Anatomy and Physiology SKELETON, MUSCLES, AND LOCOMOTION Right whales range in length from about 17 meters (55 feet) maximum for adults, 9 meters (30 feet) for one year olds, and 4-5 meters (12-15 feet) for newborns. Weighing in at about 45,500 kg (100,000 pounds), the adult right whale has a very large girth relative to its length giving it a marked rotund appearance. One 13.6 meter whale had a girth measurement of 9.2 meters. A remarkable feature about the right whale is that its head is approximately 1/3rd of its body length -- one skull was measured at 5.2 meters and weighed 1,000 kg (2,200 pounds). The jaw in this head is greatly arched, allowing the right whale to carry extremely long baleen plates, up to 3 meters (9 feet) long. About 205-270 plates are found on each side of the mouth with a clear opening in the front. Despite the great size of the right whale, its skeleton is surprisingly simple and comparatively light. Overall, the skeleton accounts for only about 14-15% of the whale's total body weight, whereas in humans, the skeleton is about xx% of body weight. One finds that the whale's spine consists of 55-57 vertebrae including 7 cervical, fused in the neck region apparantly to hold the enormous head, 14-15 thoracic, 10-11 lumbar, and 25 caudal; in comparison humans have 33 vertebrae -- 7 cervical, 12 dorsal, 5 lumbar, 5 sacral, and 4 coccygeal. Interestingly, almost all mammals have seven cervical (or neck) vertebrae (manatee and the two-toed sloth are exceptions), no matter how long the neck, including giraffes, horses, hippos, whales and humans. Right whales have 14-15 pairs of ribs while humans have 12 pairs. [The whale's ribs are very flexible and can protect the internal organs while the animal is in the water at various depths; but, they are not so successful on land. If a right whale were to beach itself for any length of time, its great weight would collapse the ribcage and lead to internal organ damage.] There arm bones (humerus, radius and ulna) in the right whale are extremely short compared to human proportions; and the pelvic region in the whale is reduced to an elongated pelvic bone, associated with small, light vestiges of femurs and tibias. The flipper of the right whale is surprisingly similar to the human hand however. There are five digits (as there are in human hands), although the phalanges (finger sections) range from 2-6 while humans have 3 phalanges in each of the fingers except the thumb which has two. The whales we know today evolved from four-footed mammals that once roamed the land. In the course of natural selection, the whale's ancestors with adaptations for the water environment survived and began to use the oceans exclusively. These adaptations included a strong tail which became more important for locomotion than limbs. The two "wings" or flukes that developed on the sides of the tail are filled with tendons and connective tissue [this is an extension from the base of the spine and not an adaptation of the legs]. The tail muscles are the largest in the whale's body and are so powerful that they can propell a 50 ton right whale out of the water into a full breach. Right whales, like other cetaceans, move their tails up and down, rather than side-to-side like fish. This motion evolved from the natural flexing of the backbone in a running mammal. However, unlike its ancestors that stayed on land, the whale lost its hind limbs and its front limbs evolved into flippers which are used for steering and stabilization (but not for propulsion). Scientists believe that the dorsal fin (absent in the right whale) may be used for stablization in fast-moving cetaceans. The up stroke of the up-and-down oscillation of the tail is what powers the whale's forward progress. The down-stroke returns the fluke to the starting position. If you've ever gone sculling in a boat you've used the same principle -- the oar (which stays underwater the whole time) is pulled upward powering the vessel forward with the follow through returning the oar to the original position. If you can get to a swimming pool, try swimming like a whale , then like a fish. A whale swims with its tail going up and down. Try it. Keep your legs together and move them up and down together. You'll find you'll be doing the traditional dolphin kick used in the butterfly. Now try swimming like a fish. You can't do it. Mammalian bodies just don't have enough power that way. Our spines and musculature are designed for up and down motion, not side-to-side. SKIN, CALLOSITIES AND WHALE LICE Right whales, for all their size, have very thin skin. This layer of smooth, black skin can be easily rubbed off, yet offers an important protection for the whale, serving as a barrier between the whale and the salty ocean water. Researchers have observed numerous white marks on right whales, indicating scarring from such hazards as entanglements with ropes and netting, collisions with boats, and encounters with orcas. Some 60% of all known right whales show entanglement scars. The skin