What do salmon eat wikipedia

The expansion of mariculture can reduce pressure on wild fish, shrimps and molluscs, because they reduce their market price and by this the investments in fishing fleets. However, they can also increase the pressure due to the use of fishmeal in feed for some mariculture-species Naylor et al. Some forms of mariculture provide good quality food and the production is more efficient than that of terrestrial animals; roughly half the level of feed input per unit output is necessary CBD, [2].

Due to freshwater scarcity in many areas of the world it is expected that mariculture eventually will become the dominant form of aquaculture Wecker, [3]. The main species that are used in mariculture are indicated in Tab.

Products obtained from mariculture are not only used for food, but also as raw material for e. Despite the rapid growth of mariculture and the great potential for food production, only a small part of the world's food supply comes from mariculture. Only 1. These figures show that the potential of mariculture as a food source is still far underused. The ocean area suitable for mariculture is many times larger than the area currently used Oyinlola et al.

Several environmental problems are associated with mariculture. These problems depend on species, culture method, stocking density, feed type, husbandry practice, hydrodynamic site conditions and the sensitivity of the receiving ecosystem Troell et al. Many of these problems can be mitigated with appropriate measures. Farmers are in general aware that mariculture itself in the long run depends on good quality of the environment. Mariculture can play an important role, especially in rural areas, for food security, economic and social welfare.

In densely populated coastal areas, mariculture is in competition with other human activities for space and other resources. These other activities can for example be: fisheries, tourism , harbour operations, nature conservation and industry.

Legislation on mariculture and its enforcement vary widely in different countries around the world. No further consideration is given here to this topic. Different kinds of mariculture are presented here according to a subdivision by species type. Different types of species require different systems that have different characteristics and effects.

Only the most common systems are mentioned CBD, [2]. Growout: Larvae that have set to their substrate are grown in hanging cultures suspended from floating rafts or long lines on strings, trays, stacks or mesh bags , vertical or rack culture sticks or platforms , bottom culture shells, stones, rocks or cement slabs added to the ground , or in land-based systems CBD, [2].

Nowadays there is a trend towards hatcheries. Growout: takes place in earthen ponds, concrete raceways and tanks CBD, [2]. This includes macro- and micro algae as well as seagrasses. The major source of broodstock is wild collection. Most culture is now dependent on hatchery production of the early life stages monospores, zoospores, gametophytes, sporophytes which are attached to growing media and transferred to marine sites.

Other propagation methods involve fragmentation. Growout: Young plants are cultured by 3 different methods: suspended longline and raft , bottom cultures at the sea large rocks or artificial shapes of concrete are placed on the seabed and inland tank cultures CBD, [2].

Most species are grown from larvae or fry produced in hatcheries. Spawning is often stimulated with a hormone application.

Growout: Cage culture can be divided into inshore and offshore cages and can be fixed, floating or submerged. Inshore cages are located in protected, shallow areas with less water circulation. Offshore cages are located in deep water and open areas with less protection from storm but with better water exchange.

Nets and fish pen are located in shallow water and their edges are anchored to the bottom. A typical fish pond system consists of the following basic components: pond compartments enclosed by dikes, canals for supply and drainage of water and gates or water control structures CBD, [2].

Enhancement or Sea Ranching is mostly developed with marine finfish. Both terms refer to the deliberate release of organisms from hatcheries into the natural ecosystem. In enhancement, fry are released to restock wild populations. In sea ranching, fish are harvested from artificially enclosed areas CBD, [2]. It is also possible to co-culture different species: this will be further described in the section about mitigation. Environmental impacts depend on husbandry parameters species, culture method, feed type and the nature of the receiving environment physical, chemical, biological characteristics.

The state of the receiving ecosystem also depends on the release of waste products from other anthropogenic sources e. Eutrophication defined as nutrient enrichment mainly N and P is considered by some the most important pollution threat to marine waters Wu, [17] ; Bouwman et al.

This problem is often mentioned in the context of intensive culture of fish and shrimp, where a lot of artificial feed are used. Waste consists of uneaten feed and faeces moving down into the benthos: below fish cages in areas with low currents waste sedimentation leads to a shift in benthic populations towards pollutant-resistant species.

This effect is mostly limited to a distance of m from the mariculture facilities. Another part of the waste products consists of CO 2 , dissolved organic carbon and various soluble nutrients e.

To date, anthropogenic input of nutrients not only by mariculture have caused major changes in structure and functioning of phyto- and zooplankton, benthic and fish communities Wu, [17] ; Troell et al. For example, observations over a two-decade period show that long-term exposure to aquaculture effluents with high nutrient concentrations are a serious threat to coastal ecosystems along the whole Chinese coast, and in particular to seagrass meadows, which have largely disappeared Thomsen et al.

Areas with limited water exchange are at even greater risk. Algal blooms can shade seafloor vegetation and when they collapse their decay on the seafloor may lead to hypoxia or anoxia and hence mass mortality of benthos and fish Troell et al. The opposite of eutrophication may occur at intensive open ocean bivalve cultures: They take nutrients away from the marine foodweb. Excessive nutrient depletion limits the growth of other herbivores and phytoplankton and those that live off them.

Apart from that, bivalves filter suspended particulate matter and change it into denser particles that fall to the bottom faecal pellets. But a group of area fishermen were convinced that their salmon were special.

Working with Jon Rowley, a seafood business consultant based in the Seattle area, the fishermen introduced restaurant chefs in the Pacific Northwest to Copper River salmon, often personally walking into the kitchens and coaxing them to try a box or two. The chefs in turn spread the gospel by specifying Copper River on their menu descriptions, in effect giving the fish a brand name.

Because Copper River fishermen thought their salmon were special, they also decided to treat them accordingly by adopting more conscientious handling practices than were the industry norm.

Thea Thomas, who has fished Copper River for more than 20 years, was among those who saw the importance of maintaining quality. I hopped a ride with her for a firsthand look at how a Copper River salmon made the journey from ocean to dock. It was a rare sunny day as we motored out of mountain-rimmed Orca Inlet, with its sea otters and seals. Once out in the open Gulf of Alaska, Thomas set out a gill net as long as three football fields, hoping to intercept some inbound salmon.

After about 45 minutes, she began to retrieve the net on a tractor-wheel-sized mechanical reel mounted behind the cabin on her boat. Copper River fishermen are encouraged to pull in their nets frequently so the salmon come aboard while still alive. I'd been on salmon gillnetters before, so I had a few preconceptions of what might happen next—fish violently shaken from the net onto the deck, getting kicked around and stepped on before being tossed like so many chunks of stove wood into a plastic container, piling on top of each other by the hundreds and with no ice to keep them cold.

So I was surprised to see Thomas extract her salmon from the net individually, sever their gills so that they bled cleanly and quickly, then immediately place then in a slurry of ice chips and seawater.

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