Are marine mammals just predators?
No! They can also be prey
How do marine mammals adjust their foraging behavior in the presence of a predator (think of Bottlenose Dolphin case study)?
- Prey biomass of bottlenose dolphins is higher in shallow water
- Therefore, bottlenose dolphins will forage for prey in shallow waters
- Tiger sharks (predator) are also common in shallow warm waters
- To avoid predation, bottlenose dolphins forage in shallow cold waters (away from tiger sharks)
Marine mammals do NOT just go where their prey is
Define oligotrophic
Nutrient poor region
Typically tropical regions with warmer waters
How can marine mammals (such as baleen whales) be considered providers?
Baleen whales provide significant energy into oligotrophic systems during winter months
In what ways can baleen whales provide energy to their surroundings?
- Placentas
- Carcasses
- Sloughed skin
What larger ecosystem effects do the presence of baleen whales have on their surroundings?
- Baleen whales provide a predictable and significant source of energy to their surroundings
- Attract predators (white sharks, tiger sharks, killer whales) who can take advantage of food resource
- Whale falls provide habitat and energy to deep sea organisms
What effects can marine mammals have on predation (think of Seals and Northern Cod case study)?
- Depletion of fish stocks
- 1992, cod stock collapsed in New Finland
- Proposed solution was to kill seals in order to replenish cod stocks
Is this a good solution?
Define meso-predator
A predator in the middle of the food web
What are some possible scenarios that could explain the depletion of the Northern Cod fish stock?
- Seals eat commercially important fish
Result: Killing seals replenishes cod stocks - Seals eat meso-predators (ex: squid) which are feeding on cod stock
Result: Killing seals increases meso-predator population cod is further depleted - Multiple trophic interactions contributed to cod depletion (not just seals)
Overall, all trophic interactions must be understood in order to figure out what led to the depletion of a particular resource
Describe a bottom up trophic effect
Relative abundance of organisms at lower trophic levels drives the abundance of organisms in the middle and upper trophic levels
Describe a top up trophic effect
Opposite of bottom up. Relative abundance of organisms at upper trophic levels drive abundance of organisms in the middle and lower trophic levels.
Describe a trophic cascade
The indirect effect of predators on lower trophic status species through top-down forcing
What is a Keystone species?
A species whose impact on is community or ecosystem is large relative to its abundance.
What happens when a keystone species is removed?
A phase shift (trophic cascade) can occur which results in dramatic changes in ecosystem structure and function
Describe the phase shifts associated with sea otter abundance in the North Pacific Kelp Forests
- Sea otters feed on sea urchins
- Sea urchins feed on kelp forests
- When sea otter abundance is high, sea urchin populations are kept in check and kelp forests thrive
- When sea otter populations are low, a phase shift occurs, sea urchin populations go unchecked and kelp forests cannot grow (urchin barren)
How do killer whales effect the sea otter abundance, sea urchin abundance and growth of kelp in Northern Kelp Forests?
- When killer whale predation is high, sea otter abundance decreases
- Sea urchin abundance increases
- Kelp forests are depleted
How is kelp growth affected by sea urchin predation?
- Because sea otter predation levels are higher closer to the surface, sea urchin populations are greater at deeper levels
- Therefore grazing intensity on kelp is highest at deeper levels
- Kelp species that are well defended against herbivores grow at deeper level than kelp that have poor defense against herbivores
Entire system is driven by otter predation
What is the Cleaver Equation?
Relates the metabolic rate and mass of an organism
Is the Cleaver Equation effective for estimating the consumption of marine mammals?
Not really because it is hard to measure the metabolic rate of marine mammals
What are some methods involving marine mammal behavior and prey data that can be utilized to estimate prey consumption in marine mammals?
- High resolution tag data can be used to track lunge feeding events
- Morphometric data: filtration rates of water (baleen whales)
- Fishery acoustics can measure prey density at different depth
All of these data methods can be used to roughly estimate prey consumption per year
How can drone data be used to estimate consumption in baleen whales?
- Can measure seasonal changes in body condition (how fat they are)
- Baleen whales accumulate energy reserves during the summer foraging season and utilize these energy reserves during the breeding season
- Changes in body condition can be utilized to estimate the annual energetic budget of whales
How can marine mammal population sizes be used to estimate consumption?
Take individual consumption estimates and multiply them by population size estimates
This is a very challenging estimate
Describe an El Nino event?
- Trade winds (east to west) weaken
- Warm water is pushed East
- Results in little to no upwelling of nutrient rich cold water
Describe coastal upwelling
- Driven by the Coriolis effect
-Nutrient rich cold water surfaces - Allows the growth of organisms such as plankton and algae in the photic zone
- Results in increased productivity
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Marine Mammal Taxonomic Groups27
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Diving Physiology25
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Thermoregulation39
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Morphology and Locomotion36
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Foraging and Feeding27
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Trophic Interactions26
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Acoustics and Echolocation41
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Acoustics and Communication36
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Population Biology25
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Life Histories37
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Assessing Humpback Whale Body Condition Using Drones26
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Marine Mammal Managemengt In The U.S41
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Fisheries Bycatch28
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Conservation Case Study II: Large Whales26