covers a thick layer of blubber, strong muscles, and a lightweight skeleton. Cetacean skin shapes the package into its streamlined, torpedo-like shape which is hydrodynamically suited for the ocean environment. Few appendages interrupt the flow. Skin flaps on the dorsal (bottom) side of the whale cover its genitalia (two nipples and birth canal in the female and a retracted penis in the male). The whale's genital slit is located further back along the central dorsal line from the navel but before the anus. One unusual feature on right whales that seems to interrupt its streamlined appearance is the formation of callosities. These areas of cornified epidermis (thick skin patches), which are visible even on newborns, are unique to each whale. Researchers use these callosity patterns to identify individuals; photographs taken since the 1950s have helped in the identification process. Callosities occur on whales in all the same areas that humans have hair -- on the top and sides of their heads, over their eyes (eyebrows), near their ears (sideburns), around their blowholes (moustaches) and under their lips and chins (beards). Idenfications are made by photographing the whales and then describing the shape, position, and surface topography of the callosities. Matching a pattern to a known whale can be very time consuming. Sometimes, waves or spray can hide part of the pattern, or the photo's orientation may obscure part of the head. Glare from the sun may also be a factor. In addition, callosity patterns can change. Although scientists have found that most patterns tend to stay unchanged in adult male right whales, nearly two-thirds of the cows displayed minor changes in the callosity pattern of the "bonnet" (area at the top of the head in front of the blowhole). Most calves displayed changes in callosity patterns during the first few years. Living on these callosities are some unusual creatures. These "hitchhikers" are whale lice (or cyamids) which are less than an inch long and spend their entire lives aboard whales -- with each whale species hosting specific cyamid species. For the right whale, it's Cyamus ovalis and C. gracilis in particular, and occasionally C. ceti, C. erraticus, and C. catadontis. No one really knows the function of these whale lice. They were first described in 1675 by Friederich Martens, a surgeon on a whaling ship. He catagorized them as a type of crayfish but wrote that "they can hold fast as well in the skin of man as of the whale...and hence...are given the name of louse." But although they look like the human pest, these lice are amphipod crustaceans (not insects). The nearest relative to the family Cyamidae is the skeletal shrimp. The cyamids may be consuming sloughed skin in a natural cleaning process. Some scientists speculate that the lice may also play a role in cleaning wounds and aiding the healing process. Each cyamid has 10 legs, each with a sharp curved hook at the end. Unlike stationary barnacles, cyamids walk about the whale's surface in a forward motion (not sideways like crabs) and when not moving about, dig in with their hooks for the ride. They can withstand the force of a full breach. Since they can only survive on whales, cyamids would find that getting dislodged could be a fatal mistake. Whale lice also play a role in whale identification -- or misidentification. Most callosities are naturally gray or black, but the growth of whale lice in these areas gives them a white, pink or yellowish color. As the whale lice move around the callosity, they may change the appearance of the callosity without changing the actual shape. Right whales only have a few vestigial hairs left over from the times when their ancestors were fur-bearing, land animals. These hairs are usually associated with the callosities. Why did the whale's hair disappear when other marine mammals, such as seals, retained their fur coats? The answer lies in the percentage of time each animal spends out of the water. Seals can often be found out of the water on the ice where bare skin would be damaged in subfreezing temperatures. Whales live their whole lives in water, where temperatures never get below the freezing point, therefore their skin does not need that extra protection. BLUBBER No wonder the whalers loved the right whale. It's a storehouse of blubber in one nice, compact package. About 40% of the whale's body weight is composed of this layer of fat. Why so much fat? The blubber layer plays a three-fold role in the whale's survival in the marine environment. First, the blubber serves as a barrier, keeping the warmth inside the whale and preventing loss to the much colder ocean water. Second, the blubber serves as a food reservoir, especially important when the whales cannot find large patches of zooplankton in northern waters or when pregnant whales move to warm southern waters. During this calving period, cows (mother whales) spend all of their time nursing and caring for their young, expending large amounts of their blubber. The southern