The predicted future shortfall in seafood production from tropical small-scale fisheries demands support to help diversify income streams and food production for coastal communities. Livelihood diversification can comprise the enhancement or addition of components to existing fisheries, yet the likely socioeconomic impacts are unclear. With a long history of nondeleterious introductions, the marine snail “trochus” (Rochia nilotica) was introduced to Samoa from 2003 to 2006 to offer a new artisanal fishery resource. Some 15 years later, we surveyed 303 fishers using structured questionnaires and mixed effects models to evaluate how the fishery has contributed to fisher well-being and what factors have influenced the socioeconomic impacts. Most fishers consumed part of their catch and both fisherwomen and fishermen shared harvests informally within communities, thereby bolstering resilience of the social-ecological systems at the community level. More than one-quarter of fishers sold part of their catch and the new earnings represented 17% of their gross income from all sources. Fishing incomes were gender equitable and influenced by fishing frequency and capital assets (boats). Most fishers were satisfied with income from the relatively new fishery and improved income was reported by a majority of fishers, especially those younger and less experienced. Additional money from the fishery was most often spent on food, church tithing, and school fees. This relatively new fishery fostered positive well-being outcomes that were gender inclusive. Extrapolations of annual incomes across the fishery reveal a rapid return on investment from foreign-aid funded development. The study reveals that certain coastal artisanal fisheries can be gender equitable and that benefits are likely underestimated because of subsistence consumption and informal distribution networks. Diversifying the marine resources accessible to small-scale fishers offers a promising strategy to support coastal livelihoods and strengthen resilience of social-ecological systems.