Training course in fish stock assessment and fisheries management
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fish stock assessment and fisheries management National Institute of Oceanography and Fisheries Fish population Dynamics Lab 10-14 November, 2013ns
description
Training course in fish stock assessment and fisheries management. National Institute of Oceanography and Fisheries Fish population Dynamics Lab 10-14 November, 2013 ns. Su rplus Production models (Biomass Dynamic Models ). Prof. Dr. Sahar Fahmy Mehanna Head of fish population dynamics lab - PowerPoint PPT Presentation
Transcript of Training course in fish stock assessment and fisheries management
Training course in fish stock assessment and fisheries
managementNational Institute of Oceanography and Fisheries
Fish population Dynamics Lab
10-14 November, 2013ns
Surplus Production models(Biomass Dynamic Models)Prof. Dr. Sahar Fahmy Mehanna
Head of fish population dynamics lab
National Institute of Oceanography and Fisheries
Surplus Production models
• The level of the biomass of a population at time t+1 will depend to different phenomena.
• While recruitment and individual growth contribute to its increase
• mortality due to both natural causes and removals by fishing activity will contribute to its decline
Surplus Production models
Bt+1 = Bt + Recruitment + Growth effects - Natural Mortality – CatchWhen there is no fishing, the combination of recruitment and growth is called Production
Bt+1 = Bt + Production (P) - Natural Mortality (M)
Surplus Production modelsIn the case P>M, the population will grow. The “Surplus Production” is defined as the increased amount of the population biomass in the absence of fishing or the amount of catch that can be harvested keeping biomass constant. Bt+1 = Bt + Surplus Production – Catch in the case Catch > Surplus Production, the biomass will decrease.
Surplus Production models
Data requirements • In general use data on catch and effort• Equilibrium• Problems with quantification of
effective effort• Multispecies-multigear fisheries
(target, spatial and temporal changes…)
Some definitionsCatch= landed fraction + discards + undefined incidental deathsEffort: Fishing effort (f) is the labour, vessels, skill and technology used in catching fish.One unit of fishing effort removes a certain constant fraction of a stockthis effort is directly related to the fishing mortality (F) through a constant called catchability coefficient (q)Is catchability constant along time?
Some definitions
F = qf
q is the fraction of F produced by a unit of effort
hence q may be a different value depending on
which unit of effort is used!
The choice of a suitable unit of effort
Catch
Annual catches (avoidance of errors) due to:
• Under-reporting (critical for management with TAC’s)
• Discard at sea (individuals under legal size)
• Not quantified incidental deaths (fish that is able to escape but successively will die due to bad conditions)
Effort
• Definition of effort for such gear (trawlers, gill nets, hooks, traps)
• Partitioning among species and fisheries• Standardization by vessels characteristics• Technological improvements along time
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The more classical relationship between stock biomass and surplus production
In general, there is no available information on Biomass, but on an abundance index as CPUE (Catch per unit of effort).
The most popular versions of production models use data of catch and fishing effort in order to define which is the yield that is likely to be produced at different levels of exploitation.
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Fishing effort
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PRODUCTION MODEL
SCHAEFER (1954)
Bt+1=Bt + rBt (1-Bt/K)-Ct - t+1
FOX (1970)
Bt+1=Bt + rBt (1-(lnBt/LnK))-Ct - t+1
PELLA & TOMLINSON (1969)
Bt+1=Bt + rBt (1-Bt/K)p - Ct - t+1
B=biomass
r= intrinsic rate of population growth
K= Virgin stock biomass ( “carrying capacity”)
CW = catch in weigth
P= shape parameter
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MSYMSY
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Sustainable means the value obtained assuming f remains unchanged for a certain number of years (equilibrium)
The population adapt to the different levels of effort and reach a new equilibrium under each exploitation rate. In this case, a direct relationship between fishing effort and biomass in equilibrium (and hence with catch) can be defined
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Equilibrium concept
Recruitment (annual contribute of the new generations or cohorts) of similar entity
Survival rates unchanged along the lifespan of the species (for all the observed cohorts)
In consequence, demographic structure of the population remains similar along time
USE OF FISHERIES DEPENDENT DATADATA ON DEMOGRAPHIC STRUCTURE OF THE CATCHES NOT AVAILABLE
ONLY CATCH AND EFFORT DATA AND STOCKS NOT IN EQUILIBRIUM Penaeus kerathurus
EFFORT CATCH1990 17760.00 3454.4651991 14640.00 3293.4021992 11760.00 1956.6141993 10320.00 1389.9321994 10800.00 1652.7741995 12000.00 3171.5091996 12560.00 1699.1051997 12640.00 2467.7961998 12560.00 5066.2931999 12160.00 3322.6022000 11760.00 6577.8582001 11360.00 5210.5652002 11280.00 3406.5282003 11286.67 6065.7232004 11260.00 4915.0342005 11200.00 6458.907
ASPIC 5.0 (Prager, 1994, 2005) A Stock-Production model Incorporating Covariates
• non-equilibrium • continuous-time • observation-error estimator
• dBt/dt = (r-Ft)Bt-(r/K)Bt2
MAIN OUTPUTS OF ASPIC
FITTING MODELS
FORECASTING
TARGET AND LIMIT REFERENCE POINTS
ASPIC (Prager, 1994, 2005)
Reference Points derived from the Threshold Biomass approach
T is a threshold value of Biomass that is supposed to be a lower limit below which depensation mechanisms can be triggered
Fmax is the level of F that produces the maximum Yield
Ymax is the maximum yield potentially obtained
FT (threshold) is the value of F corresponding to BT
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TOTAL
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TOTAL
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TOTAL
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TOTAL
Overall Maximum Sustainable Yield can be risky for the less productive species
Multispecies Surplus production models
Y
Fishing effort
