First Record of Pygmy Killer Whales (Feresa attenuata) in the Gulf of California, Mexico: Diet Inferences and Probable Relation with Warm Conditions During 2014

The pygmy killer whale (Feresa attenuata) is one of the least studied cetacean species. It is a pantropical toothed whale not previously reported in the Gulf of California (GC). The aim of this study is to analyze the first sighting for this region in environmental and dietary terms. In October 2014, three pygmy killer whales were stranded and three others were sighted at sea in the Bay of La Paz, Baja California Sur, Mexico. We analyzed stomach contents and used skin samples from the dead individuals to evaluate stable isotopes of N and C. We found high delta N-15 (19.2 +/- 0.2%) and low delta C-13 (-16.5 +/- 0.1%) values, similar to those reported for other teuthophagous cetaceans in the GC. We also identified the remains of purpleback flying squids (Sthenoteuthis oualaniensis) in the stomach of the stranded individuals. The presence of tropical species, like the pygmy killer whale and probably the purpleback flying squid, appeared to be related to the anomalous SST in the GC in 2014, which was 1 to 1.5 degrees C warmer than the same period during 2013. This highlights the importance of monitoring how environmental changes alter the composition and distribution of cetacean species and their prey.