Browsing by Subject "North Atlantic right whale"

Animals experience hydrodynamic forces (lift, drag, and side) and moments (pitching, yawing, and rolling) as a result of motion in an aqueous medium. Under selective pressure, most cetaceans, including porpoises, dolphins, and whales, developed a streamlined body shape and modified limbs, which delay the separation of flow, create lower drag when they swim, and therefore decrease their locomotor cost. In order to calculate the locomotor cost and propulsive efficiency of cetaceans, accurate estimates of drag on marine animals are required. However, extra momentum imparted into the fluid from lift and side forces as well as pitching, rolling, and yawing moments (here, the parasitic loads) results in extra drag force on the animal. Therefore, in addition to streaming and delaying flow separation, animals must also minimize excess fluid momentum resulting from parasitic loads. Given the endangered status of the North Atlantic right whale (Eubalaena glacialis; hereafter NARW), analyzing the hydrodynamic characteristics of the NARWs was the focus of this work. Additionally, previous studies showed that body shape of NARWs changes with life stages, reproduction status, nutritive conditions or prey abundance, and the effects of entanglement in fishing gear. Therefore, in this study, computational fluid dynamics (CFD) analysis was performed on multiple 10 m three-dimensional NARW models with different body shapes (e.g., normal condition, emaciated, and pregnant) to measure baseline measurements of flow regimes and hydrodynamic loads on the animal. Swimming speeds covering known right whale speed range (0.125 m/s to 8 m/s) were simulated in most scenarios. In addition to the hydrodynamic effects of different body shapes, drag was also considered a function of parasitic loads. The NARW models were embedded with bone segments that allowed one to manipulate the body pose of the model via adjusting the flippers or the spine of the animal before measuring hydrodynamic drag. By doing so, momentum from parasitic loads was expected to be eliminated. CFD simulations revealed that drag on NARWs is dictated by its irregular outline and that the drag coefficient (0.0071-0.0059; or dimensionless drag) of on NARWs is approximately twice that of many previous estimates for large cetaceans. It was also found that pregnant NARW model encounters the lowest drag coefficient due to delayed flow separation resulting from enlarged abdomen, whereas the emaciated NARW model experiences the highest drag coefficient possibly due to the concavity at the post-nuchal region. These results suggested that drag on NARWs and their thrust power requirements were indeed affected by its body shape but the differences between the three NARW models tested were small. Lastly, minimum drag, which corresponds to the elimination of the parasitic loads, can be obtained by adjusting the pose of the animal. Thus, minimum drag occurs at the neutral trim pose. For the static, normo-nourished NARW model, simulations revealed that by changing the angle of attack of the flippers by 4.03° (relative to the free-stream flow) and pitching the spine downward by 5° while maintaining fluke angle, the drag was lowered by approximately 11% across the flow speeds tested. This drag reduction was relative to the drag study conducted on the same animal model but without body pose adjustments. Together the studies included in the present work explored and highlighted the capability of numerical methods in investigating the hydrodynamics and energetics of cetaceans. Future studies should address how computer solutions can be used to solve problems from a wider aspect. For instance, extra parasitic loads caused by attached gear as well as possible injuries due to the encounter with fishing gear should also be considered while evaluating the energy budget of the North Atlantic right whales.

Locomotion in any environment requires the use of energy to overcome the physical

forces inherent in the environment. Most large marine vertebrates have evolved

streamlined fusiform body shapes to minimize the resistive force of drag when in

a neutral position, but nearly all behaviors result in some increase in that force.

Too much energy devoted to locomotion may reduce the available surplus necessary

for population-level factors such as reproduction. The population of North Atlantic

right whales has not recovered following legal protection due to decreased fecundity,

including an increase in the intercalf interval, an increase in the years to first calf and

an increase in the number of nulliparous females in the population. This reproductive

impairment appears to be related to deficiencies in storing enough energy to meet the

costs of reproduction. The goal of this study was to determine whether increases in

moving between prey patches at the cost of decreased foraging opportunities could

shift these whales into a situation of negative energy gain. The first step is to

understand the locomotor costs for this species for the key behaviors of traveling and

foraging.

This study investigated the cost of locomotion in right whales by recording the

submerged diving behaviors of free-ranging individuals in both their foraging habitat

in the Bay of Fundy and their calving grounds in the South Atlantic Bight with a

suction-cupped archival tag. The data from the tags were used to quantify the oc-

currence of different behaviors and their associated swimming behaviors and explore

three behavioral strategies that reduce locomotor costs. First, the influence that

changes in blubber thickness has on the buoyancy of these whales was investigated

by comparing the descent and ascent glide durations of individual whales with differ-

ent blubber thicknesses. Next, the depth of surface dives made by animals of different

sizes was related to the depth where additional wave drag is generated. Finally, the

use of intermittent locomotion during foraging was investigated to understand how

much energy is saved by using this gait. The final piece in this study was to deter-

mine the drag related to traveling and foraging behaviors from glides recorded by

the tags and from two different numerical simulations of flow around whales. One, a

custom developed algorithm for multiphase flow, was used to determine the relative

drag, while a second commercial package was used to determine the absolute mag-

nitude of the drag force on the simplest model, the traveling animal. The resulting

drag estimates were then used in a series of theoretical models that estimated the

energetic profit remaining after shifts in the occurrence of traveling and searching

behaviors.

The diving behavior of right whales can be classified into three stereotyped be-

haviors that are characterized by differences in the time spent in different parts of the

water column. The time budgets and swimming movements during these behaviors

matched those in other species, enabling the dive shapes to be classified as foraging,

searching and traveling behaviors. Right whales with thicker blubber layers were

found to perform longer ascent glides and shorter descent glides than those with

thinner blubber layers, consistent with the hypothesis that positive buoyancy does

influence their vertical diving behavior. During horizontal traveling, whales made

shallow dives to depths that were slightly deeper than those that would cause ad-

ditional costs due to wave drag. These dives appear to allow whales to both avoid

the costs of diving as well as the costs of swimming near the surface. Next, whales

were found to glide for 12% of the bottom phases of their foraging dives, and the

use of `stroke-glide' swimming did not prolong foraging duration from that used by

continuous swimmers. Drag coefficients estimated from these glides had an average

of 0.014 during foraging dives and 0.0052 during traveling, values which fall in the

range of those reported for other marine mammals. One numerical simulation deter-

mined drag forces to be comparable, while the other drastically underestimated the

drag of all behaviors. Finally, alterations to the behavioral budgets of these animals

demonstrated their cost of locomotion constitutes a small portion (8-12%) of the

total energy consumed and only extreme increases in traveling time could result in a

negative energy balance. In summary, these results show that locomotor costs are no

more expensive in this species than those of other cetaceans and that when removed

from all the other stressors on this population, these whales are not on an energetic

`knife edge'.