Are "Fish in a barrel" and "Sitting ducks" similar?

Do the phrases "Fish in a barrel" and "Sitting ducks" convey the same thing?

In my opinion, they have the same tone and express something to be an easy target.

Eg: Out there, they are just fish in a barrel.

Out there, they are sitting ducks.

Can they be used interchangeably or are there some differences in their usage?

Solution 1:

Yes they are similar, but not interchangeable

The wording is

It is as easy as shooting fish in a barrel: ridiculously easy

and

They are like sitting ducks: someone or something vulnerable to attack

So you would say - Making them look stupid is like shooting fish in a barrel e.g. you are actively hunting them versus

The noobs are like sitting ducks in this flame war e.g they have made themselves an easy target

In your case:

Look at them out there: Like sitting ducks

or

Look at them out there, getting at them would be like shooting fish in a barrel

Solution 2:

While they are similar, "Fish in a barrel" tends more towards the mindset of the predator: many opportunities for easy gain.

"Sitting ducks" tends more towards mindset of the prey: they are unaware that they are being stalked.

EDIT: Added Calvin and Hobbes comic strip

Calvin can say that dropping a snowball on Susie is "like shooting fish in a barrel" because it's both easy for him to target her and difficult for him to miss her. This is the predator's point of view.

Before Calvin drops the snowball, Calvin (and the reader) would call Susie "a sitting duck." However, Susie does not know that she is vulnerable at this stage. She could not say, "I'm a sitting duck." Nor could she say, "I'm a fish in a barrel."