Fish stock
Fish stocks are subpopulation
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

s of a particular species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, for which intrinsic parameters (growth, recruitment, mortality and fishing mortality) are the only significant factors in determining population dynamics
Population dynamics
Population dynamics is the branch of life sciences that studies short-term and long-term changes in the size and age composition of populations, and the biological and environmental processes influencing those changes...

, while extrinsic factors (immigration and emigration) are considered to be insignificant.

The stock concept

All species have geographic limits to their distribution, which are determined by their tolerance
Physiological tolerance
Physiological tolerance or drug tolerance is commonly encountered in pharmacology, when a subject's reaction to a drug is reduced at a later time even though the dose or concentration at the effect site is the same. This means that larger doses are required to achieve the same effect...

 to environment
Natural environment
The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....

al conditions, and their ability to compete
Competition is a contest between individuals, groups, animals, etc. for territory, a niche, or a location of resources. It arises whenever two and only two strive for a goal which cannot be shared. Competition occurs naturally between living organisms which co-exist in the same environment. For...

 successfully with other species. In marine
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

 environments this may be less evident than on land because there are fewer topographical
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...

 boundaries, however, discontinuities still exist, produced for example by mesoscale and sub-mesoscale circulations that minimize long-distance dispersal of fish larvae .

For fishes, it is rare for an individual to reproduce randomly with all other individuals of that species within its biological range. There is a tendency to form a structured series of discrete populations which have a degree of reproductive isolation from each other in space, in time, or in both. This isolation is reflected in the development between sub-populations of gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

tic differences, morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 variations and exposure to different chemical regimes and parasitic species. Sub-populations also respond to fishing in such a way that fishing on one population appears to have no effect on the population dynamics of a neighbouring population.

The currently accepted definition of a stock in fisheries science, is that of Begg et al. (1999), “…[a “stock”] describes characteristics of semi-discrete groups of fish with some definable attributes which are of interest to fishery managers.”.

Stock identification is a field of fisheries science
Fisheries science
Fisheries science is the academic discipline of managing and understanding fisheries. It is a multidisciplinary science, which draws on the disciplines of oceanography, marine biology, marine conservation, ecology, population dynamics, economics and management to attempt to provide an integrated...

 which aims to identify these subpopulations, based on a number of techniques.

Straddling stock

The United Nations
United Nations
The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

 defines straddling stocks as "stocks of fish such as pollock
Pollock is the common name used for either of the two species of marine fish in the Pollachius genus. Both P. pollachius and P. virens are commonly referred to as pollock. Other names for P...

, which migrate between, or occur in both, the economic exclusion zone (EEZ) of one or more states and the high seas". Sovereign responsibility must be worked out in collaboration with neighbouring coastal states and fishing entities. Usually this is done through the medium of an intergovernmental regional organisation set up for the purpose of coordinating the management
Straddling Fish Stocks Agreement
The Straddling Fish Stocks Agreement was created by the United Nations to enhance the cooperative management of fisheries resources that span wide areas, and are of economic and environmental concern to a number of nations.The full name of the agreement is:...

 of that stock.

Straddling stocks are usually pelagic
Pelagic fish
Pelagic fish live near the surface or in the water column of coastal, ocean and lake waters, but not on the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and reef fish which are associated with coral reefs.The marine pelagic...

, rather than demersal. Demersal species move less than pelagic species, since they tend to relate to bottom topography. Pelagic species are more mobile, their movements influenced by ocean temperatures and the availability of zooplankton as food. Example pelagic fish are capelin
The capelin or caplin, Mallotus villosus, is a small forage fish of the smelt family found in the Atlantic and Arctic oceans. In summer, it grazes on dense swarms of plankton at the edge of the ice shelf. Larger capelin also eat a great deal of krill and other crustaceans...

, herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...

, whiting
Whiting is the name of several species of fish:*Merlangius merlangus, the original species to receive the name; a common food fish of the cod family found in the northeastern Atlantic Ocean around Europe and the Mediterranean regions...

, mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...

 and redfish
Redfish is a common name for several species of fish. It is most commonly applied to members of the deep-sea genus Sebastes, or the reef dwelling snappers, Lutjanus. It is also applied to the slimeheads or roughies , and the alfonsinos ....

, There are, however, a few demersal species that are straddling, such as the Greenland halibut
Greenland halibut
The Greenland halibut or Greenland turbot belongs to the Pleuronectidae family , and is the only species of the genus Reinhardtius. It is a deepwater fish distributed from 200 to 1600 m but has been caught at depths more than...

 migrates in feeding/spawning migrations to Greenland in the west and to the Faeroes in the east.

Straddling stock can be compared with transboundary stock. Straddling stock range both within an EEZ as well as in the high seas. Transboundary stock range in the EEZs of at least two countries. A stock can be both transboundary and straddling.

Stock Assessment

In fisheries science
Fisheries science
Fisheries science is the academic discipline of managing and understanding fisheries. It is a multidisciplinary science, which draws on the disciplines of oceanography, marine biology, marine conservation, ecology, population dynamics, economics and management to attempt to provide an integrated...

 and ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

, stock assessment
Stock assessment
Stock assessments provide fisheries managers with the information that is used in the regulation of a fish stock. Biological and fisheries data are collected in a stock assessment.A wide array of biological data may be collected for an assessment...

 is an important tool in fisheries management
Fisheries management
Fisheries management draws on fisheries science in order to find ways to protect fishery resources so sustainable exploitation is possible. Modern fisheries management is often referred to as a governmental system of appropriate management rules based on defined objectives and a mix of management...


In particular, to ensure continued, healthy, fish stocks, measurements of the Spawning Stock Biomass
Biomass (ecology)
Biomass, in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms,...

 (the stock population capable of reproducing) allows sensible conservation
Conservation biology
Conservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...

 strategies to be developed and maintained through the application of sustainable fishing quotas
Individual fishing quota
Individual fishing quotas also known as "individual transferable quotas" are one kind of catch share, a means by which many governments regulate fishing. The regulator sets a species-specific total allowable catch , typically by weight and for a given time period. A dedicated portion of the TAC,...


External links

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