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Puget Sound's resident orcas basically refuse to eat anything other than Chinook (King) salmon -- 97% of their diet is salmon, 78% is Chinook salmon. A variety

Puget Sound's resident orcas basically refuse to eat anything other than Chinook (King) salmon -- 97% of their diet is salmon, 78% is Chinook salmon. A variety of old dams without salmon runs have been blocking their ideal spawning grounds, but many of them are being demolished or upgraded to let the fish pass. https://en.wikipedia.org/wiki/Southern_resident_killer_whales https://en.wikipedia.org/wiki/Southern_resident_killer_whale...

stevenwoo 9y ago
This is true but doesn't address the why within one human generation the population size change in salmon returning to spawn ( five years in Pacific versus current two-three years in Pacific versus 10000 years prior history at five years). Also I believe the article says that Alaska orcas are now feeding on the salmon before they get to the Puget Sound orcas, and not in the article but linked that marine mammal populations take a larger number of salmon than orcas, so there is pressure on salmon population from all types of natural predation/less habitat.
- Scaevolus 9y ago
  The resident orcas have declined enough to be endangered, largely tracking the decline in Chinook.
  - Tiktaalik 9y ago
    Yeah the Orcas are starving. http://www.cbc.ca/news/canada/british-columbia/low-orca-birth-rates-linked-to-lack-of-chinook-salmon-1.4183609 http://www.cbc.ca/news/canada/british-columbia/low-orca-birt... Ship traffic is also likely a factor in that it's likely disruptive to their hunting. Unfortunately the Canadian government is set on approving the TransMountain diluted bitumen pipeline expansion, which will increase oil tanker traffic through the Haro Strait 7 fold. This will probably be dangerously disruptive to the orcas even if there's never any diluted bitumen spill The orcas are probably doomed :(
- AnimalMuppet 9y ago
  Overfishing? Hypothesis: Before the latest jumps in industrial fishing in the Pacific, enough salmon could live to five years to dominate the numbers of those returning to spawn. But now, with fishing becoming more "efficient", the probability of a fish living to five years while swimming free in the Pacific has dropped to very close to zero. But some still make it two or three years. Those are all that are left to return to spawn.
- bc_skier 9y ago
  On theory I have heard relates to the fishing pressure in the North Pacifci Gyre. From what I understand Chinook and other anadromous species typically make one revolution per year (it's not uncommon for US born fish to be caught off Japan and Kamchatka). With an increase in fishing pressure fish just don't live as long any more without being caught. So the one, two, and three salt fish (two salt being a fish that has spent 2 years in the salt water), are more likely to pass on there genes. Being that how long a fish stays in salt water is largely genetic it would be easy to remove those genes from the gene pool in a relatively short time. I'm sure other factors like dams without fish passage on the Upper Columbia and Elwah (two rivers known for their large salmon) also played a factor. Additionally fish hatcheries largely select for fish that return at a younger age as they will return in larger numbers, and with such a huge amount of hatchery fish that would further drive down the average size. As would any spawning between wild and hatchery fish (although the reproductive fitness of hatchery fish is particularly bad).

stevenwoo 9y ago

This is true but doesn't address the why within one human generation the population size change in salmon returning to spawn ( five years in Pacific versus current two-three years in Pacific versus 10000 years prior history at five years). Also I believe the article says that Alaska orcas are now feeding on the salmon before they get to the Puget Sound orcas, and not in the article but linked that marine mammal populations take a larger number of salmon than orcas, so there is pressure on salmon population from all types of natural predation/less habitat.

Scaevolus 9y ago
The resident orcas have declined enough to be endangered, largely tracking the decline in Chinook.
- Tiktaalik 9y ago
  Yeah the Orcas are starving. http://www.cbc.ca/news/canada/british-columbia/low-orca-birth-rates-linked-to-lack-of-chinook-salmon-1.4183609 http://www.cbc.ca/news/canada/british-columbia/low-orca-birt... Ship traffic is also likely a factor in that it's likely disruptive to their hunting. Unfortunately the Canadian government is set on approving the TransMountain diluted bitumen pipeline expansion, which will increase oil tanker traffic through the Haro Strait 7 fold. This will probably be dangerously disruptive to the orcas even if there's never any diluted bitumen spill The orcas are probably doomed :(
AnimalMuppet 9y ago
Overfishing? Hypothesis: Before the latest jumps in industrial fishing in the Pacific, enough salmon could live to five years to dominate the numbers of those returning to spawn. But now, with fishing becoming more "efficient", the probability of a fish living to five years while swimming free in the Pacific has dropped to very close to zero. But some still make it two or three years. Those are all that are left to return to spawn.
bc_skier 9y ago
On theory I have heard relates to the fishing pressure in the North Pacifci Gyre. From what I understand Chinook and other anadromous species typically make one revolution per year (it's not uncommon for US born fish to be caught off Japan and Kamchatka). With an increase in fishing pressure fish just don't live as long any more without being caught. So the one, two, and three salt fish (two salt being a fish that has spent 2 years in the salt water), are more likely to pass on there genes. Being that how long a fish stays in salt water is largely genetic it would be easy to remove those genes from the gene pool in a relatively short time. I'm sure other factors like dams without fish passage on the Upper Columbia and Elwah (two rivers known for their large salmon) also played a factor. Additionally fish hatcheries largely select for fish that return at a younger age as they will return in larger numbers, and with such a huge amount of hatchery fish that would further drive down the average size. As would any spawning between wild and hatchery fish (although the reproductive fitness of hatchery fish is particularly bad).