I. National Science Standards covered
II. Conceptual background
III. Scientific methods
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Module
II. Elephant Seal Diving and Fasting
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I.
National Science Standards covered
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I. National Science Standards Life Science Content Standard C: Matter, Energy, and Organization in Living Systems (from: National Science Education Standards, NAS, 1996, p.186) All matter tends toward more disorganized states. Living systems require a continuous input of energy to maintain their chemical and physical organizations. With death, and the cessation of energy input, living systems rapidly disintegrate. The energy life primarily derives from the sun. Plants capture energy by absorbing light and using it to form strong (covalent) chemical bonds between the atoms of carbon-containing (organic) molecules. These molecules can be used to assemble larger molecules with biological activity (including proteins, DNA, sugars, and fats). In addition, the energy stored in bonds between the atoms (chemical energy) can be used as sources of energy for life processes. The chemical bonds of food molecules contain energy. Energy is released when the bonds of food molecules are broken and new compounds with lower energy bonds are formed. Cells usually store this energy temporarily in phosphate bonds of a small high-energy compound called ATP. The complexity and organization of organisms accommodates the need for obtaining, transforming, transporting, releasing, and eliminating the matter and energy used to sustain the organism. The distribution and abundance of organisms and populations in ecosystems are limited by the availability of matter and energy and the ability of the ecosystem to recycle materials. As matter and energy flow through different levels of organization of living systems—cells, organs, organisms, communities—and between living systems and the physical environment, chemical elements are recombined in different ways. Each recombination results in storage and dissipation of energy into the environment as heat. Matter and energy are conserved in each change. This module introduces the methods scientists use to study the physiology of the large and cumbersome elephant seals on land and at sea. Students will learn how these animals "work" - how their metabolism is specially adapted to their extreme environments and living conditions. Students will learn about some of the remarkable findings on adaptations these extreme animals have to be able to survive and thrive in the cold, dark, high pressure environment below the ocean surface and their 3-month fasting periods while on land. It is almost as though they are two animals. Information in this module illustrates real life examples of science concepts that include matter, energy and organization in living systems, and interdependence of organisms (predator-prey relationships).
Elephant seals are the largest
of the 34 living species of pinnipeds (pinni = winged, peds = feet; "winged
feet" for how they swim through the water). There are two species in the
genus Mirounga; the northern elephant seal (M. angustirostris) and
the southern elephant seal (M. leonina). Most of the data on physiology
and metabolism have been collected on the northern elephant seal population
located at Año Nuevo Island and mainland 30 miles north of Santa
Cruz, California. No other population of elephant seals is as easy to get
to and so close to a research university.
Two areas of research with elephant seals that have provided valuable information on their amazing adaptations to life on land and at sea are studies on fasting on land and diving at sea. Elephant seals spend 70% of their lives at sea, 30% on land. The methods used to research on elephant seals at sea are very different from the research methods used on land. The equipment used in the two habitats is different, and the questions scientists seek to answer often vary according to the environment. Scientists work with the animals directly when they are on land, and collect data indirectly when they are at sea. They look at about everything, as the elephant seals are pretty easy to work with and are accessible for a day’s work. |
When seals are on
land, scientists look at:
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When the seals are at sea,
scientists look at:
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While the animals are on land, some of them will get fitted for at-sea experiments. Scientists glue an electronic data recorder (time/depth recorders, or TDR’s) to the animals’ backs that will collect information on their activities during their feeding migrations. At sea, these little black boxes record where the animals go, how deep they dive and for how long, and how their bodies respond to diving. When the animals return to land to molt, the recorder falls off with the molted fur. Scientists collect the recorder, take it into the computer lab, and download the data onto computers. After careful statistical analysis, scientists are able to learn about the elephant seal’s life when it is hidden from view on the surface. Using remote sensors is a major innovation in the study of animals that spend the majority of their lives in the ocean. It opens a whole new window to their lives. One TDR will get the record of the entire trip (2 megabytes for the whole 9,000 km round trip, roughly the distance from L.A. to Boston. Elephant seals make this trip twice a year. Females have been recorded traveling as far as 11,000 km in a single round trip). TDRs can also generate temperature and light data but it takes up more memory space and the TDR may not last the entire trip.
