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Fish stocks are subpopulations of a particular species of fish, for which intrinsic parameters (growth, recruitment, mortality and fishing mortality) are the only significant factors in determining population dynamics, while extrinsic factors (immigration and emigration) are considered to be insignificant.
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The stock concept
All species have geographic limits to their distribution, which are determined by their tolerance to environmental conditions, and their ability to compete successfully with other species. In marine environments this may be less evident than on land because there are fewer topographical 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 genetic differences, morphological 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 which aims to identify these subpopulations, based on a number of techniques.
Straddling stock
The United Nations defines straddling stocks as "stocks of fish such as pollock, which migrate between, or occur in both, the economic exclusion zone of one or more states and the high seas.1
Straddling stocks are usually 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, herring, whiting, mackerel and redfish, There are, however, a few demersal species that are straddling, such as the Greenland halibut migrates in feeding/spawning migrations to Greenland in the west and to the Faeroes in the east.2
Notes
References
- Begg, G.A., Friedland, K.D. & Pearce, J.B. (1999) Stock identification and its role in stock assessment and fisheries management: an overview. Fisheries Research 43:1-8
- Booke, H.E. (1999) The stock concept revisited: perspectives on its history in fisheries. Fisheries Research 43:9-11
- S.X. Cadrin, K.D. Friedland, J.R. Waldman. (2004) Stock Identification Methods : Applications in Fishery Science. ISBN 0-12-154351-X
See also
- Lake Pohjalampi (in Finland)
- Overfishing
External links
- Identification of stocks of horse macekerel, Trachurus trachurus
- Identification of stocks of herring, Clupea harengus
- FAO Fisheries Department and its SOFIA report addressing fish stocks
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- This page was last modified on 15 November 2008, at 05:54.
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