|Notes to Supplement the Marine Mammal Lecture Outline. Use these notes with the outline. Also use PowerPoint show on website.
Porpoises belong to the family Phocoenidae. Hey differ from dolphins in having blade-like (spatulate) teeth and never possess a beak. Her are only 6 species of porpoises making them a much less successful group than the dolphin family in an evolutionary sense. Three species are harbor porpoises.
Most porpoises are coastal and as a consequence have been most affected by man=s activities - including habitat destruction of bays and estuaries they favor and by entanglement in gillnets set close to shore to capture fish. Gill nets are nearly invisible to fish and marine mammals. Fish swim into the nets that are set out in the water for a day and collected with fish stuck in the net. Porpoises feeding on the fish have been caught in these nets. An especially impacted population is the California harbor porpoises in Washington State at the mouth of the Columbia River. Gill nets are not very closely regulated and few if any porpoises are now caught. Populations levels appear to be stable. California harbor porpoises are fond in three populations - Washington State, N. Calif. And Central Calif. They do range to So. Calif.
The Avaquita@ (Phoecina sinus) or Gulf of California harbor porpoise was thought to be extinct until the early 1980s. Gill netting for the totoaba fish and also the elimination of water from the Colorado River due to construction of the Hoover Dam and agricultural diversion in the U..S. into the Gulf of California ,and agricultural run-off were all thought to contribute to the extinction of this species. The range of the vaquita is from the Colorado River to San Felipe across the Gulf 70 miles to Puerto Penasco, a very small area. Today the population is endangered but is protected in its range by the Mexican Gov=t declaring the first ABiosphere Reserve@ (see article in notes) restricting fishing and access to where this small creature is found. It is thought that there are between 300-600 today.
Dall=s porpoise is an exception and is a very fast swimming robust porpoise in large numbers. It is part of the Japanese whaling/fishing industry and about 10% of those passing through the fishing grounds are captured each year. The population is able to sustain this level of fishing.
Marine mammal protection has been discusses some with respect to the IWC. (The IWC website and links to whale biology, populations, whaling, etc. is linked to the class website - see the Aadditional reading link and go to the bottom of the page). There is a god summary in the outline of your notes. Amend your notes to include that the high-frequency tactical sonar used by the US Navy does seriously harm marine mammals, and while the Navy has made attempts to only use it where mammals are not found, the US Courts have barred the Navy from using this type of sonar off California is readiness maneuvers that are currently taking place.
While there is some increased whaling pressure - the Japanese scientific hunt this year will take 935 So. Minke Whales, 50 fin and for the first time 50 humpback whales, the main threat today is to the toothed whales - mostly dolphins. There is limited direct fishing of dolphins by Sri Lanka and Peru, but the main problem is most likely to be from fishing and competition for the fish and squid that the dolphins eat.
Reproduction and Natural History.
The great whales have a two-year reproductive cycle. Females are either pregnant or weaning young, feeding, and preparing for another pregnancy. The gestation period is usually 12 months. Feeding grounds are most often in cold polar regions or areas of tidal upwelling such as the mid-riff islands of the Gulf of California.
The young are born relatively large (see notes) but need to undergo rapid weight gain and the mothers lactate milk with fat up to 53% compared to human breast milk at 2-3% fat. Young may gain up to 15lbs. Per day. Whales may also be very long-lived.
The California Gray Whale is a good example of whale feeding and breeding migration. The course notes present this well. Gray whale mating requires two males - the observation that the Avoyeur male@ who rolls the female over as she keeps rolling onto her back to avoid mating, is recruited by the mating male. Current theory suggests that this is female selection of a mate who is capable of getting others to assist him - something that may be o value during migration or in protection of here young.
Order Pinnipedia. These marine mammals are closely related to carnivores such as bears. All but one species requires a Arookery@ - that is a place to haul out of the water and also for mating. There are two families.
The Otariidae are the eared- seals or sea lions with external early flaps (pinna) and front flippers that can be rotated forward for walking. The front flippers also contribute to swimming along with the rear fins/legs. The characteristics of this group are well presented in the outline. (Diving adaptation will be covered later in a separate section). The sexes are dimorphic (females look different than males). Mature (territorial) males have a large sagittal crest (bump on the head) and can weigh1000 lbs while the females and non-territorial (see below) males are considerably smaller and lack the crest.
