Characteristics and magnitude of sea turtle bycatch in US mid-Atlantic gillnet gear

From 1995 to 2006, US federal fisheries observers deployed aboard commercial fishing vessels in the US mid-Atlantic region documented captures of loggerhead Caretta caretta, green Chelonia mydas, Kemp’s ridley Lepidochelys kempii, and leatherback Dermochelys coriacea turtles in commercial sink gillnet gear. Data collected by these observers were used to characterize sea turtle bycatch in sink gillnet gear, including the temporal and spatial distribution, fishing characteristics, species composition, and sizes of turtles captured. In addition, these data were used to develop a generalized additive model to evaluate and predict bycatch rates (turtles per metric ton of fish landed) of sea turtles. These rates were then applied to commercial gillnet landings over the same time period to estimate total bycatch of loggerhead turtles. Bycatch rates of loggerheads were correlated with latitude, sea surface temperature, and mesh size. Highest predicted bycatch rates occurred in warm waters of the southern mid-Atlantic, in large-mesh gillnets. From 1995 to 2006, the average annual bycatch estimate of loggerheads was 350 turtles (coefficient of variation = 0.20, 95% CI over the 12 yr period: 234 to 504). Characteristics and magnitude of bycatch can help inform population assessments, while the distribution of bycatch rates can be used to help inform bycatch mitigation options.