From the Urban Dictionary:

Catch and release - n - the practice of hooking up with someone and not becoming emotionally/physically attached to them.

As a result, other people have a chance to hook up with this person because he or she has been "caught and released" back into the wild.
Ben: "Yo I nailed this girl last night"

Dave: "So are you going to call her later?"

Ben: "Hell no man, I practice catch and release. That way, you can have a shot with her next weekend."

If you hook up it is lol

Not necessarily. Sometimes it just means there isn't a good ft .

Hope they use barbless hooks.

Catch and release satisfies whoever is casting that metaphorical reel. It's mostly an emotional/ego fueled ploy to see 'if they still got it' in terms of attracting people. Quite common that the poor soul who does bite down on that fancy bait and tackle ends up emotionally, and mentally drained, confused, and hurt.

Hookups can also follow this trend, but there are also many cases wherein it's a mutual desire and no one gets needlessly emotionally hurt in the process. Which is not the case for CnR dating which almost always hurts the recipient.

Better to do it to humans figuratively than to do it to innocent fishies literally.....

When it looks and feels like a salmon at first, but turns out to be a carp.

Poor fish!

it sounds like you throw them back if they measure up