How do fisherman catch only the fish they want?

I’m watching Deadliest Catch, and I have to wonder: how do only King Crab get into the pots? I mean…I’m sure there’s the odd shrimp or lobster or other crab species in there, but in watching the show it looks to be 99% king crab.

And for fishing boats for actual fish, ones that swim, I assume they use large nets? How do they only get mackerel, or tuna, or salmon? Are their fish finders, instincts, and knowledge of what fish congregate where that good?

It’s too cold for lobster up there. I would assume that the shrimp have a preferred area that isn’t where the king crabs are. I’ve also heard that male king crabs and female king crabs tend to congregate separately, but I can’t vouch for that.

Well, they don’t just catch the fish they want. If they set their nets on a school of tuna or mackeral, that’s mostly what they will get. However, often there will be a good deal of what is called “bycatch,” non-commercial fish that are simply discarded, often in a dead or dying condition. Commercial fishing can sometimes be very wasteful.

Keep watching. They find some pretty big octopuses (octopi?).

Octopuses. “Octopi” is not a correct Latin plural (which is octopodes), although it has been mistakenly used for so long it appears in some dictionaries.

Can’t they sell the byproducts? I know cats are pretty fussy but there must be some poor cats in China that would be happy to get any kind of “fish mash”

Generally it’s discarded because 1) it’s not economically worthwhile in terms of time to sort through for the few saleable species, and 2) the low-value stuff would take up cargo space that could be used for the valuable species. You’re not going to fill up your hold with species suitable for cat food when you need it for tuna.

Here’s some discussion of bycatch issues.

It is not that the incidental bycatch is not marketable, (there is a market for most all fish) but that the bycatch are species that are protected and not allowed to be kept. And they must be thrown overboard to prevent the boat from profiting by ‘accidental’ catches. Even though these fish are dead and valuable they must be discarded.

This incidental bycatch can determine when the fishing season must end.
numbers below are used for example only

Say it is bottomfish season here in the Pacific NW and a million pounds is the seasonal quota for the sole, flounder, etc that can be caught. But yellow-eyed rockfish are endangered and an incidental bycatch of 10000 lbs is the limit. Once that 10000 lbs is caught (and discarded) the season is OVER for the entire fleet, even if 600,000 lbs of the allowable sole, etc is still uncaught. The gives the fleet incentive to fish in areas where they are less likely to catch the yellow-eye. The industry is highly regulated including onboard cameras and GPS.

As far as crab and the Deadliest Catch goes, crab pots are designed to allow for escape for non-target species, and under-size and females can be safely tossed back without harm to the crab.

How far down to king crabs live?

Yes the byproducts are desireable. I spent 29 years working as a manager at a plant that used the scrap and otherwise undesireable human food grade fish to make fishmeal, fishoil, pet food flavors and hatchery fish feed among other things.
The hatchery feed was mainly for salmon and required a high level of fish protien since that is what salmon eat, other fish. What protien we could not make ourselves had to be imported from South American as fishmeal.

Fish meal is a huge worldwide commodity. White fish from Alaska, anchovy from Peru and Chile, menhaden from the gulf of Mexico. But these are caught fairly close to shore in one or 2 day trips. If you are fishing tuna the boats go very long distances and you would not want to use the space to keep so called ‘trash’ fish.

The captains tend to have spots where they caught large loads of crabs in the past. However, this doesn’t alway work as there can be few crabs or the wrong type. I remember one episode where a ship caught a huge load of crab. Unfortunately, the crab were all female and had to be thrown back.

I have an uncle who caught crabs. He was in the Navy, though.

As deep as 500 fathoms (3000 feet):

They will use the occasional cod that slips into the pots as fresh bait. They can also adjust the pots to catch cod.

I wondered about this also. One of the guys on the show was talking about the rope tied to the pot as 600 feet long.

Actually, it IS a correct Latin ending, but it’s not a correct Greek plural, which is where Octopus comes from.

Why do they call them “pots” when they are clearly not made from pottery materials, such as porcelain or ceramic (some of them could be made of cast iron, I suppose, but the pictures I’ve seen don’t really look like it)? In fact, they look a lot like cages.

It’s a correct ending for second declension nouns. Since octopus is third declension, it’s an incorrect Latin plural.

See the Staff Report by bibliophage on Latin plurals.

I think pots is just the slang term they use for the crab traps. I have never seen them talk about why they use pots rather than traps.