HPU partners on study revealing dominant stranding threat to Hawaiian green sea turtles

New research from Hawai‘i Pacific University has revealed that entanglement in monofilament fishing gear is now the primary cause of injury for stranded Hawaiian green sea turtles, a threatened species. Stranded sea turtles, found either on land or in the water, may be dead, injured or exhibiting signs of illness or abnormal behavior.

From 2010 to 2019, fibropapillomatosis disease was the leading stressor in stranded honu, accounting for 25% of cases, followed by fishing lines (22%), hooks (8%), shark predation (5%), boat strikes (5%) and net entanglements (3%). However, since 2016, fishing gear-related strandings have surged, the researchers said, surpassing fibropapillomatosis as the primary threat to honu in Hawaiʻi.

Monofilament fishing lines, often nearly invisible, accumulate on reefs and in nearshore waters throughout the state, endangering marine life and ecosystems. Oʻahu, due to its dense human population and high coastal fishing activity, is a hotspot for hook and line-induced trauma. Researchers believe the increase in fishing gear-related strandings is due to the growing honu population and expanded fishing activities, which result in more overlap between sea turtles and coastal fishing.

“The source of these nylon monofilament fishing lines are from fishers casting from shore or trolling from boats in nearshore waters,” said Jennifer Lynch, Ph.D., a biologist with the National Institute of Standards and Technology and co-director of the HPU Center for Marine Debris Research (CMDR). “It is unfortunate that our activities result in this damaging plastic pollution and collide with the survival of marine species. Society should take additional steps to prevent this problem while also continuing to remove it and rescue the turtles that are harmed by it.” 

The new research article, published in Marine Pollution Bulletin titled, “Marine debris impacts on Hawaiian green sea turtles (Chelonia mydas): High prevalence of hook-and-line fishing gear in strandings,” highlights how fishing line entanglement has become the primary stranding threat to honu. Research, led by scientists from multiple organizations, analyzed over 10,300 strandings between 1982 and 2024 and found that fishing line entanglements have increased over time, accounting for more than 30% of strandings annually in recent years. 

The research was co-authored by Lynch, Marthe Høiberg, Francesca Verones, Jan Borgelt and Philip Mostert from the Norwegian University of Science and Technology, Shawn Murakawa and Summer Martin from NOAA’s Pacific Islands Fisheries Science Center and Jon Gelman from Hawai‘i Marine Animal Response (HMAR). The team identified fishing gear-related strandings as the dominant anthropogenic threat to Hawaiian green sea turtles since 2016. 

In-water marine debris clean-up dives led by HMAR detail the scale of the problem. Since 2019, HMAR has measured and logged large amounts of marine debris collected during in-water clean-up activities from 137 events, revealing how monofilament lines accumulate on Oʻahu’s reefs, damaging coral habitats and posing significant risks to marine life. Over the past three years, more than 17,000 meters of fishing line have been collected, which is the equivalent of over 10.5 miles of fishing line removed from Oʻahu reefs by HMAR alone (noting that other organizations also undertake reef cleanup activities).

Each organization plays a pivotal role in addressing this issue. 

Norwegian University of Science and Technology (NTNU) researchers contributed advanced spatial modeling techniques to predict areas of high fishing line accumulation. NOAA’s Pacific Islands Fisheries Science Center provided decades of stranding data and facilitated collaboration with local response networks. HMAR’s targeted debris clean-ups and response efforts have worked to respond to and rescue entangled turtles. The National Institute of Standards and Technology (NIST) and HPU’s CMDR have been analyzing debris composition and promoting public awareness through community engagement.  

Adding to these efforts, HPU recently partnered with HMAR to open a sea turtle emergency care and rehabilitation facility on O‘ahu. The facility, HMAR Care Center, began operations in the summer of 2024 at HPU’s Makapu‘u Campus. It provides critical care to O‘ahu turtles found injured by fishing gear and other threats. Supported by a grant from the National Fish and Wildlife Foundation, the center helps rehabilitate sea turtles and offers opportunities for research, education and internships for HPU students.

Timely intervention is critical for improving survival rates among entangled honu. Many turtles affected by fishing lines are found alive, with survival rates significantly increasing through prompt in-field response. Research indicates that turtles with hook injuries have an 86% survival rate, while those entangled in lines have a 64% survival rate. Line entanglement is one of the most harmful threats turtles face, making conservation measures—such as assistance from fishers, public reporting and rapid response by trained professionals—essential for their protection.

How to help

If you encounter an entangled turtle, NOAA advises immediately calling the NOAA Marine Animal Hotline at 888-256-9840 for guidance. This may include cutting the line close to the hook to prevent further injury.

There are also multiple fishing line recycling programs across Hawai‘i, including on Maui, Hawai’i Island, Honolulu and Kauaʻi. Fishermen are urged to dispose of their gear responsibly and take care not to lose it in the environment.

For more information on NOAA’s tips for fishing around sea turtles, click here. To learn more about research at HPU’s CMDR, visit www.hpu.edu/cmdr.