Seasonal co-occurrence of sea turtles, bottlenose dolphins, and commercial gill nets in southern Pamlico and northern Core Sounds, and adjacent coastal waters of North Carolina, USA

Abstract

We assessed the seasonal co-occurrence of sea turtles and bottlenose dolphins Tursiops truncatus with commercial gill nets in southern Pamlico and northern Core Sounds, and adjacent coastal waters of North Carolina, USA, from 41 aerial surveys conducted from 2004 to 2006. Generalized linear models were used to examine the influence of several variables (month, year, habitat type [coastal and estuarine], sea surface temperature, and visibility conditions) on counts of turtles, dolphins, and gill nets. A total of 86 turtles, 1559 dolphins, and 378 gill nets were observed. Predicted counts of turtles and dolphins were highest concurrent with gill nets in spring and autumn in both habitats. Observed spatial overlap of dolphins and gill nets occurred throughout the estuary from spring to autumn, but was limited mainly to the eastern portion of the estuary in winter; spatial overlap of turtles and gill nets occurred predominantly in the eastern portion of the estuary in spring and autumn, and throughout the estuary in summer. During all seasons, dolphins (57 to 75%) and gill nets (80 to 88%) were predominantly observed in shallow (<2 m) waters of the estuary; turtles (75%) were seen most often in shallow estuarine waters in spring. Along the coast, observed spatial overlap of turtles and dolphins with gill nets occurred most often in the region extending from Cape Hatteras south to Ocracoke. These findings improve our knowledge of habitat use by these species, and may also help manage interactions.