Shrimp Loss Associated with Turtle Excluder Devices: Are the Historical Estimates Statistically Biased

Abstract

Estimates of penaeid shrimp losses associated with the use of turtle excluder devices (TEDs) in offshore waters of the southeastern USA are derived from a single study conducted from 1988 to 1990. The estimates were based on paired tows in which the inboard and outboard nets on one side of the vessel were equipped with TEDs while the nets on the other side were not. Comparison of the mean catch rates from the TED and control nets provided an estimate of shrimp loss. However, the net positions were not rotated by trip, the try net (i.e., a small shrimp trawl fished off one side of the vessel in front of the trailing inboard net) was fished in front of the inner standard net 70% of the time, and the data show that catches in the standard net trailing the try net were significantly reduced by operation of the try net. These findings warranted a new analysis excluding data from inner net pairs, as is done in the modern gear testing protocol. The reanalysis suggests that the shrimp loss rates for Georgia TEDs with and without accelerator funnels were 5.5% and 7.5%, respectively, and that the highest level of shrimp loss (15%) was associated with the “Super Shooter” TED with an accelerator funnel. The results of the historical study indicated that the shrimp loss rate associated with the Super Shooter design was only 1% and that the shrimp loss rates associated with the Georgia TED with and without accelerator funnels were 3.6% and 13.6%, respectively. Overall, we conclude that the historical estimates are biased. A reanalysis suggests that the shrimp loss rate associated with TED use in offshore waters of the southeastern USA is on the order of 6%. We also conclude that a new, well-designed National Marine Fisheries Service-approved study is needed.