FISH 475: MARINE MAMMALOGY
SPRING 2009
Summary of scores, final examination:
Maximum possible score: 360
Mean score: 307 (85%)
Median score: 315 (87%)
Distribution of scores:
220-240:
241-260:
261-280:
281-300:
301-320:
321-340:
341-360:
1
3
7
4
9
15
4
N: 43
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FISH 475: MARINE MAMMALOGY.
SPRING 2009
FINAL EXAMINATION.
NAME: KEY
UW STUDENT NUMBER: N/A
PLEASE LIMIT RESPONSES TO SPACE PROVIDED. USE REVERSE SIDE OF
PAGE IF ABSOLUTELY NECESSARY. RESPOND TO ALL QUESTIONS ON THE
EXAM FORM.
20 pts. per question except as noted. Total of 360 pts. possible.
1 (4 pts. each part). Indicate the common name typically associated with each of the
following families that include marine mammals: Graded by Brianna Blaud.
Monodontidae: Beluga and/or narwhal
Trichechidae: Manatees
Mustelidae: Marine otters (“Otters” is acceptable)
Phocidae: Seals
Balaenidae: Right whales
2. Global climate change is thought to have caused changes, already, in the migratory and
foraging patterns in the eastern North Pacific population of gray whales, which migrates
along the west coast of North America. One observed pattern is an apparent increase in the
length of the migration to more northerly locations for foraging, and a reduction in the
nutritional quality of prey resources available to the whales on the feeding grounds. How
might these changes influence calving intervals in adult female whales? Graded by
Brianna Blaud.
The calving interval should increase under the circumstances described. The
combination of the longer migratory swims and the reduced nutritional and energetic
value of prey populations will, on the average, cause a reduction in the body condition
of adult females and increase the relative stresses associated with pregnancy, lactation,
and protection of dependent calves. Available data in the literature indicate that
calving interval of large whales generally should increase in association with increased
physiological stress.
NAME: KEY
3 (10 points each part). Recall the logistic (density-dependent) equation for population
growth: Graded by Teresa Mongillo.
Nt+1 = Nt + Ntr(1 – [Nt/K]z)
Where Nt = population size at time t;
t = time in years;
K = Carrying capacity of the population;
z = shape parameter
For a hypothetical marine mammal species, indicate how the range, and upper and lower
limits, of population sizes within “Optimum Sustainable Population” would be altered by:
a) A decrease in “K” caused by global climate change;
b) A substantial increase in “z”, from a value of 2.0 to a higher value, resulting from
improvements in matching population models to population survey data.
a) Range: Reduced
Upper limit: Reduced
Lower limit: Reduced
b) Range: Reduced
Upper limit: No change
Lower limit: Increased
4. During the breeding and lactation periods of northern elephant seals, “super weaner”
pups are sometimes observed. These pups are individuals that learn to nurse from their own
mother, but also “steal” milk from other lactating females to which they are apparently not
related. Why should lactating female seals discourage “milk theft” by pups to which they
are not related? Graded by Teresa Mongillo.
The female victimized by the thief may not be able to produce enough milk to sustain
her own pup as well as that amount taken by the thief. As a result, the theft of milk
could jeopardize the probability that her own pup will wean in good condition, and
will survive and reproduce over the long term. Thus, the female should discourage
theft in order to enhance the long-term fitness of her own offspring, and therefore of
herself.
NAME: KEY
5. Describe an underlying assumption of line transect survey methods (also know as
“distance sampling”) that differs from assumptions that underlie strip transect methods.
Graded by Teresa Mongillo.
Strip transect methodology assumes that all objects within the strip have an equal
sighting probability, regardless of distance from the trackline. In contrast, line
transect methodology assumes that sighting probability is constant at 1.0 for objects on
the trackline, but allows sighting probability to decline as a function of distance from
the trackline.
Other reasonable and accurate responses will be considered.
6. Describe a major type of data or information, not currently available (there are a number
of possible answers) that would improve our ability to protect the critically endangered
western North Pacific population of gray whales. Graded by Teresa Mongillo.
