"in the water among the empty beer cans and dead barracudas"
: "Barracudas are elongated fish, pike-like in appearance, with prominent sharp-edged fang-like teeth, . . . which are set in sockets of their large jaws."
This sentence suggests the fishermen of Havana throw out any barracuda they catch. The flesh can be eaten, but some species may cause ciguatera poisoning, which is perhaps why these fish have been rejected.