Changes in the abundance, concentration, and composition of the microplastics and fibers in gray seals (Halichoerus Grypus Atlantica) scat on Nantucket Island in July and November 2019 and January 2020

Marine mammals are important bioindicators for pollution such as microplastics and ecosystem health. This study is the first to report the presence of fibers and microplastics (hard fragments, foams, films, tire pieces, and knots) in gray seal (Halichoerus grypus atlantica) scat from Nantucket Island in the Northwest Atlantic. Microplastics and fibers (MPF) were found in 100 % of the scat (n = 19) with an average of 34 ± 23 MPF/scat. Differences in the amount, size, and type of microplastics and fibers present in the scat were observed. July scat contained the highest abundance of fibers and microplastics compared to the November and January scat. July scat also contained more microplastics >500 μm compared to November and January samples. November samples were dominated by microplastics <500 μm. In the samples, 32-24 % of the fibers and particles were synthetic and 68-76 % were cellulose-based (e.g. cellulose acetate, cotton). Polyester and nylon were always the dominant synthetic polymers observed. However, changes in polystyrene, polypropylene, and polyethylene along with unique polymers occurred between sampling times. Changes in the amount, size, and composition of the microplastics and fibers could potentially be due to changes in diet or seasonal changes in plastic inputs and passage through the food web. These changes in the amount and type of plastics and fibers could impact the health of all seal age classes indicating the need for more understanding of how microplastics and fibers change throughout the year and how they move through food webs.