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The larval anchovy (Engraulis japonicus) fishery in relation to the environmental factors in coastal waters of Fangliao, Taiwan
ELSEVIER
Fisheries Research 26 ( 1996) 3748
The larval anchovy (Engraulis japonicus) fishery in relation to the environmental factors in coastal waters of Fangliao, Taiwan M.A. Lee *, K.T. Lee Lkpnrtnwnt
oj’Fishery Science, National Taiwan Ocean University, Keelung. 20224, Taiwan, ROC
Accepted 20 May 1995
Abstract Daily commercial catches, school densities and school sizes of larval anchovy (EngruufisjuponiUS), and oc:eanographic and meteorological variables for the spring fishing season (January to June) from 1988 to 1990 were analyzed by multiple regression analysis to identify factors influencing the aggregation and abundance of larval anchovy in the coastal waters of Fangliao, Taiwan. The results suggest the important factors were school density, that related to the mean body length of the larvae, surface water temperature, that determined the occurrence of Engraulis japonicus, surface water salinity, that was affected by river discharge and spring and neap tides, and the phosphate content and solar radiation, that affected plankton production. Kevwords:
Anchovy fishery; Engraulis japonicus; Larval anchovy
1. Introduction Larval anchovy is fished for human food because of its high protein content and attractive taste (Sun, 1988; Lee, 1991). Anchovy is also utilized for fish meal (Lasker, 1988). A long fishing period, coastal fishing grounds and a significant exploitation proportion of the recruits are the main characteristics of this fishery (Lee et al., 1990)) which constitutes one of the most important fisheries in the coastal waters of Fangliao, Taiwan (Fig. 1) . Several types of gear have been used. These include trawlnet, light attracting lift net, beach seine and set net. Of these the trawlnet operated by a pair of trawlers, introduced in 1979, has been the most effective and dominant gear (Lee et al., 1994). According to the landing records of the Fangliao Fishermen’s Association, the annual catch of larval anchovy during * Corresponding
author.
016%7836/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDlO165-78X6(95)00412-2
M.A. Lee, K.T. Lee/Fisheries Research26 (I 996) 3748
38
Isobath
--.--_.SOm
-... ---
Fig.
-...
30m
--10m
I. Larval anchovy fishing ground (shaded area) in the coastal waters of Fangliao, Taiwan.
the period from 1980 to 1993 averaged 550 tons, with a cash value of NT$35 million (US$ 1.4 million). This accounted for about 20% of the total annual production of larval anchovy in Taiwan. The catches were primarily composed of the larvae (total length, 1.5-4 cm) of Engraulis japonicus, Encrasicholina punctifer, E. heteroloba and commercially unimportant species of the family Engraulidae. Larvae of other species from such genera as Scombridae, Carangidae, Leiognathidae and Elopidae were rare (about 5-10%) (Sun, 1988; Liu, 1989). Because of the economic importance of the fishery and concern for its possible effect on coastal resources, the stock abundance, biology and oceanography of larval anchovy have been studied intensively in Taiwan and other countries (Murphy, 1974; Lasker, 1978; Chen, 1980; Koslow, 1981; Lasker, 1981; Parrish et al., 1981; Chen and Jean, 1982; Methot, 1983; Fiedler et al., 1986; Bando, 1987; Lasker, 1988; Mitani, 1988; Cheng et al., 1989; Tzeng and Wang, 1992; Young et al., 1992; Lee et al., 1993; Lee et al., 1994). With respect to environmental factors affecting the fishery, Lee et al. ( 1990) indicated that in the coastal waters of southwest Taiwan, larval anchovy aggregated along the region of intermediate salinity (between 33.85 p.p.t. and 34.5 p.p.t.) between the flow axis of river discharge with low salinity and that of the offshore current with high salinity. In Sagami
M.A. Lee, K.T. Lee/Fisheries
Research 26 (1996) 37-48
39
Bay, Japan, the location of larval anchovy fishing grounds was also reported to be related to surface water salinity (Mitani and Hasegawa, 1988). Lasker ( 1988) noted the effects of storms and upwelling, and suggested that if newly hatched larvae did not find suitable food as soon as they were ready to eat then they would die. The present study analyses the daily data of commercial catches, school densities and school sizes of larval anchovy, and oceanographic and meteorological variables, by multiple regression analysis to identify factors controlling the abundance and aggregation of larval anchovy in coastal waters of Fangliao.
