14-8 Catching and Raising More Fish and Shellfish
Where Do We Get the Fish and Shellfish We Eat? Ocean and Freshwater Ecosystems and Fish Farms
The world’s third major food-producing system consists of fisheries: concentrations of particular aquatic species suitable for commercial capture in ocean or freshwater ecosystems, or suitable for raising in ocean or freshwater fish farms.
In recent years, the annual world harvest of fish and shellfish from natural ecosystems has remained about the same from year to year, but production from freshwater and saltwater fish farms has been increasing steadily.
How Are Fish and Shellfish Harvested? Hunt and Gather As Much As You Can
The world’s commercial marine fishing industry is dominated by industrial fishing fleets using global satellite positioning equipment, sonar, huge nets and long fishing lines, spotter planes, and large factory ships that can process and freeze their catches.
Trawler fishing is used to catch fish and shellfish—especially shrimp, cod, flounder, and scallops—that live on or near the ocean floor. It involves dragging a funnel-shaped net held open at the neck along the ocean bottom and weighed down with chains or metal plates.
Purse-seine fishing, involves catching surface-dwelling species such as tuna, mackerel, anchovies, and herring, which tend to feed in schools near the surface or in shallow areas. After locating a school the fishing vessel surrounds it with a large net called a purse seine. Then they close the net like a drawstring purse to trap the fish.
Fishing vessels also use longlining. It involves putting out lines up to 130 kilometres (80 miles) long, hung with thousands of baited hooks. The depth of the lines can be adjusted to catch open-ocean fish species such as swordfish, tuna, and sharks or bottom fishes such as halibut and cod. Longlines also hook endangered sea turtles, sea-feeding albatross birds, and pilot whales and dolphins.
With drift-net fishing, fish are caught by huge drifting nets that can hang as much as 15 metres (50 feet) below the surface and be up to 64 kilometres (40 miles) long. This method can lead to overfishing of the desired species and may trap and kill large quantities of unwanted fish and marine mammals (such as dolphins, porpoises, and seals), marine turtles, and seabirds.
Connections: How Are Overfishing and Habitat Degradation Affecting Fish Harvests? Dropping Yields
Fish are renewable resources as long as the annual harvest leaves enough breeding stock to renew the species for the next year. Overfishing is the taking of too many fish, particularly the larger and sexually mature fish, so that too little breeding stock is left to maintain numbers. Prolonged overfishing leads to commercial extinction, when the population of a species declines to the point at which it is no longer profitable to hunt for them. Fishing fleets then move to a new species or a new region, hoping that the overfished species will recover.
Should Governments Continue Subsidizing Fishing Fleets? Too Many Boats Chasing Too Few Fish
Overfishing is a big and growing problem because we have too many commercial fishing boats and fleets trying to hunt and gather a dwindling supply of the most desirable fish.
It costs the global fishing industry about $120 billion (U.S.) a year to catch $70 billion worth of fish. Government subsidies such as fuel tax exemptions, price controls, low-interest loans, and grants for fishing gear make up most of the $50 billion annual deficit of the industry.
What Is Aquaculture? Feedlots of the Sea
Aquaculture involves raising fish and shellfish for food like crops instead of going out and hunting and gathering them. It is the world’s fastest- growing type of food production and accounts for about one-third of the fish and shellfish we eat.
There are two basic types of aquaculture.
One, called fish farming, involves cultivating fish in a controlled environment (often a coastal or inland pond, lake, reservoir, or rice paddy) and harvesting them when they reach the desired size.
The other is fish ranching. It involves holding anadromous species such as salmon that live part of their lives in fresh water and part in salt water in captivity for the first few years of their lives, usually in fenced-in areas or floating cages in coastal lagoons and estuaries.
What Is the State of Aquaculture in Canada? Healthy but Not Problem-Free
Aquaculture is practised in all the provinces as well as the Yukon. British Columbia and New Brunswick are the largest producers, accounting for 75% of production (Figure 14-29, p. 330). More than 70 species of fish, shellfish, and plants are licensed for aquaculture in Canada.
Where fish and plants are raised together, the term aquaponics is often used; the nutrient-rich pond water is used hydroponically to nourish the plants. The plants cleanse the water, which can then be returned to the fish ponds.
One problem associated with farming salmon has been the need to feed these predatory fish with food pellets made from small fish. This can deplete stocks of small fish. As well, the body oils of these small fish may contain PCBs and dioxins that can be passed on to the farmed salmon.
Another problem is that fish farming can have a variety of other impacts on wild fish populations, including transmission of disease from captive stocks; escapes of non-native and genetically altered fish from fish farms; and water quality issues such as excess wastes, antibiotics, and pesticides that build up in the waters surrounding fish farms.