Name: シャチの母系の内部 - ダレン・クロフト (Inside the killer whale matriarchy - Darren Croft)
Uploaded: 2021-01-14T08:00:52.000Z
Duration: 5 min 4 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

Off the rugged coast  of the pacific northwest,

pods of killer whales  inhabit the frigid waters.

These matriarchs can live eighty years  or more,

while most males die off  in their thirties.

Though killer whales inhabit  every major ocean,

until recently we knew  very little about them.

The details of their lives  eluded scientists

until an organization called  the Center for Whale Research

near Washington State and  British Columbia in 1976.

we've learned a great deal  about these whales,

the more this population's elders'  vital role comes into focus.

Each grandmother starts her life as a calf

born into her mother's family group,  or matriline.

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

Both sons and daughters spend their entire lives with their mothers' families.

That doesn't mean a young whale  only interacts with her relatives.

her matriline shares a dialect  with nearby families,

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

The relationships don't go much  beyond mating—

while the male returns to his own mother.

she gives birth every 6 years on average.

which is almost unheard of  in the animal kingdom.

In fact, humans, killer whales and  a few other whales

are the only species whose females  continue to live for years

grandmothers take the lead  hunting for salmon,

the Southern Residents' main food source.

But when the salmon head  towards shore in droves to spawn,

where to find the most fertile  fishing grounds.

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

overfishing and habitat destruction have  decimated salmon populations,

putting the whales at near-constant  risk of starvation.

can mean the difference between  life and death for their families–

It's almost always advantageous for a female to continue reproducing,

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

A couple unique circumstances  change this equation for killer whales.

leave their families of origin  is extremely rare—

This means that as a female  killer whale ages,

consists of her children  and grandchildren,

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

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

whereas younger females should  invest in reproducing.

An older female can further her genes without burdening her family

who sire calves other families will raise.

This might be why the females have evolved

to stop reproducing entirely  in middle age.

Even with the grandmothers' contributions,

the Southern Resident killer whales  are critically endangered,

We urgently need to invest in restoring  salmon populations

In the long term, we'll need more studies  like the Center for Whale Research's.

What we've learned about  the Southern Residents

we might uncover more  startling adaptations,

and anticipate their vulnerabilities  to human interference