san cocho in fishing means what?
"san cocho" when fishing and the bait comes back with just a head the mates say "san cocho"
Just a bit of a wild guess here. I suspect that the fisherman in question is saying "sancocho", which is a rich soup made with a variety of roots and vegetables, and either beef, chicken of fish.
For fish sancocho, you typically use bits like the head bones, that add a lot of flavor to the soup, even if they are not very meaty.
So I expect that the expression means that the bits that are "rescued" are only fit for sancocho. Obviously you cannot fillet a head....