Application of stable isotopes to assess the feeding ecology of long-finned pilot whale (Globicephala melas) in the Northeast Atlantic Ocean

• Pilot whales ingest benthic prey and/or frequent coastal waters in Northwest Iberia.
• Pilot whales ingest pelagic prey and/or frequent oceanic waters in Scotland.
• Eledone cirrhosa is the main prey ingested by pilot whales in Northwest Iberia.
• In Scotland, Histiouteuthis sp. or Todarodes sagitattus are main prey of pilot whales.
• Stable isotope analysis supports previous stomach contents analysis studies.

In order to improve our knowledge on the feeding ecology of long-finned pilot whales (Globicephala melas) in Northeast Atlantic waters, skin samples of 68 long-finned pilot whales stranded in Northwest Iberia (n = 22) and Scotland (n = 46) were analysed using stable isotopes of δ13C and δ15N. Isotopic mixing models were applied to obtain a quantitative estimate of the proportion of the main prey species in the diet of pilot whales. Stable isotope analysis revealed that 57.8–73.8% of the diet in Northwest Iberia consisted in curled octopus (Eledone cirrhosa), followed by European flying squid (Todarodes sagittatus), while in Scotland the predominant prey species was either Histioteuthis sp. or T. sagittatus, depending of the trophic enrichment factor applied. These results are generally in accordance with previous stomach content studies; however, the isotopic analysis may provide new information regarding key prey species and habitat use that could be missed or underestimated if only stomach contents analysis were used. Additionally, considering that the Atlantic Coast of Iberia was responsible for 95% of the landings of the main prey consumed by pilot whales in this area, between 2000 and 2010, these data provide trophic baseline information to be taken into account in fishery impact assessment studies and management decisions.