This question has a number of reasonable responses, and there is no specific “right answer”.
Very little is known about risks to the western North Pacific population of gray whales during
the southbound migration in the fall, during the overwintering period (during which the
locations of western gray whales remain unknown), and during the northbound migration in
the spring. For these three important and poorly understood phases of gray whale life history,
it would be helpful to conservation efforts if we knew more about the following:
a) Sources and rates of mortality of adults and subadults;
b) Sources and rates of non-lethal injuries or disturbances to adult female gray
whales that might influence rates of pregnancy and birthing, and survival of
dependent calves.
A number of factors could contribute risk in the context of the above unknown categories.
Although western North Pacific gray whales are under intensive observation during summer
feeding activity, it remains possible that natural or anthropogenic factors harmful to the
whales are present on the feeding grounds but have not yet been detected by researchers.
NAME: KEY
7. Assume the following for shallow, sandy-bottom habitat patches in Shark Bay, Australia:
a) Fish are more abundant in areas with dense sea grass beds than in areas with sparse sea
grass beds; and b) Dugongs are more vulnerable to attack by tiger sharks in the middle
portions of sandy habitat patches than along the edges. Given the assumptions, indicate
whether fish are likely to be more abundant in the middle of sandy patches or along the
edges. Explain your response. Graded by Glenn VanBlaricom.
On the average, fish are likely to be more abundant in the middle portions of sea grass
beds on the sandy shallows of Shark Bay.
The reasoning is as follows:
a) Dugongs feed primarily on sea grasses. It follows that, in general, sea
grasses will be less dense in areas with relatively high dugong density than
in areas with relatively low dugong density.
b) Based on information provided by Dr. Wirsing in his lecture of 29 May, it is
apparent that dugongs generally avoid the middle portions of sea grass beds
on sandy shallow areas because they are more vulnerable to attack in
middle areas from tiger sharks. Thus, dugongs generally will be at higher
densities along the edges of sandy bottom habitat patches with sea grass
beds in order to reduce risk of shark attack.
c) Since dugongs generally will be more dense on the edges of sea grass
patches than in middle portions, sea grasses in middle portions will be
grazed less intensively and will be denser, supporting relatively greater
numbers of fish.,
8. Explain the apparent fact that elephant seals (both species) are thought to be able to
“glide” (i.e., move passively without using swimming muscles or flippers) during descents
on deep dives, but not during ascents. Graded by Glenn VanBlaricom.
As elephants seals dive, increasing ambient hydrostatic pressures cause collapse of the
thoracic region, a consequence of highly compressible air spaces within the lungs.
Thoracic collapse causes a reduction in the displacement volume of the seals, with a
resulting loss of buoyancy. As depth increases, the seals may become negatively
buoyant, and are, therefore, able to sink passively without any muscular exertion.
Because elephant seals cannot access air at depth to replenish diminished thoracic
volume, there is no available mechanism for them to regain lost buoyancy. As a result,
upward “gliding” is impossible until the seals reach shoal depths where gas spaces
within lungs can expand and return positive buoyancy to the animal.
NAME: KEY
9. Polar bears have the potential to give birth to and raise a larger litter of offspring (up to 3
cubs) than any other species of marine mammal on earth. Suggest a reason. Graded by
Glenn VanBlaricom.
Polar bear cubs are born altricial (helpless, largely immobile, and very small in
proportion to size of adults of same species), and require less physiological investment,
in the form of lactation, during the early days of life. Because adult female polar bears
occupy dens at the time cubs are born, and for a number of weeks after, their
physiological reserves can be devoted almost entirely to lactation, with almost no
competing demands.
Nearly all other marine mammals produce precocial young (able to swim immediately,
and proportionately large relative to size of adults of same species). Because many
marine mammals are born in the water, swimming ability at the moment of birth is
essential. In addition, small body size is disadvantageous with regard to
thermoregulation (ratio of surface to volume is too high). As a result, precocial birth is
essential. Because precocial young mammals impose high demands on lactating
mothers, litter sizes larger than one typically are not manageable or sustainable.
