Tuna penning

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Tuna penning is a practice used in marine aquaculture, in which smaller tuna are caught off shore and moved back to large, in-water enclosures. The pens are typically located in the relatively shallow waters of sheltered areas, such as bays or coves. [1] Tuna penning is primarily used for Atlantic Bluefin Tuna (ABT), a highly profitable stock for the global fish market. The tuna caught for penning are typically caught between May and July by purse-seine vessels, and then transported back to pens, where they are fattened until October–January before being frozen and shipped out. While in the pens, the tuna are fed primarily fresh fish, such as sardines, squid, and mackerel. In the past decade, tuna penning has become a large sector within the fish aquaculture industry, and takes place primarily in the Mediterranean. [2] In 2010, ABT constituted 8% of global fish exports, the majority of which was shipped to Japan. [2] Tuna penning is regulated by the International Commission for the Conservation of Atlantic Tunas (ICCAT), and each farm is required to register both the number of tuna it has and the total capacity of the farm. [2]

Contents

Geography

Large scale tuna penning production began in the 1980s off the coast of Canada. In the 1990s, the practice was moved over to Spain, and quickly spread through the Mediterranean. In the Mediterranean, the main producers are Italy, Malta, and Spain. Other tuna penning locations include Turkey, Croatia, Cyprus, Greece, Tunisia, and Libya. As of a 2010 census, there are over 60 tuna farms in the Mediterranean, with a total capacity of nearly 61,000 tons of tuna. [2]

Environmental impacts

Tuna penning is faced with a multitude of controversy regarding the impact it has on the local marine environment. The largest concern in the Mediterranean is the local eutrophication of a naturally oligotrophic environment. Because the Mediterranean Sea is a naturally oligotrophic environment, the majority organisms living in the marine ecosystems of that area are not equipped to handle high levels of nutrients. [3] The rapid influx of nutrients that occurs from fish farming has adverse effects on the surrounding ecosystems for this reason. A large contribution of this eutrophication is an excess in feed used for the cages. An estimated 25% of fish feed is actually consumed by Tuna, with the remaining 75% sinking to the sea floor to decompose. This feed is high in organic material and nutrients that then get released into the surrounding environments. [2]

Water pollution

Tuna penning causes a number of changes in the physical water qualities of surrounding areas. Areas surrounding tuna farms typically see a decrease in dissolved oxygen. This is a direct result of increased aerobic respiration from the high density of tuna present and from the increased decomposition of excess fish feed. [1] Dissolved oxygen is important for the metabolic processes of many living organisms. [3] A decrease in dissolve oxygen makes for more adverse conditions for many of the naturally occurring species in the Mediterranean, and is correlated to a direct decrease in species richness in areas surrounding tuna farms. [2] Tuna penning also increases the concentration of dissolved nutrients in the surround water. This can cause an increase in primary productivity, resulting in algal blooms. This may increase turbidity in the water, preventing the sea floor organisms from receiving sunlight. [1] Some algal blooms can be damaging to local marine plant life, causing leaf fragility and death. [1] Overall, eutrophication, increased turbidity, and decreased dissolved oxygen make it difficult for organisms designed to live in an oligotrophic environment to survive successfully. This caused a decline in local biodiversity and can cause a collapse in the ecosystem. [2]

Sediment deposition

Tuna penning causes a large increase of biodeposition on the surrounding sea floor. This increase is largely due to the accumulation of excess fish feed that sinks down to the bottom. [2] As a result, the sediment composition of the benthic communities surrounding tuna pens is shifted, with increased organic material and nutrient concentrations. The increased amount of organic material leads to increased aerobic respiration, causing a decrease in the oxygen content of the benthic sediment. [3] Additionally, the average grain size of the sediment becomes significantly smaller, which can lead to the smothering of plant life. [1] These shifts in the benthic community have been linked to decreased biodiversity in areas surrounding tuna pens. [3]

There have been some suggestions of moving tuna pens farther offshore as a method of mitigating the sediment deposition and water pollution that occurs in shallower waters. Deeper water tends to have stronger ocean currents and water movement. By moving towards offshore aquaculture, excess nutrients and biodeposition could be swept away by the increased water flow. It would also allow for an increase in mixing of the water column, which could potentially mitigate the decrease in dissolved oxygen around the area.

