virtual population analysis
- virtual population analysis
-
A mathematical modelling technique used in
stock assessment, whereby the number of
fish in each
cohort is estimated from numbers in the next oldest or next youngest
age group, adjusted for the changes due to fishing and
natural mortality; see also
cohort analysis.
An analysis of the catches from a given
year class over its life in the fishery. If 10
fish from the 1968
year class were caught each year for 10 successive years from 1970 to 1979 (age 2 to
age 11), then 100
fish would have been caught from the 1968
year class during its life in the fishery. Since 10
fish were caught during 1979, then 10
fish must have been alive at the beginning of that year. At the beginning of 1978, there must have been at least 20
fish alive because 10 were caught in 1978 and 10 more were caught in 1979. By working backward year by year, one can be virtually certain that at least 100
fish were alive at the beginning of 1970. A
virtual population analysis goes a step further and calculates the number of
fish that must have been alive if some
fish also died from causes other than fishing.
For example, if in addition to the 10
fish caught per year in the fishery, the instantaneous
natural mortality rate was also known then a
virtual population analysis calculates the number that must have been alive each year to produce a catch of 10
fish each year plus those that died from natural causes. If one knows the
fishing mortality rate during the last year for which catch data are available (in this case, 1979), then the exact abundance of the
year class can be determined in each and every year. Even when an approximate
fishing mortality rate is used in the last year (1979), a precise estimate of the abundance can usually be determined for the
stock in years prior to the most recent one or two (e.g., 1970-1977 in the example). Accuracy depends on the rate of
population decline and the correctness of the starting value of the
fishing mortality rate (in the most recent year). This technique is used extensively in
fishery assessments since the conditions for its use are so common; many fisheries are heavily exploited, the annual catches for a
year class can generally be easily determined, and the
natural mortality rate is known within a fairly small range and is low compared with the
fishing mortality rate.
Fisheries — dictionary.
Aardward.
2004.
Look at other dictionaries:
Virtual population analysis — (VPA) is a modeling technique commonly used in fisheries science for reconstructing historical fish numbers at age using information on death of individuals each year. This death is usually partitioned into catch by fisheries and natural… … Wikipedia
virtual population analysis — an algorithm for computing historical fishing mortality rates and stock sizes by age or length, based on data on catches, natural mortality, and certain assumptions about mortality for the last year and last age group. Essentially reconstructs… … Dictionary of ichthyology
Population dynamics of fisheries — A fishery is an area with an associated fish or aquatic population which is harvested for its commercial or recreational value. Fisheries can be wild or farmed. Population dynamics describes the ways in which a given population grows and shrinks… … Wikipedia
cohort analysis — virtual population analysis (an algorithm for computing historical fishing mortality rates and stock sizes by age or length, based on data on catches, natural mortality, and certain assumptions about mortality for the last year and last age group … Dictionary of ichthyology
Population transfer — is the movement of a large group of people from one region to another by state policy or international authority, most frequently on the basis of ethnicity or religion. Banishment or exile is a similar process, but is forcibly applied to… … Wikipedia
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. Population dynamics deals with the way… … Wikipedia
Virtual Tribunal of the Special Court for Sierra Leone — About the Virtual Tribunal of the Special Court for Sierra Leone [http://www.ocf.berkeley.edu/ changmin/] = Professor David Cohen, Director of the Berkeley War Crimes Studies Center (WCSC), and Professor Ruzena Bajcsy of the Department of… … Wikipedia
Contents of the United States diplomatic cables leak (analysis of individual leaders) — Contents 1 Afghanistan 2 Albania 3 Argentina 4 Armenia … Wikipedia
VPA — virtual population analysis … Dictionary of ichthyology
Fisheries glossary — This is a glossary of terms used in fisheries, fisheries management and fisheries science. A * Abundance is a measure of how many fish are in a population or a fishing ground. See relative abundance and absolute abundance.* Acoustic survey a… … Wikipedia
