This paper presents a novel method to detect an important flow feature, vortices, in the ocean. Our method can detect closed streamlines around vortex cores. Coupled with existing vortex core detection, the entire vortex area, which is the combination of the vortex core and surrounding streamlines, can be detected. A variety of feature extraction methods are presented, and those more pertinent to this study are implemented. Detection results are evaluated in terms of accuracy, clarity and usability.