Research Aims to Reduce Sea Turtle Bycatch Mortality in Pound Nets

Over the past 30 years, nesting populations of North Pacific loggerhead sea turtles Caretta caretta in Japan have decreased over 50-90%. Contributors to this decline include turtle harvesting, coastal development and beach armoring, and incidental capture in coastal and pelagic fisheries.

In this trial, a submerged sea turtle is unable to escape through an experimental pound net escape 
             device ("PED").
In this trial, a submerged sea turtle is unable to escape through an experimental pound net escape device ("PED").

Upon returning from their oceanic migrations, subadult and adult loggerhead turtles spend considerable time in coastal and nearshore habitats of Japan and other Asian countries where there is high risk of interactions with coastal pound net fisheries. Recent reports suggest the interaction rate between sea turtles and these fisheries can be quite high; in particular, high mortalities have been recorded in mid-water pound nets. In one instance, for example, during one month a single mid-water pound net in Mie Prefecture, Japan, is reported to have killed over 50 adult loggerheads. Given the potentially high mortality rates of turtles that interact with these fisheries, and the high reproductive value of adult and subadult turtles, research to develop and test bycatch mitigation solutions, including means to enable captured turtles to escape from pound nets, is clearly warranted.

John Wang, a Pacific Islands Fisheries Science Center researcher employed by the University of Hawaii Joint Institute for Marine and Atmospheric Research, along with staff from the NOAA Fisheries Pacific Islands Regional Office, provided technical information and expertise to the Sea Turtle Association of Japan (STAJ), Tokyo University of Marine Science and Technology, and ProPeninsula to help develop methods to identify mitigation measures useful in reducing sea turtle bycatch in mid-water pound net fisheries. In the initial phase of this project, the researchers designed and constructed a 50% scale model of the cod end of a pound net (4.5m x 4.5m x 3m). The scale model was used to test turtle escape solutions in a controlled tank environment to simulate the conditions experienced by sea turtles inside actual pound net gear.

A system of panels was designed that allowed researchers to change out different prototype pound net escape devices (PEDs) during testing. Six PED designs were developed based on observations of gear in pound net and other fisheries. By testing these designs, a protocol was established for handling turtles and characterizing turtle escape behavior. Tests of the six potential PEDs ruled out several designs, provided a better understanding of PED design pitfalls, and identified one promising PED prototype. In addition, useful insight was gained on the design of the pound net scale model used for testing the PEDs.

In this video sequence, a sea turtle is escaping from a prototype PED in the roof of a submerged pound 
             net.
In this video sequence, a sea turtle is escaping from a prototype PED in the roof of a submerged pound net.

The next phases of the project will involve further PED tests in controlled experimental environments (and eventually in actual pound nets) by researchers in Japan and engagement of fishermen, gear manufacturers, and fishery officials in the design and testing of PEDs. Involvement of these partners will increase the efficacy of PED design and the likelihood of future PED adoption.