waters are ideal for their calves which need the warm water since they cannot thermoregulate well, but the waters are poor in zooplankton. Even if the right whale wanted to feed, she would not have much luck in getting enough food. The third function of blubber is as a fairing material. Webster's describes "fairing" as: "a member or structure whose primary function is to produce a smooth outline and to reduce drag (as on an airplane)." This streamlining is also found on the whale. Blubber smooths out the body proportions and heightens hydrodynamic properties in the whale. But compared to other whales, the right whales have gone a bit too far -- they have a relatively large girth to their length. Perhaps that's why they are one of the slowest swimming whales. INTERNAL ORGANS The internal organs of a right whale constitute about 14-15% of the whale's overall body weight. The skeleton takes up a similar percentage of the animal's weight. BALEEN, MOUTH, AND DIGESTION Food passes through the whales mouth into its esophagus, on its way to the whale's multi-chambered stomach. Scientists believe the baleen whales have three major chambers (and perhaps a fourth smaller chamber which may be an extension of the intestine). This similarity to ungulates may not just be chance. Perhaps the whales are descended from the same line of land animals that gave rise to ruminants -- even-toed, hoofed animals, with four-chambered stomachs (usually) like cows, sheep, giraffes, camels, and deer. Food then passes through the intestine, with the remaining waste materials being eliminated into the ocean. The total capacity of the stomach of a large whale is about 760 liters (200 gallons). This is relatively small compared to the cow with a capacity of 209 liters (55 gallons) and the human with a capacity of 17 liters (4.5 pints). The first chamber in all whales is a dilatable, sac-like, extension of the esophagus with no digestive glands. This is the compartment that "chews" the food -- as the gizzard does in birds (remember -- baleen whales have no teeth and toothed whales don't use their teeth to chew). In baleen whales, the first compartment is quite small (little need to "chew" since their prey is so small), while in toothed whales the compartment is relatively large. The second chamber is where digestive juices are released -- pepsin and hydrochloric acid have been found in this part of the stomach of some whales. Most cetaceans have a third large chamber which is the pyloric part of the stomach. The intestine is quite large, usually five to six times the length of the body (human intestines run about two times body length or about 12-13 feet in an adult). Baleen whales also contain a distinctive caecum and colon, and, as with other mammals, have a pancreas and liver which deliver digestive enzymes by way of a duct into the digestive tract (there is no gall bladder in contrast to humans). These large mammals, eating some of the smallest prey, need upwards of a million calories a day to maintain body functions. That amounts to about 2,000 kilograms (4,400 pounds) of plankton daily. In contrast, the average human requires only 3,200 calories for mainenance. But these numbers can be deceiving. A million calories to a 50 ton animal is equivalent to 1,500 calories to a 150 pound person. So the whale actually has a more efficient system than the human. This relationship of lower metabolic rate with greater size is seen throughout nature. For example, mice and birds have extremely high metabolisms compared to humans. KIDNEY AND URINATION Among mammals, cetaceans and pinnepeds have the most lobes in their kidneys. One researcher compared this organ to a bunch of grapes. In a comparison between other baleen and toothed whales, researchers have found that the right whale has up to fives times the number of lobes (or reniculi), however, the significance of this lobulation is unknown at this time. As in humans, the kidneys are used for cleaning the blood, separating out the waste products for later removal from the body. In one juvenile right whale (12 meters or 36 feet), a kidney (there are two) weighed in at 32.4 kilograms (about 71.3 pounds). In an adult human male, a kidney (there are also two) weighs about 140 to 187 grams (4.5 to 6 ounces). Eliminating the waste products extracted by the kidney (mainly urea) requires water. All mammals require a certain amount of water intake in order to function properly. Not only is water necessary for the production of urine, but for feces, oxygen extraction in the lungs, and in most mammals for sweating (temperature regulation). Without the need for large amounts of water for perspiration, whales take in (proportionately) a lot less water than other animals. But how can whales, living in a salt water environment, get the fresh water their bodies need? It is well known that a person who drinks seawater will become even more thirsty. The body, attempting to eliminate the excess salt, will draw upon its own fluid supply, thereby increasing dehydration . Most air breathing vertebrates cannot tolerate seawater, but some are less restricted than others, including whales. Seals (pinnipeds) and cetaceans remove salt from their systems in a conventional manner. Scientists believe these animals do not drink seawater, but satisfy their need for water with the fluids contained in their diets. Fish-eaters, such as humpback whales, would get ample amounts of water from their food alone. Herring, for example are 80% water and have an osmotic concentration of about one-third sea water, i.e. a low salt content of about 1.2%. (Seawater is 3.5% salt.) One calculation based on seal studies shows that: 100 calories/1,250 gm of fish eaten, produces 1,000 gm of water directly and 121 gm of water from the oxidative breakdown of the fat and protein taken in, for a total of 1,121 gms of water; the seal uses 106 gms of water to saturate the air in its lungs and 200 gms for feces production, leaving 815 gms for urine. But plankton are in osmotic equilibrium with seawater, i.e. their salt content is 3.5%. Plankton-eaters, such as right whales, must produce a urine that is more concentrated than seawater in order to accommodate their invertebrate diet and any incidentally swallowed seawater. Physiological studies of cetaceans suggest that their kidneys are able to dispose of the concentrated salt solution without troublesome effects. Whales lose additional water when they nurse their young. One solution is the concentrated milk (30-40% fat) as compared to cow's milk (4% fat). This energy-rich milk is not just needed for fast growth of the baby, but to economize on the mother's fluid levels. A more watery milk would dehydrate the mother who cannot easily feed with a newborn by her side. BLOWHOLE, LUNGS, AND RESPIRATION A simple rule of thumb to distinguish baleen and toothed whales is to look at their blowholes. Toothed whales have one hole, baleen whales have two. This difference evolved millions of years ago. In calm winds, the blow from a right whale has a distinctive V-shape (the two branches veering off at angles from one another). Other whales tend to have a bushier blow. The placement of the blowholes (nostrils) at the top of the whale's head is an important evolutionary development, which allowed the whale to stay almost completely submerged while breathing (unlike other animals with nostrils located at the tip of the snout and who must lift their heads almost completely out the the water to breathe). In addition, the nasal ridge (or rostrum) around the blowhole acts like a splashguard to keep water from entering the nostrils. The windpipe (or trachea) is also completely isolated from the esophagus-- there is absolutely no way water from the mouth can enter the lungs while the animal is eating. In fact, the whale can breathe and swallow at the same time. Also, breathing has become a voluntary action for whales. Unlike humans, who can breathe even when unconscious, whales must consciously control each breath. Therefore, scientists believe that whales do not sleep like we do. Studies on other cetaceans have shown that the animals shut down half their brain at a time while they "log" or float at the surface. The blow that we see at the surface is the whale's exhaled breath, which is due in part to the atomization of the water that was left around the blowhole as the whale surfaced. In addition, contributing to the visibility of the blow is condensation of this compressed, warm, moist air from the lungs [just as our breath appears on a cold day]. Blows can be seen and heard almost a mile away on a clear, calm day. But this surface time is minimal for whales. Most of their time is spent underwater -- most right whales average 5 to 10 breaths at intervals of 15 to 30 seconds before diving for 5 to 30 minutes. Most deep dives are about 20 minutes. The lungs on whales are not as large as one would suppose with animals of this size and the fact that they spend much of their time diving and holding their breath. Proportionally, lung volumes of whales are about one half that of terrestrial mammals. Fin whales have been calculated to have a maximum lung capacity of 2,000 liters while humans measure in at 4-5 liters. Scientists have also found that cetaceans fill and empty their lungs much more quickly and completely than humans and other mammals. They can exchange up to 85-90% of the air, as compared to humans who exchange only 15%. This is termed the tidal volume or the amount of air moving in and out with one breath (in humans about 500 ml, in the fin whale, about 1.8 liters). In whales, oxygen exchange is a lot more efficient than in most other animals. Research also indicates that cetaceans can use about twice as much oxygen from a given volume of air. Whale red blood cells are larger than in humans and other animals, plus there are more red blood cells per unit of blood (almost twice that of humans). These two factors allow for a speedy exchange of oxygen from the lungs to the hemoglobin -- the oxygen-carrying, red blood cell