CERT
TRAC
Comité d'évaluation des
ressources transfrontalières
Transboundary Resources
Assessment Committee
Document de travail 2014/42
Working Paper 2014/42
Ne pas citer sans
autorisation des auteurs
Not to be cited without
permission of the authors
Surplus Production of Georges Bank Yellowtail Flounder
Estimated from 2013 VPA Model Results
Loretta O’Brien
NEFSC, Woods Hole, Ma
Georges Bank Yellowtail Flounder Diagnostic Benchmark TRAC
April 14-18, 2014
Woods Hole, Ma
Ce document est disponible sur l’Internet à :
This document is available on the Internet at :
http://www.mar.dfo-mpo.gc.ca/science/TRAC/trac.html
Introduction
• Surplus production defined as
SP = (Yield + recruitment + growth) – natural mortality
•
•
•
•
Estimate trends in SP for GB YT during 1973-2012
Apply methods of Rivard (1980) using cohort analysis
Input data from results of the 2013 VPA for YT (Legault 2013)
Method does not require assumption of ‘equilibrium’ state ;
Calculations refer to transient state
2
Biomass and Recruitment Time Series
40
35
Biomass (mt)
30
25
Biomass
age 1+ and age 4+
Ages 1+
20
15
10
Ages 4+
5
1975
1980
1985
1990
1995
2000
2005
2010
2015
Age 1 Recruits (millions)
1970
Recruitment - age 1 fish
1972
1977
1982
1987
1992
1997
Yearclass
2002
2007
2012
3
Exploitation rate, Ages 4-5 and Fref = 0.25
0.90
4-5 Exploitation Rate
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
1970
Fref (0.25) u
1975
1980
1985
1990
1995
2000
2005
2010
4
Equations and Calculations
Age 2 recruitment = By (age2)
delta B = change in biomass = [yt,at– yt-1, at-1]
M(biomass) y = Ny,a* Mean wty,a *(My,a/Zy,a) *(1 – exp(Zy,a))
F(2+ biomass) y=Yield = Ny,a* Mean wty,a *(Fy,a/Zy,a)*(1 – exp(Zy,a))
Production = Py = delta By,a + Fy,a (biomass) + My,a (biomass)
Total Production = By (age 2) + Py
Surplus Production = Py – My (biomass)
Net Production = SPy – Yieldy
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Results : Growth and Biomass
Thousands metric tons
50
100%
Ages 2-6+ Growth
Age 2 Biomass
% Growth
40
80%
30
60%
20
40%
10
20%
0%
1977
1982
1987
1992
1997
2002
2007
2012
Percent growth of Age 2 fish represent > 50% of stock growth ~ 68% of years
6
Surplus Production
40
70%
Surplus Production
Ages 2-6+ Yield
rct/prod
Thousands metric tons
60%
30
50%
20
40%
30%
10
20%
1976
1980
1984
1988
1992
1996
2000
2004
-10
2008
2012 10%
0%
Rct/Prod – relative contribution of recruitment to total production
85% of years, recruitment accounted for > 40% of total Production
Positive Net production : 15/40 ~ 38% of 40 year time series
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Literature Cited
Legault, C., L. Alade, W.E. Gross, and H.H. Stone 2013. Stock assessment of
Georges Bank Yellowtail Flounder for 2013. TRAC Working Paper 2013/15
Rivard, D. 1980. Back-calculating production from cohort analysis, with discussion
on surplus production for two redfish stocks. CAFSAC Res. Doc. 80/23
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