FISH 475: MARINE MAMMALOGY, SPRING 2006.
MIDTERM EXAMINATION.
NAME: Key
PLEASE LIMIT RESPONSES TO SPACE PROVIDED. 100 points total.
SHORT ANSWER SECTION. 10 POINTS PER QUESTION. RESPOND TO ALL
QUESTIONS IN THIS SECTION.
1.
Indicate the common name(s) associated with the following families that include
marine mammals:
Otariidae: Sea lions and fur seals (half credit if just one)
Phocoenidae: Porpoises
Dugongidae: Dugongs (or: Dugongs and sea cows; half credit if just sea cows)
Balaenidae: Right whales (or: right whales and bowhead whales; half credit
if just bowhead whales)
Monodontidae: Belugas and narwhals (half credit if just one)
2.
Summarize trends in numbers of teeth in jaws of archaeocete and odontocete
whales over an evolutionary time scale, beginning in the late Eocene and
continuing to the present.
Numbers of teeth in the jaws of the early whales increased over time, from
the earliest whales in the Eocene until the Miocene. As the precursors to the
modern groups of odontocetes began to appear in the Miocene, the number
of teeth in odontocete jaws began to decrease, a pattern that has continued to
the present.
3.
What is the significance of collapsible alveolar sacs in the lungs of phocid seals,
with regard to the known ability of phocids to make long deep dives at frequent
intervals?
A major challenge for marine mammals that make long deep dives is the
dissolution of molecular nitrogen into the bloodstream. Because saturation
level for dissolved nitrogen in blood relates both to ambient pressure and to
duration of exposure, long deep divers have the potential for high
concentrations of nitrogen in blood. This becomes a problem when the
animals must ascend to the surface to breath, thus experiencing reduced
ambient pressure and the risk that nitrogen will evolve out of solution too
rapidly, forming bubbles in the blood and causing circulatory blockages that
may cause injury. This condition is known as decompression sickness or “the
bends”.
Most marine mammals, including phocid seals, have collapsible alveolar sacs
to which are connected reinforced airway tubules. As a result, under
pressure the sacs collapse more quickly than the tubules, such that air in the
lungs is forced into the tubules. Since transfer of gasses from lung airspaces
to solution in blood occurs in the sacs but not in the tubules, the collapsibility
of the sacs reduces the exposure of the animal to high levels of dissolved
nitrogen in blood, thus reducing risks of decompression sickness.
4. You are interested in collecting heart rate data for a sea lion species and a
porpoise species in a region thought to be strongly influenced by global climate
change. For each species, briefly describe one major advantage and one major
disadvantage of a satellite telemetry tag with downloading capability, as
compared to an archival tag, in the context of your study.
List of possible advantages/disadvantages:
Sea lions tagged with a satellite telemetry device:
Advantages:
- Can receive data while animal is still at sea;
- Can receive data even if device falls off animal (up until it falls off,
of course!);
- Do not need to retrieve device from the animal in order to obtain
data.
Disadvantages:
- Relatively high cost;
- Satellite bandwidth limitations prevent obtaining all data collected
by the device.
Sea lions tagged with archival device:
Advantages:
- Relatively lower cost;
- Can acquire and save large quantities of data, with multiple
variables measured, without concern regarding bandwidth
limitations;
- Readily retrievable if species in question has strong fidelity to
haulout sites.
Disadvantages:
- Data are lost of the device falls off the animal before it returns to
the haulout;
- Animal must be recaptured on the haulout in order to retrieve the
device and the data.
Porpoises tagged with a satellite telemetry device:
Advantages:
- Can receive data even if device falls off animal (up until it falls off,
of course!);
-
Do not need to retrieve device from the animal in order to obtain
data.
Disadvantages:
- Relatively high cost;
- Satellite bandwidth limitations prevent obtaining all data collected
by the device.
Porpoises tagged with archival device:
Advantages:
- Relatively lower cost;
- Can acquire and save large quantities of data, with multiple
variables measured, without concern regarding bandwidth
limitations;
Disadvantages:
- Data are lost of the device falls off ;
- Very unlikely that recapture of the animal and retrieval of the
device and data would be possible.
