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Ecol Evol. 2016 Dec 11;7(1):92-106. doi: 10.1002/ece3.2615. eCollection 2017 Jan.

Entanglement is a costly life-history stage in large whales.

Author information

1
Massachusetts Institute of Technology-Woods Hole Oceanographic Institution Joint Program in Oceanography/Applied Ocean Science and Engineering Cambridge MA USA; Biology Department Woods Hole Oceanographic Institution Woods Hole MA USA.
2
NOAA Fisheries Northeast Fisheries Science Center Woods Hole MA USA.
3
Biology Department Woods Hole Oceanographic Institution Woods Hole MA USA.

Abstract

Individuals store energy to balance deficits in natural cycles; however, unnatural events can also lead to unbalanced energy budgets. Entanglement in fishing gear is one example of an unnatural but relatively common circumstance that imposes energetic demands of a similar order of magnitude and duration of life-history events such as migration and pregnancy in large whales. We present two complementary bioenergetic approaches to estimate the energy associated with entanglement in North Atlantic right whales, and compare these estimates to the natural energetic life history of individual whales. Differences in measured blubber thicknesses and estimated blubber volumes between normal and entangled, emaciated whales indicate between 7.4 × 1010 J and 1.2 × 1011 J of energy are consumed during the course to death of a lethal entanglement. Increased thrust power requirements to overcome drag forces suggest that when entangled, whales require 3.95 × 109 to 4.08 × 1010 J more energy to swim. Individuals who died from their entanglements performed significantly more work (energy expenditure × time) than those that survived; entanglement duration is therefore critical in determining whales' survival. Significant sublethal energetic impacts also occur, especially in reproductive females. Drag from fishing gear contributes up to 8% of the 4-year female reproductive energy budget, delaying time of energetic equilibrium (to restore energy lost by a particular entanglement) for reproduction by months to years. In certain populations, chronic entanglement in fishing gear can be viewed as a costly unnatural life-history stage, rather than a rare or short-term incident.

KEYWORDS:

Eubalaena glacialis; bioenergetics; blubber; capital breeder; cetacean; emergency life‐history stage; energy storage; marine mammal

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