Seasonal abundance with biomass and
distribution patterns of European hake
Merluccius merluccius (L.) in Izmir Bay (Turkey)
Esin Yalcin, Rasit Gurbet, Okan Ozaydin, Erdem Sayin, Sencer Akalin,
Semih Leblebici
esin.yalcin@mail.ege.edu.tr
Ege University, Fisheries Faculty, Department of Fisheries and Processing
Technology, İzmir/Turkey
Main Objective
The hypothesis; main abiotic factors (e.g. temperature, salinity,
water masses) and also oceanographic conditions (e.g. eddies,
wind-driven circulation, thermohaline-driven, baroclinic circulation)
may also influence fish-biomass fluctuations in Izmir Bay.
Exhibition of relationship between monthly abundance and
distribution patterns of stability in time and space with some
important hydrographic conditions (e.g. temperature) by using
GIS (Geographical Information System) tools and statistical
techniques.
This study deals with the monthly abundance (number/h) with
biomass (kg/h) and distribution patterns of European hake (M.
merluccius) in the Izmir Bay, Turkey.
The goal of the present study is to learn more about the factors
that might modulate the spatio-temporal aggregation patterns of
species.
• This study belongs to one of the TUBITAK (The
Scientific and Technological Research Council of
Turkey) project which name is “Investigation
effects of abiotic environmental factors on
commercially important demersal fish
population in Izmir Bay” (2007-present).
• PhD thesis:
The effects of environmental variables on red
mullet (Mullus barbatus) and European hake
(Merluccius merluccius) populations in Izmir Bay.
Aegean Sea & Izmir Bay
Aegean Sea, GFCM / GSA-22
Total Landings of European hake
GSA-22 (Aegean Sea) Turkish Coast Site 1990-2007
European hake (Merluccius merluccius)
10000
tonnes
8000
6000
4000
2000
19
90
19
92
19
94
19
96
19
98
20
00
20
02
20
04
20
06
0
year
TURKISH STATISTICAL INSTITUTE (TurkStat) Annual Fishery Statistics
European hake (Merluccius merluccius) is one of the most important demersal
target species of the commercial fisheries in the Aegean Sea (geographical subarea 22).
Material & Methods
• Use of trawl surveys seasonal data; 7 research trawl surveys
•
•
•
•
•
•
performed between 2007 and 2008 (present)
Evaluations of abundance with swept area method; 10 bottom
trawling by depth ranges of stations by km²
Use of oceanographic in situ data, 10 hydrographic & 7 current
meter stations (depth range 20-70 m)
Use of monthly meteorological data, wind data sets of Izmir
Bay from the Turkish State Meteorological Service
Evaluations of distribution patterns with GIS tools; Spatial Analysis
extension of ArcGIS (ESRI)
Using statistical techniques to arrange data sets; One-Sample
Kolmogorov-Smirnov Test and Bonferroni Test
Using flexible regression analysis to analysis all data together; A
GLM multifactor ANOVA was used for the dependent
variable in relation to factors
GIS Tools
• With the analytical tool contained in the Spatial
Analyst extension of Arc GIS 9.2 (ESRI, 2006)
• Interpolations of temperature value was done
using the krigging techniques.
• The external limits of the areas (contours)
occupied by each range of values.
• Spatial distribution of abundance of species as
kg/h & number/h exhibited by different colored
fish symbol in each stations.
Fig.1. GIS Model
Fig.2. Bathymetry of Izmir Bay and hydrographic stations.
Prohibited Area, Izmir Bay
Commercial fisheries annual circular 2006-2008. Prohibited time scale: 15 April-15 September
Fig. 3. Geographical distribution of abundance (kg/h) of European hake
in autumn with temperature.
Fig. 4. Geographical distribution of abundance (numbers/h) of European
hake in autumn with temperature.
Fig. 5. Geographical distribution of abundance (kg/h) of European hake
in winter with temperature.
Fig. 6. Geographical distribution of abundance (numbers/h) of European
hake in winter with temperature.
Fig. 7. Geographical distribution of biomass (kg/h) of European hake in
spring with temperature.
Fig. 8. Geographical distribution of abundance (numbers/h) of European
hake in spring with temperature.
Data Analysis
Factors
Dependent
Description
M. merluccius Kg/h
Number/h
Categorical
Month
Station
7 month (3 seasons)
10 station
Quantitative
Depth
Temperature
Salinity
m
C°
psu
Table.1. Factors available for inclusion in the analysis.
Statistical Analysis
• The dependent variables were found to be app. log-normally
distributed. They were log10-transformed to stabilize their
variance by One-Sample Kolmogorov-Smirnov Test.
