Estimated Magnitude of Sea Turtle Interactions and Mortality in US Bottom Trawl Gear, 2014-2018

This paper reports total estimated interactions and mortalities of loggerhead (Caretta caretta), Kemp’s ridley (Lepidochelys kempii), leatherback (Dermochelys coriacea), and green (Chelonia mydas) sea turtles in bottom otter trawl gear operating in the US Mid-Atlantic and Georges Bank regions from 2014-2018. Interaction rates for each turtle species were estimated with stratified ratio estimators, where rates were stratified by Ecological Production Unit (Georges Bank and Mid-Atlantic), latitude zone, season, and depth. In the Mid-Atlantic region, a total of 571 loggerhead (CV = 0.29, 95% CI = 318-997), 46 Kemp’s ridley (CV = 0.45, 95% CI = 10-88), 16 green (CV = 0.73, 95% CI = 0-44), and 20 leatherback (CV = 0.72, 95% CI = 0-50) turtle interactions were estimated to have occurred in bottom trawl gear over the 5 year period. On Georges Bank, 12 loggerheads (CV = 0.70, 95% CI = 0-31) and 6 leatherback (CV = 1.0, 95% CI = 0-20) interactions were estimated to have occurred. Approximately 272 loggerhead interactions, 23 Kemp’s ridley interactions, 8 green interactions, and 13 leatherback interactions resulted in mortality over the 5 year period. Roughly 2,668 sea days would be needed annually to monitor loggerhead interactions with 30% precision across bottom trawl fleets in the Mid-Atlantic, based on results of this analysis. Monitoring levels were not estimated for Kemp’s ridley, leatherback, or green turtles in this analysis, nor for loggerheads on Georges Bank, because of their low probability of capture. Monitoring for these other turtles and on Georges Bank would still occur, but the targeted level of monitoring would be driven by other marine species groups.