Population dynamics of fisheries
It is the basis for understanding changing fishery patterns and issues such as habitat destruction, predation and optimal harvesting rates.
Overpopulation may indicate any case in which the population of any species of animal may exceed the carrying capacity of its ecological niche.
Virtual population analysis (VPA) is a cohort modeling technique commonly used in fisheries science for reconstructing historical fish numbers at age using information on death of individuals each year.
More specifically MVP is the smallest possible size at which a biological population can exist without facing extinction from natural disasters or demographic, environmental, or genetic stochasticity.
As a reference standard, MVP is usually given with a population survival probability of somewhere between ninety and ninety-five percent and calculated for between one hundred and one thousand years into the future.
In population ecology and economics, the maximum sustainable yield or MSY is, theoretically, the largest catch that can be taken from a fishery stock over an indefinite period.
Once it reaches a foothold population it will go through a rapid growth rate that will start to level off once the species approaches carrying capacity.
The idea of maximum sustained yield is to decrease population density to the point of highest growth rate possible.
[12] This fraction differs among populations depending on the life history of the species and the age-specific selectivity of the fishing method.
The size of fish populations can fluctuate by orders of magnitude over time, and five to 10-fold variations in abundance are usual.
Annual fluctuations often seem random, and recruitment success often has a poor relationship to adult stock levels and fishing effort.
[18] Myers solved the problem "by assembling a large base of stock data and developing a complex mathematical model to sort it out.
A current operational model used by some fisheries for predicting acceptable levels is the Harvest Control Rule (HCR).
[23] A metapopulation generally consists of several distinct populations together with areas of suitable habitat which are currently unoccupied.
Often fish in younger age class structures have very low numbers because they were small enough to slip through the sampling nets, and may in fact have a very healthy population.
There are a number of factors which influence population change such as availability of food, predators, diseases and climate.
Trophic cascades may also be important for understanding the effects of removing top predators from food webs, as humans have done in many places through hunting and fishing activities.
An extension to these are the competitive Lotka–Volterra equations, which provide a simple model of the population dynamics of species competing for some common resource.
In the 1930s Alexander Nicholson and Victor Bailey developed a model to describe the population dynamics of a coupled predator–prey system.
According to the authors of the alternative view, the data show that true interactions in nature are so far from the Lotka–Volterra extreme on the interference spectrum that the model can simply be discounted as wrong.
