Modeling loggerhead sea turtle (Caretta caretta) interactions with US Mid-Atlantic bottom trawl gear for fish and scallops, 2005–2008

Interactions between sea turtles and northwestern Atlantic trawl fisheries are of global concern, and the National Marine Fisheries Service is considering expanding bycatch reduction regulations, including deployment of turtle excluder devices (TEDs). To inform bycatch mitigation strategies, the number of loggerhead sea turtle (Caretta caretta) interactions was estimated for US Mid-Atlantic bottom trawl fisheries for fish and scallops. A generalized additive model of interactions was developed using 1994–2008 Northeast Fisheries Observer Program data from trawl fisheries that were not required to deploy TEDs. Predicted loggerhead interaction rates were applied to 2005–2008 commercial fishing data to estimate the number of interactions for the trawl fleet. For trawl fisheries in which TEDs were required, an experimentally-determined TED exclusion rate (97%) was applied to estimate the number of loggerheads that were excluded by TEDs. Latitude, depth, and sea surface temperature (SST) were associated with the interaction rate. Average annual interactions for 2005–2008 were estimated at 292 (CV 0.13, 95% CI 221–369) loggerheads, with an additional 61 (CV 0.17, 95% CI 41–83) excluded by TEDs. The interaction rate was highest south of latitude 37°N in waters <50 m deep with SST >15 °C; interaction magnitude in terms of adult equivalents was highest at latitude 37–39°N, depth <50 m, and SST >15 °C. Predicted average annual loggerhead interactions decreased compared to 1996–2004, likely due to decreased commercial fishing effort in high-interaction areas. Additional sea turtle conservation measures can be informed by the high-interaction-rate and -magnitude areas identified through this analysis.