UH research finds tangled plastic and fishing gear in pilot whales

A new study by University of Hawaiʻi at Mānoa researchers shows that nearly 23% of short-finned pilot whales that stranded over 13 years in the main Hawaiian Islands ingested several pounds of plastic ropes, netting, fishing gear and plastic bags that were discarded in the ocean.

Published in Marine Pollution Bulletin, the study was led by the UH Health and Stranding Lab within the College of Tropical Agriculture and Human Resilience. Researchers examined the stomachs and digestive tracts of 13 stranded short-finned pilot whales; necropsies of three adult males revealed large masses of tangled plastic debris inside their stomachs. 

The recovered debris was estimated at 4 to 12 pounds per whale, yielding a staggering 6,283 to 35,543 distinct plastic pieces larger than 5 millimeters – about the width of a standard pencil eraser – per individual.

“The presence of human-made materials in the stomachs of these ocean sentinels serves as a stark reminder of the impact of global plastic pollution,” said Kristi West, director of the UH Health and Stranding Lab and corresponding author on the study. “It is a clear message of the importance of keeping these materials out of our ocean.”

The debris was primarily abandoned, lost or otherwise discarded fishing gear, such as monofilament lines, ropes and netting. Sheet plastics, including garbage or carrier bags, were the next most common items. Plastic longer than 200 millimeters – or about 8 inches, about the length of an iPad – contributed more than 70% of the overall debris weight across all three whales.

Pilot whales in Hawaiʻi were found to be highly vulnerable to ingesting marine debris. A squid diet and the proximity of the Hawaiian Islands to the Great Pacific Garbage Patch, located northeast of the archipelago, may increase the risk of marine debris ingestion in these animals.

Although the whales demonstrated normal body conditions, and the debris was not identified as the direct cause of death, researchers warned that plastics cause nutritional stress and have toxic chemicals that accumulate in whale and dolphin tissues.

Data collection spanned seven years, supported by 25 lab members and funding from the Commander, United States Pacific Fleet, Environmental Readiness Division, and the NOAA Fisheries Prescott Grant program.