Working with scientific
data
1. Buoyancy (based
on research by Paul Webb, Ph.D. student of Dan Costa 1994-99)
There are two major mechanisms for buoyancy regulation in aquatic organisms: Hydrodynamic buoyancy is lift generated by movement through the water, and depends on the shape of the body and appendages, particularly the pectoral fins. Hydrostatic buoyancy depends on overall body density, with less dense organisms achieving a greater positive buoyancy than dense ones. Not very much is known about buoyancy regulation in marine mammals, and much of what is known is anecdotal, such as accounts of whether animals sink or float when killed. Elephant seals are excellent test subjects to learn more about buoyancy control, as they are relatively easy to work with on land; they almost always come back to the same place from which they left, and their fat composition changes dramatically throughout the year. Elephant seals use an evolutionary strategy for hydrostatic buoyancy control: they reduce overall body density and air volume by increasing the amounts of lipids and blubber. With a low-density body, there is no longer a need for a large air volume in the lungs to compensate for negative buoyancy. This decreases the range of buoyant forces and allows them to change depth frequently and rapidly without continual adjustment of their buoyancy to compensate. One way elephant seals make diving a little easier is that they drift during their dives. Even in transit dives, seals drift for significant portions of the descent. For juveniles this drifting represents an energetic saving of 23% of their oxygen stores. However, Webb’s study found no relationship between ascent rate and buoyancy. This indicates that regardless of their buoyancy, seals probably power upward during ascent, and swim continuously until they reach the surface. There is some drifting upwards during the final stags of ascent. Those initial kicks to begin the ascent from depth are very energetically expensive, however. When diving, elephant seals have a low body density due to their large blubber layers, a low air volume because they dive after exhalation, and they have relatively light bones. "For a seal diving with collapsed lungs and light bones an extensive blubber layer can be sufficient to impart neutral buoyancy to the animal" (Webb, 99).
2. Fasting Metabolism
The factors that control survival during the first year of life are fundamental components of the life history pattern of long-lived vertebrates. There are a variety of factors that determine juvenile survival, but they can be broken down to a suite of proximate (immediate or present) and ultimate (final) processes. Basically, survival during the first year of life requires that the young find sufficient food and avoid being preyed upon. Elephant seals at Año Nuevo State Reserve offer a unique system of study to address both proximate and ultimate factors that determine juvenile survival. This is because the period of maternal investment is short (28 days) and weaning is abrupt. The mother simply leaves the beach and the pup is left on its own. The pup then remains on the beach, fasting for 2.5 months, before it goes to sea and develops the skills to forage and survive on its own. If the skills aren’t developed it perishes. The way and rate at which the pup’s energy reserve is utilized over the 2.5-month fast onshore and the following period of time at sea are critical in determining whether the pup can survive its first foraging trip. Elephant seals’ primary energy reserve is stored as fat in blubber. The blubber layer, however, is not only an energy store but also the animals’ primary thermoregulatory system. Because of this, there appears to be a conflict between energy storage and thermal insulation, two functions of marine mammal blubber. Reduction of the blubber layer and a change in body composition during the postweaning fast may result in a thermal challenge for the pups when they enter the cold ocean water to forage for the first time and are faced with the increased energy requirements of swimming to obtain food. In addition, pups during their first foraging trip are novices in capturing prey and therefore may not be able to end their fast immediately upon entering the water, which increases their energetic burden.
Although there is no relationship
between weanling body mass and survivorship to year 1 in northern elephant
seal pups (LeBoeuf et al. 1994), it is likely that survivorship at sea
during the first year may be related to body composition and thermoregulatory
ability.
Using data gathered from different sized pups on body composition, blubber properties, and metabolic rates in water at various temperatures at the end of the fast, Dawn models how soon different sized pups will have to be successful in acquiring prey in order to survive their first foraging trip. She also hopes to be able to predict which northern elephant seal pup "body types" are most likely to be successful, and compare her predictions to actual survivorship data. The results of this study will help determine whether body condition and/or thermoregulatory abilities of different sized pups are related to survivorship during the first foraging trip. In addition, by increasing our understanding of the range of weanling body conditions and energetic requirements in the water, she will augment our ability to predict effects of changes in prey availability, on pup survivorship.