pigment. This oxygen supply is then transported throughout the body. Where whales differ from humans and other terrestrial animals is in their myoglobin content -- the oxygen-carrying pigment in the muscle. Whales show 2-8 times as much myoglobin as terrestrial mammals; that's why cetacean muscle is much darker than beef and other animal meats. The oxygen-holding capacity of the muscle and blood is the secret behind the whale's ability to perform long dives (it is not a factor of held breath as it is with humans). According to one estimate, total oxygen storage in a human diver is: 34% in the lungs, 41% in the blood, 13% in the muscles, and 12% in other tissues. In the whale, the proportionately smaller and compressed lungs hold only 9% of the oxygen, with 41% in the blood, 9% in tissues, and 41% in the muscles. But why don't whales get the bends like humans do, since they seem to make relatively deep dives with quick returns to the surface (one whale was recorded as routinely diving to 300 meters or close to 1,000 feet)? Dr. Steve Katona writes in his "Field Guide to Whales, Porpoises and Seals" that: "Whales and porpoises always fill their lungs with air before submerging, but they probably never get the bends, no matter how often or deep they dive. Two factors protect them. First, at depth the air is compressed to a very small volume. As water pressure increases, the ribs, most of which are not firmly connected to the breastbone, collapse inward compressing the lungs and forcing air into nonabsorptive portions of the lung (bronchioles, bronchi, and trachea). Second, lung compression reduces blood flow to the lungs. Both processes (and perhaps others) minimize absorption of air into the blood, preventing excessive quantities of nitrogen from dissolving in the blood. As the whale ascends, the compressed air expands again, refills the lung, and blood flow and gas exchange resume." Also, the air the whale starts off with is the air it comes up with, unlike SCUBA divers who are taking in compressed air (and compressed nitrogen) during the dive. If the diver didn't decompress during the dive and expel some of the nitrogen, the expanding nitrogen would cause dangerous (possibly fatal) consequences upon surfacing. THERMOREGULATION AND CIRCULATION What happens on a cold day when you forget your gloves and wear only a thin coat? Naturally, your hands get cold, as does the rest of your body. What happens when you spend too much time in the ocean off Cape Cod even in the middle of the summer? Most people start to shiver. Heat loss in the water is more than 25 times greater than in air. That's why people who fall overboard in cold water can get hypothermia so quickly, sometimes in only a matter of minutes. So why don't whales get cold in the ocean, where water temperatures can reach close to freezing? The answer here is blubber and body shape. The whale's layer of fat, up to one-and-a-half feet thick in right whales, acts like an overcoat. And, as opposed to popular conceptions about getting cold, this blubber layer does not keep the cold out -- its purpose is to keep the animal's body heat in. (This can be related to one of the important laws of thermodynamics -- heat flows, cold is the absence of heat.) In land-based animals, hair or fur or feathers create a barrier, trapping warm air against the skin. For humans, it is recommended that people dress in layers on cold days -- again to trap the heat and prevent it from escaping to the outside. During the course of evolution, whales lost most of their hair , but the protective layer moved internally to the blubber beneath the skin. In right whales, two-fifths or 40% of their body weight is blubber -- the largest percentage among all whales (blue, fin and humpback whales all carry about 25% blubber) The rotund body with few extremities also keeps most of the heat near the inner core. If the whale were to have long appendages, such as our arms and legs, with blood vessels located closer to the surface, it would naturally lose more heat. (Take a survey of other animals found in cold versus warm locations -- you'll probably find that the majority of animals in hotter regions have longer legs, arms, tails, necks, etc. than animals found in colder climes.) Whales also have decreased breathing rates, which also adds to their ability to maintain body heat without expelling it (via warmed air) to the environment. But what seems to be an ideal solution to a heat loss problem can also turn out to be troublesome. What about times when the animal has excess heat -- perhaps when it's in warmer waters, as in the Georgia/Florida calving grounds or during times of prolonged exercise. For right whales this is especially critical since the surface to volume ratio is the lowest among cetaceans (they have the greatest volume for their skin surface area and therefore cannot lose heat as efficiently). For humans and many land animals, condensation is a cooling process. We sweat. But this option is unavailable in the watery world of the