• Abundance data were also incremented by 1 (data+1) to avoid
censoring all zero sample sizes from subsequent
transformations used to stabize data variances.
• In descriptive statistics, a boxplot (box-and-whisker diagram)
was used as a convenient way of graphically depicting groups
of numerical data.
• Adjustment for multiple comparisons by Bonferroni Test.
• Significance level was set to α = 0,05 in statistical analysis.
Interaction plots of mean values
Fig.9. Interaction plots of mean values expressed in months.
g
e
e
r
r
_
_
k
a
Boxplot (box-and-whisker diagram)
Log10 (hake_kg/h+1)
,
0
0
5
,
0
0
2
,
0
0
1
,
0
0
m
,
3
0
_
1
,
0
0
0
,
5
0
l
l
o
1
o
g
g
_
m
m
m
2
Log10 (hake_number/h+1)





0
,
0
1
0
0
2
3
4
5
s
6
t
8
a
9
t
1
i
01
o
n
,
0
1
1
s
0
2
3
4
5
s
6
t
8
a
9
t
1
i
Fig.10. Differences between monthly abundance (number/h) and
biomass (kg/h) by boxplot.
01
o
1
n
s
Statistical Model
• A GLM (Generalized Linear Models) multifactor
ANOVA was used for the dependent variable in
relation to factors.
• The dependent variable under examination was
indices of fish density in number and biomass.
• All factors (month, station, species, depth,
temperature, salinity) were initially included in
the model.
GLM multifactor ANOVA for European hake biomass
log (kg/h+1) by stations month WITH temperature & salinity & depth
Fig.11. This test is based on the linearly independent pairwise comparisons
among the estimated marginal means of month.
GLM multifactor ANOVA for European hake abundance
log (number/h+1) by stations month WITH temperature & salinity & depth
Fig.12. This test is based on the linearly independent pairwise comparisons
among the estimated marginal means of month.
European hake (Merluccius merluccius)
Biomass (kg/km²)
Dep
<30 m
CPUE (kg/HP)
30-50 m
>50 m
Total
<30 m
30-50 m
>50 m
Total
Sep
-
61029,24
47591,93
108621,17
-
131,81
102,79
234,60
Dec
3031,12
6,50
43808,84
46846,46
6,55
0,01
94,62
101,18
Jan
1515,56
13413,02
4851,60
19780,18
3,27
28,97
10,48
42,72
Feb
6314,84
17772,25
6894,77
30981,85
13,64
38,38
14,89
66,92
Mar
19852,48
25496,71
13271,45
62186,37
42,88
55,07
28,665
134,31
505,19
3267,03
27388,73
33603,75
1,09
7,06
59,15
72,58
Apr
May
Table.2. European hake Biomass (kg/km²) and CPUE (kg/HP)
Autumn (October, November) and Summer (June, July, August) data will be collected in
2008 and in 2009.
RESULTS & DISCUSSION
• European hake were higher exploited fish species in all fishing
allowed area of the Izmir Bay.
• European hake were mainly distributed in middle of the bay.
• Significant differences among stations and temperature were
observed in Izmir Bay by using flexible regression analysis; GLM and
supported by GIS Model.
• The mean regional density of hake was observed to vary monthly,
being higher mainly abundance (number/h) of fish in autumn,
biomass (kg/h) of fish in winter. It is supported by ArcGIS analysis.
• European hake Biomass (kg/km²) and CPUE (kg/HP) mainly
distributed higher in depth range of 30-50 m. The most high value
displayed in September.
RESULTS & DISCUSSION
• In view of the limited understanding of the dynamic ecology of
European hake, it is necessary to consider all possible causes for the
observed of fishery.
• It is necessary to take all data for each month in a year to consider
all possible effects on European hake distribution in study area.
• Additional years of data would be useful in further testing the
stability of the suggested distribution patterns.
• Other oceanographic factors such as current, salinity, density,
Dissolved Oxygen, pH, klorofil-a, etc. are also important and should
evaluated with all season data.
• All collected biological and population data should be evaluated
when the project was finished.
Acknowledgements
• This study was founded in TUBITAK (The
Scientific and Technological Research Council of
Turkey) project which name is “Investigation of
effects of abiotic environmental factors on
commercially important demersal fish population
in Izmir Bay”.
• The authors want to express their gratitude to all
colleagues and volunteer students involved in
the surveys and data processing.
• Special thanks to Elizabeth Tunka Eronat, Gokay
Aydogdu and S. Ahmet Özdemir.