We investigated the ecology and spatial distribution of saithe (Pollachius virens) and hake (Merluccius merluccius) in a relevant region for fishery economy: the North Sea. While saithe is an important commercial species with spawning stock biomass declining in recent years, hake occurrence have been increasing in the area. In order to understand if these two species are spatially correlated, their potential habitat was studied during winter using binomial generalized linear models (GLMs) based on the 1st quarter data of the International Bottom Trawl Survey from 1991 to 2012. Species occurrence was modeled as a function of different external factors at the scale of the statistical rectangle. Explanatory variables were grouped by category (abiotic, biotic and spatial factors). Each group was then tested either separately or in combination. Biotic explanatory variables included several fish species with a supposed trophic link: saithe, hake, cod (Gadus morhua), Norway pout (Trispoterus esmarkii) herring (Clupeus harengus) and blue whiting (Micromesistius poutassou). Abiotic factors included depth, temperature and sediment type. Based on results we decided to exclude spatial factors before variable selection. The results were then used to map potential habitat for both species and study, for the first time in the North Sea, their spatial overlap. This has been performed by comparing an early (1991-1996) and a late period (2007-2012). An increase in the probability of presence for both saithe and hake has been noticed. Although saithe coverage has remained spatially consistent over the last 20 years (IVa and IIIa), hake distribution has expanded toward south. Whereas the overlap between the two species slightly expanded, the probability of presence of both species together has greatly increased. These results are important in a context of an ecosystem approach to fisheries and will be completed with stomach content analysis study currently in progress.

1. SAITHE AND HAKE SPATIAL INTERACTIONS
IN THE NORTH SEA
ICES/NAFO Symposium
C.
Loots1 ,
K.
Rabhi1 ,
Xochitl Cormon1,2 ,
M. Rouquette1 , S. Vaz1 , Y. Vermard1 and
P. Marchal1
1 IFREMER Boulogne-sur-Mer
Fishery Science Departement
2 Université
Lille 1
Sciences and Technology
15-18 October 2013, Saint Andrews, NB, Canada

2. Introduction
Context
The North Sea:
An European area
An ecosytem changing..
Environmental
factors1
Human activity
1
ICES, 2008
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3. Introduction
Context
The North Sea:
An European area
An ecosytem changing..
Environmental
factors1
Human activity
with consequences..
on species
distribution2
and species
interactions3
1
2
3
ICES, 2008
Perry et al., 2005
Klein et al., 2008
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4. Introduction
Context
The North Sea:
An European area
An ecosytem changing..
Environmental
factors1
Human activity
with consequences..
on species
distribution2
and species
interactions3
1
2
3
ICES, 2008
Perry et al., 2005
Klein et al., 2008
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5. Introduction
Species presentation
Two species of interest:
Which species?
Saithe, Pollachius virens
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Hake, Merluccius merluccius
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6. Introduction
Species presentation
Two species of interest:
Which species?
Saithe, Pollachius virens
Hake, Merluccius merluccius
600
Historical trends of SSB4
300
0
100
200
SSBS_1000t
400
500
Saithe
(IIIa, IV and VI)
Hake
(IIIa, IV, VI, VII and VIIIa,b,d)
1970
4
1980
1990
2000
2010
ICES, 2013
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7. Introduction
Species presentation
Two species of interest:
Which species?
Saithe, Pollachius virens
Hake, Merluccius merluccius
Presence-absence ratio per statistical rectangles of the area of interest over years
(Data from DATRAS, 1991-2012, Q1)
1.00
1.00
0.75
0.75
0
0.50
0.50
1
0.25
0.00
0.25
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
0 00
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
Saithe
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Hake
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8. Materials and methods
Species presence and overlap
Understand their spatial distribution and overlap
1
2
Data from DATRAS, 1991-2012, Q1
Presence-absence GLM (binomial, logit)
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9. Materials and methods
Species presence and overlap
Understand their spatial distribution and overlap
1
2
Data from DATRAS, 1991-2012, Q1
Presence-absence GLM (binomial, logit)
Response: saithe, hake or overlap
4
5
Bergstad, 1991
Dubuit, 1991
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10. Materials and methods
Species presence and overlap
Understand their spatial distribution and overlap
1
2
Data from DATRAS, 1991-2012, Q1
Presence-absence GLM (binomial, logit)
Response: saithe, hake or overlap
Descriptors:
ENV: temperature, bathymetry and sediment type;
ORG: saithe, hake, cod groups (G. morhua), Norway pout (T.