whale. Instead, the animal must lose heat to the environment through conduction. Whales also have some sections on their bodies where the blubber layer is thinner and blood vessels are closer to the surface, as in the flippers and tail of the right whale. Other whales also use their dorsal fins but right whales have none. THE SENSES Whales can open their brownish-red eyes underwater to see, as wellas use them above the surface (when they bring their heads out of the water it's called "spyhopping"). Protecting these eyes from the salty seawater are oily tears that constantly coat the eye surface, but without the worry of dust or sweat, whales have no need for eyebrows or eyelashes. However, whales do have eyelids to protect the eye from superficial injury. With eyes widely separated on either side of its large head, the right whale has a blind spot directly in front of it. Might this be a factor contributing to right whale collisions with ships -- we don't really know. When a whale is swimming along and trying to stay within a plankton patch, it just may not see the vessel traveling in a head-on direction. But there is also a question of whether the whale actually uses vision to locate and move within a plankton patch, or if it involves another means. The whale eye has a rounded lens (fish-eye), and contains more and bigger rods (rods are black/white receptors, the light sensitivy nerve cells of the retina) than terrestrial mammals. (Researcher have found cones -- the color receptors -- in some whale eyes.) Whales are also able to compensate for the low light levels of the oceanic environment (at 30 feet, 90% of the light is absorbed) with a special layer near the retina that reflects light like a mirror -- just like the glowing eyes of cats and ungulates. Eyesight is only one of the senses employed by the whale -- and in murky waters this sense is probably not very important. Sound seems to be the most highly developed sense in all cetaceans. Although they do not have vocal cords, whales can create a wide range of different sounds, including splashes, clicks, grunts, and, according to early whalers, screams when they are wounded. Whales make these sounds by moving air through nasal air sacs and other passages in the head orby slapping the water. The whales may be using these sounds to navigate, find food (echolocation), or communicate with others whales. The sounds, especially the lower tones, can travel great distances (possibly up to hundreds of miles). With its widespread and dispersed migration patterns, the right whale may use these long-range communications to coordinate travel to mating and feeding grounds. Ears on the great whales are hidden behind small holes near the eyes and under the skin surface. They operate in a similar fashion as other mammalian ears, with sound waves causing the eardrum to vibrate. Scientists also believe that whales have a strong sense of touch. Researchers have repeatedly seen right whales nuzzling and stroking each other with their flippers and tail flukes. Mothers and calves constantly display this touching behavior. According to researchers, baleen whales may not have lost the ability to smell, but this sense is greatly reduced in adults and probably of little importance in daily living. The sense of taste is also poorly understood in whales. All of these senses (and the other metabolic functions) are controlled by the brain. Humpback brains average about 5 kilograms (11 pounds) with one large sample weighing in at 6.75 kilograms (15 pounds), (these numbers are probably comparable to the right whale). Human brains, in contrast, weight about 1.35 kilograms (3 pounds). One scientist, in contrasting brain-weight to body surface, found that humans topped the list with the highest ratio, followed by toothed whales and apes, then ungulates, baleen whales and carnivores, with rodents trailing the field GENITALIA Right whales exhibit similar reproductive organs as other mammals, with some distinctive differences. The female's mammary nipples are hidden within skin slits on either side of the ventral line of her body just forward of the genital slit. The umbilicus (belly button) is forward on this ventral line. The anus is located closer to the tail stem. In males, the penis is coiled within the body cavity. The erect penis may reach a length of 10 to 11 feet. A male's testes may weigh up to a ton or more. REPRODUCTION While collisions with ships and entanglement in fishing gear are partially to blame for the slow recovery of the right whale population, scientists are also investigating whether a decreasing birth rate may also be a factor. Researchers only spotted seven new calves in 1995, and there are some indications that calving intervals for individuals may be increasing. Inbreeding depression due to low genetic diversity, bioaccumulation of toxins, and habitat degradation could all contribute to a low birth rate. To determine whether these trends are real, biologists first need to learn about the reproductive biology of