5. Some models of global climate change predict that the mean speed of northerly winds
along the California coast will increase gradually over time as global mean sea surface
temperatures increase during the next two centuries. How would the predicted increase
in wind speed affect the primary productivity of the ocean’s surface layers off California
(i.e., is productivity likely to increase or decrease?)? Why?
Such an increase would increase average rates of primary productivity in
surface layers of the ocean off California. Winds that blow from north to
south along the California coast drive the transport of surface waters to the
right of wind direction. Thus, surface waters along the coastline are moved
offshore, and are replaced by water transported upward from greater
depths. Because waters at depth are typically enriched in nitrate, and
because nitrate is often the limiting factor for primary production at sea, an
increase in wind velocity will increase the supply of nitrate to the surface by
upwelling, and will increase the average rate of primary production.
6. During week 4 we observed dissections of a Dall’s porpoise (Monday) and a harbor
porpoise (Thursday) in our lab sessions. We observed that swimming muscles of the
Dall’s porpoise were much darker in color than swimming muscles in the harbor
porpoise. Why does the color difference occur? What is the significance of the color
difference in terms of differences in behavior between species?
The color difference is the result of higher average concentrations of myoglobin in
the swimming muscles of Dall’s porpoises as compared to harbor porpoises.
Myoglobin is a respiratory pigment that facilitates storage of oxygen in the muscle
cells of marine mammals. The greater concentration of myoglobin in the muscle
tissues of Dall’s porpoise reflects the typically higher level of diving performance
(i.e., deeper, longer doves) in Dall’s porpoise as compared to harbor porpoise.
“ESSAY” QUESTIONS. CHOOSE ANY ONE OF THE FOLLOWING QUESTIONS
TO ANSWER. USE THE FOLLOWING BLANK PAGE FOR YOUR RESPONSE.
LIMIT RESPONSE TO THE FRONT AND BACK OF THE PAGE. 40 POINTS.
1.
During large-scale climate/ocean disturbances known as “El Niño”, the intensity
of subtropical trade winds is reduced dramatically in the equatorial Pacific Ocean.
How would such disturbances influence abundance and productivity of marine
mammal populations in equatorial pelagic habitats?
N=20 responses.
Subtropical trade winds include the northeast trade winds north of the
equator, and the southeast trade winds south of the equator. Viewed on a
large scale, both types of wind cause movement of surface waters away from
the equator. The result is a large region of equatorial ocean water,
particularly in the eastern half of the Pacific, characterized by strong
upwelling of deep, nutrient-rich waters that move up to replace diverging
surface waters. The upward movement of deep, nutrient rich waters into
shallow depths where light is plentiful results in high rates of primary
productivity. Primary production at sea, driven by phytoplankton
populations, forms the base of marine food webs and ultimately supports
higher trophic levels, including populations of marine mammals.
During “El Niño” events, intensity of trade winds diminishes such that rate
of divergence of surface waters is diminished. As a result, upwelling rate,
and the associated rate of upward transport of nutrients crucial for primary
production, is curtailed. Primary production rates decline, and support of
upper trophic levels also declines. Thus, the ultimate large-scale effect of an
“El Niño” event on marine mammal populations in the region is a reduction
of food supply. A number of responses by marine mammal populations are
plausible, among them:
-
dispersal from regions of reduced productivity;
reduced birth rate;
increased calving interval;
increased mortality rate.
Any combination of the above results in reduced numbers and productivity
of marine mammals in regions influenced by “El Niño” events.
2.
Describe physiological challenges that may be experienced by northern fur seals
during their extended period of activity at sea during fall, winter, and early spring
of each year. Describe underlying mechanisms that contribute to the
physiological challenges.
N=4 responses.
From fall through spring northern fur seals are at sea in pelagic North
pacific habitats virtually 100% of the time. Fur seals are generally too small
to accumulate large energy stores that would allow fasting while at sea, so it
is likely they must forage actively throughout this time period to survive.
Thus, they key challenges for fur seals during the specified time period are to
locate and consume adequate food and water to maintain body mass,
maintain vital organ functions, and allow somatic and fetal growth necessary
to participate successfully in reproductive activities during the coming
summer breeding season. These challenges must be overcome without the
advantages that come with hauling out (e.g., rest and the opportunity for
thermoregulatory recovery).
