There is a growing global demand for a more sustainable seafood industry, and pre-competitive initiatives have emerged on multiple continents to meet this demand. Such initiatives could have “cascading effects,” suggesting that their impacts may extend beyond their direct participants to effect broader, industry-wide change. To date, little research has been conducted to determine whether pre-competitive initiatives are triggering such cascading changes, in part as a result of the limitations of existing methods for monitoring and quantifying such impacts. This study represents a methodological advance and presents an empirical analysis of potentially cascading corporate sustainability engagement, using the initiative Seafood Business for Ocean Stewardship (SeaBOS) and the Japanese seafood industry as a case study. The study first provides an overview of the sustainability reporting landscape within the Japanese seafood industry. It then examines the evidence for the impacts of SeaBOS on Japan’s 17 largest seafood companies, including three SeaBOS member companies (Maruha Nichiro Corporation, Nissui – or Nippon Suisan Kaisha, and Kyokuyo Co. Ltd.). The results illustrate that the Japanese seafood industry is characterized by diverse company profiles, a wide range and scale of factors influencing corporate sustainability, and varying performance on sustainability across companies. Due to the inherent complexity of the seafood industry, determining whether the SeaBOS initiative has triggered cascading effects or industry-level transformation is challenging. However, there are indications of cascading stewardship effects: SeaBOS member companies have been early movers in the Japanese seafood industry, and other companies have followed similar pathways. Further analysis of these cascading effects will require diverse methodological approaches, continuous monitoring, and increased transparency and disclosure from companies.