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Right now,

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beneath a shimmering blue sea,

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millions of fish are having sex.

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(Cheers)

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And the way they're doing it
and strategies they're using

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looks nothing like what we see on land.

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(Laughter)

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Take parrotfish.

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In this species, all fish are born female,

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and they look like this.

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Then later in life,

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she can transition into a male
and she'll look like this.

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But it's not just
a spectacular wardrobe change.

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Her body can reabsorb her ovaries
and grow testes in their place.

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In just a few weeks,

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she'll go from making eggs
to producing sperm.

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It's pretty impressive,

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and in the ocean it's also pretty common.

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In fact, I'll bet nearly all of you
have at some point had a seafood dish

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made up of an individual
that started life as one sex

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and transitioned to another.

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Oysters?

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Grouper?

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Shrimp?

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Seeing some heads nodding, yeah.

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But not all fish that change sex
start as females.

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Those clownfish we know
from "Finding Nemo"?

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They're all born male.

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So in the real world,

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when Nemo's mother died,

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Nemo's dad Marlin would
have transitioned into Marlene

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(Laughter)

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and Nemo would have likely mated
with his father turned mother.

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(Laughter)

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You can see -- (Laughter)

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Yeah.

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You can see why Pixar

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took a little creative license
with the plot line, right?

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(Laughter)

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So sex change in the ocean
can happen in either direction

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and sometimes even back and forth,

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and that's just one of the many
amazing strategies animals use

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to reproduce in the ocean.

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And trust me when I say

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it's one of the least surprising.

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Sex in the sea is fascinating,

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and it's also really important,

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and not just to nerdy
marine biologists like me

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who are obsessed with understanding
these salty affairs.

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It matters for all of us.

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Today, we depend on wild caught fish

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to help feed over two billion people

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on the planet.

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We need millions of oysters and corals
to build the giant reefs

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that protect our shorelines
from rising seas and storms.

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We depend on medicines that are found
in marine animals to fight cancer

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and other diseases.

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And for many of us,

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the diversity and beauty of the oceans
is where we turn for recreation

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and relaxation and our cultural heritage.

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In order for us to continue
to benefit from the abundance

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that ocean life provides,

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the fish and coral and shrimp of today

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have to be able to make fish
and shrimp and coral for tomorrow.

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To do that, they have to have
lots and lots of sex.

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And until recently,

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we really didn't know how sex
happened in the sea.

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It's pretty hard to study.

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But thanks to new science and technology,

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we now know so much more
than even just a few years ago,

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and these new discoveries
are showing two things.

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First, sex in the sea is really funky.

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Second, our actions are wreaking havoc
on the sex lives of everything

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from shrimp to salmon.

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I know. It can be hard to believe.

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So today, I'm going to share a few details
about how animals do it in the deep,

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how we may be interrupting
these intimate affairs,

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and what we can do to change that.

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So, remember those sex-changing fish?

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In many places in the world,

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we have fishing rules that set
a minimum catch size.

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Fishers are not allowed
to target tiny fish.

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This allows baby fish to grow
and reproduce before they're caught.

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That's a good thing.

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So fishers go after the biggest fish.

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But in parrotfish, for example,
or any sex changer,

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targeting the biggest fish means
that they're taking out all the males.

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That makes it hard for a female fish

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to find a mate

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or it forces her to change sex sooner

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at a smaller size.

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Both of these things can result
in fewer fish babies in the future.

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In order for us to properly care
for these species,

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we have to know if they change sex,

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how, and when.

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Only