10. Sea otters living off California are known to have a strong preference for abalones and
sea urchins as prey. Generally, the foraging activities of sea otters reduce densities of
abalones and sea urchins to very low levels. How do sea otters avoid starvation when this
happens? Graded by Glenn VanBlaricom.
Sea otters can readily switch to other prey species. Although the energetic and
nutritional value of other prey may be less than those of abalones and sea urchins,
other prey are often sufficiently abundant and nutritious to sustain sea otters over the
long term. Sea otters are known to consume over 150 different prey species across
their geographic range.
NAME: KEY
11. Why is it important to observe foraging behaviors of free-ranging marine mammals,
rather than relying only on anatomical or physiological information, when characterizing
methods by which prey capture is accomplished? Graded by Teresa Mongillo.
Marine mammals may capture prey in surprising ways, sometimes entirely contrary to
expectation based on information about anatomy or physiology. Although anatomical
and physiological attributes can provide important insights to the foraging ecology of
marine mammals, such attributes may be misleading if they are not combined with
observations in the field of free-ranging animals during foraging activity.
The classic example of this matter is of course the video of killer whales using tail slaps
to disable and capture schooling herring in a Norwegian fjord. Nothing in the
available information on the anatomy or physiology of killer whales would have
allowed us to plausibly predict such methods for prey capture.
12. Why are population models based on the Leslie Matrix generally preferred over
classical aggregative population models (as displayed in question #3 above) when one is
modeling small populations of marine mammals? Graded by Teresa Mongillo.
Marine mammals typically reproduce at low rates compared to most other animal
species. Litter sizes are small, birthing intervals may be large, and ages at first
reproduction are large as compared to many other species. Given those attributes,
changes over time in small marine mammal populations may be erratic, because only a
few animals are reproductive, and because the abilities of the reproductive animals
will vary from year to year depending on age and time since last reproduction. These
patterns are difficult to model accurately with aggregative approaches that rely more
on “average” patterns of per capita reproduction, and generally fail to capture details
that become important in small populations. In contrast, population models based on
Leslie Matrices capture important details about age structure and age-specific rates of
birthing and mortality. Thus, matrix-based models have a greater probability, in
general, of producing outputs that match well with real data.
NAME: KEY
13. Why is Pakistan the best place to look for the fossil remains of archaeocetes, the earliest
known marine-dwelling ancestral group to the modern whales? Graded by Brianna
Blaud.
Fossil-bearing rock formations in parts of Pakistan are formed from marine sediments
that were deposited during the Eocene time as part of the Tethyan Sea bottom. The
rocks, and the fossils they contain, were since uplifted by tectonic forces and have
become part of the terrestrial environment. It is broadly accepted that the Tethyan
region was the location of emergence of the earliest archaeocetes, through evolution
and natural selection. The Tethyan region was characterized by warm, shallow waters
with dense populations of small fish and other mobile marine species. These
conditions are thought to have facilitated the colonization, over evolutionary time
scales, of nearshore marine habitats by terrestrial mammals.
14. Humpback whales utilize sounds at relatively low frequency to communicate with other
humpback whales during the winter breeding season. One of the apparent reasons for the
choice of frequency range is the long distances over which sounds of such frequencies can
travel in the ocean. Why do odontocete cetaceans not use sounds in the same frequency
range for echolocation? Graded by Brianna Blaud.
Although low-frequency sounds carry for long distances in the ocean with minimal
attenuation, they are not used by odontocetes for echolocation. The ability to resolve
detail in reflected sounds (i.e., “echos”) is inversely proportional to the wavelength of
the reflected sounds. That is, sounds with short wavelengths generally provide greater
resolution in echolocation than sounds with long wavelengths. Because the frequency
and wavelength of sound are inversely related, sounds with short wavelengths are
generally of high frequency.
