Behavioral impacts of disentanglement of a right whale under sedation and the energetic cost of entanglement

Abstract

Protracted entanglement in fishing gear often leads to emaciation through reduced mobility and foraging ability, and energy budget depletion from the added drag of towing gear for months or years. We examined changes in kinematics of a tagged entangled North Atlantic right whale (Eg 3911), before, during and after disentanglement on 15 Jan 2011. To calculate the additional drag forces and energetic demand associated with various gear configurations, we towed three sets of gear attached to a load-cell tensiometer at multiple speeds. Tag analyses revealed significant increases in dive depth and duration; ascent, descent and fluke stroke rates; and decreases in root mean square fluke amplitude (a proxy for thrust) following disentanglement. Conservative drag coefficients while entangled in all gear configurations (mean ± SD Cd,e,go = 3.4x10-3 ± 0.0003, Cd,e,gb = 3.7x10-3 ± 0.0003, Cd,e,sl = 3.8x10-3 ± 0.0004) were significantly greater than in the nonentangled case (Cd,n = 3.2x10-3±0.0003; P = 0.0156, 0.0312, 0.0078 respectively). Increases in total power input (including standard metabolism) over the nonentangled condition ranged 1.6%-120.9% for all gear configurations tested; locomotory power requirements increased 60.0%-164.6%. These results highlight significant alteration to swimming patterns, and the magnitude of energy depletion in a chronically entangled whale.