Large-scale relationships between changes in abundance of coastal breeding Herring (Larus argentatus) and Great Black-backed (L. marinus) gulls and commercial fisheries landings of bottom-dwelling groundfish spanning 28 years in four of Canada's east coast Provinces were investigated. Herring and Great Black-backed gull abundance data were compared between survey periods prior to (1986–1990) and following (2002–2006 and 2010–2014) the widespread reduction of groundfish fishing activities due to a moratorium that began in 1992. Regionwide declines in the number of breeding Herring and Great Black-backed gulls were observed between the 1986–1990 and 2002–2006 survey periods (Herring Gull: -3.7% per year; Great Black-backed Gull: -3.6% per year) and between the two periods following the moratorium (Herring Gull: -1.6% per year; Great Black-backed Gull: -4.1% per year). Total groundfish landings reported for the study area declined by 76% between the 1990–1992 and 2002–2006 fishing periods, and declined by an additional 25% between the two periods following the moratorium. A positive relationship was found between Province-wide groundfish landings and the number of breeding Great Black-backed Gulls corrected for coastline length. These results support the hypothesis that the moratorium reduced the availability of discards, which in turn played a role in the region's widespread decline of breeding Herring and Great Black-backed gull populations. In addition to continued declines in available discards, additional factors are likely influencing recent regional breeding population trends, including declines in available refuse and forage fish and increases in novel food sources such as expanding American mink (Neovison vison) farms.