Written by Mallory Reading

*Cover image courtesy of Hakai Magazine*

Of the seven species of sea turtles still alive today, two are threatened and five are endangered according to the US Endangered Species Act. Why is it that populations are dwindling to critically low levels? The answer to this is complex, and has to do with the different ways humans have used and exploited sea turtles in the past. While some species like the hawksbill suffer most from direct harvesting of their shells (ever heard of tortoiseshell?), others for their meat or eggs, no species is safe from ending up entangled and drowning as bycatch in fishing nets. Because of all these threats to sea turtle populations, most species are endangered and some populations are dangling at the precipice of extinction.

You may be thinking: What can we do to help? Is it too late? The answer to these questions is: No, it’s never too late to minimize future damage to a species, and luckily humans are already making efforts to reduce bycatch, one of them being the Turtle Excluder Device (TED).

*Bycatch image courtesy of World Wildlife Fund*

Before we get into exactly how bycatch is minimized via the TED, let’s look into just how big of a problem bycatch is for turtles. One study analyzed US data between 1990 and 2007 and measured the rates of bycatch before and after the implementation of bycatch mitigation measures for US Fisheries. TEDs were initially mandated on a limited basis in 1987, but several acts in 1989, 1990, 1994, and 1995 ramped up enforcement of this to effective levels (Evans, 1998). The authors found that there were an average of 346,500 yearly fishery interactions with sea turtles, resulting in 71,000 annual deaths before bycatch minimization measures were taken. These numbers put a serious damper on the population.

*Turtle Excluder Device image courtesy of* *NOAA Fisheries*

The way that Turtle Excluder Devices work to minimize bycatch is by inputting a set of metal bars in a trawl net. Prior to the installation of these devices, the turtles would end up tangled in the cod end of the net (see picture below, it’s just the end of the net that caught fish end up in) and, not being able to surface, drown and die in it. (If you didn’t know turtles can’t breathe underwater, that’s okay, you’re not alone). The metal bars put in are far enough apart to let shrimp or other desired catch to pass through to the cod end, but too close together for a turtle to fit. Instead, the turtle is guided down along the sloped bars to an opening in the net where it may exit safely and swim along on its way.

Turtle Excluder Devices were more thoroughly mandated and enforced in and around US waters in the mid 90s, mandating that all skimmer trawl vessels that are 40+ feet in length utilize TEDs. Some shrimpers in the southeast still do not use them, but the mandation in the US made a dent in bycatch. After this, yearly rates found in the 1990-2007 study declined 60% in interactions, from 346,500 down to 137,800 yearly interactions, and saw a 94% reduction in mortality estimates, from 71,000 to only 4,600 annual deaths. These declines in bycatch and bycatch related mortality, though subject to some uncertainty, are significant enough to show the efficacy of TEDs in the field. Not only this, but TEDs have been found to either have no effect on, or even increase size and yield of desired catch in trawling methods.

*TED model with cod end courtesy of Queensland Government*

Though it took some encouragement from the government and environmentalists to implement this device, the results have made all that effort worthwhile. This innovative device is saving thousands of turtles’ lives every day, and helping to keep these marine reptiles from complete extinction. Anyone can help reduce bycatch, because it’s not only turtles who suffer, and conservationists and fisheries both benefit from preventing incidental catch of non-target species. The World Wildlife Fund holds an International Smart Gear Competition, which encourages realistic designs to minimize bycatch, and offers a cash prize to its winners. For any designers looking to make an impact, this might be a great place to start.

Mallory Reading is an intern at AMSEAS.