If the fish are deep in means that there is a low pressure system, or the water temp is wrong, and the fish are shocked and are not eating. Let down your nets. They'd fished all night, into dawn, prime time, and they hadn't caught a thing. They'd come in, mended and put the nets away. Clean up is a big deal when you run nets.
Deep water is a desperation move.
Then Peter says some fulcrum words, words upon which a life gets its leverage. Peter listened to Jesus. Now the word listening is interesting. It is an active process. It is more than hearing sounds or words, listening implies action.