Download Analysis of spatio-temporal fluctuations of East China

Environmental Coastal Regions III, C.A. Brebbia, G.R. Rodriguez & E. Perez Martell (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-827-9
Analysis of spatio-temporal fluctuations of East
China Sea fishery resources using GIS
F. Su, C. Zhou, Q. Shao, Y. Du & S. Wang
State Key Lab. of Resource & Environmental Information System,
Institute of Geography, Chinese Academy of Sciences, China
Abstract
Catch data from the East China Sea from 1987 through 1997, and other
environmental factors, were overlain using Geographic Information System
(GIS) technology. Maps of the spatio-temporal density of the demersal and
pelagic fishery resources were produced. After analyzing the density
distribution, we analyzed relationships between spatio-temporal distributions and
environmental factors. The Kuroshio Current plays a major role in determining
the fishery density distribution, especially for the demersal fishery. The South
Yellow Sea Water Mass and the expansion of the Chang) iang Diluted Water
(ECDW) are two other main environmental factors. The demersal fishery
resource is mainly distributed between the 200-m isobath and the central route of
Kuroshio Current. Density shifts of the demersal and pelagic fisheries were
analyzed by calculation of centers of gravity. Trend analyses showed that the
fishery resources generally decreased in the study area during the 11-year period.
1 Introduction
In our research, we used GIS to analyze the spatio-temporal fluctuation of
fishery resources in the East China Sea. The East China Sea is a marginal sea
which lies between the Asian continent and the Pacific Ocean. Its current system
is composed of littoral currents and the Kuroshio Current system. Therefore,
water in this region is composed of littoral diluted water and water from the far
sea. The littoral diluted water has low salinity, low transparency, and great interannual variability in temperature. The temperature and salinity of the far sea
water are high, so that gradients of temperature and salinity in the East China Sea
Environmental Coastal Regions III, C.A. Brebbia, G.R. Rodriguez & E. Perez Martell (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-827-9
250 Environmental Coastal Regions HI
are steep. Biomass in this region is low compared with other regions in the
world, only 3.92 tonnes per square kilometer. Approximately 11 percent of
production in this region is pelagic fishes and 40 percent is demersal fishes [1].
This region is the most important fishing area for China, generating 40 percent of
China's total fishery production [2].
Weizhong Chen analyzed the change of fishery resources in the East China Sea
based on the biographic characteristics of sample fish, total catch production,
and production of the main species[3]. Weihai Liu and Benyi Zhan calculated the
correlation between CPUE and catch effort, and analyzed the utilization of
fishery resources using two surplus production models, the Schaefer Model and
the Fox Model. [2]However, none of these analyses contains a spatial
component.
GIS is still not widely used in fisheries management, as the typical stock
assessment models do not include spatial information. There are several areas in
which the use of GIS in management of marine fisheries is emerging [4-5]. One
area is for Pacific salmon in the USA. Olivier et al. [6] analyzed the relationship
between fishery resource fluctuations and environment factors, including fishing
effort. Several studies have analyzed spatial and temporal variation of
groundfish assemblages off the east coast of North America [7-13]. Also, GIS is
now being used in for modeling fish habitat in U.S. estuaries [14].
2 Data
Sample data for 1987-1997 were obtained from four of the biggest fishery
companies in China. The catch of these four companies totals 12 percent of the
total catch from the region by all Chinese companies. The East China Sea was
divided into regular grid with 10' x 10' each cell (Figure 1). Each grid cell has
one catch record per day for each gear type. Trawl catches were used as a
measure of demersal fish density; catches in purse seines were used as a measure
of the density of pelagic fishes. There was a 54 percent probability that two
companies were fishing in the same cell on the same day, with an over 80%
overlap if the low-production records are deleted. The results are only slightly
changed if the records of any one company are deleted, which demonstrates the
robustness of the sample data set.
3 Analysis
3.1 Fishery resource distributions and environment in the East China Sea
3.1.1 Demersal fish distribution
Demersal fishes are caught primarily on the shelf (Figure 1). There are three
areas where the density of demersal fishes is high: Changjiangkou Zhoushan,
Kuroshio and Dasha. The Kuroshio area is divided into four subareas in Figure 1.
Densities in the majority of cells in the Changjiangkou Zhoushan and Kuroshio
areas is 0.5-2 tonnes per tow, with some over 2 tonnes Per tow. In the Kuroshio
area, high density occurs strictly between the central line of the Kuroshio Current
Environmental Coastal Regions III, C.A. Brebbia, G.R. Rodriguez & E. Perez Martell (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-827-9
Environmental Coastal Regions HI 251
and the 200-m isobath, resembling a belt along the Kuroshio. The
Chang) iangkou Zhoushan
area lies between the 50-m
and 100-m isobaths. In
half of the cells in the
Dasha area, the density of
the demersal fishery is in
the 0.5-2 tonne range. The
last two areas resemble
two slices of a pie .