Nearly all pinnipeds feed on fish and squid
, especially schooling fish. Sometimes sea lions feed in association with other species in what are called Amixed-species feeding frenzies@. We see this in the Gulf of California frequently.
Reproduction in the California sea lion involves returning to the exact same rookery every year at the same time. The males compete for breeding territories primarily by displays and there is not contact or physical harm to each other. The dominance is a simple alpha, beta type where the most dominant gets the best, second most dominant the second best site
, etc. The species is polygynous, meaning they form harems, sometimes as large as 14 females. The males and females reach breeding age at 5 yrs but the males have Adelayed@ social maturity which gives them extra time to grow before they have to compete with the other
, larger, males. They are still capable of breeding at the younger age and do so when possible. The territorial males do their best to protect the females but breeding is selected by the females. The males Aprotect@ by chasing other males and barking - in and out of the water. Males without territories may rush into a territory as a group where many females will mate with the intruders, also females may leave the territory temporarily to mate with another males and then return to the territory.
The sea lion have what is called Adelayed implantation@. They breed one month after giving birth while still at the rookery. The embryo develops only to a hollow all of cells (blastocyst) and then stops growing. This allows the mother to nurse her new-born and hunt for food without the energy loss of pregnancy. The female then weans the pup and the 8 month development of the new pup begins at the 4th
month after giving birth. This also means that when she returns to the rookery in June she will be ready to have the pup and breed again. Mothers recognize pups and pups mothers by vocalization and smell.
The family Phocidae are the seals. They differ from the Otariidae in have no external pinna and have small front flippers. The cannot move on flippers but move very quickly with a Aflopping@ motion. Locally we have the California Harbor Seal which is small, gray with black patches. They are found near to shore. A population in Baja likes to lay out in the Estero de Punta Banda where Biology 11A and Biology 11B are taught and feed in the shallow bay.
Also included in this family are the elephant seals. Elephant seals form harems (see sea lions below for similarity). Males establish dominance by slashing each other=s thick necks and sides (doing not real harm) until one tires and gives up. When a males displaces another dominant male he will most often kill all the pups by crushing them with his very large body. Males can weigh up to 5000 lbs. Santa Barbara Island directly off our coast and Ano Nuevo off the central Calif. Coat are established breeding areas. Elephant seals have mad a strong repopulation comeback after near extinction by 1880. Their oil was second only tot he sperm whale in demand. A small number on Guadelupe Island off Mexico has expanded to colonize in large numbers as far north as the Farallon Island.
Sea Otters - Family Mustelidae. Sea otters are split into two distinct populations - the Northern (Alaskan) and Southern (California) populations. They are voracious predators of shell fish and consume 1/3 their body weight or about 10 lbs of urchins
, scallops, clams, mussels, snails, etc. per day. They are the prey of sharks and killer whales. Sea otters prefer the protection of kelp beds where they shelter and have their pups. Hey are completely aquatic animals with no need for land rookeries.
The population biology and changes in populations are well-presented in the notes.
Today sea otter populations are declining after a high in late 1980s. The reduction in population number is attributed to increased had-shelled clams that damage teeth and cause infections along with land-based viruses transmitted from cats primarily by run-off and sewage. Changes in the north Pacific ecosystem, due largely to whaling in the 19th
century, has also caused Orcas to feed on smaller prey such as sea otters
, further reducing their populations.
While the range of the sea otters was restricted to above Point Conception to protect the shell-fish industry from decimation by these voracious predators, today the restriction has been lifted and they are being allowed to move south. It is uncertain when or if they will reach southern California.
Special Adaptations - Temperature regulation. Marine mammals have a serious problem with maintaining body heat in the water. Being large and feeding low on the trophic structure where food is plentiful has been discussed. Blubber is a good insulator and may make up over 30% of the mass of the animal. Additionally they have Acounter-current exchange@ in their flippers, fins, etc where they are not insulated by blubber. This means that large artery carrying warm blood away from the core of the animal is surrounded by several small veins that carry blood back into the core. He heat from the warm arterial blood is transferred to the colder blood in the veins which is then taken back into the core. This reduces heat loss conserving heat. Sea otters are unusual in that they are the only marine mammal without blubber and that rely on their fur. Sea otters have the thickest coat and have to constantly preen (fluff) their coat to maintain its insulating ability. This is also why oil spills kill otters so quickly as the insulating properties of their fur are lost when if is slicked by oil. The also must eat HUGE amounts of food in order to generate body heat lost through the fur.
