Fish stocks aresubpopulations of a particularspecies offish, for which intrinsic parameters (growth, recruitment, mortality and fishing mortality) are traditionally regarded as the significant factors determining thestock's population dynamics, while extrinsic factors (immigration and emigration) are traditionally ignored. Stocks fished within biologically sustainable levels decreased from 90% in 1974 to 62.3% in 2021.[1]
All species have geographic limits to their distribution, which are determined by theirtolerance toenvironmental conditions, and their ability tocompete successfully with other species. Inmarine environments this may be less evident than on land because there are fewertopographical boundaries, however, discontinuities still exist, produced for example by mesoscale and sub-mesoscale circulations that minimize long-distance dispersal of fish larvae.
For fish, 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 ofgenetic differences,morphological variations and exposure to differentchemical regimes andparasitic 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 offisheries science which aims to identify these subpopulations, based on a number of techniques.This concept is applied insustainable development goal 14 where target 14.4 is measured a fish stock sustainability indicator 14.4.1.[2]
TheUnited Nations defines straddling stocks as "stocks of fish such aspollock, which migrate between, or occur in both, theeconomic exclusion zones (EEZ) of one or more states and thehigh seas".[3] Sovereign responsibility must be worked out in collaboration with neighbouringcoastal states and fishing entities. Usually this is done through the medium of an intergovernmental regional organisation set up for the purpose ofcoordinating the management of that stock.
Straddling stocks are usuallypelagic, rather thandemersal. 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 arecapelin,herring,whiting,mackerel andredfish, There are, however, a few demersal species that are straddling, such as theGreenland halibut migrates in feeding/spawning migrations to Greenland in the west and to theFaeroes in the east.[4]
Straddling stock can be compared withtransboundary stock. Straddling stock range both within anEEZ 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.[5]
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Infisheries science andecology,stock assessment is an important tool infisheries management.
In particular, to ensure continued, healthy, fish stocks, measurements of theSpawning StockBiomass (the stock population capable of reproducing) allows sensibleconservation strategies to be developed and maintained through the application of sustainablefishing quotas.[6]
TheWorld Wildlife Fund and theZoological Society of London jointly issued their "Living Blue Planet Report" on 16 September 2015 which states that there was a dramatic fall of 74% in world-wide stocks of the important scombridae fish such asmackerel,tuna andbonitos between 1970 and 2010, and the global overall "population sizes of mammals, birds, reptiles, amphibians and fish fell by half on average in just 40 years."[7] It is hoped that global efforts like the United NationsSustainable Development Goal 14 meets its targets aimed at reversing these trends.[8]
The UNFood and Agriculure Organization found that stocks fished within biologically sustainable levels decreased from 90% in 1974 to 62.3% in 2021..[9]
The stocks for individual marine species can "boom and bust" in linked and compensatory ways. For example, inbillfishlongline fisheries, the Atlantic catch of blue marlin declined in the 1960s. This was accompanied by an increase in sailfish catch. The sailfish catch then declined from the end of the 1970s to the end of the 1980s, compensated by an increase in swordfish catch. As a result, the overall billfish catch remained fairly stable. AtGeorges Bank, a decline in cod during the 1960s was accompanied by a rise in flatfish, and more recently, with the collapse of the predatory Atlantic cod, lobster catches inMaine have boomed.[10]
This article incorporates text from afree content work. Licensed under CC BY-SA 3.0 IGO (license statement/permission). Text taken fromIn brief, The State of World Fisheries and Aquaculture, 2018, FAO, FAO.
