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Off the rugged coast [br]of the pacific northwest,

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pods of killer whales [br]inhabit the frigid waters.

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Each family is able to survive here

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thanks mainly to one member,

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its most knowledgeable hunter:

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the grandmother.

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These matriarchs can live eighty years [br]or more,

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while most males die off [br]in their thirties.

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Though killer whales inhabit [br]every major ocean,

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until recently we knew [br]very little about them.

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The details of their lives [br]eluded scientists

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until an organization called [br]the Center for Whale Research

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began studying a single population

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near Washington State and [br]British Columbia in 1976.

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Thanks to their on going work,

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we’ve learned a great deal [br]about these whales,

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known as the Southern Residents.

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And the more we learn,

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the more this population’s elders’ [br]vital role comes into focus.

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Each grandmother starts her life as a calf

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born into her mother’s family group, [br]or matriline.

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The family does everything together,

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hunting and playing, even communicating [br]through their own unique set of calls.

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Both sons and daughters spend their entire[br]lives with their mothers’ families.

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That doesn’t mean a young whale [br]only interacts with her relatives.

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Besides their own special calls,

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her matriline shares a dialect [br]with nearby families,

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and they socialize regularly.

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Once a female reaches age fifteen or so,

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these meetings become opportunities [br]to mate with males from other groups.

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The relationships don’t go much [br]beyond mating—

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she and her calves stay with her family,

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while the male returns to his own mother.

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Until approximately age forty,

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she gives birth every 6 years on average.

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Then, she goes through menopause—

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which is almost unheard of [br]in the animal kingdom.

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In fact, humans, killer whales and [br]a few other whales

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are the only species whose females [br]continue to live for years

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after they stop reproducing.

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After menopause,

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grandmothers take the lead [br]hunting for salmon,

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the Southern Residents’ main food source.

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Most of the winter they forage offshore,

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supplementing salmon with other fish.

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But when the salmon head towards shore in [br]droves to spawn the killer whales follow.

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The matriarch shows the younger whales

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where to find the most fertile [br]fishing grounds.

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She also shares up to 90% of [br]the salmon she catches.

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With each passing year,

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her contributions become more vital:

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overfishing and habitat destruction have [br]decimated salmon populations,

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putting the whales at near-constant [br]risk of starvation.

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These grandmothers’ expertise can mean

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the difference between life and death [br]for their families–

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but why do they stop having calves?

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It’s almost always advantageous for a[br]female to continue reproducing,

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even if she also cares for her existing [br]children and grandchildren.

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A couple unique circumstances [br]change this equation for killer whales.

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The fact that neither sons nor daughters

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leave their families of origin [br]is extremely rare—

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in almost all animal species,

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one or both sexes disperse.

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This means that as a female [br]killer whale ages,

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a greater percentage of her family

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consists of her children [br]and grandchildren,

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while more distant relatives die off.

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Because older females are more closely [br]related to the group than younger females,

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they do best to invest in the family [br]as a whole,

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whereas younger females should [br]invest in reproducing.

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In the killer whale’s environment,

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every new calf is another mouth to feed

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on limited, shared resources.

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An older female can further her genes[br]without burdening her family

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by supporting her adult sons,

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who sire calves other families will raise.

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This might be why the females have evolved

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to stop reproducing entirely [br]in middle age.

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Even with the grandmothers’ contributions,

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the Southern Resident killer whales [br]are critically endangered,

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largely due to a decline in salmon.

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We urgently need to invest in restoring [br]salmon populations

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to save them from extinction.

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In the long term, we’ll need more studies [br]like the Center for Whale Research’s.

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What we’ve learned about [br]the Southern Residents

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may not hold true for other groups.

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By studying other populations closely,

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we might uncover more [br]startling adaptations,

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and anticipate their vulnerabilities [br]to human interference

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before their survival is at risk.