Figure 1: Density distribution of demersal
fishes
3.1.2
Pelagic
fish
distribution
The pelagic fishes occur
mainly near the coast
(Figure 2). There are four
areas where the density of
pelagic fishes is high: Dasha,
Chang] iangkou
Zhoushan,
Wentaimindong, and Duima.
The density of pelagic fishes
per cell in the Dasha area
ranges from 2-50 tonnes per
purse seine. One-third of
these cells has densities
between 2 and 10 tonnes per
purse seine, the middle third
has densities of 10-20
tonnes per purse seine, while
the highest third
has
densities over 20 tonnes per
purse seine. Densities in the
other three areas are
between 2 and 10 tonnes per
purse seine.
3.1.3
Relationships
between fish density and
the environment
Figure 2: Density distribution of pelagic
The fishing ground for
demersal fishes in the
fishes
Kuroshio area occurs in the
updraft current, which lies to the left of the Kuroshio Current. The bottom drops
steeply east of the 200-m isobath, which enhances the intensity of the ascending
current. These factors have important influences over the demersal fishing
grounds. The fishing grounds in Changjiangkou Zhoushan area lie in the
Environmental Coastal Regions III, C.A. Brebbia, G.R. Rodriguez & E. Perez Martell (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-827-9
252 Environmental Coastal Regions III
temperature-front zones between the Changjiang Diluted Water (ECDW), the
Yellow Sea Cold Water Mass, and the Taiwan Warm Current. There are two
temperature fronts in the upper waters of the Dasha area. One, on the west, is
formed by the Yellow Sea Warm Current and the Yellow Sea Matrix Water. The
other, to the east, is formed by the littoral water of Korea and the Duima Warm
WaterMass[15-16].
The Kuroshio Current plays a major role in determining the density of the
bottom-fishery resource. High biomass areas typically lie to the left of major
currents in the Northern Hemisphere [17]. The catch data indicates that fishery
productivity is high where high primary productivity occurs. Xuechuan Wong,
Fenqi Li and Beiwei Lu's [18-19] have shown that chlorophyll-a concentrations
are high in the middle of the East China Sea's shelf, and distributed
discontinuously in a belt along the 200-m isobath as the same as the ditribution
of high fish density areas(Figure 1).
3.2 Changes in fishing ground location
Changes in the location of fishing grounds over the 1987-1997 period were
evaluated by calculation of the annual "center of gravity" for each fishing ground
[20]. The following formula was used to calculate the center of gravity.
xc = — xw(x, .y)(Wy, .yc = -—
M
M
D is the area being analyzed, (xc, yc) are the coordinates of the center of gravity,
M is the total biomass, and u (x, y) is the density at the point of (x, y). For use
with the sample data, we re-arranged the above two formulas as follows.
In these formulas, d is the area of the fishing ground and P (x, y) is the
density offish in the cell (x, y).
3.2.1. Demersal resources
For the demersal resource, centers of gravity were calculated for the four
fishing grounds shown in Figure 1. The position shifts of each fishing ground
are shown in Figure 3. The center of the Dasha fishing ground shifted to the
northwest almost continuously during the study period. The net distance
shifted was 56 nautical miles to the west and 28 nautical miles to the north.
The center of Changjiangku Zhoushan fishing ground shifted primarily to the
south. The net distance moved was 22 nautical miles. The center of the first
Environmental Coastal Regions III, C.A. Brebbia, G.R. Rodriguez & E. Perez Martell (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-827-9
Environmental Coastal Regions III 253
Kuoshio
fishing
ground
drifted erratically, with a net
change of 24 nautical miles to
Dasha Fishing Groun<
the west and 15 nautical
miles to the north. The center
of the second Kuoshio fishing
1987
ground also drifted erratically.
The net distance shifted was
29 nautical miles to the south
and 10 nautical miles to the
east.
3.2.2 Pelagic resources
For the pelagic resource,
Second Kuroshio
1997
centers
of gravity were
Fishing Ground
calculated for the four fishing
1987
grounds shown in Figure 2.
1987
First Kuroshio
The position shifts of each
Fishing Ground
fishing ground are shown in
1997
Figure 4. The center of the
90
Dasha Fishing Ground shifted
Nautical Mile
to the west continuously from
1987 to 1997, with a net
FigureS:Locations of the centers of gravity
change of 31 nautical miles.
for the East China Sea demersal fishing
Over the entire 1987-1997
grounds
period, the center of the
Changjiangkou fishing ground
shifted to the south slightly from 1987 to 1997, but the inter-annual shifts were
considerable, about 20 nautical miles. The center of the Zhoushan fishing ground
shifted about 30 nautical miles inter-annually, but without a discernable pattern.
The center of the Wentaimingdong fishing ground shifted to the northeast, with a
net position change of 30 nautical miles to the east and 15 nautical miles to the
north.
