Pinniped, Polar Bear, Sea Otter, and Sirenian Foraging

main prey taken by pinnipeds

usually fish and squid

walrus - mollusks

crabeater and antarctic fur seal - krill

leopard seals - penguins

some eat other pinnipeds (stellar’s sea lions and souther sea lions)

tooth morphology and diet in pinnipeds

peg-shaped — biting and holding, fish and squid

cusped teeth — crabeater seal, multicusped to strain water because they eat small krill

optimal foraging theory

stay longer in patch if it took a long time to get there

stay longer in patch if it is high quality

trade offs between costs and benefits

depth to prey — deep (fewer, higher quality prey) vs shallow (more, lower quality prey)

sex differences in northern elephant seal foraging behaviors

female — continuous foraging during migration, follows DSL, primarily eats squid, low quality prey and long foraging time

male — heads straight to destination of the Aleutian Islands, forages at destination only, primarily benthic prey (skates, rays, dogfish), eats at bottom so constant depth, high quality prey and short foraging time, much larger than females for breeding competition

major hunting strategies by polar bears

primarily eat ringed seals

75% still hunting and 25% stalking

likes lots of ice cover, uses breathing holes, sniff out pups hidden in subnivian lairs

presence alters behaviors of seals — don’t sleep for long time, skittish, pups are white, don’t defecate in lair, quiet, have several breathing holes to avoid still hunting

still hunting for belugas and narwhals

unique tool use and prey preference in sea otters

high MR so 33-50% of the day is feeding

benthic prey — urchins, crabs, sea stars, mussels

area influence — rocky bottom (bivalves and urchins) vs soft bottom (bivalves, worms, and innkeeper worms)

prey preference learned from mother

rocks used as hammer or anvil to open shells and stored in armpit pouch

keystone role played by sea otters in kelp forest ecosystem

Sea otters play a crucial keystone role in maintaining the balance of kelp forest ecosystems by preying on sea urchins, which helps prevent overgrazing of kelp. Their presence fosters biodiversity and supports other marine species by sustaining healthy kelp habitats.

urchins decimate kelp forests when no sea otters present and leave urchin barrens

sea otter decline due to orca predation due to decline in pinnipeds

in southern hemisphere — sea otters don’t exist so kelp have more chemical defenses against herbivores

sirenian diets and feeding behaviors

dugong — sea grass, downturned snout, low quality food, chew with cornified pad on mouth roof, only six molars in life time

manatee — sea grass, floating algae, some soft inverts, more forward snout, higher quality food, prehensile oral bristles and upper lips to move food into mouth, unlimited tooth replacement

low energetic quality diet so spend a lot of time feeding but can exist on low quality diet because of low metabolic rate