Abstracts Category : Other

Effects of added drag on cetaceans : fishing gear entanglement and external tag attachment

by der Hoop van

Animal movement is motivated in part by energetic constraints, where fitness is maximizedby minimizing energy consumption. The energetic cost of movement depends onthe resistive forces acting on an animal; changes in this force balance can occur naturallyor unnaturally. Fishing gear that entangles large whales adds drag, often altering energybalance to the point of terminal emaciation. An analog to this is drag from tags attachedto cetaceans for research and monitoring. This thesis quantifies the effects of drag loadingfrom these two scenarios on fine-scale movements, behaviors and energy consumption.I measured drag forces on fishing gear that entangled endangered North Atlantic rightwhales and combined these measurements with theoretical estimates of drag on whalesbodies. Entanglement in fishing gear increased drag forces by up to 3 fold. Bio-loggingtags deployed on two entangled right whales recorded changes in the diving and fine-scalemovement patterns of these whales in response to relative changes in drag and buoyancyfrom fishing gear and through disentanglement: some swimming patterns were consistentlymodulated in response. Disentanglement significantly altered dive behavior, and can affectthrust production. Changes in the force balance and swimming behaviors have implicationsfor the survival of chronically entangled whales. I developed two bioenergetics approaches toestimate that chronic, lethal entanglements cost approximately the same amount as the costof pregnancy and supporting a calf to near-weaning. I then developed a method to estimatedrag, energy burden and survival of an entangled whale at detection. This application isessential for disentanglement response and protected species management.Experiments with tagged bottlenose dolphins suggest similar responses to added drag:I determined that instrumented animals slow down to avoid additional energetic costs associatedwith drag from small bio-logging tags, and incrementally decrease swim speed asdrag increases. Metabolic impacts are measurable when speed is constrained. I measuredthe drag forces on these tags and developed guidelines depending on the relative size ofinstruments to study-species.Together, these studies quantify the magnitude of added drag in complementary systems,and demonstrate how animals alter their movement to navigate changes in their energylandscape associated with increased drag.