The key underlying principal is that reflected sound will contain the most information
about the reflecting target if the wavelength of the sound is roughly similar to the
dimensions of the target. For example, most ondotocete prey are a few centimeters to
a few tens of centimeters in length. Sounds with wavelengths of similar sizes typically
have very high frequencies – much higher than the sounds used by humpback whales
to communicate.
NAME: KEY
15. Physical upwelling of deep water, known to be important to biological productivity in
the oceans, is generally more widespread and intensive along the eastern edges of the major
ocean basins (particularly in the Pacific and Atlantic Oceans) than along the western
margins. Why is this so? Graded by Brianna Blaud.
Coastal upwelling generally is most intensive on a large scale when prevailing winds
cause surface ocean waters to move away from shore, forcing replacement by deeper
waters that contain high concentrations of the nutrients required to support high rates
of primary production, and as a consequence, high rates of secondary production by
species utilized as prey by coastal marine mammal populations. In both the northern
and southern hemispheres, prevailing winds along the eastern margins of the major
basins in the Atlantic and Pacific tend to be directed toward the equator, while those
along the western margins of the same basins are either weak and variable, or tend to
blow poleward. Because surface waters are displaced to the right of wind direction in
the northern hemisphere, and to the left in the southern hemisphere, offshore
transport of nearshore surface waters should be the norm on the eastern edges of the
ocean basins, and the exception along the western margins.
16. Most species of beaked whales lack functional teeth. Those teeth that are present often
function in social or reproductive contexts much more so than in feeding. How are such
species able to capture and ingest prey items? Graded by Brianna Blaud.
All beaked whales have a “piston tongue” morphology in their mouths, an
arrangement of muscles and tendons below and behind the tongue that allows rapid
retraction of the tongue, creation of negative pressure within the mouth, and strong
resultant suction that draws prey and associated water into the mouth. Beaked whales
also have throat pleats, allowing the throat to expand and accommodate incoming
water when the tongue is retracted. The above mechanism allows beaked whales to
capture prey without the presence of functional teeth.
NAME: KEY
17. You have just performed a necropsy on the first carcass to be recovered for a new
species of phocid, just discovered on ice floes over deep water in the Southern (Antarctic)
Ocean. On internal examination you note that the spleen of the new species appears to be
much smaller than Weddell Seals, which are known to occur in the same area as the newly
discovered species. Which species (Weddell or the new one) is likely to be capable of
diving for longer durations? What is the basis for your response? Graded by Glenn
VanBlaricom.
Based on available information, one would predict that Weddell seals would have the
capability for longer-duration dives than the new species. Weddell seals have a very
large spleen, known to function in enhancing total blood volume and hematocrit
(concentration of red blood cells) during extended diving episodes, with the
consequence of an increased ability to make dives of long duration. The large size of
the spleen also allows Weddell seals to “recover” extra blood volume and red blood
cells out of the blood stream during periods of rest on the surface, to avoid problems
with increased blood viscosity.
Factors other than splenic volume could of course affect diving performance in the
new species. One would want to test the predictions of dive longevity with empirical
field studies, such as deployment of time-depth recorders, if opportunities were
available.
18. Why do most species of dolphin maintain relatively slow swimming speeds, even when
traveling long distances to reach areas that support vital food resources? Graded by Glenn
VanBlaricom.
For any object moving through a fluid medium, drag forces oppose the direction of
travel. Because drag forces tend to increase with the square of an increase in velocity,
increases in travel speed are associated with exponential increases in energetic costs
associated with drag. Thus, there is always a short-term energy gain when travel
speed is reduced. Increases in travel speed are particularly problematic if the change
in speed places the moving object above the velocity at which boundary layer
separation occurs. Once in this realm, a new source of drag known as “pressure
drag”, caused by turbulence behind the object associated with boundary layer
separation, adds additional costs to those associated with other drag forces. Thus,
travel above the speed of boundary layer separation is extremely costly, and typically
not sustainable energetically except in short bursts.
As a result of the above factors, travelling dolphins typically will swim at relatively
slow speeds to minimize costs associated with drag forces, even if arrival at a food-rich
destination in a short time is important to survival.