2. STOCK RECRUITMENT RELATIONSHIP
• Introduction
• Recruitment overfishing results in when the parent
stock is reduced to the extent that enough young fish
are not produced to compensate the stock.
• There has been a great deal of effort devoted to
determine relationship between the number of adults
and the number of recruits they produce.
• Recruitment
• The process by which a fish or shrimp of an age group
integrates itself for the first time to the exploitable
stock is known as recruitment, which is a function of
age and is a progressive event.
3. STOCK RECRUITMENT RELATIONSHIP
Recruitment conted....
• The animals added on to the population are called the
recruits.
• The concept of stock recruitment relationship is
related to the concept of surplus production.
• It is a general concept that when population becomes
smaller, the reproduce success increases.
1. Increased growth and better fecundity of a species
2. Good food supply / individual
3. Good survival of eggs and larvae due to reduced
cannibalism
4. Optimal fishing effort
4. STOCK RECRUITMENT RELATIONSHIP
• Recruitment conted....
• When the environment variables are at
optimal level, relationship between stock and
recruitment will be accurate.
5. Stochastic models possess some inherent
randomness.
The same set of parameter values and initial
conditions will lead to an ensemble of different
outputs.
There are many different ways to add
stochasticity to the same deterministic skeleton.
Stochastic models in continuous time are hard.
Gotelli provides a few results that are specific to
one way of adding stochasticity.
6.
7. BRPs are of two types, Target and Limit
Target Reference point (TRP) indicate the
desirable status of the fishery
Limit Reference points (LRP) if crossed will
cause collapse of the fishery
8. MSY is the maximum long-term average yield that can be
achieved through conscientious stewardship by controlling F
through regulating fishing effort or total catch levels.
MSY is a reference point for judging the potential of the
resource.
Other factors influence the choice of a management
objective, such as socioeconomic considerations or
conservation and ecosystem concerns for other marine life
indirectly affected by fishery harvests.
9. The methods of estimating MSY, and MSY itself, may be
controversial.
One of the major objectives of fish stock assessment is
regularisation or optimisation of effort.
Standardization of fishing effort – increasing the effort in
the long term gives highest yield.
The basic principle is smaller a population, when effort is
not put at required level, the greater will be production.
10. At optimal level of effort, the production will be maximum
for a given Fmsy.
At optimal level of effort, the production will be
maximum for a given Fmsy.
For all practical purposes, the effort should be
monitored at various levels of fishing mortality.
11. The basic principle in stock assessment models is to
provide estimates of optimum yield.
The environmental factors, economic factors are to be
taken into account for arriving at appropriate
management decisions.
When intensity of fishing is not monitored, the
population of a stock show sign of depletion and there
will be a decrease in mean length of fish and length at
minimum maturity.
12. In principle as age increases the number of survivors will be
less
In a virgin (unfished) biomass, the population is at
equilibrium
13. The population neither grows nor declines which means that
each year’s recruitment is balanced by each year losses due
to mortality.
When a stock is brought below b level, the population
grows.
The maximum surplus production is achieved when the
stock biomass is reduced to ½ of the level of B.
14. In principle, the highest yield achieved on a long term basis
for a particular effort is the Fmsy and the corresponding yield
is MSY or Maximum Sustainable Yield.
