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26-28 May 2009 Dr. Mala Supongpan

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Recruitment

Growth

Natural DeathsDisease

EmigrationImmigration

Recruitment Usable StockGrowth

Natural DeathsDisease

EmigrationImmigration

Yields Dynamics of fish stock Fishing mortality=F


FMGR

R = Recruitment G = GrowthM =Natural mortalityF = Fishing mortality

Can be controlled?

HOW?




Yield against effort CPUE against effort

Holistic methods

Analytical methods



Catches, Species and Sizes composition

Abundance

Biomass estimation

Analytical methods and Holistic methods

Parameter estimation (recruitment, growth, mortality-

natural

mortality, fishing mortality and total mortality)

Catch and effort data from statistic record (time

series)

Population size and catchability

Using catch per unit effort to find original population

size and

catchability

The fish stock assessment needs:

26-28 May 200926-28 May 2009 Dr. Mala SupongpanDr. Mala Supongpan

Parameters for fish stock assessment

1. Length-weight

WLWLba tt ,,,,,

2. Growth parameter RWLtK ,,,, 0

3. Mortality qMFZ ,,,

And data on production

Catch and effort, production and biomass


Modal Progression Analysis

26-28 May 200926-28 May 2009 Dr. Mala SupongpanDr. Mala Supongpan



1. Estimation of initial population size and catchability coefficient from the fishing success to catch or effort

0N Original population size catchability q

For virgin stock or limited data

Leslie’s method tt

t qKqNf

C 0

tt

t qEqNf

C )ln(ln 0DeLury’s method

Cumulative catch+

Cumulative effort+

Z=M+FZ=M+qfF=qf

(Roughly virgin stock size)


2. Estimation of Z using CPUE data

ZtCPUE

tCPUE

tt

)2(

)1(ln

12

1

3. Natural mortality estimation

0N

NeS tM

When no fishing

)ln(ln0N

NSM t

4. Fishing mortality estimation

F=Z-M

Dr. Mala Supongpan26-28 May 2009

Estimation of total mortality (Z) 1. CPUE data

2. Catch curve based on length composition data 3. Cumulative catch curve based on length composition data 4. ’Beverton and Holt s Z equation 5. Plot Z on effort

1. Estimate Z from CPUE daaa ))12((

12 * ttZtt eNN

ZN

N

tt t

t

2

1ln12

1

tqNtCPUE )(

)2(

)1(

2

1

2

1

tCPUE

tCPUE

qN

qN

N

N

t

t

t

t

ZtCPUE

tCPUE

tt

)2(

)1(ln

12

1

From above equations, then gives:

*


Plot Z against effort to estimate F and M

Z = M + q*f F = Z - M


B = CPUE * A /a*X1

B = Biomass (tons/ km2)

A = total area (km2) (101,384 km2)

a = Swept Area = D*h*X2

{ D= (V*t) = 2.5*1} h ( head rope) (= 39 m) X2 = 0.5

a = (2.5*1.852) * (0.039*0.5) = 0.090285

X1 = 0.5

X2 = 0.5

Biomass estimation


Swept area to estimate biomass



Survey strata by depth


aMBYmax

Sustainable yield estimation

MBY 5.0max

ZBY 5.0max

)(5.0max MBYY

Virgin biomass

For conservation, a- should be=0.3

B

ZB = (F+M)B and the catch Y = FB

MBY 3.0max


Definition

Catchability ( ): A fraction of a fish stock

which is caught by a defined unit of the fishing effort.

When the unit is small enough that it catches only

a small part of the stock-0.01 or less-it can be used

As an instantaneous rate in computating population

change. Also called catchability coeffifient.

q


Availability:

The fraction of a fish population which lives

in regions where it is susceptible to fishing

during a given fishing season. This fraction

receives recruits from or become mingled with

the non-available part of the stock at other seasons,

or in other years.


Catch per unit of effort (CPUE):

The catch of fish, in number or in weight,

taken by a defined unit of fishing effort.

Also called Catch per effort, fishing success,

availability.


Biomass:

The weight of a fish stock, or of some defined

portion of it.

Fishing effort:

The total fishing gear in use for a specified period

of time. When two or more kinds of gear are used,

they must be adjusted to some standard type.


References

Gulland, J.A. 1983. Fish stock assessment.

(FAO/Wiley series on food and agriculture; v. 1),

223 pp.

Ricker, W.E. 1975. Computation and interpretation

of biological statistics of fish populations,

pp.151-155.


Exercises 1 and 2

Documents

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