either above or below the grid so that the creatures that are stopped by the TEDs are allowed to escape the net, relatively unharmed. Targeted species such as shrimp however, are pushed to the back of the net. The target design effectiveness of TEDs is 97%, but the field effectiveness is often far lower. Seagrasses and other debris reduce fishing effectiveness of TEDs and in some situations may block sea turtles from exiting the net. In addition, it is easy to tamper with TEDs so as to increase the fishing efficiency of the net, while eliminating the turtle-excluding properties of the TED. Failings and drawbacks While turtle excluder devices have been somewhat successful in lessening sea turtle casualties as by-catch, they still have a few failings and drawbacks. It has been acknowledged that the larger sea turtles, primarily large loggerheads and leatherbacks, are too large to fit through the escape hatches installed in most TEDs. These turtles remain trapped within the net and perish. U.S. legislation introduced in 2003 attempted to address this issue by increasing the size of the escape chutes in the devices. It is difficult to enforce TED compliance as TEDs can reduce the efficiency of the net system, resulting in a loss of some of the catch. On a per boat basis, turtles are rarely caught; in one study, only one turtle was caught per 322.5 hours in the Gulf of Mexico. This creates an incentive for the trawler to cheat. The catch loss can be eliminated by simply tying the turtle escape opening shut with a tie. The tie is removed when the vessel returns to port, thus avoiding detection by enforcement officers, but placing turtles at risk while trawling. It has been theorized that the spike in dead turtles seen in the Gulf of Mexico in June and July 2010 was due to shrimp boats that were taking advantage of lax marine enforcement due to the gulf oil spill. Occasionally TED use becomes impractical due to debris in the water. When a TED is clogged with debris, it can no longer catch fish effectively or exclude turtles. For example, in September 2008 following Hurricanes Gustav and Ike, the National Marine Fisheries Service (NMFS) allowed temporary use of "Tow Times" in lieu of TEDs. Vessels were required to limit their tows to 55 minutes from the time the trawl doors entered the water until they