In eastern Canada during the early 1990s, a shift in the distribution of Capelin (Mallotus villosus) resulted in a prolonged absence (at least 8 years) of the preferred prey for the Atlantic Puffin (Fratercula arctica) breeding at Gannet Islands, Labrador. It has been documented that there is no suitable alternative prey to Capelin in the northwest Atlantic for seabirds, thus these extreme changes in food supply may have negative effects on reproduction and adult survivorship. In this study, foraging behavior, chick growth and productivity of Atlantic Puffins at the Gannet Islands, Labrador during 1996-1998 were compared to data in a study undertaken in 1981-1983, prior to the decline in Capelin abundance. It was confirmed that the dramatic change in Capelin abundance was reflected in chick diet as Atlantic Puffin chicks received 50-70% (by mass) less Capelin in 1996-1998 than in 1981-1983. Hatch dates did not differ among decades and breeding success, chick wing growth and fledge mass were unaffected. The only breeding parameter significantly affected by the change in food supply was chick growth (mass gain). Taken together, our data indicated that following a decline in Capelin abundance, the Atlantic Puffin did not experience breeding failure and effectively reared young utilizing suitable alternative prey which included post-larval sandlance and other small fish and invertebrates.