Foraging and Feeding

Question 1

What are some ways in which marine mammalian diets can be observed?

Answer 1

• Direct observation
• Stomach contents
• Chemical composition of tissues: Fatty acid analysis and stable isotope analysis

Question 2

What is a limitation of utilizing stomach contents to study marine mammal diet?

Answer 2

It only gives you information about prey items that were recently consumed

Question 3

What are some limitations of direct observation of mammalian diets?

Answer 3

Biased towards…
- Near surface prey capture
- Large prey
- prolonged capture events
Only reliable with otters

Question 4

What are some ways that scientists can obtain samples of the stomach contents of marine mammals?

Answer 4

• Lethal research (not done anymore)
• Strandings
• By-catches
• Lavage of live animals (washing out an organ)

Question 5

What “hard parts” are utilized to identify prey types?

Answer 5

• Otoliths (ear bone in fish)
• Squid beaks
  Species specific

Question 6

What are some biochemical approaches to studying the diet of marine mammals?

Answer 6

• Fatty acid signature
• Stable isotope analysis

Question 7

What are some benefits of utilizing biochemical approaches to study marine mammal diets?

Answer 7

Provide diet information over a broad time frame (several weeks to months)

Question 8

How can fatty acid signatures be used to study diet in marine mammals

Answer 8

The fatty acid signature of a marine mammal is equivalent to the fatty acid signature of the prey that they eat

Question 9

How can stable isotope analysis be used to study diet in marine mammals

Answer 9

• N2 levels increase as trophic levels increase (can identify the trophic level of prey items)
• C13 can be used to to identify if marine mammals are foraging in shore vs. offshore

Question 10

Describe the feeding ecology of pinnipeds

Answer 10

Graspers: forage for single prey items

Question 11

Describe the feeding ecology of sirenians

Answer 11

Grazers: feed on grass / plants

Question 12

Describe the feeding ecology of otters

Answer 12

Graspers: forage for single prey items

Question 13

Describe the feeding ecology of mysticetes

Answer 13

Strainers: forage for multiple prey items

Question 14

Describe the feeding ecology of odontocetes

Answer 14

Graspers: forage for single prey items

Question 15

Describe bubble net feeding in whales

Answer 15

• Cooperative feeding technique
• Whales dive below a school of fish while blowing bubbles to stun / trap the fish
• The whales then surge towards the surface with their mouths open and throats extended

Question 16

Describe suction feeding in beaked whales

Answer 16

• Beaked whales have a gular region
• The gular region can be expanded to create a “vacuum” in the mouth

Question 17

Describe otter foraging behavior

Answer 17

• Individual otters have different feeding behaviors
• The foraging behavior of otters remains the same throughout their lifetime
• Foraging behavior is inherited maternally

Question 18

What are the different foraging behaviors of bottlenose dolphins

Answer 18

• Strand feeding
• Fish-whacking
• Kerplunking
• Crater feeding
• Begging

Question 19

Describe strand feeding

Answer 19

Dolphins will herd fish into shallow water then half beach themselves in order to eat them

Question 20

Describe fish-whacking

Answer 20

Dolphins will whack fish with their flukes in order to debilitate them

Question 21

Describe kerplunking

Answer 21

Dolphins will slam their flukes again the water to scare fish out of their hiding spots so that they can be easily caught

Question 22

Describe crater feeding

Answer 22

Dolphins dive head first into the sand in order to catch prey

Question 23

Describe begging

Answer 23

• This behavior has been acquired through human interaction
• Dolphins will approach the edge of a boat and beg in order to get food from humans

Question 24

What are the three phases of cooperative foraging

Answer 24

1. Finding food
2. Concentrating food
3. Capturing food

Question 25

What are the costs and benefits of cooperative foraging?

Answer 25

Cost: Sharing food
Benefit: Increased foraging success

Question 26

Describe cooperative foraging in transient killer whales

Answer 26

• Transient killer whales hunt other marine mammals
• Found most ofter in groups of three where they were able to catch the most prey
• Smaller groups: harder to chase down individual prey items
• Larger groups: too loud
  Communication is key in cooperative hunting, killer whales communicate using echo location as well as their prey items

Question 27

Describe the foraging technique of Hawaiian Spinner Dolphins

Answer 27

• Take advantage of dial vertical migration
• Hunt for prey at night (prey = closer to the surface)
• Rest in coves during the day (prey deeper in water column)
• Cooperatively “bulldoze” (herd) prey in order to aggregate it
• Surround prey in circle formation
• Take turns going into fish aggregation to feed