Abstract
Floating and submerged structures in the ocean, such as marine energy devices and relevant oceanographic instruments, use mooring lines tethered to them and to an anchor to hold them in place on the seafloor. Mooring lines and mooring systems may be fabricated from a variety of materials in different configurations depending on the type of device to be tethered, the depth, and the seafloor topography of the location. As the marine energy industry and the need for ocean observation increase, concerns around the effects of devices, mooring systems, and moored observing equipment will need to be addressed to minimize potential risks to marine animals. One such concern is the potential for marine mammals, sea turtles, large fish, diving seabirds, and other marine animals to become entangled in mooring systems and lines associated with devices and buoys. Because of devices, instruments, and their mooring systems acting as artificial reefs and fish aggregating devices, the large predatory animals may become attracted to these artificial structures, increasing the risk of interacting with the mooring systems. Entanglement in lines or cables could cause serious harm to animals, such as tissue damage, make movement difficult for animals, and even drowning and death. Since few marine energy devices have been deployed, research around entanglement risk has had to focus on surrogates such as data collected from other ocean industries, including offshore oil and gas production, fishing, etc. While the characteristics of mooring systems depend on the site’s conditions and the structure to secure, those used for large vessels, oil platforms, floating wind turbines, and marine energy devices are very similar in configuration, material, and line diameter. For example, mooring systems used for floating wind turbines have a line diameter between 76 mm and 234 mm, while those used in the oil and gas industry vary between 95 mm and 290 mm, and those for marine energy devices between 130 mm and 203 mm. In contrast, mooring lines used to secure oceanographic instruments are much thinner, with a diameter between 4.8 mm and 25 mm. The goal of this white paper is to summarize the available information about entanglement risk for marine megafauna from the mooring systems associated with marine energy devices and oceanographic instruments. The literature associated with configurations and materials used for mooring systems for both technologies, as well as the factors that may increase the risk of entanglement for various marine megafauna, such as distribution, swimming behavior, and detection capabilities, are synthetized. Mitigation and reduction strategies for decreasing entanglement risk around moorings are discussed.