Diving. (See figure ASummary of the Marine Mammal Diving Response@). Marine mammals have several types of adaptations that allow them to dive. The adaptations are divided into anatomical (structure of the body), physiological (specialized metabolism) and behavioral. ESSAY QUESTION.
To summarize: when marine mammals dive they store oxygen in their blood for use by the brain, reduce their heart rate, and the muscles work without oxygen in what is called anaerobic respiration (see respiration from you notes early in the class).
include a larger capacity circulatory system 7-15% larger than terrestrial mammal. More oxygen binding hemoglobin in the blood
, hemoglobin that can give up 90% of its oxygen to the cells compared to 20% for humans, more myoglobin in the muscles to store oxygen for muscle use in swimming.
Behavioral adaptations are part of the mammalian diving response
. When a marine mammals dives the lungs collapse and the only air that is carried down below the surface is in cartilage lined spaces (see echolocation). Cartilage does not allow gas to diffuse into the blood. (If the air was absorbed into the blood under pressure during dives the animals would be subject to decompression illness, or Athe bends.@) Also the heart rate drops about 90% and the blood vessels that lead to the extremities closed down preventing the flow of blood to the muscles. All the blood flow is between the brain and heart. The flow of blood and blood pressure to the brain remains constant.
Anaerobic respiration (-O2
) (during dive)
C6O12O6 ---------->CO2 + H2O + 2ATP + LACTIC ACID
(after dive) \C>Aerobic respiration (+ O2
) + 34 ATP
the metabolism of the muscles shifts to anaerobic respiration - that is the muscles produce ATP from glucose (sugar) without oxygen and build up lactic acid as a result. This allows the animal to swim without oxygen being supplied to the muscles, since the blood vessels are closed down and all the blood is going to the brain. Lactic acid is stored in the muscles.
When the dive ends the blood vessels open up to the lactic acid now reaches every cell in the body. Each cell takes up the lactic acid and converts the lactic acid so that it can go through aerobic respiration now to produce 34 ATP and the heart rate returns to normal. For a period as short as 2 minutes the oxygen consumption of the animal goes up as extra oxygen is required to convert the lactic acid that was stored in the muscles and carry it through aerobic respiration. The extra oxygen that is used is said to be Arepaying the oxygen debt@ - that is using up the lactic acid that was produced by the muscles during the dive.
Echolocation. (See figure of AWhale Echolocation Anatomy@). The members of the toothed whale families use echolocation, or biological sonar) to find their position in the water column
, position relative to objects, and find food. Sound is very effective in water as it travels 5 times faster in water than in air. The sound is treated by the brain similar to the way light sensed by the eyes is treated such that they can form an image with the sound.
Cetaceans use low frequency sound to locate distant objects, such as the ocean floor or shoreline
, and large objects such as schools of fish, squid, etc. Low frequency sound travels far but does not allow fine discrimination of objects. High frequency sound is used for short distances to discriminate shapes. Dolphins have been shown to be able to distinguish between species of fish of the same size with their echolocation.
Sound is produced by forcing air through the equivalent of our vocal cords, the sound reflects off objects
, is sensed by receptors in the lower jaw and then transmitted to the ear and brain, and then the image is produced. A great deal of nervous tissue is required by the brain to carry this out and helps account for the large volume of the cetacean brain relative to the body size.
Sound is produced by the melon, or spermaceti organ. Air is taken in through the nares
, or blow hole, and passed through the right nasal passage to the frontal air sac that sits in front of the frontal bone, or forehead. The air stored in the frontal air sac if now forced through the left nasal passage and then through the Amonkey=s lips@, which vibrate similar to air forced from the stretched opening of a balloon
, creating sound of a broad range of frequencies. The air is collected in the distal air sac and returned to the frontal air sac via the right nasal passage. All of the air passages are lined with cartilage so that the air is not absorbed into the bloodstream.