3. Remote measuring of
diving patterns
Elephant seals are among the deepest diving mammals; the maximum depth recorded 1503 meters. The recorded maximum dive time of a sperm whale was 73 minutes, measured by TDR (Watkins et al, 1993). The maximum depth of a sperm whale dive is 2250 meters (Ridgway and Harrison, 1986). At 1500 meters, pressure bearing on the elephant seal is 150 atm or roughly the amount of pressure equivalent to (How many African elephants, school buses, etc. would need to stand on your eyeball to exert an equivalent amount of pressure? The eye is used since it is approximately one inch in diameter). Elephant seals feed at much deeper depths than other marine mammals, fish, and humans, so there is little overlap and competition for food at these depths. It could be this low competition for food is one reason why they had such a rapid recovery from near-extinction around 1900. Once the hunting pressure was off they did quite well. The depth at which elephant seals feed has very little light, the twilight zone of the ocean where light fades to extinction. They are visual predators and it is suspected that they feed on bioluminescent organisms, including some fish and squid. They also feed on non-bioluminescent animals so the amount of light, depending on where they are diving in the water column, probably dictates what they eat. The function of the deep diving is thought to be related to three possibilities: feeding, predator avoidance, and energy conservation. (more details available from Le Boeuf et all, 1987, and LeBoeuf et al, 1991) Here are some interesting elephant seal dive facts found by UCSC researchers using time/depth recorders (TDRs):
1. All elephant seals of both
sexes and all ages dive deep, long and continuously for the entire period
that they are at sea.
In general, the average dive depth of elephant seals is 400-600m and the average dive duration is 20 min. The deepest dive on record is 1506m and the longest dive duration is at 119 min.
In a landmark study of seven
adult female elephant seal dive patterns (Le Boeuf et al, 1987) it was
discovered that the dive pattern of female elephant seals is very different
from other pinnipeds. The females dived continuously for the first 14-27
days at sea following lactation. Even though elephant seals have long,
deep dives, they have the same short surface interval (time they spend
at the water surface breathing) between dives. Other pinnipeds don’t dive
continuously, especially longer and deeper dives, without increasing their
surface interval between dives.
In another landmark study, one 8-year old female’s swim speed and dive patterns were monitored for 29 days—swim speed, distance, depth, and duration of free-ranging dives. She did no surface swimming. Angles of descent of the dives were less steep (30-56%) than angles of ascent (53-85). The mean total horizontal distance traveled per dive ranged from .6 to 1.3 km, depending on dive type. Each dive type was hypothesized to have one of the following principal functions: transit, foraging (pelagic and benthic), and process (serving rest, food processing, or anaerobic metabolite clearance). The primary reason that elephant seals dive is because they are diving to where the food is. Their migrations are primarily for foraging. Adult males eat bottom-swelling creatures, such as skates, rays, ratfish, small sharks, and hagfish. Females are pelagic feeders and eat a wide variety of fish and invertebrates that live in the water column. Juvenile diet predominantly squid and Pacific hake, and includes fish, sharks, rays, and cephalopods (squid) In one study on juveniles using tag re-sights (Condit & LeBoeuf, 1984), it was found that juveniles migrate north of their birthplace. Elephant seals born in central California are commonly seen as far north as British Columbia. They are concentrated in two areas, Northern California and around the southern end of Vancouver Island. Seals born in Southern California were commonly seen in central California and scattered much further north. Mexican-born seals congregated in Southern California. Mean latitudes for the three rookery groups are significantly different. (mean latitude 41°N, 36°N, and 33°N). Yearlings reliably home during the spring molt and fall rest period. They have a dive pattern similar to free-ranging adults which provides an excellent opportunity for scientists to conduct short-term studies of diving and measuring physiological variables such as the effects of diving on heart-rate and body temperature. Yearlings are much easier to work with than adults are. Satellite tags which work only when the animals are in the air are used to tell researchers when the animal is on the water surface, and when it has arrived back on the beach, but nothing of what it is doing while submerged. Radio tags are used by elephant seal researchers to locate the animals once they are on the beach. Some research underway with sharks and elephant seals uses acoustic tags and transponders. This system only works when the animals