Dive behavior of North Atlantic right whales on the calving ground in the Southeast USA: implications for conservation

The North Atlantic right whale Eubalaena glacialis is a Critically Endangered whale whose habitat overlaps with areas of high human use. On feeding grounds, aspects of its behavior increase the vulnerability of this species to anthropogenic threats such as entanglement in fishing gear and vessel strikes. On the calving ground, natural dive behavior and the implications for conservation efforts in this species remain to be evaluated. In this study, we used 102.17 h of tag data collected over 15 deployments of archival tags on 14 individuals to describe the dive behavior of right whales in the Southeast USA. Lactating females spent up to 80% of the time at depths = 3.5 m, leading to increased risk of vessel strike compared to other whale groups that spent a maximum of 30% of the time at those depths in this habitat. Non-lactating whales had significantly deeper maximum dive depths (12.1 m) than lactating females (7.3 m) and spent more time in the bottom phase of dives, closer to the sea floor (45 vs. 37% of the dive duration, respectively). Time spent closer to the sea floor increases the probability of interaction with fishing gear. Therefore, these dive data are useful to justify seasonal closures of fishing activity on the calving ground to protect both lactating and non-lactating whales. Opportunistic comparisons revealed that diel period, calf presence and calf age affect dive behavior of female right whales. In the face of the impacts of anthropogenic mortality on right whale populations, these results will aid vessel strike and entanglement risk assessment on the Southeast USA calving ground.