right whales. So far they don't know much. Researchers also don't have baseline data with which to compare current birth rates. The low numbers and endangered status of the right whale makes it difficult for scientists to study right whale reproductive biology, so researchers must rely on sightings of cows with calves, observations of courtship behavior, examination of stranded whales, and records from whaling ships. Nobody has ever witnessed a right whale, or any large whale, giving birth. Researchers don't know the length of the female reproduction cycle or the gestation period, although current estimates for southern right whales are between 350 and 400 days. Females reach reproductive maturity between seven and ten years old, although one female gave birth when she was only five. Calving takes place during the winter off the coasts of Georgia and northern Florida. The calves are four to five meters (13.2-15.5 feet) long at birth and weigh approximately 800 kg ( 1760 pounds). The mother nurses the calf for 10 to 12 months during which the calf grows to between 8 and 10 meters (26-33 feet) and 5,000 kg (11000 pounds). This lactation period exacts an enormous energy cost for the mother, and researchers speculate that females require one to three years to recover between calvings. Calving intervals are three to five years, which includes a one year lactation period and a one year gestation period. Males, on the other hand, don't participate at all in raising the calf. Researchers have rarely spotted males in the calving grounds off the southeast coast, and the only times males and females interact is during apparent courtship behavior. Because of the disproportionate energy costs between males and females, scientists speculate that the female has an enormous stake in the strongest, healthiest male, and that the males must compete with each other for the opportunity to mate. Researches have observed what they consider to be courtship behavior throughout the year from the Florida coast to the Bay of Fundy. However, scientists have seen the most intense courtship activity in the Scotian Shelf during August and September. They have observed pairs of whales floating together for up to a couple of hours, occasionally touching each other or rolling around. But more often, researchers have seen whales gathering in groups of between three and 30 individuals. Scott Kraus, a right whale researcher at the New England Aquarium in Boston, has watched these "surface active groups" and attempted to interpret their dynamics. In situations where he has been able to determine the sex of the individuals, he has found that the groups are most often composed of a single adult female surrounded by multiple males. Typically the female meanders upside-down in slow circles along the surface, her head submerged, and her genitalia above the water. Two males, which Kraus has designated alpha males, swim on either side. These alpha whales are in the best position to mate with the female when she rolls over to breath, and do so repeatedly until they are displaced. Videos taken underwater show whales mating while the female was rolling over. Other males, designated betas, follow closely behind and attempt to displace the alphas. The males may even use their callosities as weapons-scraping competing males as they jockey for position. Typically a beta replaces the alpha every 30 minutes. On the outskirts of the group swim the "peripheral" whales who apparently do not compete for the alpha position. Researchers have yet to see one of these groups form, but these groups stay together for an average of one hour from the time they are spotted, with some groups sticking together for four to five hours. The number of males in the groups increase with time, and researchers have observed males as far as two km away swimming quickly (for a right whale) towards the activity. The groups break up when the female rolls and dives deeply. Kraus' interpretations of these behaviors are only speculative. According to his theory, this courtship behavior ensures that the male with the greatest stamina succeeds. In other species, females choose males based on visual cues or on which male has acquired the best territory. However, the waters right whales inhabit are too murky for females to see other whales, and dense plankton patches are too variable for males to defend successfully. Instead, it may be a battle of attrition with the male who can get the most sperm into the female succeeding. Male right whales have the largest testes for their body size of any whale, so they are capable of producing copious quantities of sperm. These testes can weigh over a ton-equivalent to a small car. If Kraus' theories are true, he says that it would be to the female's advantage to gather as many area males as possible to ensure that the strongest succeeds. She may even use vocalizations to attract them. More observations and paternity studies will be needed to determine how many, if any, males emerge as consistently dominant.