2. Materials and methods During the spring fishing seasons (January to June) from 1988 to 1990,39 hydroacoustic surveys were conducted, using the method described by Lee et al. ( 1993)) in coastal waters of southwestern Taiwan (Fig. 1) . For each survey an echosounder (Model he301, Honda Inc.) with a 200 kHz transducer (Lee et al., 1987) was deployed on the trawler ‘Hsin-linpo 226’ and towed at the side of the vessel at a speed of 1.5 m s- ’ at a depth of 1.5 m. The echosounder was set at 5 pings per second, a pulse duration of 0.6 ms, a beam angle ( - 3 dB ) of 12” and a bandwidth of 3 kHz. Each hydroacoustic survey lasted for 4 h. In addition, surface water temperature, salinity and current speed and direction were recorded by an SD201 multiparameter probe and an SD4 current meter. Surface water temperature was measured with a mercury thermometer, and salinity by a conductivity salinometer and standard seawater. One liter of seawater was collected and frozen for nitrate and phosphate analyses In the laboratory, the echo traces of larval anchovy schools on the echogram were selected, using the rnethod described by Lee et al. (1988a) and Sun (1988), for the measurements of vertical thickness (V) and horizontal extension width (H). The school size was estimated for each hydroacoustic survey by the formula S = ITH~V/~, as the shape of the school was defined as the cylinder described by Sun (1988). In addition, the echo signals on the magnetic tape obtained from the surveys were monitored on a synchroscope (Lee et al., 1987). Also. echo signals of larval anchovy schools were selected (Lee et al., 1988b), and their average backscattering strength (S,) and school density were measured by the method described by FAO (1983) and Lee et al. (1989). The school density (D) was estimated by the formula S, = S, + IOlogD (Pieper and Bargo, 1980)) where S, is the target strength. The S, value was estimated from the mean body length (BL) of the larvae using the formula S, = 26.421ogBL - 110.65 estimated by Lee et al. ( 1989). For each day of the hydroacoustic survey, commercial catches of larval anchovy were obtained from the Fishermen’s Association of Fangliao. Samples of scoops of the larvae were collected from the catches. The species composition of the sample was determined (Chen, 19X7), and body lengths of individual larvae in the sample were measured. The occurrence rate (O,.) of Engraulis japonicus was estimated by the following equation: 100 O’=“‘X(Mi+M,)
40
M.A. Lee, K.T. Lee/Fisheries
Research 26 (1996) 3748
where 4 is the abundance of Engraulis japonicus in the samples, and MOis the abundance of Encrasicholina punctiyer and E. heteroloba in the samples; these are the major species caught in this fishery. Meteorological data, including air temperature, wind speed, precipitation, solar radiation and atmospheric pressure, were obtained from the HengChun station of the Taiwan Central Weather Bureau. Daily discharges of the Linpein river in the vicinity of Fangliao were obtained from the Hsinpin station of the Taiwan Provincial Water Conservancy Bureau. The tide levels in the coastal waters of Fangliao were obtained from the Chinese Naval Hydrographic and Oceanographic Office. Multiple regression analysis (Johnson and Wichern, 1988) was used to relate the daily catches, school densities and school sizes of larval anchovy (dependent variables) to oceanographic and meteorological data (independent variables). The independent variables were surface water temperature, surface water salinity, current speed, phosphate and nitrate content, air temperature, atmospheric pressure, precipitation, river discharge, wind speed, solar radiation and cloud cover. In addition, the species composition and body length of the larvae were used as independent variables. All data were standardized by linear transformation using the formula (Xi -X) /SD to remove differences due to scaling. Xi is the observation of datum i, and X and SD are the mean and standard deviation of the data, respectively (Johnson and Wichern, 1988). The correlation coefficients of dependent and independent variables are obtained by using linear regression methods. If the coefficient between independent variables is high and attains the 1% significance level, the correlation coefficients between dependent and independent variables are compared with each other. The factor which affects the dependent variable with a high correlation coefficient is then chosen. Finally, by using the stepwise procedure of multiple regression analysis, the factor that affects the dependent variables is obtained. The dependent variable could generally be described by the joint probability density function of independent variables. This equation is
where Y is the dependent variable, a, is a constant value about zero and m is the number of independent variables. bi and Xi are the ith partial correlation coefficients and standardized value of independent variables among the joint probability density function, respectively.
