- In Luke 5, as Jesus was standing by the Lake of Gennesaret (Luke 5:1), He commissions Peter to cast his nets into the water (Luke 5:4). Peter does, and despite having had no luck catching anything all night (Luke 5:5), in obeying Christ, they bring in an enormous catch of fish, which begins to tear the nets (Luke 5:6). Peter then says to Christ, “Go away from me, Lord; I am a sinful man!” (Luke 5:8). Jesus then calls Peter to become a fisher of men (Luke 5:10). Peter is with James and John and unnamed others when this occurs (Luke 5:9-10).
- Then you have John 21:1-19, the post-Resurrection appearance of Christ to the Apostles “by the Sea of Galilee” while “Simon Peter, Thomas called Didymus, Nathanael from Cana in Galilee, Zebedee's sons, and two others of His disciples” (John 21:2) are fishing. After an unsuccessful night of fishing Christ tells them to cast their nets over the right side of the boat, and they catch such a large amount of fish that they can't bring it in (John 21:6). Later, Christ commissions Peter to bring in the net, and he's able to do it single-handedly (John 21:10-11). I've looked at the implications of this before. But Christ segues to His commission of Peter as shepherd of the sheep (John 21:15-17).
There's a lot of theological meat there to chew on. Christ has made Himself manifest in a way that reminds the Apostles, and particularly Peter, of their original agreement: to become fishers of men. He then show Peter that not only does he need to Evangelize (that is, "catch" the fish), but he has to lead as a Pastor (to continually tend and care for the sheep). The first event is foreshadowing the second, but they're clearly two separate events.
Nevertheless, the NAB is convinced that this means it must be the same event. The footnotes says:
There are many non-Johannine peculiarities in this chapter, some suggesting Lucan Greek style; yet this passage is closer to John than John 7:53-8:11. There are many Johannine features as well. Its closest parallels in the synoptic gospels are found in Luke 5:1-11 and Matthew 14:28-31. Perhaps the tradition was ultimately derived from John but preserved by some disciple other than the writer of the rest of the gospel. The appearances narrated seem to be independent of those in John 20. Even if a later addition, the chapter was added before publication of the gospel, for it appears in all manuscripts.And:
This may be a variant of Luke's account of the catch of fish; see the note on Luke 5:1-11.It's an outrageous statement. It's only a variant if John or Luke is lying, since they both specify the time and place, and they don't match up. Nor would this be a mistake. The whole point in John 21 is that it's a Resurrection appearance of Christ, while in Luke 5, it's Jesus at the very start of His ministry.
Besides being faithless, it's silly. They're i at different times (start of Jesus' ministry v. after His Resurrection), with different people, and while the nets begin to tear in Luke 5:6, John says that the nets don't tear at all in John 21:11. Virtually none of the details are the same other than: they're fishing, and after Christ miraculously causes a great catch of fish, He uses this as a metaphor for Evangelization -- and specifically Peter's role as earthly head of the Church.
But none of this is surprising or requires a conspiracy theory, since four of the Apostles are fishermen, including Peter. You might as well assert that any story that someone says happened "while I was at work" must have happened on the same day as all of their other work stories. Fishing is Peter's job. And the connection between fishing and Evangelization is an obvious metaphor for Christ to pick up upon: there are numerous fishing and shepherding references in the Gospels. Besides that, Christ builds upon the fishing metaphor here in a way He doesn't in Luke 5. It's much more sensible to view John 21 as a fulfillment of Luke 5, in the same way that the Crucifixion is a fulfillment of Abraham's sacrifice of Isaac, rather than the same story.