are in the water, and requires 3 buoys. This data is sketchy and has not yet been published. Satellite data gives time and date at different intervals but not an unbroken record. Elephant seal researchers use satellite tags to supplement TDR data. TDR data is collected every 30 seconds and only records depth, time, and temperature, but not distance. Satellite tags are used more with whales; you don’t need to retrieve the tags to collect the information, and it gives tracking data that is useful other than dive data. The TDR will also give information on where the animal goes, using temperature and light-sensing options. The TDR stores surface-seawater-temperature (SST) and light level (LL) data when the instrument is at or very near the surface. The light level data are extracted, plotted, and used to determine the times of dawn and dusk, which is used to determine what day it is and where the animal is on the earth in relation to the sun. The time midway between dawn and dusk, the local apparent noon, determines the seal’s longitude and the day length are used to determine latitude. The best efforts yield locations for elephant seals that are about + 1° of latitude and longitude. How can elephant seals stay down so long? They can store oxygen in different places--for humans; 1/2 of their oxygen is stored in their lungs, which collapse at depth. Elephant seal lungs collapse below 30-40 meters, so the bulk of their oxygen is stored in blood and in the muscles. Males feed on the bottom, females feed mid-water in relation to the bottom contours. Elephant seals drift while they descend, and sink while they drift. They swim continuously on the ascent. Pregnant females actually float when they drift because of their increased body fat (40%). All this can be seen in the dive records.
Annual
cycle - elephant seals have an annual cycle that is divided into four
phases spent on land. The cycle is different for northern elephant seals
versus southern elephant seals. The northern elephant seal annual cycle
is:
Buoyancy
- a force derived from Archimedes’ principal, which states that the upthrust
on a body in a fluid is equal to the weight of the fluid displaced by the
body.
Buoyancy is important to marine
mammals because it is a force that they must overcome to maintain position
in the water column, to dive to, or ascend from depth. Working against
buoyancy has an energetic cost, and organisms that can regulate buoyancy
to reduce their swimming costs will have advantages over organisms without
them.
Dive Profile - Elephant seals have distinctive patterns when they dive. These patterns or dive profiles can be observed by looking at dive records that are taken by small time/depth recorders that are glued to their backs. By looking at these records, it can be seen whether the animal was searching for food, travelling, or even sleeping while diving. Elephant seals spend most of their lives at sea diving. Fast - Elephant seals live primarily at sea where they are constantly eating. The two times when they come to haulout on land during the year are once when they molt and once when they reproduce. While they are hauled out on land, they do not eat or drink water. Their bodies are normally very fat which enables them to fast for up to 3 months (male) and one month (female). They lose up to 42% of their original body weight during their fast. Molt - Each year, elephant seals undergo a drastic molt and lose their hair and topmost layer of skin. Of all the marine mammals, only elephant seals and monk seals do this. Elephant seals return to the beaches where they were born to molt. Females and juveniles molt from mid-march through May (females who first arrive in mid-March were those who gave birth in early December and are returning from their 3-month foraging trip). Males return to molt June through August. Pup - A newly born elephant seal. It remains a pup while nursing from its mother, but becomes a weaner when the mother leaves the beach 28 days later.
Weaner
- An elephant seal pup whose mother has left the beach and returned to
the sea for 8 months. This usually happens about 28 days after the pup
is born. The mother fasts the entire time she is nursing the pup. After
fasting for a month, the mother is ready to return to the sea to eat. She
leaves the beach to end her fast and begins her foraging trip out to sea.
The mother weans the pup by leaving it on the beach. A weaner will stay
on the beach with short forays into the water for 10-weeks (2 1/2 months).
Then they are ready to dive and go on foraging trips of their own.
Description
Elephant seals use an evolutionary strategy: they collapse their lungs and reduce any spaces that capture air. Over time, they have reduced their body density by increasing their amounts of lipids and blubber, so they no longer need a large air volume to compensate for negative buoyancy (pressure to sink). This decreases the range of buoyant forces and allows them to change depth frequently and rapidly without continual adjustment of their buoyancy to compensate.
