Research Article
Julio C Reyes and Koen Van
Abstract
The Lesser Beaked Whale Mesoplodon peruvianus Reyes, Mead & Van Waerebeek 1991 Revisited, with Biological Observations on New Specimens from Peru Despite three decades since its discovery, information on the biology of Mesoplodon peruvianus remains scant. Adding 46% to the global specimen catalog (presently N=36) we document 10 new specimens plus one tentative case, all from Peru, augmenting knowledge about its natural history. Enhanced samples substantiate initial insights of morphological features. High values for girth at axillae, girth halfway from anus to flukes and maximum flipper width, and low values for dorsal fin height and distance from the tip of the rostrum to dorsal fin contain diagnostic value among Mesoplodon spp. Adults exhibit pronounced sexual dimorphism. Lateral excrescences of the maxillae on the distal rostrum, a raised jawline, two mandibular teeth protruding above gum level, extensive tooth scarring of skin and a broad white swath across anterior body are exclusive to adult males. Dimorphic also is the degree and direction of vomeral proliferation in the mesorostral canal. Atlas, axis and 3rd cervical vertebrae ankylose in adults. Colouration consists of a basic counter-shading pattern in juveniles, females and subadult males. Fully adult males show a bold white swath, although significant individual and geographic variation may occur. Apparent high density zones include Peru's continental slope/shelf waters (ca. 60% of known specimens), the Eastern Tropical Pacific and the Gulf of California. The latitudinal reach is at least from 42°31'S to 36°47'N. In Peru, by-catches and sightings were recorded predominantly in late spring and early summer. M. peruvianus is the only mesoplodont frequently captured in smallscale coastal fisheries. Phyllobothrium delphini and Tetrabothrius forsteri (Cestoda) and Campula sp. (Trematoda) are new host records. Stomach contents included squid beaks (i.a. Gonatus sp., Teuthowenia megalops, and Histioteuthis sp.), unidentified fish otoliths and vertebrae, as well as the crustaceans Acanthephyra sp. and an unidentified gammarid.