REVISION OF THE FRIGATE TUNAS (SCOMBRIDAE, AUXIS), WITH DESCRIPTIONS OF 2 NEW SUBSPECIES FROM THE EASTERN PACIFIC

Two cosmopolitan species of frigate tunas, Auxis thazard (Lacepede) an d A. rochei (Risso), are differentiated primarily by the width of the corselet under the origin of the second dorsal fin and by the anterior extent of the dorsal scaleless area above the pectoral fin. Auxis tha zard has five or fewer scales in the corselet under the second dorsal fin, and the dorsal scaleless area extends anterior to the tip of the pectoral fin; A. rochei has six or more scales and the dorsal scaleles s area does not reach the tip of the pectoral fin. Of nine morphometri c characters examined with ANCOVA, four body depth measurements were s ignificantly different between the species. Auxis rochei is a slender species with each of the four body depth measurements approximately eq ual, whereas A. thazard is more tuna-shaped, with a deeper, more robus t body and with more unequal body depth measurements. For both species , eastern Pacific populations differ from Atlantic and Indo-West Pacif ic populations at what we consider the subspecific level. The eastern Pacific A. thazard brachydorax new subspecies has more gill rakers, us ually 43-48 vs. usually 38-42 in A. t. thazard. Body depth at anal-fin origin, pectoral-fin length, and corselet width were also significant ly different between A. thazard brachydorax and A. t. thazard. The eas tern Pacific A. rochei eudorax new subspecies has an even wider corsel et than that of A. rochei rochei, usually more than 20 scales wide com pared with 6-19 scales.