Objective for student learning
Students will design a model elephant seal using ziplock bags, rocks, Crisco, and air to understand what determines whether an object sinks or floats. Materials and preparation
Day before:
To purchase:
Locate in classroom:
Day of: 1. Each student selects one potato, ziploc bag, 1 cup of Crisco (spooned out onto paper towel) and returns to lab table with water filled container in middle of table. 2. One student from each group picks up a timer (if no timers available, have one student with a timer on their watch in each group). 3. Using air, potato, Crisco, and ziploc bag, design a model elephant seal that is neutrally buoyant (neither sinks nor swims; stays in the water column half-way between top and bottom). 4. Using these materials, design an elephant seal that sinks to the bottom fastest. Time the sinking rate with the stop watch. Using these materials, design an elephant seal that is very hard to sink—pressure must be used to push it down into the water.
Assessment: (this section
will be printed as a downloadable data sheet)
This fat tides them over during fasting and breeding periods, and is important for keeping warm in the deep cold water where they dive for food. But having lots of fat makes them have to work harder to dive because fat makes them more buoyant. Reproduction is very important for all living things, and living things have many adaptations that are primarily to enhance their chances of reproducing. The way the elephant seals reproduce requires that they stay on the beach for long periods of time without leaving the beach to eat—males for up to 3 months, females about 1 1/2 months (the reasons for this mode of reproduction are found in Module I, Reproduction). Elephant seals need fat so they can fast during the breeding season. They also fast when they haul out to molt (they lose the top layer of skin/fur and haul out on land to do it. They are weak from fasting and their skin is in a tender unprotected state—they could be vulnerable to sharks if they molted while at sea.) So there is a trade-off between the need for a large blubber layer for thermoregulation and energy stores, and the possible extra energy required to overcome the effects of buoyancy during diving. They need the fat, but have to work harder to dive because of the fat. Sounds complicated, but this system has worked so far—elephant seal numbers continue to increase along the coast of California, even though the juvenile mortality rates are high. How does fat affect sinking rates? What else affects sinking rates?
1. Which bags sink the fastest?
Why? What does the potato represent? The Crisco?
Additional Assessments:
Exploring the web site
Extensions
Elephant seal fasts parallels hibernation. True hibernation refers to a state where body temperature drops almost to the level of the animal's surroundings. Metabolic rate, heart rate, respiration, and many other functions are greatly reduced. The animal is torpid and shows little response to external stimuli such as noise or being touched. Most animals that hibernate are small, such as many rodents, small birds, and bats. Bears may sleep during much of the winter, but most physiologists say that they are not true hibernators. Their body temperature drops only a few degrees, they show only a moderate drop in metabolic rate and other physiological functions, and the females often give birth to the cubs during the winter. Elephant seals, as well as other seals, exhibit a drop in metabolic rate during extended fasting periods. They also breathe apenustically (periodic breath-holds) and sleep a lot. What are some things that elephant seal weaners can do to prepare themselves for life at sea? (They can fast, practice swimming, practice longer and deeper dives, chase fish in shallower water—all these activities utilize protein and redistribute muscle mass, making them less buoyant. Remember, the fatter they are the harder (that is, the more energetically expensive) it is to dive. Only 46% of the weaners survive the first year after they leave the beach.)
Description
Elephant seals use negative buoyancy to drift downward during descent, but may swim continuously during ascent, powering to the surface. Video records of diving animals show that even in transit dives, seals drift for significant portions of the descent. For juveniles this represents an energetic saving of 23% of their oxygen stores which translates to an additional 3 minutes of gliding, or 1.1 minutes of swimming at 2 meters/sec-1 (Williams et al, 1996). Scientists think that buoyancy plays a significant role in shaping diving behavior in elephant seals, and that they may adjust their behavior to suit their buoyancy, rather than adjusting their buoyancy to suit a dive. Elephant seals travel great distances to feed, as seen in their migration pattern data [link to migration pattern image from web here]. This tracking information is collected using satellite devices attached to the animal that records their position every time they surface. However, when you measure the distance they travel up and down the water column during their travels, they actually travel much further than the distance measured on the ocean surface, i.e., from Año Nuevo to the Aleutian Islands. There are two ways of measuring how far elephant seals travel during their feeding migrations. One is horizontal distance traveled—measuring from point a to point b on a horizontal line, as though the animal were traveling on the surface of the water. Looking at this data is how we learn where the animals go when they migrate to forage for food—satellite transponders put on the animals register every time they surface. These instruments don’t work under water, but they are essential to understanding where the animals go to feed. Males go up the Aleutian Islands off Alaska, and females go due west into the open Pacific Ocean. (slide with migration paths).
