Estimates of length at birth and growth in the first year were made for northern and southern offshore spotted dolphins. Length at birth, the length at which 50% of the specimens are postnatal, in northern offshore spotted dolphins in the eastern tropical Pacific has been estimated to be 85.4 cm. The estimate is a function of kill per set and data were stratified accordingly to investigate and account for this. Average length at birth for southern offshore spotted dolphins has been estimated to be 83.2 cm, although sample sizes are considerably smaller for this stock. An analysis of monthly distributions of length revealed that two cohorts are born per year in the northern offshore spotted dolphin, at least in part of their geographical range, but only one in the southern offshore spotted dolphin. Growth curves were fitted to the progressions of mean length by month to give estimates of length at one year of 129.4 cm for the northern offshore spotted dolphin (the mean of the estimates from the growth curves of the two cohorts), and either 127.9 cm or 130.6 cm for the southern offshore spotted dolphin depending, respectively, upon whether length at birth was estimated using southern data or the combined data. Length at one year was estimated to be 123 cm for the northern stock from a growth curve fitted to the lengths and ages of specimens aged by dental growth layer groups (GLGs).

Technical Report

Pacific Ocean