Virtual Population Analysis
Encyclopedia
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 mortality
.
VPA is the most commonly used term to refer to cohort
reconstruction techniques used in fisheries. It is virtual in the sense that the population size is not observed or measured directly but is inferred or back-calculated to have been a certain size in the past in order to support the observed fish catches and an assumed death rate owing to non-fishery related causes.
Virtual population analysis was introduced in fish stock
assessment by Gulland in 1965 based on older work. The technique of cohort reconstruction in fish populations has been attributed to several different workers including Professor Baranov from Russia in 1918 for his development of the continuous catch equation, Professor Fry from Canada in 1949 and Drs. Beverton and Holt from the UK in 1957. Because cohort reconstruction is essentially an accounting exercise it was likely independently conceived many times.
Several different software implementations of cohort reconstruction for fish populations exist including ADAPT, which is often used in Canada and the USA, and XSA which is commonly used in Europe. The back-calculations in these implementations work the same way but they differ in the statistical methods used for "tuning" to indices of population size.
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...
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 mortality
Fish mortality
Fish mortality is a term widely used in fisheries science that denotes the loss of fish from a stock through death. The term is also commonly used in British English as a synonym for fish kill. Fish mortality can be divided into two types:...
.
VPA is the most commonly used term to refer to cohort
Cohort (statistics)
In statistics and demography, a cohort is a group of subjects who have shared a particular time together during a particular time span . Cohorts may be tracked over extended periods in a cohort study. The cohort can be modified by censoring, i.e...
reconstruction techniques used in fisheries. It is virtual in the sense that the population size is not observed or measured directly but is inferred or back-calculated to have been a certain size in the past in order to support the observed fish catches and an assumed death rate owing to non-fishery related causes.
Virtual population analysis was introduced in fish stock
Fish stock
Fish stocks are subpopulations of a particular species of fish, for which intrinsic parameters are the only significant factors in determining population dynamics, while extrinsic factors are considered to be insignificant.-The stock concept:All species have geographic limits to their...
assessment by Gulland in 1965 based on older work. The technique of cohort reconstruction in fish populations has been attributed to several different workers including Professor Baranov from Russia in 1918 for his development of the continuous catch equation, Professor Fry from Canada in 1949 and Drs. Beverton and Holt from the UK in 1957. Because cohort reconstruction is essentially an accounting exercise it was likely independently conceived many times.
Several different software implementations of cohort reconstruction for fish populations exist including ADAPT, which is often used in Canada and the USA, and XSA which is commonly used in Europe. The back-calculations in these implementations work the same way but they differ in the statistical methods used for "tuning" to indices of population size.