On a horizontal plane, male
elephant seals from Año Nuevo travel the most northerly and westerly;
one male traveled round-trip 7,500 km to the eastern Aleutian Islands in
southern Alaska, roughly the distance from L.A. to Boston. Adult males
travel far to get to their destination, then do concentrated foraging dives
for up to two months before returning to the breeding rookery. The females
tended to migrate further when they were pregnant.
Another way to look at how far elephant seals travel in their foraging migrations— a truer look into exactly how much energy they have to use to travel this far—is to look at the depth of their dives and factor that distance into the total distance traveled. This is how we normally measure how we travel in cars or bikes—how many miles is it from here to there—miles traveled vs. distance as the crow flies. The distance traveled going up and down a hill from point a to point b is quite a bit farther than if you were going straight from point a to point b on a flat plain. The distance measured by the satellite tags is as the crow flies—surface distance only, not underwater dive distance.
Learning Objective
Materials and preparation
Day before:
Day of Activity:
What you see on the surface does not always tell the whole story. Scientists need to collect a number of different types of data records to determine what the animals are actually doing while underwater. They collected data from the time/depth recorders to determine how deep and how often the animals were diving. They obtained data from the satellite recorders to determine the location to which the animals traveled. Use this data to figure out how far the animals actually travel.
With student responses, Instructor
will complete DS2 either on the overhead
projector or in small groups.
Extensions
Description
Learning Objective
Activity
Day before:
Day of Activity:
Each group will write their
answers on a sheet of paper to give an oral presentation to the class.
Presentation can include graphs enumerating types of dives and number of
times their elephant seal did a certain dive. What do you think is going
on with this animal? Is it a male, female, or yearling? Are they feeding
or in transit?
Exploring the web site
Extensions
Activity
4a: All fat is good fat for elephant seals
Additional Content Standards
for Activity IV activities:
Matter, energy, and organization
in living systems
The chemical bonds of food molecules contain energy. Energy is released when the bonds of food molecules are broken and new compounds with lower energy bonds are formed. Cells usually store this energy temporarily in phosphate bonds of a small high-energy compound called ATP.
The behavior of organisms
Description
Though elephant seals have evolved to depend upon a rich fat diet, all fat is not good fat for humans. Foods that are high in saturated fat (the kind found in red meat and whole-milk products) raise your cholesterol level much more than foods that are high in cholesterol. These harmful dietary fats (and obesity) increase the level of low-density lipoprotein (LDL), the "bad" cholesterol that streaks the inside walls of arteries with fat. This buildup of fatty deposits narrowing of the blood vessels, which sets the stage for a heart attack or stroke. Obesity is a major cause of high blood pressure, which is a powerful risk factor for heart disease and stroke. At weaning, a healthy weaner averages 48% fat (for comparison, a healthy level for adult women is from __ to __% fat, for men it is ___ to ___% fat ). During the first two weeks of a weaner’s fast, it loses about 2.2 to 4.4 pounds a day. During the last eight to ten weeks of the fast, it will lose close to 1.5 pounds a day. At the end of ten weeks a typical weaner will have lost from 115 to 146 pounds (35 to 55% of their initial weight at the point of being weaned from their mother).
Objective for student learning:
Goals
To comprehend the level of these dramatic weight gains and losses, students will first calculate how much a human baby would weigh after drinking elephant seal milk for 28 days. They then will calculate how many kg pups lose in the two and a half months when they are a weaner—an elephant seal pup whose mother has weaned and left behind on the beach to fend for himself. Materials and preparation list:
Day before:
Purchase plastic spoons (one
for each student)
Activity Whole class option: Display TM4a on overhead projector. Work with students to fill out the table. Small group work option: .Divide students into pairs or small groups with one data sheet per group. Students will read the text and fill out the table. Have whole group discussion at end.
