Feeding whales are at risk of ingesting floating debris: Mapping distribution of risk in the Stellwagen Bank National Marine Sanctuary
Plastic pollution has emerged as a major and widespread threat to wildlife in the marine environment. Stellwagen Bank National Marine Sanctuary and the surrounding waters within Massachusetts Bay are an important summer feeding ground for mysticete whales including humpback (Megaptera novaeangliae), fin (Balaenoptera physalus), minke (B. acutorostrata) and the critically endangered North Atlantic right whale (Eubalaena glacialis). The feeding ecologies of these species, many of which employ lunging or skimming at the surface, may put them at direct risk of ingesting floating debris leading to morbidity and mortality. Ingestion has been documented in several cetacean species; however, knowledge regarding to what extent plastic pollution poses a threat to cetaceans is lacking. In order to better understand areas of overlapping distribution and the potential risk in the Sanctuary we used distance sampling methods to quantify and map at-sea distribution of debris and three cetacean species (humpback, fin, and minke whale) using data collected on board commercial whale watch vessels.
A total of 17,700 km of trackline was surveyed in the summer of 2014 for debris and cetaceans. We estimated an abundance of 31,500 (CIs: 15,100 - 65,900) pieces of marine debris in the region with a density of 5.7 objects per km2 (CIs: 2.73 - 11.91). Debris is widely distributed throughout the region while distribution of cetacean species, especially humpback whales, is more localized and influenced by underlying bathymetric features. Minke whales have the most wide ranging distribution of the three species analyzed and may be particularly sensitive to interactions with debris. Cetaceans are increasingly susceptible to ship strike, entanglement, and stranding which complicates assessing the threat of marine plastics. Additionally, the highly mobile nature of these animals makes it difficult to attribute documented ingestion to any specific region. Attempts to quantify debris distribution in important cetacean areas will help clarify potential regional impacts and guide future management plans.