esmarkii), herring groups (C. harengus) and blue whiting
(M. poutassou) presence-absence4,5 ;
4
5
Bergstad, 1991
Dubuit, 1991
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11. Materials and methods
Species presence and overlap
Understand their spatial distribution and overlap
1
2
Data from DATRAS, 1991-2012, Q1
Presence-absence GLM (binomial, logit)
Response: saithe, hake or overlap
Descriptors:
ENV: temperature, bathymetry and sediment type;
ORG: saithe, hake, cod groups (G. morhua), Norway pout (T.
esmarkii), herring groups (C. harengus) and blue whiting
(M. poutassou) presence-absence4,5 ;
Selection based on parsimony and sensitivity (true positive rate)
calculated on a separate predictive dataset
4
5
Bergstad, 1991
Dubuit, 1991
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12. Materials and methods
Species presence and overlap
Understand their spatial distribution and overlap
1
2
Data from DATRAS, 1991-2012, Q1
Presence-absence GLM (binomial, logit)
Response: saithe, hake or overlap
Descriptors:
ENV: temperature, bathymetry and sediment type;
ORG: saithe, hake, cod groups (G. morhua), Norway pout (T.
esmarkii), herring groups (C. harengus) and blue whiting
(M. poutassou) presence-absence4,5 ;
Selection based on parsimony and sensitivity (true positive rate)
calculated on a separate predictive dataset
3
4
5
Mapping
Bergstad, 1991
Dubuit, 1991
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13. Materials and methods
Species presence and overlap
Understand their spatial distribution and overlap
1
2
Data from DATRAS, 1991-2012, Q1
Presence-absence GLM (binomial, logit)
Response: saithe, hake or overlap
Descriptors:
ENV: temperature, bathymetry and sediment type;
ORG: saithe, hake, cod groups (G. morhua), Norway pout (T.
esmarkii), herring groups (C. harengus) and blue whiting
(M. poutassou) presence-absence4,5 ;
Selection based on parsimony and sensitivity (true positive rate)
calculated on a separate predictive dataset
3
Mapping
4
R software
4
5
Bergstad, 1991
Dubuit, 1991
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14. Materials and methods
Species presence and overlap
Understand their spatial distribution and overlap
1
2
Data from DATRAS, 1991-2012, Q1
Presence-absence GLM (binomial, logit)
Response: saithe, hake or overlap
Descriptors:
ENV: temperature, bathymetry and sediment type;
ORG: saithe, hake, cod groups (G. morhua), Norway pout (T.
esmarkii), herring groups (C. harengus) and blue whiting
(M. poutassou) presence-absence4,5 ;
Selection based on parsimony and sensitivity (true positive rate)
calculated on a separate predictive dataset
3
Mapping
4
R software
4
5
Bergstad, 1991
Dubuit, 1991
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15. Results and discussion
Models fit
Models fit
Some of the relevant descriptors effects
adjR2
Saithe
0.45
Hake
0.38
Overlap
0.29
S
NS
H
NA
TEMP
S
H
O
NA
SAITHE
DEPTH
O
NORWAY POUT
HAKE
NA
NA
HERRING juv
Other descriptors
Sediment type is never significant except for fine sand for all models (´);
Cod is significant for saithe and overlap models (`) while adults herring is only for
hake and overlap ones (`), blue whiting is only significant for hake (`).