Optional activity
:
Exploring the web site
Description
The fat serves a unique purpose at sea: it is not a matter of using fat to keep the cold water out or insulate against the cold, but the fat keeps the heat from escaping the source (their heart). It essentially holds in the heat.
Objective for Student Learning:
Goals
Materials and preparation list
Option 1 : Materials for classrooms
with four hotplates available:
Option 2. Materials for classrooms
with no hotplates. Requires microwave oven.
Day before:
Day of:
Activity
1. Leave the hot plates turned
off. Record the temperature.
Questions for whole class
discussion, or copy onto paper for small group discussion:
Option 2: Work with
the Activity I potatoes.
Students will work in threes with an insulated and uninsulated potato, and a potato in ice water. Insert a cooking thermometer into each potato. Record initial temperature of all three potatoes. Wait 5 minutes and record temperatures again. Repeat. Make a graph of temperatures. Discuss questions.
Questions for whole class
discussion, or copy onto paper for small group discussion:
Extensions
Description
While fasting during the breeding season, elephant seals still use up a lot of energy for mating, fighting, and nursing young. On the other hand, females that fast during nursing do not have to feed while nursing, as sea lion and fur seals do, so they transfer lots of milk energy to their pups in a short time, and they can forage later without having to care for their young.
Objective for student learning:
Goals
To better understand how well-adapted elephant seals are to long fasts, students will learn about the importance of a good start: an extremely rich milk diet for pups. Students will also calculate how much weight the animals really lose during fasting periods. They will compare it to "what would happen if?" they fasted for 3 months.
Materials and Preparation
List
Activity
Day before:
Day of:
Day 2: Assessment
1. Use the fasting statistics for an elephant seal female, male, or pup (as shown in table) to determine how much you would weigh after fasting during a reproductive season. (Students take their weight, calculate how many pounds would equal a 30%, 32%, or 42% loss for themselves). 2. Discussion question: How long could you survive on a complete fast—remember, no liquids either. (humans can survive only 3 days without water) 3. Written answer or open discussion: Make a list of what lifestyle choices you would have to make to be able to withstand three months with no food or water. Reduce water loss, have thicker skin, sleep almost all the time, breathe less frequently, use muscles only for the most important functions like reproduction (male), avoidance of mating (female), and feeding pups.
Exploring the web site
(optional)
Look at a photo of females in January. Now look at them in late February or early March. Do they look different? Look at a photo of a newborn pup around mid-January. Now find a weaner soon after its mother has left the beach, around mid-February. Is it much bigger than a pup? Now, look at a weaner one-month later (mid-March). Can you tell the difference in size?
Extensions
How elephant seals survive
the pressure of the deep sea is an enigma. To illustrate this to students,
develop a figure and give them pressures (PSI) at many depths all the way
down to the deepest elephant seal dive depth. At each mark of a pressure
and depth, we could give an example of how heavy the water would feel (i.e.,
an elephant standing on your head). There are many activities used to illustrate
pressure that perhaps teachers are already using. It would be better to
refer them to existing web sites on general pressure experiments.
Module II Background Data MILK COMPOSITION
Female milk composition (approximate)
WEANERS/JUVENILE DATA
Juvenile growth
JUVENILE CYCLE
MOLT
HEART RATES
SIZE
PREDATORS
This seal with a cookie cutter wound was photographed on Isla Guadalupe at the
southern end of the elephant seal range... the wounds are less common on seals
that haul out in central California.
MOLTING SEASON
TRIPS TO SEA
DIET
MORE DETAILS ON BUOYANCY
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Cookie cutter sharks are members of the dogfish family
and are small sharks. Their upper teeth are all connected together as are
the lower teeth. This tooth arrangement creates more of a blade-like morphology
within the mouth of the shark.These sharks use suction to attach to their
prey items. They latch onto their prey, bite, and then spin. This movement
removes an almost perfect circular chunk from their prey. Look for these
circular scars on the bodies of elephant seals, especially right behind the head.
CSUMB Elephant Seal Project 05/23/00 |