Marine Mammals

I. Groups of Marine Mammals and what they eat
        A. Order Carnivora
        1. polar bear
        2. sea otter
        3. suborder Pinnipedia
            a. sea lions and fur seals (family Otariidae)
                (1) have external ears
                (2) can move their rear flippers forward (rotate pelvis), so can use all 4 limbs to move on land
                (3) swimmers, relying mostly on the front flippers
                (4) sexual dimorphism
                (5) many eat fish and squid
            b. seals (family Phocidae)
                (1) no external ear
                (2) have rear flippers that can not be moved forward
                (3) swim with the rear flippers
                (4) eat mostly fish and squid (except crabeater seals)
            c. Walrus (family Odobenidae)
                (1) Tusks (upper canines)
                (2) Feeds mostly on benthic invertebrates, like clams

    B. Order Sirenia
        1. Manatees, dugong, extinct Stellar’s sea cow
        2. Front flippers but no rear limbs
        3. Only vegetarian marine mammals
        4. Only 4 species left, and all are in danger of extinction
    C. Order Cetacea – whales, dolphins and porpoises
        1. Front limbs are flippers; no rear limbs
        2. Muscular tail ends in a pair of fin-like horizontal flukes
        3. Nostrils are on top of the head
        4. Two groups
            a. Toothless whales (SO Mysticeti)
                (1) Baleen whales -- rows of flexible, fibrous plates (baleen) hang from the upper jaws
                (2) Blowhole has two openings; symmetrical head
                (3) Largest is the blue whale (Balaenoptera musculus) – largest mammal ever
                (4) Different species have different lengths of baleen with differing spacing between the bristles

            b. Toothed whales (SO Odontoceti)
                (1) use teeth only to catch and hold prey, not to chew it – food is swallowed whole
                (2) blowhole has one opening; asymmetrical skull
                (3) sperm whale is the largest
                        ambergris
                (4) killer whale, orca

                         travel in groups (pods) that sometimes specialize on one food type
                (5) dolphins – social, also tend to travel in pods; eat fish and squid

II. Role in the Ecosystem
    A. Plankton feeders – baleen whales, crabeater seals
        1. estimated that the baleen whale population before human exploitation (~90% reduction estimated)
            consumed ~190 million metric tons of krill – about 2X the world fisheries catch
        2. during exploitation of whales, populations of Antarctic birds and pinnipeds tripled – was this due to extra food availability?
    B. Grey whales – when take mouthfuls of sediment leave large, irregular depressions and can be a major structuring force of benthic communities
    C. Carnivores, including top predators
        1. Cetaceans may consume more prey than the entire world’s fisheries (although less than fish themselves)
        2. Very important in polar seas, particularly the Antarctic
    D. Whale carcasses sink and provide food for deep-sea creatures
    E. Dugong grazing on seagrass beds in Australia may have reduced biomass by up to 96% and prevented expansion of dominant species
    F. Sea otters are a keystone species in the kelp community

III. Behavior
    A. Communication
        1. Visual – movements, bubble displays
        2. Sound – vocalizations
            a. pinnipeds - vocalizations associated with behaviors - e.g., maintaining territories during reproduction, recognizing young
            b. some whales (humpbacks, finbacks and blue whales) create low frequency sounds that can be detected hundreds of km away
            c. some humpback songs may be used to attract mates or mediate male-male interactions during breeding season
            d. some dolphin species have individual ‘signature’ whistles
            e. orcas have both individual calls and ‘dialects’ that are unique to pods
    B. Echolocation
        1. most toothed whales and perhaps some baleen whales
        2. function
            a. avoid predators
            b. find prey
            c. provide information on topography (low frequency sounds)
            d. stun prey (low frequency sound)
        3. morphological modifications of the head and respiratory system permit sending and receiving sound waves over a wide range of frequencies
            a. sounds are produced by movement of air through the nasal passage and associated air sacs
            b. rounded forehead contains the melon -- a large, fat-filled structure (spermaceti); melon is an acoustical lens to focus the outgoing waves
            c. incoming sound waves (reflected waves) are received primarily in the bone, oil and fat deposits of the lower jaw and in the middle ear
        4. amazing detection abilities
    C. Reproduction – slow reproduction; long-lived adults
        1. pinnipeds
            a. breed on land
            b. many polygamous and territorial on breeding grounds
            c. generally give birth at most once per year
        2. cetaceans
            a.  give birth in water
            b.  one young per year or less
    D. Migration
        1. Pinnipeds
        2. Baleen whales
        3. Whales may have a geomagnetic sense -- analysis of mass strandings
    E. Other complex behavior (often anecdotal)
        1. assistance of pod members; cooperative defense
        2. group hunting
        3. often are matriarchal schools
        4. imitative behavior (dolphins)

IV. Special Adaptations
    A. Temperature Maintenance -- water has a 25X higher thermal conductivity than air
        1. Large body size; less SA/V and lose heat less quickly
        2. Thick layer of insulating blubber
        3. Sea otters have no blubber, but thick fur and ‘waterproofing’ lipids
        4. Countercurrent system of circulation that saves heat
        5. Can overheat
    B. Diving and locomotion
        1. Take quick breaths
        2. Exhange 90% of the oxygen contained in the lungs with each breath
        3. larger blood volume
        4. higher oxygen capacity per volume of blood (more hemoglobin)
        5. bradycardia – slowing of heartbeat during dives
        6. blood supply cut off from some organs during dive – some muscles, digestive system, kidneys (leaves it for the CNS [brain] and heart)
        7. muscles contain myoglobin – better at storing oxygen
    C. Osmotic Regulation
        1. derive most of their water from metabolic breakdown of their prey
        2. make very concentrated urine

V. Human Use/Exploitation of Marine Mammals
    A. Historical
        1. pinnipeds -- (for blubber, skin, meat)
            northern elephant seal

        2. Sirenia
                Stellar’s sea cow

         3. Cetaceans
            a. Hunted in prehistoric times
            b. 1600's European started exploiting the great whales in the North Atlantic; harpooning from small open boats
            c. Products: blubber – ‘train oil’ for soap and lamp oil; baleen (whalebone); meat; ambergris, spermaceti…
            d. Expanded with explosive harpoons; power ships
            e. North Atlantic right whale
            f. Early 1900’s whaling moved to Antarctica; factory ships were developed
            g. Last US whaling ship wrecked off the MA coast in 1924; shore based whaling on W. Coast;
                last whaling station closed in Richmond, CA in 1972
            h. Great expansion of whaling in Russia, Japan, Norway and Great Britain. 
            i. Peaked in the 1930’s.  More than a million whales taken from Antarctica alone
            j.Blue whales, Fin whales…kept switching to smaller whales as stocks collapsed
    B. Regulations
        1. 1946 established the International Whaling Commission (IWC)
           
        2. Marine Mammals Protection Act (MMPA) – 1972 (US)
           
        3. Long drift net ban in international waters (voluntary; 1993)
    C. Current Situation
        1. Status of marine mammals (IWC)
           
            a. Dolphins not protected and have replaced great whales as the most threatened cetaceans
            b. Dolphin safe tuna methods -- during the 1970s, 200,000 dolphins died annually, 1997 estimate 1,112
            c. Female harp seals in E. Canada
            d. problems with lost drift nets – ‘ghost nets’, pollution
        2. Conflicts
        3. Fisheries/Marine mammal interactions
       

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