Chapter 8: Feeding ecology

Baleen whales

mainly plankton eaters

➢Gulpers (blue whale) ventral grooves & specialized tongue

➢Grey whales stiff & short plates: bottom feeder filters sediment

➢Short baleen - piscivorous diet (e.g. Minke whale)

➢Skimmers (bowhead whale 4m) have long plates with fine baleens continuous straining of small prey (copepods)

Sirenians

➢Adapted to feeding on plants

➢Dugongs bottom feeder

➢Manatees special bristles - feed both bottom and

surface feeders, generalist herbivores

Otters

➢Fish: detailed sensory-motor coordination & benthic invertebrates: use forepaws for sensing and catching benthic organisms

➢Use paws: Tool (stone) usage

Polar bears

➢Hyper Carnivores preying on ice-living seals and consuming their energy-rich blubber, but also on cetaceans e.g. beluga whales and narwhals, reindeer, birds and their eggs, fish and marine invertebrates

Capital breeders

Energy & nutrients are stored prior to breeding- fast for months, then use storage for breeding!(large baleen whales, polar bears, large phocids, male otariids)

Income breeders

➢Few energy reserves and must continuously feed during breeding(most odontocetes, small phocids e.g. harbour seal females but males can fast longer (larger body size), female otariids)

➢Sea otters (smallest of all marine mammals) - must forage continuously to keep body temperature in freezing cold water - high metabolic rate - consume 20-25% of body weight daily!

Marine mammal foraging behavior

➢Most Marine Mammals are large-bodied, long-lived with low reproduction rates - temporal & spatial flexibility in foraging

➢High fat storage - feed irregular over large distances (e.g. Baleen whales, elephant seals)

➢Foraging behaviour adjustment to prey abundance

➢ Differences between sex and size - males travel further

e.g. elephant seals➢Prey switch, e.g. Killer whales in Norway

Foraging behavior adjustment to prey abundance

Example Sperm whales:Females can only survive 3 months without feeding - they move to better feeding areas under food shortage

- only 5-6 days to travel 500km or more!

Generalist predators

Most marine mammals

(Harp seals 100 species, Grey seals 40 species, Bottlenose dolphin 43 species) but 70-80% only 2-3 species = prey preference

Sea Otter eat 160 different species

but individual prey preference – maternally transmitted (6 months association)

Prey selection

Marine Mammals specialize when foraging, different foraging tactics for different prey (plasticity in foraging behaviour!)

Examples:

➢ Bottlenose dolphins – chase fish onto mud banks, stun and kill prey with flukes, use sponges on rocky surface ...

➢Humpback whales use bubble net feeding

➢Bryde’s whales treadmill feeding ...

Marine Mammals can switch prey during changes in environment and prey availability➢Sea otters switched to eating red crabs when the El Nino conditions brought them to California ➢Humpback whales started to feed on herring when it became available to them on their migration journey in northern Norway

Top down effects

Sea otters changes coastal ecosystem "keystone species": Abundance low but impact high, e.g. sea urchins are kept in «control»

Example northern hemisphere kelp forests / Lofoten

- Otter numbers decreased by hunting -> sea urchins exploded -> kelp forest diminished!

➢Whales feed on substantial masses of krill or fish, but leave vital faeces / nutrients!

➢"Whale Pump"= ecosystem adapted to predation

➢Cultivation Grazing by Dugongs on seagrass- favour growth of more nutrient species of seagrass

Bottom-up effects

Primary and secondary production often influenced by El Nino phenomena

➢Galapagos seals adapted in caring longer for their young (2yrs) but many new-born calves died

➢Sea otters switch prey to red crabs

Overfishing

➢Change of migration (Killer whales after herring collapse in Norway)

➢Hunting method changes (sperm whales feeding of long-line fisheries, killer whales feeding from purse seiner)

➢or death (mass stranding of pilot whales Australia)

➢ Climate change: example of Norway mackerel moves further north - new species of dolphins / Killer whale populations?

Fishermen caught tuna fish in Vestfjord 24