Related Research Articles

Aquaculture Farming of aquatic organisms

Aquaculture, also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants. Aquaculture involves cultivating freshwater, brackish water and saltwater populations under controlled or semi-natural conditions, and can be contrasted with commercial fishing, which is the harvesting of wild fish. Mariculture, commonly known as marine farming, refers specifically to aquaculture practiced in seawater habitats and lagoons, opposed to in freshwater aquaculture. Pisciculture is a type of aquaculture that consists of the culturing of fish to obtain fish and fish products as food.

Mariculture Cultivation of marine organisms in the open ocean

Mariculture or marine farming is a specialized branch of aquaculture involving the cultivation of marine organisms for food and other animal products, in enclosed sections of the open ocean, fish farms built on littoral waters, or in artificial tanks, ponds or raceways which are filled with seawater. An example of the latter is the farming of marine fish, including finfish and shellfish like prawns, or oysters and seaweed in saltwater ponds. Non-food products produced by mariculture include: fish meal, nutrient agar, jewellery, and cosmetics.

Plankton Organisms that are in the water column and are incapable of swimming against a current

Plankton are the diverse collection of organisms found in water that are unable to propel themselves against a current. The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as bivalves, fish and whales.

Algal bloom Rapid increase or accumulation in the population of planktonic algae

An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term algae encompasses many types of aquatic photosynthetic organisms, both macroscopic multicellular organisms like seaweed and microscopic unicellular organisms like cyanobacteria. Algal bloom commonly refers to the rapid growth of microscopic unicellular algae, not macroscopic algae. An example of a macroscopic algal bloom is a kelp forest.

Eutrophication Excessive plant growth in response to excess nutrient availability

Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytoplankton productivity". Water bodies with very low nutrient levels are termed oligotrophic and those with moderate nutrient levels are termed mesotrophic. Advanced eutrophication may also be referred to as dystrophic and hypertrophic conditions. Eutrophication in freshwater ecosystems is almost always caused by excess phosphorus while in marine systems nitrogen and phosphorus may both be important in different locations.

Dead zone (ecology) Low-oxygen areas in oceans and large lakes caused by nutrient and fertilizer pollution

Dead zones are hypoxic (low-oxygen) areas in the world's oceans and large lakes. Hypoxia occurs when dissolved oxygen (DO) concentration falls to or below 2 ml of O2/liter. When a body of water experiences hypoxic conditions, aquatic flora and fauna begin to change behavior in order to reach sections of water with higher oxygen levels. Once DO declines below 0.5 ml O2/liter in a body of water, mass mortality occurs. With such low concentration of DO, these bodies of water fail to support the aquatic life living there. Historically, many of these sites were naturally occurring. However, in the 1970s, oceanographers began noting increased instances and expanses of dead zones. These occur near inhabited coastlines, where aquatic life is most concentrated.

Bioturbation Reworking of soils and sediments by organisms.

Bioturbation is defined as the reworking of soils and sediments by animals or plants. These include burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a primary driver of biodiversity. The formal study of bioturbation began in the 1800s by Charles Darwin experimenting in his garden. The disruption of aquatic sediments and terrestrial soils through bioturbating activities provides significant ecosystem services. These include the alteration of nutrients in aquatic sediment and overlying water, shelter to other species in the form of burrows in terrestrial and water ecosystems, and soil production on land.

Lake ecosystem Type of ecosystem

A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of lentic ecosystems, which include ponds, lakes and wetlands, and much of this article applies to lentic ecosystems in general. Lentic ecosystems can be compared with lotic ecosystems, which involve flowing terrestrial waters such as rivers and streams. Together, these two ecosystems are examples of freshwater ecosystems.

Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen and are conditions of hypoxia. The US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre. This condition is generally found in areas that have restricted water exchange.

Southern bluefin tuna Species of fish

The southern bluefin tuna is a tuna of the family Scombridae found in open southern Hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S. At up to 2.5 metres and weighing up to 260 kilograms (570 lb), it is among the larger bony fishes.

