Marine mammals are wide-ranging, relatively long-lived organisms that play a crucial role in maintaining healthy ocean ecosystems. Often referred to as ecosystem engineers and sentinel species in marine ecosystems, these charismatic megafauna feed at a variety of trophic levels, affecting food web dynamics and cycling of chemicals and nutrients in the water column as well as in benthic habitats, both nearshore and in the deep ocean. An understanding of their abundance and distribution is an essential starting point for evaluating their role in ocean ecosystems. Accordingly, marine mammals have been included among key variables to monitor in ocean observing systems, from core variables for the U.S. Integrated Ocean Observing System (IOOS) to an Essential Ocean Variable (EOV) for the Global Ocean Observing System (GOOS). They also contribute to several Essential Biodiversity Variables (EBVs) for the Group on Earth Observations Biodiversity Observation Network (GEO BON). Further, evaluation of the health of marine mammal populations will help deliver societal benefits by contributing to the UN Decade of Ocean Science for Sustainable Development; informing reporting activities such as the World Ocean Assessment; and supporting achievement of Sustainable Development Goal 14, the post-2020 framework for the Convention for Biological Diversity, and a new treaty for conservation and sustainable use of marine biodiversity beyond national jurisdiction. The goal of this Interagency Ocean Observation Committee task team was to advance the integration of existing biological observations from local, regional, and federal sources using best practices to inform national needs and ultimately feed seamlessly into the Global Ocean Observing System, as appropriate. To accomplish this goal the subgroup focused on marine mammals to: 1. Reconcile the IOOS core biological variables with GOOS EOVs and the GEO BON EBVs, identifying where there are clear synergies in terms of spatial and temporal observing requirements and existing observation infrastructure and delivery including best practices/standards. 2. Identify and improve pathways for data flow for observations of these variables from Federal sources, such as the stock assessments conducted by NMFS and FWS, into IOOS with a focus on identifying and implementing best practices surrounding standardized data collection and delivery adhering to the FAIR and CARE data principles, as appropriate.