://doi.org/10.3354/meps14708

ABSTRACT: In Iceland, occurrences of long-finned pilot whales Globicephala melas and strandings in coastal waters are irregular and thought to be related to prey movements; however, little is known about the population’s trophic ecology, making it difficult to assess its role in the regional ecosystem. To investigate the trophic niche of the species, we measured δ¹³C and δ¹⁵N values from skin and muscle samples collected from 16 strandings (12 single and 4 mass strandings) spanning 33 yr (1988-2021). We tested the effects of sex, age class and body length on δ¹³C and δ¹⁵N values within the species. We found that δ¹³C values did not differ between sexes or age classes, nor did they vary with body length. Values of δ¹⁵N did not vary with sex or body length, but varied slightly between adults and juveniles, albeit not sufficiently to support a difference in trophic levels. Whales from different mass stranding events showed similar stable isotope niche widths (approximately 0.20‰²) and overlapping isotope niches (generally >45% of the standard ellipse area corrected for small sample size). Overall, pilot whales in this region showed a narrow isotopic niche width and low intraspecific variation in isotopic niche. Future analyses using complementary chemical tracers and stomach contents will be important to identify the factors driving these patterns. The first measurements of the stable isotope niche of pilot whales presented here provide a baseline for future studies to determine niche overlap between cetaceans in Iceland, contributing to their management and conservation.

KEY WORDS: Isotopic niche · Intraspecific variation · Ontogeny · δ¹³C · δ¹⁵N