Feeding and Ecology

odontocete teeth

homodont

for grabbing, not chewing

typically conical, but can be rounded pegs (belugas), flattened cones, or tusks (narwhal)

mysticete baleen

keratin, dermal in origin

always growing

varying lengths

skimmers

feed by swimming slowly through the water with their mouths open

gulpers

feed by intaking mouthfuls of water and then filtering it out

pinniped teeth

heterodont (less specialized)

larger canines on otriids

some phocids specialized with filtering post-canines

walrus feeding

tusks wear on front

suction feeding on bivalves

sirenian feeeding

no front teeth

horny plates in mouth

molars replace back to front (move forward)

manatee oral disk (dexterity)

sea otter teeth

no sharp cutting edges (unusual carnivore)

polar bear teeth

largest canines of any bear

unspecialized post-canines (less omnivorous)

cetacean stomachs

multiple chambers

dolphin

• forestomach - storage, physical breakdown, no digestion/secretions

• fundic and pyloric - digestive enzymes

• no gall bladder

manatee gut

typical long herbivore gut

MM diet categories

fish and cephalopod

zooplankton

marine mammal/bird

benthic inverts

herbivores

fish and cephalopod eaters

most common for pinnipeds and odontocetes, many balaenopterids

most species are opportunists/generalists/creative

squid specialists - deep divers with reduced dentition

some cooperative foragers, many are not

zooplankton eaters

krill, copepods - right, bowhead whales

amphipod - gray whales

southern ocean giant krill - whales, crabeater/leopard seals, penguins…

marine mammal and bird eaters

killer whales, leopard seals, polar bears

some other pinnipeds (usually males)

• some stellar sea lions and walrus eat N fur seal pups, ringed and harbor seals

  • S fur seals eat penguins

orca feeding

apex predator of the ocean

pods attack any size whale or dolphin

ecotypes - specializations/adaptations by pods

attack on beaches, ice, open ocean

• spyhopping - swimming upward to see over a patch of ice

• team up to send swells over ice to knock off seals

work in teams

leopard seals

will break through ice under penguins/seals

will pursue humans on ice

shake penguins inside out

polar bears diet

mainly ringed seals (pup in dens and leave) - peel and eat blubber/skin

walrus calves, beluga, narwhal, eggs, birds, small mammals, carrion, grass, seaweed, garbage

will stalk and eat people

techniques - stalking and breathing hole hunting

dolphin feeding (video)

push fish onto shore and “rush”

bubble and mud nets

tails slapping to stun prey

hydroplaning behavior in shallow waters

bubble net feeding

surrounding a school of fish with a wall of bubbles, causing them to squeeze together

used by species of whales and dolphins

benthic invert eaters

most coastal MMs do some

few specialists

• suckers/spitters - walrus, bearded seal, beluga

• sea otters - molluscs, crustaceans, fish, urchins

  • 75% dive efficiency - use paws and store in pouch

  • tool use - rocks and kelp

herbivores

sirenians only

florida manatees - 60+ prey species (seagrasses, algae, leaves, bushes, water hyacinth, hydrilla…) and incidental inverts

Do energetic expenditures differ between salt marsh and coastal dolphins?

yes. Traveling coastal dolphins swim faster on average (1.28 times faster = 2.26 times more energy)

What proportion of the total annual primary production in North Inlet is required to support the resident dolphins?

3-7% goes toward supporting the equivalent of 6 fulltime resident dolphins

How do dolphins interact with tidal currents?

Dolphin groups with neonates (0-6 months old) spent 35.6% of their time in tidal node areas, compared to only 8.2% for groups without neonates

Strand-feeding dolphins in SC and bird interactions

Great egrets can make a living off of dolphin scraps

• 95% C.I. for avg. # fish caught per hour of strand feeding

Great blue herons cannot

Cetacean impacts on ocean productivity and carbon cycling: the “Whale Pump”

• Industrial whaling reduced baleen whale populations by 90%

• Prior to that, baleen whales consumed 430 million tons/yr of Antarctic krill (twice the current size of today’s Antarctic krill population and more than twice the size of the annual global marine fisheries catch.

• High productivity only possible due to nutrient recycling by whales

Rice’s Whale

• Population ~ 50 (Gulf of Mexico)

• Formerly subspecies of Brydes whale, but given species status in 2021

• Must exploit high quality prey to survive (shapes conservation strategies)

walrus ecology

• Eat 6.2% of body wt per day (after shelling)

• Up to 6000 individual molluscs in a single stomach

• Pacific walrus population eats 8900 tons/day (3.2 million tons/yr)

• 2.5-3 % of estimated standing stock on Bering-Chukchi shelf

Polar Bears and Melting Ice Caps

• Declining foraging period (3-4 weeks in 25+ years), longer swims

• Declining average weight (15%, Hudson Bay)

• Potential population decline >50% by 2050?

Aleutian Islands sea otters

keystone predators (rare)

Top-down impacts

All marine mammals have strong top down impacts on their ecosystems - but generally opportunistic, or community structure is too complex for a keystone impact

marine mammals as prey

Sharks are a common predator

Pinnipeds/otters (esp. pups) vulnerable to bears, wolves, coyotes, and eagles

bioenergetic findings

• Whales estimated to account for 36% of all fish predation off the Northeast US (Overholtz et al, 1991) and 45% in Barents and Norwegian Seas (Bax 1991)

• ~20% of primary production in the Gulf of Maine goes toward supporting cetaceans (Kenney et al, 1997)

• Only 3.7 orcas switching to sea otters can explain the 1990s decline in Western Alaskan sea otters of several tens of thousands (Estes et al 1998) – (do you think this was really just 4 animals? - no, trend switch of many)