A taste for squid: the diet of sperm whales stranded in Greece, Eastern Mediterranean

Sperm whales (Physeter macrocephalus) inhabiting the world's oceans, prey mainly on cephalopods, but also feed on fish when found in higher latitudes. However, the feeding habits of endangered Mediterranean sperm whales have received little attention with thus far only two individuals analysed for their stomach contents. This study expands the available knowledge using analysis of the stomach contents from nine individuals stranded in Greece between 2005 and 2014. 48,166 prey remains were examined in total and 28,258 of them were identified to show that sperm whales fed on 18 prey species (17 cephalopods and one teleost) from 14 different families. 15 of these species were deep-sea squids, which are not presently targeted by fisheries. The most important prey species, both in terms of numerical abundance (%N) and abundance by weight (%W), was the oceanic squid Histioteuthis bonnellii (%N = 48.4, %W = 66.3) followed by H. reversa (%N = 28.4, %W = 13.8) and Octopoteuthis sicula (%N = 8.5, %W = 17.2). Calf sperm whales consumed smaller cephalopods of these three prey species than non-calves, probably because larger cephalopods are more difficult to catch. The vast majority of ingested cephalopods were gelatinous, slow-swimming and small. Therefore, sperm whales inhabiting the Greek Seas and likely the whole eastern Mediterranean Sea, appear to target prey that are easy to catch, but need to be consumed in great numbers to fulfil the energy requirements of the whales.