|FISH 475: MARINE MAMMALOGY
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:
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.
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.
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.
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:
Statistical model comparing population trajectory of SRKW with prey population trajectory
Analyze SRKW space use patterns in relation to prey distribution during periods of SRKW population growth versus population decline.
Analyze animal health from periods of population growth versus decline (e.g. use fatty acids to look at changes in diet, lipid composition, etc.)
Measure toxin levels of various levels of the food chain and SRKW, compare relative levels, and model transfer pathways
Map distribution and levels of toxins throughout Puget Sound
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.
Bioenergetics: Monitor behavioral changes in the presence of vessels, and model bioenergetic impacts of changes in behavior or diving patterns
Random population fluctuations
Population modeling exercise: Construct age-structured model that allows testing of multiple scenarios to explain population fluctuations, including random walk model.
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).
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.
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.
14 (20 pts.). Respond to one of the following:
In the line transect lab, estimates of pellet density were low for several groups. What are the likely reasons?
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?
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):
Scats represent only the most recent feeding activity, when animals are near haulouts. Diet may be different when animals are farther away;
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.
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.
Other reasonable explanations considered.
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.
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.