This study documents the marine sponge fauna (Phylum Porifera) in the Northwest Atlantic, through the used of fishermen’s local ecological knowledge, fisheries observer data, trawl survey data and in situ exploration. A review of the role of structural benthic species, including ascidians, bryozoans, corals, hydroids and sponges as ecosystem engineers provides the context within which to discuss the contribution of sponges to seafloor habitat heterogeneity. Fishermen’s knowledge is useful in identifying areas of high concentration of benthic structural species, but is not particularly useful in determining the distribution of specific sponge species, with the exception of glass sponges, with the common name “Russian Hat”. Fisheries observer data from the Scotia Fundy Region and trawl survey data from the Newfoundland Region were obtained from the years 1977-2001 and 1973-2007 respectively. Despite the lack of systematic collection of information on sponge catches, prior to 2002, the information recorded show broad scale patterns of sponge distribution from the Scotian Shelf to the Eastern Arctic, and this thesis brings this information together for the first time. The move to deeper and more northern waters following the groundfish collapse in 1992 resulted in large catches of sponges, up to 5000kg per set, on the Labrador Shelf and Eastern Arctic. The combination of fishermen’s information, observer data and in situ research on the Scotian Shelf resulted in the identification of a previously undescribed and globally unique population of Vazella pourtalesi, a Hexactinellid sponge, in the Family Rossellidae. The impacts of fishing on the sponge community of the Gulf of Maine were examined by quantifying the sponge community inside and outside of the Western Gulf of Maine Closed Area. After two years, the sponge community within the closed area was dominated by the demosponge, Iophon sp. while the area that remained open to fishing had a higher diversity of sponges. The information presented in this thesis can inform marine ecosystem management, particularly in light of international obligations to protect vulnerable marine ecosystems.