Her research is focused on how large pelagic fish such as tuna and sharks utilize the open ocean. Block used her Pew fellowship to deploy a new generation of remote technology devices called pop-up satellite archival tags to track the biology, migratory patterns, and stock structure of tuna. This interdisciplinary project combined marine biology, oceanography, and engineering to develop the new technology. Through her “Tag-A-Giant” program, Block and her team pioneered the use of two types of electronic tags. She worked with both commercial and recreational fishermen to catch tuna and tag them in the field. The project then entailed collection and analysis of data to learn new information about these deep-ocean-dwelling species. This advanced technology provides marine researchers with a new tool for studying other inaccessible marine species and will provide scientific data to support sound international conservation and management of tuna populations. From the data, Block and her colleagues have published landmark papers in the prestigious journals Nature, Science, and Proceedings of the National Academy of Sciences. She was able to describe at least two populations of bluefin that occupy the North Atlantic: one that breeds primarily in the Gulf of Mexico, The Bahamas, and the Straits of Florida; and one that forages in the west but breeds in the Mediterranean.