Abundance of Marine Mammals in Waters of the U.S. Gulf of Mexico During the Summers of 2017 and 2018

In this report, we describe the results of large vessel, visual line-transect surveys conducted by the NMFS, Southeast Fisheries Science Center in U.S. waters of the Gulf of Mexico during the summers of 2017 and 2018 as a part of the larger Gulf of Mexico Marine Assessment Program for Protected Species (GoMMAPPS). The primary objective of these surveys was to collect data and samples to support assessment of the abundance, habitats, and spatial distribution of cetaceans within U.S. waters. These data and resulting abundance estimates support the assessment of marine mammal stocks as required under the Marine Mammal Protection Act (MMPA). The MMPA requires that stocks of marine mammal species in U.S. waters be maintained at or above their optimum sustainable population level (OSP), defined as the number of animals which results in the maximum net productivity. To meet this requirement, the National Marine Fisheries Service (NMFS) conducts research to define stock structure, and for each stock, estimates annual human-caused mortality and potential biological removal (PBR), the maximum number of animals that may be removed from a stock due to human activities (e.g., fisheries bycatch) while allowing the stock to reach or maintain its OSP. PBR is calculated following specific criteria using the estimated minimum abundance of the stock, its maximum net productivity rate (theoretical or estimated), and a recovery factor (Barlow et al., 1995; Wade and Angliss, 1997). The NMFS is required to prepare a Stock Assessment Report (SAR) for each stock to update abundance, stock structure, maximum net productivity, human-caused mortality, PBR, and status (e.g., Hayes et al., 2019). This study describes the results of two vessel based surveys and resulting abundance estimates for U.S. Gulf of Mexico oceanic stocks of marine mammals.