3. Results Table 1 shows the daily catches, school densities and school sizes of larval anchovy from the 39 hydroacoustic surveys, and associated meteorological and oceanographic data. Table 2 gives the matrix of correlation coefficients between the daily catches, school sizes and densities, and meteorological and oceanographic data. As shown in Table 2, the solar radiation and cloud cover, atmospheric pressure and wind speed, and phosphate and nitrate content of sea water have high correlations, with coefficients of - 0.862, 0.728 and 0.8 16, respectively. Also, the correlation coefficients of phosphate, nitrate, atmospheric
M.A. Lee, K.T. Lee/Fisheries Table 1 Biological and environmental January to June 1988-1990
Research 26 (1996) 37-48
data obtained for 39 hydroacoustic
41
surveys in the coastal waters of Fangliao, Taiwan,
Variables
Sample size
Mean
Standard deviation
Daily catches (Kg) School sizes (ml) School densities (individuals mm ‘) Phosphate content of seawater (mg I-‘) Nitrate content of seawater (gg I_ ’ ) Surface water temperature(“C) Surface water salinity (p.p.t.) Current speeli ( m s ’ ) River discharge of linpein hsi ( m3 s- ’ ) Air temperature (“C) Atmospheric pressure (mbar) Precipiation (mm) Wind speed ( m s_ ’ ) Solar radiation (cal m-’ min-‘) Cloud coverage Tide level (III) The occurrence rate of Engraulis japonicus (%) Mean body length (cm)
39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39
5730.8 4.6 1294.3 19.6 4.4 25.3 34.2 0.47 1.23 23.9 1011.3 10.76 2.94 3.17 6.12 1.45 72.33 2.45
5903.3 1.30 854.40 16.90 3.60 1.50 0.13 0.15 2.22 2.53 4.02 25.06 1.49 1.84 2.73 0.25 3 I .77 0.27
pressure, wind speed, solar radiation and cloud cover with the daily catches were - 0.128, - 0.2 16, -- 0.123, - 0.143, - 0.004 and - 0.033, respectively, suggesting that variables of phosphate content, atmospheric pressure and solar radiation were excluded in the multiple regression analysis of daily catches. Table 3 shows the results of multiple stepwise analysis for (a) daily catches, (b) school densities and (c) school sizes, and environmental variables. As shown in Table 3(a), school densities, tide level, nitrate content and the mean body length of the larvae are the major variables affecting the daily catch. The multiple regression equation, with a correlation coefficient of 0.89 1, can be expressed as follows: Y, = 0.579Y, - O.372X,s +0.247X,,
-0.206X,
where Y, is the daily catch, Yx is the school densities of larval anchovy, X,, is the mean body length of the larvae, X,, is the tide level and X, is the nitrate content of sea water. The partial correlation coefficients of the mean body length of the larvae and the nitrate content of sea water were - 0.372 and - 0.206, respectively. Fig. 2 shows the relationship between the 5day total catches and mean body lengths from February to May 1990. During the period from late March to the middle of April, the mean body lengths were smaller and the daily catches were higher as compared with those taken in the periods before late March and after the middle of April. On the other hand, the partial correlation coefficients of school densities and tide level to daily catches were 0.579 and 0.247, respectively. This implies that the daily catches increased significantly with an increase in school densities and tide level. The factors affecting the daily catches were similar to those affecting school densities. Table 3(b) shows the results of multiple regression analysis made between the school densities and the
- 0.456
- 0.255
- 0.075
+0.058
+0.471
+0.092
- 0.200
f0.158
- 0.003
+0.156
- 0.022
- 0.024
-0.160
- 0.287
+ 0.274
-0.162
- 0.682
+0.846*
- 0.079
+ 0.076
-0.217
-0.128
-0.216
- 0.420
-0.116
- 0.427
-0.194
- 0.203
-0.123
- 0.067
-0.143
- 0.004
- 0.033
+0.311
+ 0.280
- 0.559
-0.009
- 0.075
- 0.022
+ 0.060
-0.445
-0.131
- 0.360
+ 0.084
+ 0.394
+ l.c00
- 0.095
+1.000
Y,
f0.735’
Y2
- 0.003
+ l.ooQ
Y,
+0.071
+0.238
-0.069
-0.222
+0.181
+0.039
-0.139
io.049
-0.193
f0.094
f0.001
+0.058
- 0.052
f0.816’
+1.000
XI
-0.661
-0.014
- 0.222
+0.142
-0.161
+ 0.090
+ 0.092
+0.121
- 0.154
+0.011
+0.044
+0.162
+0.032
+ 1.000
XZ
+0.348
- 0.098
+ 0.276
+0.062
+0.016
- 0.266
+o.Ooo
- 0.333
f0.444
- 0.356
+0.187
+ 0.282
fl.000
X1
+ 0.262
- 0.653
+ 0.202
+0.285
-0.159
- 0.334
+0.117
-0.194
+0.260
+0.096
+ 0.295
+1.000
X,
+0.311
-0.159
+0.176
- 0.008
+ 0.092
- 0.109
- 0.079
-0.171
+0.278
+0.188
+1.OQO
XS
variables.
