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When I was in fisheries the tuna boats would bring the haul of frozen tuna into port where they’d be weighed, counted, and transferred to a cannery also in port.
A lot were fileted and cut right there too, so not all was straight to can.
Now a lot of the cans stayed fairly together by shipment. So I imagine where a lot code was split across separate pallets or shipments might a single fish be sent to different locations in can form. So I would wager the ‘rest’ of the tuna is at least on the shelf next to… itself.
As far as waste though? Some companies are super diligent about their waste streams. Fish meals and such have resale value. Others leave large amounts of parts and material in their shop floors and just power wash it back into the marine waters even while being fined and penalized by regulators. So mileage varies there.
I dunno, 3 makes wild accusations about implied meanings. Seems suspect.