The best summary of the passage, "Saving Killer Whales," is: C. The Southern Resident orca is in danger for several reasons and will be extinct if they don't get more food to eat. The salmon in their area isn't as plentiful as it once was. More people should get involved with helping to save them so they aren't eliminated from the Earth.
This option encapsulates the main ideas about the Southern Resident orcas' plight and the importance of their food source, while also suggesting the need for action to help them.