Fishing and Aquaculture “If you're overfishing at the top of the food chain, and acidifying the ocean at the bottom, you're creating a squeeze that could conceivably collapse the whole system.” - Carl Safina

Fish Harvesting As the human population increased exponentially in the earth 20th century, fish harvesting did as well. Wild capture of fish reached a plateau in 1989, with fish farming accounting for most of the growth since then. Overharvesting of fish has caused some fish stocks to collapse.

A fishery is a place where the concentration of certain fish is high enough for commercial harvesting.

Areas near river mouths tend to be highly productive due to the deposition of nutrients that enter water from land runoff. Other areas of the ocean are productive due to upwelling, where winds blow surface water aside and allow nutrient-rich water from below to rise up.

Fishing Methods One of the earliest forms of large-scale fishing is pole fishing, where a school of fish is attracted to a boat through the use of bait. The fish enter a feeding frenzy and are pulled out of the water, one at a time, using a fishing pole and line. Pole fishing in the Maldives. Photo by Greenpeace.

Blood, Sweat, and Takeaways. Episode 1: Tuna

Longline fishing is a commercial fishing technique where baited hooks are attached to a single, long fishing line that trails behind a ship.

Long Line Fishing

Compared to pole fishing, longline fishing has a much higher rate of bycatch. Sea birds are highly vulnerable during setting of the line. Sea turtles, sharks, and other fish are also accidentally caught.

Purse seining deploys large nets over schools of fish identified from aerial surveys. The top of the net is pulled together like the drawstring of a purse. Drift netting uses long nets that span large expanses of open ocean surface water.

The fastest and most efficient way to catch fish is by trawling, where a large, funnel-shaped net is dragged behind a ship. The net is weighted with chains or metal plates.

Trawling scrapes up the ocean bottom, destroying benthic habitats, including coral reefs.

Trawling has the highest rates of bycatch, since any species big enough to be caught in the net will be trapped.

Deep sea aquaculture cage Fish farming in cage Trawler fishing Sonar Spotter airplane Purse-seine fishing Drift-net fishing Float Buoy Fish caught by gills Long line fishing lines with hooks Figure 11.7 Major commercial fishing methods used to harvest various marine species. These methods have become so effective that many fish species have become commercially extinct. Deep sea aquaculture cage Stepped Art Fig. 11-7, p. 256

Bycatch Bycatch is unwanted fish, birds, and mammals that are caught alongside the desired fish species. Nearly one-third of the total annual fish catch is bycatch. Methods that use large nets, such as trawling, have high rates of bycatch.

Fishing Sustainability The maximum sustainable yield is the highest amount of a species that can be harvested without diminishing the population for future years. Overexploited fisheries are being harvested at unsustainable levels. Over time, these can become depleted fisheries with stocks so low that fishing cannot be supported.

Sustainability of a fishery can also be evaluated based on what types of organisms are harvested. Aquatic communities are organized like those on land, with different trophic levels, or place on a food chain. TL1 (Producers): Phytoplankton and algae. TL2 (Herbivores): Zooplankton. TL3 (Carnivores that eat herbivores): Small fish, crustaceans, and mollusks. TL4 (Carnivores that eat other carnivores): Medium-sized fish. TL5 (Apex predators): The largest carnivorous fish.

The Marine-Trophic Index is a measurement of the average trophic level of the total catch from a fishery. In 1992, the fishing industry in Newfoundland, Canada collapsed due to overfishing of mature cod (TL5 fish). Fishing down the food chain describes the practice of targeting fish at decreasing trophic levels as these collapses occur.

As traditionally valuable species have declined, some species of “trash fish” have been renamed or rebranded to make them more marketable. Trevally a.k.a. Snottynose Trevalla Orange Roughy a.k.a. Slimehead Chilean sea bass a.k.a. Toothfish Peekytoe crab a.k.a. mud crab

Fishing Regulations Up to the 1960s, the only regulations on fishing were territorial waters; exclusive fishing zones that reached 12 miles off each coastline. Countries are not allowed to fish territorial waters of other nations without permission. In 1982, a larger exclusive economic zone of 200 miles was established along each nation’s coastline.

Each nation has exclusive rights over all marine resources discovered within these zones, including fishing and oil extraction. The rest of the ocean is classified as international waters, meaning all nations have the freedom to use them.

Many countries now establish restrictions on the amount of fish that can be harvested within their waters. In the United States, annual catch limits have been established at levels lower than the maximum sustainable yield, meaning fish stocks are able to recover each year. These limits have been enforced by the National Oceanic and Atmospheric Administration (NOAA) since 2012.

Fully-protected marine reserves, where no living organisms can be legally harvested, have also been established to protect areas especially high in biodiversity. The Great Barrier Reef Marine Park is the largest marine reserve.

The Marine Mammal Protection Act was passed in 1972 and banned the taking and importing of marine mammals and products of marine mammals in the United States. This required fishing fleets to modify their gear with devices that allow mammals and other bycatch to escape.

Aquaculture As the limits of wild seafood harvesting have become increasingly clear, industries are now beginning use aquaculture; the process of farming aquatic organisms.

Most aquaculture operations work by taking eggs or immature fish and raising them in long, rectangular nets called fish pens. Feed and other supplements are added to the top of the pen. Wastes drop out the bottom of the pen to the sea floor. These operations are vulnerable to many of the same issues as large animal farms, including antibiotic overuse and manure.

Fish farming can be combined with hydroponics to create aquaponics. Aquaponics uses waste water from fish farming as a source of nutrients, as it is circulated through the plant roots.

TRADE-OFFS Aquaculture Advantages Disadvantages High efficiency Needs large inputs of land, feed, and water High yield in small volume of water Large waste output Can destroy mangrove forests and estuaries Can reduce overharvesting of fisheries Figure 12.18 Advantages and disadvantages of aquaculture. Question: Which single advantage and which single disadvantage do you think are the most important? Why? Uses grain to feed some species Low fuel use Dense populations vulnerable to disease High profits Fig. 12-18, p. 293

Deep sea aquaculture cage Fish farming in cage Trawler fishing Sonar Spotter airplane Purse-seine fishing Drift-net fishing Float Buoy Fish caught by gills Long line fishing lines with hooks Figure 11.7 Major commercial fishing methods used to harvest various marine species. These methods have become so effective that many fish species have become commercially extinct. Deep sea aquaculture cage Stepped Art Fig. 11-7, p. 256

Consumer Labels Any fish labeled as farmed was raised in a aquaculture or aquaponics facility. Wild caught fish is just that – it was caught from a body of water.

MSC Certification is a label attached to any seafood that follows sustainable fishing practices, as established the Marine Stewardship Council.

The Monterey Bay Aquarium has developed a Seafood Watch program that rates different types of fish based on whether they are overfished, or if their farming harms the environment.