How Seafood Is Harvested
Many different fishing techniques are employed to harvest the finfish and shellfish that enter the seafood market. Some of these methods target individual fish within a selected species, while others are less discriminating, designed for higher volume and mass production. Each can have an effect on the quality of the end product. Here's a look at eight common methods of harvesting seafood, as well as their advantages and drawbacks.
OTTER TRAWLING - A large cone-shaped net, held open by huge plates (called "doors"), is dragged through the water, scooping up everything in its path. The fish end up in the rear section, or cod end, of the net. There are two kinds of trawling: bottom trawling (in which the net is dragged across the bottom) and midwater trawling. The value of trawling is volume fishing for groundfish species like pollock and flounder. Disadvantages include a loss of quality because of the sometimes heavy tonnage hauled up in a single lift of the net - a problem that can be mitigated somewhat by reduced towing times.
TROLLING - Baits or lures are dragged behind a vessel as it moves through the water. With salmon trolling, as many as six wire lines are lowered from the boat, with "cannonballs" (lead balls) holding each wire more or less perpendicular to the hull. Off each trolling wire, as many as 20 leaders, with bait lures attached, are pulled through the water. The main lines are reeled in and out by hydraulic gurdies (spools). Albacore trolling, on the other hand, consists of a dozen or so feathered jigs, each on a single line, skimmed along the surface. The advantage of troll-caught fish is quality. One fish is hooked at a time, cleaned and bled, then stored in ice or frozen onboard.
PURSE SEINING - Schools of fish like herring, mackerel and tuna are encircled with a net, which is then "pursed" at the bottom, trapping the fish. The filled net is hauled back to the vessel through a power block; when it's alongside the vessel, the fish are usually "brailed," or pumped aboard with a suction hose. The quality of seine-caught fish is a function of the volume of the catch.	GILLNETTING - Gillnets entangle target species like salmon and sharks by their gills after they penetrate the net and get caught in the mesh, which is invisible to fish. The mesh size determines the size of the fish captured. The advantage of this method is its efficiency; its disadvantage is that it kills on capture, sometimes inflicting injuries that compromise the quality of the product.
LONGLINING - To attract fish, baited hooks are attached to a single longline, which is then set either along the bottom of the ocean or at a depth nearer to the water's surface (depending upon the target species). The ends of the set are marked by buoys and, in the case of bottom longlining, anchored to the bottom.	Mahimahi and swordfish are two examples of species that are taken, in part, by surface longlining; halibut and cod are examples of fish species taken by bottom longlining. The advantage of this method of harvest is that fish are brought aboard one at a time, usually while they're still alive, and processed quickly to ensure quality.
POT FISHING - Pots, or traps, are fished on the bottom from single lines and buoys, with one pot per line, or from longlines, with several pots to a string and buoys marking either end of the "set." Lobsters and most crab species are captured by the former method (single pots). A wire lobster pot may weigh less than 10 pounds, while a king crab trap can weigh 500 pounds. Pot fishing is highly selective, and the product is landed live for maximum quality.	DREDGING - This is a method used for capturing shellfish, primarily scallops, clams, oysters and mussels. A dredge is essentially a metal "rake" that's dragged across the ocean bottom, scraping up shellfish in its path. The shellfish are collected and held in a chain-mesh bag. Dredges vary from hand-operated to much larger, hydraulically operated versions like those used for harvesting sea scallops and surf clams.
AQUACULTURE - Aquacultured finfish and shellfish are harvested from a controlled environment in which they have been raised to market size from fingerling or larval stage. For example, salmon are grown in ocean pens, while catfish and tilapia are raised in freshwater ponds or tanks on land. Mollusks like oyster and mussels are grown in systems that suspend them off the ocean bottom.	Shrimp are farmed in ponds worldwide. In aquaculture operations, water quality and feed are carefully monitored. Farmed fish and shellfish are usually processed and shipped within hours of harvesting. As such, the quality of product is typically excellent. Aquaculture also offers a consistent, year-round supply and greater price stability than wild-caught seafood.
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