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Researching the role of marine mammals in marine ecosystems

We determined the impact that marine mammals have on ecosystems by examining:

  • marine mammal:
    • abundance
    • distribution
    • diet changes
    • energy requirements
  • prey population mortality caused by marine mammal predators

To predict how marine mammals will respond to changing prey abundances, we look at factors such as:

  • nutritional needs
  • abundance of the prey or local availability
  • specialization by the predator on particular prey
  • energy return or benefit compared to the energy needed to capture and handle the prey

Marine mammals play a varied role in marine ecosystems, which includes:

  • feeding as top level predators on animals such as:
    • other marine mammals (as do walruses and killer whales)
    • fish (as do killer whales, harp seals and hooded seals)
  • feeding at much lower levels on organisms such as:
    • benthic invertebrates (as do sea otters, walruses and grey whales)
    • pelagic invertebrates (as do harp seals)

In some cases, marine mammals play a very clear role in structuring marine ecosystems. For example, sea otters that prey on sea urchins reduce grazing pressure, which allows:

  • spreading of kelp bed forests
  • development of new ecosystems
  • increases in marine fauna density and diversity

However, marine mammals may also have a negative impact on commercial fisheries, including:

  • damaging fishing gear, such as nets and traps
  • consumption of fish, limiting their availability to fishers
  • transmitting parasites that must be removed before fish can be sold
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