Acoustic signature of plastic marine debris mimics the prey items of deep-diving cetaceans

Abstract

It is largely assumed that odontocetes voluntarily ingest plastic marine debris because they visually mistake it for prey. However, deep-diving whales do not rely on visual systems to forage and instead employ echolocation. Whether or not these whales misinterpret acoustic signals that lead to the accidental ingestion of plastic is unknown. We examined this question by measuring the target strength of prey items (squid, squid beaks) and various naturally weathered and fouled plastics sourced from the North Carolina coastline in situ at sea at 38, 70 and 120 kHz. Here we show that 100 % of plastic marine debris tested (plastics commonly found in the stomachs of stranded whales such as plastic bags, rope, and bottles) have either similar or stronger acoustic target strengths compared with that of whale prey items. These finding supports the hypothesis that consumption of plastic by deep-diving odontocetes is driven by a misperception of acoustic signals.

Keywords: Echolocation; Plastic marine debris; Target discrimination; Target strength.