Effects of Added Drag on Cetaceans: Fishing Gear Entanglement and External Tag Attachment

Julie van der Hoop, Ph.D., 2017
Michael Moore, Advisor

Fitness is maximized by minimizing energy demand of resistive forces on animals. Fishing gear entangling large whales adds drag, altering energy balance. Drag from monitoring and research tags on cetaceans is an analogue. I quantified drag loading effects from these scenarios on fine-scale movements, behaviors and energy consumption.

I measured fishing gear drag forces on entangled endangered North Atlantic right whales in the context of theoretical drag estimates. Fishing gear entanglement increased drag forces by up to 3x. Tag data from two entangled right whales recorded diving, and fine-scale movement changes in response to drag and buoyancy from fishing gear during disentanglement. Disentanglement significantly altered dive behavior, and affected thrust production. Changes in force balance and swimming behaviors affect survival of chronically entangled whales. Two bioenergetic approaches estimated that chronic, lethal entanglements costs approximated the energy of pregnancy to near-weaning. I then estimated drag, energy burden and survival of an entangled whale at detection, enhancing disentanglement and protected species management.

Small bio-logging tags incrementally slowed bottlenose dolphins with increasing drag to avoid energetic costs. Metabolic impacts were measurable when speed was constrained. Tag drag forces were measured and guidelines developed for tag size for a given animal size.