Trophic state index Measure of the ability of water to sustain biological productivity

The Trophic State Index (TSI) is a classification system designed to rate water bodies based on the amount of biological productivity they sustain. Although the term "trophic index" is commonly applied to lakes, any surface water body may be indexed.

This is a glossary of terms used in fisheries, fisheries management and fisheries science.

Ocean deoxygenation Reduction of the oxygen content of the oceans

Ocean deoxygenation is the reduction of the oxygen content of the oceans due to human activities as a consequence of anthropogenic emissions of carbon dioxide and eutrophication driven excess production. It is manifest in the increasing number of coastal and estuarine hypoxic areas, or dead zones, and the expansion of oxygen minimum zones in the world's oceans. The decrease in oxygen content of the oceans has been fairly rapid and poses a threat to all aerobic marine life, as well as to people who depend on marine life for nutrition or livelihood.

Fishing down the food web

Fishing down the food web is the process whereby fisheries in a given ecosystem, "having depleted the large predatory fish on top of the food web, turn to increasingly smaller species, finally ending up with previously spurned small fish and invertebrates".

Aquaculture in Canada

Aquaculture is the farming of fish, shellfish or aquatic plants in either fresh or saltwater, or both. The farmed animals or plants are cared for under a controlled environment to ensure optimum growth, success and profit. When they have reached an appropriate size, they are harvested, processed, and shipped to markets to be sold. Aquaculture is practiced all over the world and is extremely popular in countries such as China, where population is high and fish is a staple part of their everyday diet.

Saltwater fish Fish that live all or much of their lives in seawater

Saltwater fish, also called marine fish, are fish that live in ocean water. Saltwater fish can swim and live alone or in a large group called a school.

Saltwater aquaponics is a combination of plant cultivation and fish rearing, systems with similarities to standard aquaponics, except that it uses saltwater instead of the more commonly used freshwater. In some instances, this may be diluted saltwater. The concept is being researched as a sustainable way to eliminate the stresses that are put on local environments by conventional fish farming practices who expel wastewater into the coastal zones, all while creating complementary crops.

Human impact on marine life

Human activities affect marine life and marine habitats through overfishing, habitat loss, the introduction of invasive species, ocean pollution, ocean acidification and ocean warming. These impact marine ecosystems and food webs and may result in consequences as yet unrecognised for the biodiversity and continuation of marine life forms.

Benthic-pelagic coupling

Benthic-pelagic coupling are processes that connect the benthic zone and the pelagic zone through the exchange of energy, mass, or nutrients. These processes play a prominent role in both freshwater and marine ecosystems and are influenced by a number of chemical, biological, and physical forces that are crucial to functions from nutrient cycling to energy transfer in food webs.

Jellyfish bloom

Jellyfish blooms are substantial growths in population of species under the phyla Cnidaria and Ctenophora.

References

  1. 1 2 3 4 5 Kruzic, P.; Vjerocka, V.; Bura-Nakic, E. (2014). "Inshore capture-based tuna aquaculture impact on Posidonia oceanica meadows in the eastern part of the Adriatic Sea". Marine Pollution Bulletin. 86 (1–2): 174–185. doi:10.1016/j.marpolbul.2014.07.028. PMID   25110046.
  2. 1 2 3 4 5 6 7 8 Mangion, M.; Borg, J.; Thompson, R.; Schembri, P. (2014). "Influence of tuna penning activities on soft bottom microbenthic assemblages". Marine Pollution Bulletin. 79 (1–2): 164–174. doi:10.1016/j.marpolbul.2013.12.021. PMID   24447635.
  3. 1 2 3 4 Morata, T.; Falco, S.; Gadea, I.; Sospedra, J.; Rodilla, M. (2015). "Environmental effects of a marine fish farm of gilthead seabream (Sparus aurata) in the NW Mediterranean Sea on water column and sediment". Aquaculture Research. 46 (1): 59–74. doi:10.1111/are.12159. hdl: 10251/36706 . PMC   7159775 . PMID   32313429.
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