'han&jiangK
90 Dasha Fishing Ground
Wentaimingdong
Nautical Mile
Figure 4: Locations of the centers of gravity for the
East China Sea pelagic fishing grounds.
Environmental Coastal Regions III, C.A. Brebbia, G.R. Rodriguez & E. Perez Martell (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-827-9
254 Environmental Coastal Regions HI
3.3 Spatio-temporal analysis of the fishery-stock fluctuations
Temporal trends in density over the study period were analyzed by grid cell
using least-squares linear regression. The data were organized as in Table 1.
The regression equation was as follows:
Y = ax+b,
where Y is the density in a given cell and year, x is the number of years from
1987 (e.g., the value of x for 1991 is 1991-1987 = 4), and a and b are the
coefficients. The value of "a" is the slope of the line, and indicates the temporal
trend in the cell. A positive slope would indicate an increasing trend in catch,
while a negative slope would indicate a decreasing trend. The absolute value of
the slope indicates the magnitude of the trend.
Table 1. Density of demersal fishes by grid cell and year.
Year
Cell No
15727
87
88
89
90
92
91
93
94
95
96
97
34
64
45
58
50
14
30
24
7
15728
44
81
56
32
73
24
17
26
6
31
26
16426
16427
51
70
36
62
103
20
58
19
19
106
46
51
46
157
40
28
27
108
3
42
18
64
H-4- Miles
Nautical
Figure5 Change of density of demersal
fishes
9
27
The results of the trend
analyses were divided in
seven categories: high
decrease
,
medium
decrease, low decrease ,
unchanged, low increase ,
medium increase, and
high increase (Figure 5).
Most of the cells show
decreases for the demersal
fishery, especially in the
third and fourth Kuroshio
fishing grounds. In the
southeast of the second
Kuroshio fishing ground,
there are some cells in the
low increase category,
located southeast of the
Kuroshio Current. In the
Dasha fishing ground,
Environmental Coastal Regions III, C.A. Brebbia, G.R. Rodriguez & E. Perez Martell (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-827-9
Environmental Coastal Regions III 255
most of the cells are also
in the low
increase
category, and some are in
the medium
increase
category.
In
the
Changjiangkou Zhousha
fishing ground, some cells
are in the low increase
category. In the first
Kuroshio fishing ground,
there are some cells along
the Taiwan Warm Current
in which density has
increased slightly. In the
whole East China Sea,
there are some cells in the
high decrease category,
but no cells in the high
increase category. These
patterns are similar to the
changes
in
location
discussed
in
Section
3.2.1.
Figure6 Change of density of pelagic
Density of the pelagic
fisheries decreased
in
fishes
two-thirds of the cells in
the East China Sea during
the study period (Figure 6). In the Dasha fishing ground, there are some cells in
the high decrease category, and the number cells in the low decrease and low
increase categories is the same. In the Duima fishing ground, most of the cells
are in the medium decrease category. In the Wentaimingdong fishing ground, the
density in half of the cells are in the low increase category , while that in the
other cells are in the medium category. These patterns are similar to the changes
in location discussed in Section 3.2.2.
4 Conclusion
There are three areas in which the density of demersal fishes is high. The
Kuroshio area resembles a belt between the 200-m isobath and the center of the
Kuroshio Current. The other two areas lie in the Dasha and Changjiankou
Zhoushan areas, respectively. Fish distributions in the East China Sea are
influenced by the Kuroshio Current, the Yellow Sea Water Mass, and the
expansion of the Changjiang Diluted Water (ECDW). Over the 1987-1997 study
period, the Changjiangkou Zhoushan fishing ground shifted to the south slightly,
the Dasha and the first Kuroshio fishing grounds shifted to northwest, and the
Environmental Coastal Regions III, C.A. Brebbia, G.R. Rodriguez & E. Perez Martell (Editors)
© 2000 WIT Press, www.witpress.com, ISBN 1-85312-827-9
256 Environmental Coastal Regions HI
second Kuroshio fishing ground shifted to the southeast. The trend analysis
showed that the demersal fish resources in the East China Sea have decreased.
There are four areas in which the density of pelagic fishes is high: Dasha,
Changjiangkou Zhoushan, Wentaimindong, and Duima. Overall, the Dasha
fishing ground shifted to the west; the Changjiangkou fishing ground shifted to
the south slightly, but with inter-annual variability; the Zhoushan fishing ground
did not have a substantial net change in location, but shifted long distances interannually; and the Wentaimingdong fishing ground shifted to the northeast. The
trend analysis showed that the pelagic fish resources in the East China Sea have
decreased slightly.
Acknowledgements
We wish to thank Shixian Han, Weizhou Chen and Vincent Lyne for
discussions about this work. We are grateful to Dr. Stephen K. Brown who
edited carefully the paper and provided some relevant references. An
anonymous reviewer also contributed to the presentation. This work was
supported in part by Program 863 of China (project no. 818-07-02).
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