Data on the reproduction, growth, and morphometric characteristics of southern blue whiting(Micromesistius australisNorman) were examined to determine its stock structure in New Zealand waters. Consistent differences in the size distribution of fish, and in the timing of spawning were found between spawning grounds on the Bounty Platform, Pukaki Rise, Auckland Islands Shelf, and Campbell Island Rise. Significant differences in morphometric characteristics were found between fish from the Bounty Platform, Pukaki Rise, and Campbell Island Rise and significant differences in growth rates were found between the Bounty Platform and Campbell Island Rise. The results provide strong evidence that fish return to spawn on the grounds to which they first recruit, and suggest that the four areas should be assessed and managed as separate stocks.