FISH 475: MARINE MAMMALOGY
SPRING 2007
FINAL EXAMINATION
NAME: KEY
UW STUDENT NUMBER: n/a
PLEASE LIMIT RESPONSES TO SPACE PROVIDED. USE REVERSE SIDE OF
THE PAGE IF ABSOLUTELY NECESSARY. RESPOND TO ALL QUESTIONS ON
THE EXAM FORM.
Total of 340 pts. possible.
1 (3 pts. each part). Indicate the technical family name for each of the following species
of marine mammals:
Narwhal: Monodontidae
Stellar’s sea cow: Hydrodamalidae or Dugongidae
Marine otter (of South America): Mustelidae
Pygmy sperm whale: Kogiidae
Northern elephant seal: Phocidae
2 (20 pts.). The deep sound channel (aka SOFAR Channel) typically is deeper at low
latitudes that at higher latitudes. Why?
The deep sound channel typically occurs at the depth in the water column where sound
velocity is at a minimum. The depth of minimum velocity is determined primarily by
changes in temperature and pressure with depth. Sound velocity is positively correlated
with both temperature and pressure. Temperature normally has the dominant effect on
sound velocity in shallow water because temperature commonly is high at the surface,
quickly dropping to low levels in the upper part of the water column. Pressure has the
dominant effect at greater depths because it increases linearly with depth, and because at
great depth temperature varies only slightly with depth.
At low and middle latitudes, the depth at which temperature becomes largely constant is
somewhat deeper than at high latitudes, where the temperature at the surface often is little
different from the temperature at great depth. As a result, the depth of minimum sound
velocity, and therefore of the deep sound channel, tends to be more shallow at high latitudes
as compared to low and middle latitudes.
NAME: KEY
3 (20pts.).The logistic growth equation and the Leslie Matrix both predict growth patterns
for marine mammal populations. Which of the two requires more information before it
can be used? Why?
The Leslie matrix approach requires more information. Whereas the development
of a logistic population model requires only some population trend data, an estimate
of carrying capacity (K), and an estimate of the shape parameter (z or θ), a Leslie
matrix model requires age- or stage-specific information on both fecundity and
mortality rate.
4 (20pts.). Imagine that the Dall’s porpoise suffers a blunt-force trauma while escaping
an attack from a foraging killer whale. The injury causes permanent damage to the spleen
of the porpoise. How will the diving capabilities of the porpoise be affected? Why?
The injured porpoise likely will experience reduced ability to dive for long duration.
The spleen is known to be capable of storing red blood cells in marine mammals.
During periods of frequent diving activity, additional red blood cells may be
released into the blood stream to enhance the ability of a diving mammal to store O2
someplace other than in the lungs. The extra red blood cells are re-stored in the
spleen during periods of minimal diving. Thus, an animal with a damaged spleen
likely will have less bloodstream O2 storage capability, and will not be able to make
dives of long duration.
NAME: KEY
5 (15 pts.). Direct behavioral evidence for male-male competition, in the context of
breeding, is difficult to obtain for cetaceans. What kinds of morphological evidence
might be helpful in characterizing male-male competition in a cetacean species?
The occurrence of male-male competition in mammals is often (although not
always) accompanied by two morphological patterns: Sexual dimorphism in size,
and the presence of elaborate, visually striking secondary sexual characteristics.
With regard to size difference, in most cases the males are larger than females, but
there are some exceptions (such as some of the ice-breeding phocid pinnipeds).
Thus, an evaluation of size difference and the occurrence of prominent secondary
sexual characteristics, between sexes, would be useful is assessing the importance of
male-male competition in a cetacean for which behavioral data are difficult to
obtain.
6 (20 pts.). Since the Miocene, many odontocete cetacean families have evolved shorter
jaws and fewer teeth. Some have argued that these patterns developed because of
evolution of the ability to stun and capture prey with high-intensity sound. However, the
“acoustic stunning” hypothesis is now in doubt. Suggest other possible reasons for
evolutionary trends in cetacean jaws and teeth since the Miocene.