The challenges listed are linked to the crucial underlying requirement to
maintain core body temperature at the required level for physiological
function. For that requirement to be met, energetic intake obtained from
feeding must at least balance, and preferably exceed, energy lost due to heat
loss through the skin, the cost of locomotion, and the energy costs of
physiological function of the major organ systems. Thus, fur seals must find,
capture, and ingest food efficiently, that is, with the minimum possible
energy expenditures. This must be done during seasons of the year when
food web productivity levels are well below maxima, where risks from
physical factors such as ice and storms are maximal, and where light levels
are minimal. The challenges are enhanced by the relatively small body size,
and consequently unfavorable ratio of surface to volume, typical of fur seals.
3.
Examination of both extinct and modern sirenian species indicates that species
living at higher latitudes generally were much larger, in body size, than those
living at lower latitudes. Suggest an explanation for this pattern.
N=12 responses.
The primary explanation for such a pattern in body size lies with the issue of
thermoregulation and the relationship of surface area to volume as a
function of body size. All marine mammals must deal with the challenge of
heat conservation, and the problem is particularly acute for sirenians
because they are obligate herbivores and have a relatively low metabolic rate.
Thus, sirenians have only a limited capacity for replacing heat lost to the
environment with heat generated metabolically. The result is a crucial need
for effective conservation of heat and minimization of heat loss rate.
For objects shaped like marine mammals, an increase in the linear dimension
of a body will result in an increase in body surface area that is approximately
proportional to the square of the change in the linear dimension. However,
the same change in linear dimension will result in an increase in body volume
that is approximately proportional to the cube of the change in linear
dimension. Thus, as body size increases, the magnitude of the ratio of
surface to volume will decrease. Since volume is a reasonable surrogate for
mass, an increase in body size will result in a decrease in the surface area per
unit mass in a marine mammal body.
A reduction in surface area per unit mass will reduce the rate at which heat
is lost per unit of body mass. Since higher-latitude environments generally
are colder than those at lower latitudes, a larger body size is to be expected in
taxa for which heat retention is critical to survival.
4.
You are interested in understanding the extent to which harbor seals prey on adult
salmon populations returning to spawn in rivers that flow into Puget Sound. You
have adequate funding to either focus on collection of scats or on use of fatty acid
signature analysis, but not on both, to estimate the importance of salmon in seal
diet. Which approach would you choose? Why?
N=6 responses.
There is not a single correct “answer” to this question. Each approach has
advantages and disadvantages, and the choice of approach may depend on
available funding, the details of the question being addressed, and your
personal views regarding acceptability invasive vs non-invasive research
methods.
Scat samples are relatively inexpensive to collect. They do require quite a bit
of time for analysis in the lab, but the analysis does not require expensive
equipment that demands a high level of operator expertise. Prey hard part
remains can, in most cases, be identified to species without uncertainty. In
some cases the hard part remains can provide information about size and age
of prey items as well as their importance in seal diet.
Principal disadvantages of scat samples include potential bias against species
with small or fragile hard part remains, potential bias if some individual
seals on the haulout are producing and leaving more scats than others, and
potential bias if distant foraging locations are not as well represented in scat
samples as foraging locations close to the haul out.
Fatty acid signature analysis requires a tissue biopsy from a live animal, and
may be viewed by some as objectionable because it requires capture of live
animals and a momentarily painful sampling procedure. Initial lab
preparation work for fatty acid analysis is exacting but relatively
straightforward. Final analysis requires a gas chromatography system,
typically very expensive, available only in large university or agency research
labs, and requiring substantial experience and expertise for operation. In
total, costs of fatty acid approaches to diet characterization can be fairly
expensive. Finally, there may be some uncertainty in the actual species
composition of animals sampled for fatty acid work, particularly if a
“library” of fatty acid compositional data for prey species is incomplete or
not available.
Key advantages of fatty acid analysis include the knowledge that no animal is
sampled more than once, and the knowledge of the sex, size, and possibly age
of sampled animals. In addition, data from fatty acid analysis reflects a
fairly long period of foraging for the sampled animal, and is not
disproportionately affected by the most recent foraging activities of the
animal.