Health Effects of Gillnets on Sea Turtles along the Cape Fear River

The lower portion of the Cape Fear River in North Carolina is home to fisheries and sea turtles which is a costly combination for both. In this area, fishermen use gillnets, or large mesh nets used to capture fish, that are hazardous to both sea turtles and the fishing industry. Sea turtles can get caught in the nets, ruin them, and inflict injury or death upon themselves.

In an effort to decrease mortality rates, North Carolina law requires fishermen to supervise their gillnets during the summer months. Since gillnets are in the water for an average of twelve hours (soaked), many fishermen don’t supervise their nets for the full time in an effort to cut costs (1).

Many sea turtles escape the gillnets only to die later on from boating accidents, predators, or their injuries. In an effort to decrease sea turtle mortality, researchers from the University of North Carolina-Wilmington and Grice Laboratory in Charleston, South Carolina analyzed sea turtle blood biochemistry to determine the likelihood of survival after entanglement and release.

The researchers captured eighteen sea turtles using a mesh gillnet soaked for a maximum of six hours from May to October. To ensure the safety of the animals, the sea turtles were immediately brought to the surface if they were in danger of drowning.

Once the sea turtles were detangled/ released the researchers drew blood immediately after the turtle was brought on board. They then tested the turtles reflexes, checked for injuries, and monitored behavior before the turtle was released about ten meters from the capture site.

The scientists rated the turtles from A to D, with A meaning perfect condition and D being low activity, severe injuries, and missing or delayed reflexes.

Only three of the eighteen sea turtles rated as an A

Only three of the eighteen sea turtles rated as an A. Out of those who did not, their blood work showed elevated levels of lactate, LDH (lactate dehydrogenase), and other chemicals which cause an increase in metabolism. Due to the increased metabolism, the sea turtles have to spend longer periods of time on the surface in order to recover. These longer surface times greatly increase the risk of death for the turtles.

The researchers hope their study would determine a maximum unattended soak time for fishermen that would also minimize the unintentional capture of sea turtles. Due to other factors that lead to sea turtle deaths, the scientists recommended the current restriction remain. However, the scientists also recommend that captured sea turtles be brought onboard to assess their physical well-being.

They outline that fishermen can do a gentle touch to the tail or eyelid to assess reflexes and a simple visual inspection to check for injuries. They also suggest that fishermen take the turtles to a rehabilitation facility at the first sign of injury or distress.

1. Snoddy, J. E. (2009). Blood Biochemistry of Sea Turtles Captured in Gillnets in the Lower Cape Fear River North Carolina, USA. The Journal of Wildlife Management, 8(73), 1394-1402.