Extremely long jaws with supernumerary dentition may have been selected against
over time, even if acoustic stunning does not work as a significant prey capture
method. Long jaws may have been susceptible to injury, and preferred prey
populations may have evolved abilities to escape predation by mammals with long
jaws and many sharp teeth. The evolution of echolocation and cooperative foraging
may have made prey capture so efficient that long jaws could be replaced with
shorter, more robust jaws less susceptible to injury, and requiring less physiological
energy during development. Echolocation may also actually work better, in an
architectural context, with shorter jaws projecting in front of the animal. Other
reasonable explanations will also be considered.
NAME: KEY
7 (20pts.). The Southern Resident killer whales (SRKW) have recently been listed as
“endangered” under the federal Endangered Species Act, and the National Marine
Fisheries Service is proceeding with recovery planning for this population by considering
the potential impacts of several key factors. Prominent risk factors include a reduction in
prey quality and/or quantity, impacts of high toxin loads, direct and/or indirect vessel
impacts, and random fluctuations in a small population dealing with the cumulative
effects of combined risk factors. Based on your knowledge of SRKW and their
distribution patterns within Washington and British Columbia inshore waters, describe
(a) which risk factor you think is most important for NMFS to study first in this region
AND why you think so, and (b) a research approach to study the risk factor you identified
in (a).
(a) (10 pts) Which risk factor is identified and why is largely up to student choice (1
pt each). However, the student must answer both parts, providing clear and
reasonable justification for choice of risk factor.
(b) (10 pts) There are several reasonable approaches, and it will depend on which
risk factor chosen in (a). Here are some examples, but other reasonable approaches
also will be considered:
Prey quantity and quality:
1. Statistical model comparing population trajectory of SRKW with prey
population trajectory
2. Analyze SRKW space use patterns in relation to prey distribution during
periods of SRKW population growth versus population decline.
3. Analyze animal health from periods of population growth versus decline (e.g.
use fatty acids to look at changes in diet, lipid composition, etc.)
Toxins
1. Measure toxin levels of various levels of the food chain and SRKW, compare
relative levels, and model transfer pathways
2. Map distribution and levels of toxins throughout Puget Sound
Vessel impacts
1. Acoustics: Measure noise levels of various vessels, at a range of distances
from the source. Consider impacts, based on known levels of killer whale
hearing thresholds. Model potential of masking killer whale calls.
2. Bioenergetics: Monitor behavioral changes in the presence of vessels, and
model bioenergetic impacts of changes in behavior or diving patterns
Random population fluctuations
1. Population modeling exercise: Construct age-structured model that allows
testing of multiple scenarios to explain population fluctuations, including
random walk model.
NAME: KEY
8 (15 pts.). At birth, elephant seal pups establish olfactory and acoustic identities with
their mothers. However, mother elephant seals do not forage during lactation, and do not
leave the haul-outs until the pups are weaned. Why, then, is the ability to establish
mother-pup identity so important for elephant seals?
Even though mother and pup elephant seals do not leave breeding haul-out sites
until the pups are weaned, there are a number of ways in which mother-pup pairs
can become separated while on the haul-out. The most common is disruptions
caused by behaviors associated with harem defense in male seals. Males often
engage in fighting or pursuit that can force other animals to scatter in order to
avoid trampling. Storm events can also cause seals to move about erratically on
haul-outs, especially if storms occur during periods of high tides. During such
disturbances mothers and pups often become separated. Thus, the ability to
vocalize is crucially important in reuniting a mother and pup on the haul out,
ensuring that the pup receives adequate nutrition and security until it is weaned.
9 (15 pts.). Sirenians rarely dive to depths greater than 50m. However, the sirenian rib
cage is stronger and more rigid than rib cages of any other marine mammal category.
Explain the paradox.
A strong inflexible rib cage is of little value to deeply-diving marine mammals.
Pressure at great depth is so high that it is biologically implausible to develop and
maintain a strong-enough rib cage to withstand strong compressive forces around
the lungs and thoracic region. Thus, all deeply-diving marine mammals have light,
flexible rib cages that collapse easily, along with lung airspaces, during deep dives.
