Effects of added drag on cetaceans : fishing gear entanglement and external tag attachment
Citable URI
https://hdl.handle.net/1912/8468DOI
10.1575/1912/8468Abstract
Animal movement is motivated in part by energetic constraints, where fitness is maximized
by minimizing energy consumption. The energetic cost of movement depends on
the resistive forces acting on an animal; changes in this force balance can occur naturally
or unnaturally. Fishing gear that entangles large whales adds drag, often altering energy
balance to the point of terminal emaciation. An analog to this is drag from tags attached
to cetaceans for research and monitoring. This thesis quantifies the effects of drag loading
from these two scenarios on fine-scale movements, behaviors and energy consumption.
I measured drag forces on fishing gear that entangled endangered North Atlantic right
whales and combined these measurements with theoretical estimates of drag on whales’
bodies. Entanglement in fishing gear increased drag forces by up to 3 fold. Bio-logging
tags deployed on two entangled right whales recorded changes in the diving and fine-scale
movement patterns of these whales in response to relative changes in drag and buoyancy
from fishing gear and through disentanglement: some swimming patterns were consistently
modulated in response. Disentanglement significantly altered dive behavior, and can affect
thrust production. Changes in the force balance and swimming behaviors have implications
for the survival of chronically entangled whales. I developed two bioenergetics approaches to
estimate that chronic, lethal entanglements cost approximately the same amount as the cost
of pregnancy and supporting a calf to near-weaning. I then developed a method to estimate
drag, energy burden and survival of an entangled whale at detection. This application is
essential 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 associated
with drag from small bio-logging tags, and incrementally decrease swim speed as
drag increases. Metabolic impacts are measurable when speed is constrained. I measured
the drag forces on these tags and developed guidelines depending on the relative size of
instruments 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 energy
landscape associated with increased drag.
Description
Submitted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy at the Massachusetts Institute of Technology
and the Woods Hole Oceanographic Institution February 2017
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Suggested Citation
Thesis: van der Hoop, Julie, "Effects of added drag on cetaceans : fishing gear entanglement and external tag attachment", 2017-02, DOI:10.1575/1912/8468, https://hdl.handle.net/1912/8468Related items
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