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