There is no significant difference in total length between sexes for Z. cavirostris, with an average adult size of 6,1 m. There are several reports of specimens that exceed 7,0 m in length, but virtually all of these appear to be either estimates of lengths ar based on misidentified animals. The largest accurately measured specimen of Z. cavirostris is an adult male that measured 6,93 m from the Falkland Islands