Sirenians make only shallow dives and do not experience the strong pressure
changes common to deeply-diving mammals. Thus, a strong, rigid rib cage may be
selected, over evolutionary time, by any of several factors (possibly including
protection against blunt-force injury, predator defense, attitude stability at the
surface, and ballast during shallow dives).
NAME: KEY
10 (20 pts.). Some climate change models predict intensification of equatorward winds
that prevail in the eastern margins of the major ocean basins. If the predictions are
correct, how will mid-latitude populations of pinnipeds likely be affected?
Mid-latitude populations of pinnipeds that are located near eastern boundary
currents at middle latitudes likely will benefit by virtue of increased food web
productivity. An intensification of equatorward wind intensities in eastern
boundary current regions will cause a net increase in mean upwelling rate,
facilitating increased rate of nutrient supply to phytoplankton and an increae in the
productivity of all trophic levels. The result likely would be an increased capacity of
the system to sustain pinnipeds nutritionally, and an increase in mean pinniped
numbers.
11 (20 pts.). In the logistic population growth equation (shown below), the “shape
parameter” Z has important implications for establishment of management goals under
the auspices of the US Marine Mammal Protection Act. Explain the connection between
the shape parameter and management goals.
Nt+1 = Nt + Ntr (1-[Nt/K]z)
Where Nt = population size at time t;
t = time in years;
r = growth rate;
K = carrying capacity of the population;
z = shape parameter
The shape parameter has an important influence on changes in the slope of a plot of
abundance over time in a population. The slope of the curve in turn is directly
correlated with productivity rate in the population. The portion of the population
growth curve with the steepest slope is termed the “maximum net productivity
level” (MNPL), which is the population size at which the population grows most
rapidly. The Marine Mammal Protection Act of 1972 requires that US marine
mammal populations be managed so that they are at “Optimum Sustainable
Population” (OSP). OSP has been defined as a range of population sizes between
MNPL and K, where K is carrying capacity. When z = 1, MNPL is K/2, and OSP
becomes the range in populations sizes between K/2 and K. However, in marine
mammal species z is often > 1, caused MNPL to be > K/2. Thus, as z becomes
progressively larger than 1, the range of population sizes that satisfies OSP becomes
narrower and larger. Thus, the challenges to management of the populations
become more difficult.
NAME: KEY
12 (20pts.). Northern fur seals often rest at sea with flippers held up in the air. Why do
they do this? Explain how this behavior might interact with the function of peripheral
vascular shunts in seal flippers.
There are two possible explanations for the behavior. One is that the seals are
reducing heat loss while at rest, since heat will be lost more slowly in air than in
water (all else being equal). The second is that seals are actually gathering heat
from the sun, in cases when skies are clear. In the first case, peripheral vascular
shunts may be open to minimize blood flow to the flipper and further limit heat loss.
In the second case, shunts may be closed, resulting in full perfusion of peripheral
arteries and veins in the flippers, in order to increase efficiency of heat transfer
from the skin surface, warmed by the sun, to the body core via the blood.
13 (20 pts.). How do throat pleats help humpback whales capture prey?
Humpback whales feed primarily either on krill or schooling forage fish. These
categories of prey are behaviorally complex, and swim rapidly and in directed
fashion, and are capable of rapid movement that is coordinated at the group level.
Thus, the prey taxa consumed by humpback whales have the capability of escaping
capture unless the whales can consume them quickly. All the rorquals have throat
pleats in order to facilitate rapid capture of behaviorally complex prey. The pleats
allow expansion of the mouth and throat to enormous volume. Thus, whales can
quickly engulf large amounts of prey and water in association with rapid, lunging
movements. Once prey are engulfed and the mouth is closed, tongue expansion
forces the engulfed water out through the baleen filters, then through the lips and
out of the whales mouth and throat. Prey are retained on the baleen filter and
swallowed. Once water is expelled, the mouth and throat return to “normal”
volume.
NAME: KEY
14 (20 pts.). Respond to one of the following:
1) In the line transect lab, estimates of pellet density were low for several groups.
What are the likely reasons?
2) In the waters near the San Juan Islands, Dall’s porpoise and harbor porpoise
sometimes produce hybrid offspring. Which species is usually the father? How do
we know?
