Shrimp fisheries are the largest generators of revenue in the fisheries industry, and also play a large role in collecting unwanted bycatch in their nets. In both farmed and wild fisheries, shrimp are usually collected by a trawl. While much more efficient than other methods of catching shrimp, the trawl tows along all kinds of problems, including ocean floor habitat destruction and unwanted bycatch. In fisheries, bycatch is often coined the term “trash”, deeming it worthless to human social and economic purposes. Sea turtles have earned a category of their own because of their status as a marine conservation mascot. From such is born the Turtle Excluder Device (TED), which is fitted onto trawl nets and looks something like this:
What is a TED?
The TED is an addendum to shrimp trawling gear to help prevent sea turtles from ending up as part of the catch. They take different forms to adapt to their region of implementation, taking into consideration the bycatch species in the area, the surface of the benthic zone on which the trawls usually operate, as well as what makes sense for the scale of vessel used.
General function of TED with description of their importance — Turtle Excluder Device — from National Geographic
French Guiana Shrimp Fishery
French Guiana, one of the shrimp harvesting countries in Northeastern South America, has had bycatch problems in the shrimp trawling, as the trawls used were not equipped with any selective device. The bycatch consists of sea turtles, sharks, rays, large fish and other species of “trash” fish; a typical catch by a trawl contained bycatch way more than shrimp, and the their catch ratio was about 9:1. As shrimp is the most profitable trading commodity in French Guiana, addressing the bycatch problem was needed to benefit both fishers and ecosystem.
Tony Michel Nalovic, who is a National Oceanic and Atmospheric Administration (NOAA) Collaborative Fishery Research Fellow, worked on the development of new selective fishing gear to reduce sea turtle bycatch in the shrimp trawling in his home country, French Guiana, seven years ago. Nalovic and Troy Hartley, his advisor and Virginia Sea Grant Director, teamed with the World Wildlife Foundation (WWF) to collaboratively conduct experiments on prototypes of newly modified versions of the TED with the cooperation from shrimp fishers.
What is a “TTED”? What is the difference?
The newly developed TED was specifically designed (by combining several models together) to fit the local ecological context in French Guiana and was later named the Trash and Turtle Excluder Device (TTED), taking into account that the device was also expected to reduce bycatch of other species, or ‘trash’ species, other than sea turtles.
Testing the TTEDs
The project took about five years from the research initiation to the voluntary adaptation of the TTED as voted by French Guianese shrimp fishers. During the last two years of this five-year-long project, three TTED prototypes were tested for their abilities to retain shrimp catch and to exclude bycatch. The researchers collected weight of shrimp and bycatch for each trial for each TTED tested in the ocean.
What were the results?
Based on statistics of trial trawls conducted in 2008 and 2009, the results showing differences between trawl devices equipped with TTED and those without TTED (the control) were insignificant. This means that for those trials, the differences between the weight of shrimp caught by the TTED-equipped device and that of the control device were not great enough for the TTED-equipped device to be considered “more successful” than the control at catching shrimp. However, there is a trend showing a slight decrease in bycatch weight for TTED-equipped trawls compared to trawls without TTED. Therefore, whether or not this ongoing project can be considered “successful” is inconclusive. To be able to safely declare success would require much larger sample sizes and statistical significance between the bycatch weights.
Does it work in real life? (or real fisheries, rather)
The project report only includes the numerical result in catch composition from the experimental trials, but nothing about follow-up evaluation nor implementation of a fisheries management framework that we assume has been regulated. Problems in the real-world situation may yet become noticeable after the end of this project, as fishers and scientists see issues differently. Dr. Sarah Foster of the UBC Fisheries Centre speaks about the shrimp fishery in Mexico where mandatory use of TEDs has been implemented in the fishery regulation. Because TEDs can release turtles, they can also release large fish which fishers use to supplement their often-meager incomes. To retain the large bycatch, fishers shackled the escape opening of the trawl equipped with the TED during the actual operation once they are out of the harbour — the TED becomes null and sea turtles continue to be caught in trawls and killed.
Enforcement of Turtle Excluder Device in Texas- SeaTurtle Restoration Project as example of how it’s been enforced in the US: TED in Texas
Showing how TEDs receive resistance from shrimp fishers even in the US: TEDs in State Waters
All this to say that there is great room for improvement in the social acceptance of TEDs, never mind an innovation such as the TTED.
The effectiveness of the TED and TTED in an actual operation (not trials) largely depends on the level of compliance from fishers. Implementation of the TTED should not be the end of the project, but the start of the conversation needed to improve fisheries best practice in terms of the ecological, social, and economic aspects. Science has recognized this area of research as needing improvement. The next challenge is how have policy makers include the issue in management frameworks for implementation.