Killer whale and seal otter energetics

1
Killer whales and sea otters

• Killer whale and seal otter energetics

• Daily caloric requirements

• Male killer whale 308,000 Kcal/day or 5-7 sea
  otters

• Female killer whale 187,000 Kcal/day or 3-5 sea
  otters

• Account for 40,000 sea otters lost over 6 years?

• 5 sea otters per day per whale x 365 days x 6
  years 10,950 sea otters!

• 10,950 sea otters eaten x 4 whales would account
  for 40,000 sea otter losses

Where have all the sea otters gone?
2
Killer whales and sea otters

• Sea otters usually not main component of killer
  whale diet -- why the change?

• Some fish populations have declined in recent
  decades

• Shortage of certain fish caused substantial
  declines in harbor seals and sea lions

• Shortage of seals and sea lions resulted in
  killer whales preying on smaller sea otters

Where have all the sea otters gone?
3
Killer whales and sea otters

• Why should we care about sea otter declines?

Where have all the sea otters gone?
4
Indirect effects on communities

• Predation (or parasitism) can reduce competition,
  preventing competitive exclusion

• Predators typically feed on several types of prey

• Prey selected based on its relative abundance

• Superior competitors can reach high relative
  abundance, but predation can control such
  populations

• Example removal of starfish (Pisaster) in rocky
  intertidal results in competitive exclusion by
  mussels

Where have all the sea otters gone?
5
Indirect effects on communities

• Predation (or parasitism) can result in many
  indirect effects on other species

• Example ant-rodent interactions

• Both ants and rodents eat seeds in Chihuahuan
  Desert

• Removal of rodents caused initial increase in ant
  populations, but then a decrease

Where have all the sea otters gone?
6
Indirect effects on communities

• Keystone species species that have strong
  effect on the composition of the community

• Removal of keystone species causes a decrease in
  species richness

• Example sea otters eat sea urchins which are
  superior competitors if sea urchin populations
  increase, kelp reduced and species richness drops

Where have all the sea otters gone?
7
Indirect effects on communities

• Kelp forest

Where have all the sea otters gone?