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16. Results and discussion
Maps from models output
Saithe presence probability evolution since 1991
Probable habitat at first quarter
(1991-1996)
Changes in presence probability
over the last 15 years
1.0
60
60
0.4
0.8
58
58
0.2
0.6
56
56
0.0
0.4
54
54
−0.2
0.2
52
52
−0.4
0.0
0
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0
10
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17. Results and discussion
Maps from models output
Hake presence probability evolution since 1991
Probable habitat at first quarter
(1991-1996)
Changes in presence probability
over the last 15 years
1.0
60
60
0.4
0.8
58
58
0.2
0.6
56
56
0.0
0.4
54
54
−0.2
0.2
52
52
−0.4
0.0
0
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18. Results and discussion
Maps from models output
Overlap evolution since 1991
Probable overlap at first quarter
(1991-1996)
Changes in overlap probability
over the last 15 years
1.0
60
60
0.4
0.8
58
58
0.2
0.6
56
56
0.0
0.4
54
54
−0.2
0.2
52
52
−0.4
0.0
0
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5
0
10
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5
10
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19. Outlooks
Outlooks
1
Input efficient spatial autocorrelation consideration (SAC)
2
Stomach content analysis study (in progress)
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20. Outlooks
Outlooks
1
Input efficient spatial autocorrelation consideration (SAC)
2
Stomach content analysis study (in progress)
3
Combination of modeling and experimental results
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21. Outlooks
Outlooks
1
Input efficient spatial autocorrelation consideration (SAC)
2
Stomach content analysis study (in progress)
3
Combination of modeling and experimental results
4
Enter in a predictive mode
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22. Outlooks
Outlooks
1
Input efficient spatial autocorrelation consideration (SAC)
2
Stomach content analysis study (in progress)
3
Combination of modeling and experimental results
4
Enter in a predictive mode
5
Application to management in multispecific and ecosystemic approach
context
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23. Outlooks
Outlooks
1
Input efficient spatial autocorrelation consideration (SAC)
2
Stomach content analysis study (in progress)
3
Combination of modeling and experimental results
4
Enter in a predictive mode
5
Application to management in multispecific and ecosystemic approach
context
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24. The End
The End...
Thank you for your attention.
Any question?
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25. References
References
Bergstad, O. A. (1991). "Distribution and Trophic Ecology of Some Gadoid Fish of the
Norwegian Deep .1. Accounts of Individual-Species." Sarsia 75(4): 269-313.
Borcard, D., Gillet, F. and P. Legendre (2011)."Eigenvector-Based Spatial variables and Spatial
Modelling." Numerical Ecology with R: 243-279. Springer, UseR!
Dubuit, M. H. (1991). "Food and feeding of saithe (Pollachius virens) off Scotland." Fisheries
Research 12(4): 307-323.
ICES (2013). "Saithe in Subareas IV, VI and Division IIIa." Report of the Working Group on the
Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK): ICES
CM/ACOM:13 : 565-609.
ICES (2013). "Hake in Division IIIa, Subareas IV, VI and VII and Divisions VIIIa,b,d (Northern
stock)" Report of the Working Group on the Assessment of Southern Shelf Stocks of Hake,
Monk and Megrim (WGHMM): ICES CM/ACOM:11 : 34-73.
ICES Database of Trawl Surveys (2013). "ICES Database of Trawl Surveys (DATRAS)"
Extraction JUNE 2013 of International Bottom Trawl Survey (IBTS). ICES, Copenhagen”
Klein, D. R., H. H. Bruun, et al. (2008). "Climate change influences on species
interrelationships and distributions in high-Arctic Greenland." Advances in Ecological Research,
Vol 40 40: 81-100.
Perry, A. L., P. J. Low, et al. (2005). "Climate change and distribution shifts in marine fishes."
Science 308(5730): 1912-1915.
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26. Annex
Non-spatial or spatial?
Comparison of non-spatial and spatial models
Saithe
Model type
ENV+ORG
ENV+ORG+MEM
NbTot
11
25
NbORG
6
3
NbENV
5
3
TPR
0.84
0.88
Dev ě 1%
4
7
SAC
5*** 0.25
4*** 0.15
Model type
ENV+ORG
ENV+ORG+MEM
NbTot
13
21
NbORG
5
1
NbENV
8
5
TPR
0.88
0.90
Dev ě 1%
6
10
SAC
9*** 0.35
8*** 0.25
Model type
ENV+ORG
ENV+ORG+MEM
NbTot
10
14
NbORG
4
0
NbENV
6
4
TPR
0.89
0.93
Dev ě 1%
8
8
SAC
5*** 0.30
4*** 0.20
Hake
Overlap
Models without SAC consideration are chosen
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