3) Describe two major biases in using scat samples to characterize pinniped diet.
Option 1: As discussed during lab sessions, there were two likely possible reasons.
First, because of trampling of grass by previous groups, the ability of a group to
effectively detect pellets right on the track line might have been reduced, thus
violating a key requirement of line transect sampling theory, which is that detection
probabilities for objects on the track line are 100%. Second, some of the groups
may have simply covered the transects too quickly, effectively reducing the sighting
probabilities for all pellets within the sampled area.
Option 2: Harbor porpoises are usually the father of the observed hybrids. We
know this because young hybrids are almost always seen traveling closely with adult
Dall’s porpoises. Since young porpoises stay close to their mothers, it is apparent
that Dall’s porpoises are usually the mothers, and harbor porpoises the fathers, of
the hybrids.
Option 3: Scats often contain otoliths and other hard part remains of prey. If these
parts can be identified to species, then information about diet is obtained. There are
a number of biases associated with this approach to diet characterization (full credit
for any two):
a) Scats represent only the most recent feeding activity, when animals
are near haulouts. Diet may be different when animals are farther
away;
b) Some species of prey have larger or more robust hard part remains
than others. Thus, some species of prey may be underrepresented in
scats, relative to their actual importance in the diet.
c) There is no way of knowing if the number of scats on a given haulout
is equally representative of all animals using the haulout. If some
animals defecate more frequently than others while hauled out, then
dietary data based on scat analyses may not be an unbiased
representation of the diet at the population level.
d) Other reasonable explanations considered.
NAME: KEY
15 (20 pts.). Why do many species of marine mammals dive deeper during the day
than at night when they forage?
A large proportion of marine mammal species feed on animals of the deep
scattering layer (DSL) at sea. DSL animals live in relatively deep water during
daylight hours. Each evening they migrate to shoaler depths in search of their
own prey, returning to deeper water at the following dawn. The diving depth of
marine mammals, when foraging on DSL prey, matches the depth distribution of
the prey. Thus, foraging dives are deeper during daylight than at night for
marine mammals that forage routinely on DSL prey.
16 (20 pts.). You find the skull of a small pinniped on Richmond Beach in North
Seattle. Based on your location and the size of the skull, you know that it is either
from a phocid or an otariid. Assuming the skull is in good condition and relatively
fresh, how would you determine the family of the marine mammal from which it
came?
There are several ways to determine the family:
1. If supraorbital processes are present, it is an otariid. If not, it is a phocid.
2. If the auditory bullae are rounded and appear “inflated”, it is a phocid. If the
auditory bullae are angular and appear “flattened”, it is an otariid.
3. If the forward ends of the frontal bones project forward, between the rear
ends of the nasal bones, it is an otariid. If the rear ends of the nasal bones
project rearward, between the forward ends of the frontal bones, it is a phocid.
NAME: KEY
17 (20 pts.). What information is provided in the first row of the Leslie Matrix?
The first row in the matrix provides age- or stage-specific fecundity rates (mean
number of offspring per female per year) for the species in question, with the
lowest age or stage at the left, increasing to the right. All other rows in the
matrix provide information about age- or stage-specific survival rates.
18 (20 pts.). Sea otters are relatively shallow divers, and have large lung volume
relative to body mass. Weddell seals are deep divers with small lung volumes relative
to body mass. Explain the paradox.
As deep divers, Weddell seals are at risk of dissolution of high levels of
molecular nitrogen (N2) because of high ambient pressures at depth. Risks are
minimized by storing O2 primarily in blood (bound with hemoglobin), muscle
(bound with myoglobin), and to some extent in other tissues. As a result, storage
of respiratory gasses in the lungs is less important, and a small lung capacity has
evolved as a result. The seals also are able to minimize N2 dissolution by virtue
of fine scale design features in the lungs, such that air stored in lungs is only
minimally exposed to the absorptive surfaces within alveolar complexes during
dives to great depth.
Sea otters are relative shallow divers, and are at much less risk of N2 dissolution
at high concentrations in the blood during dives. As a result, sea otters have
retained the more primitive condition of large lungs (relative to body mass) as a
primary location for storage of respiratory gasses during dives.