+ 0.090
- 0.056
-0.138
-0.005
to.021
- 0.033
+0.142
- 0.089
f0.026
+1.OQo
X6
f0.213
- 0.301
+0.572
-0.170
+ 0.323
- 0.503
-0.133
-0.616
+1.000
Xl
+ 0.057
-0.167
- 0.681
- 0.258
+0.120
+ 0.728’
- 0.038
+1.OfKJ
X,
-0.063
-0.059
-0.237
+0.442
-0.532
-0.061
+ l.OOll
X9
+0.030
+0.061
-0.661
-0.158
f0.062
fl.000
Xl0
+0.148
-0.069
+0.182
-0.862’
f1.000
X,,
-0.165
+0.005
-0.134
+I.000
X,2
-0.051
-0.026
+ l.ooo
XI3
-0.461
+ 1.000
XM
+ I.@30
XIS
YI. daily commercia1 catch; YI, school size; Y,, school density of larva1 anchovy; X,, phosphate content of sea water; X,, nitrate content of sea water; X,, surface water temperature; X4, surface water salinity; X5, mean C~~enf sped; X,, discharge of the Linpein river; X,. air temperature; X,, atmospheric pressure; X,, precipitation; X,,,, wind speed; X, ,, solar radiation; X1*. cloud cover; X,,, tide level; X1.,.occurrence rate of Engraulis juponicus; X Ls, mean body length of larvae. * p < 0.01
Variables
Correlation coefficients between dependent (Y,, Y?, Y,) and independent (X,-X,,)
Table 2
M.A. Lee, K.T. Lee/Fisheries Research26 (1996) 37-48 Table 3 Multiple regression stepwise analysis to determine the component (b) the school densities and (c) the school sizes of larval anchovy
43
effects on (a) the daily commercial
catches,
(a) Daily catches steps %
I 2 3 4
Y,
XI,
XI,
xz
13,
b>
b,
J,,
-0.001 +0.737 I + 0.545
- 0.00 -0.001 -0.001
- 0.402 -0.381 -0.372
+0.292 +0.247
-0.206
x,5
X,
XI,
X,
&
X,
(10
b,
bz
bl
bs
b,
b,
+ 0.000 + 0.000 +0.000 + 0.000 + 0.000 + 0.000 + 0.000
- 0.477 - 0.362 -0.193
+0.558 +0.579
R’
F
Degrees of freedom
0.5416 0.6663 0.6539 0.7940
43.73 35.94 35.74 32.76
(1.37) (2,36) (3,35) (4,34)
R?
F
Degrees of freedom
0.2274 0.3231 0.4177 0.3920 0.4670 0.5348 0.5755
10.89 8.59 8.37
( 1.37)
(2,36) (3,35) 11.60 (2,36) 10.22 (3,35) 9.77 (4.34) 8.95 (5,33)
R’
F
Degreesof freedom
0.7168
93.66
(1.37)
(b) School densities Steps
I
2 3 4 5 6 I
- 0.330 -0.355 -0.414 -0.521 -0.624 -0.578
+0.34s +0.431 + 0.404 +0.631 +0.636
- 0.295 -0.355 -0.301
+0.368 +0.418
-0.219
(c) School sizes
steps
I
Xi?
“0
b,
0.000
0.845
oceanographic and meteorological variables in the present experiment. The partial correlation coefficients of the occurrence rate of Engraulis juponicus (X,,) and surface water salinity (X,,), surface water temperature (X,), discharge of the Linpein river (X,) and current speed (X,) were 0.636, 0.418, - 0.578, - 0.301 and - 0.219, respectively. This implies that the school densities and catches of larval anchovy increased significantly with an increase in the occurrence rate of Engraulis japonicus and surface water salinity, but decreased with a rise in river discharge (Fig. 3), surface water temperature and current speed. Table 3(c) shows that cloud coverage is the major factor affecting the school sizes of larval anchovy. This correlation coefficient of 0.845 implies that the school sizes were correlated with the cloud coverage and solar radiation (Table 2). 4. Discussions and conclusions The results of this study suggest that daily catches and school densities of larval anchovy are affected by biological factors such as the occurrence rate of Engraulis juponicus and
44
M.A. Lee, K.T. Lee/Fisheries
Research 26 (1996) 3748
30
3.5
25 3.0 m z ,o
20 C _c 15
25 3
c 0 ;
a m”
10 20 5
0
1.5 February
March
April
May
Date Fig. 2. Five-day catches (open bars) and mean body length (continuous waters of Fangliao, Taiwan, February to May 1990.
line) of Iarval anchovy
in the coastal
Month Fig. 3. Monthly mean variation of catches and river discharge of the Linpein hsi in the coastal waters of Fangliao, Taiwan. The solid circles and vertical lines represent the mean and range of observation variables, respectively.
M.A. Lee, K.T. Lee/Fisheries
Research
26 (1996) 3748
45
the body length of the larvae, and by physical and chemical factors including surface water temperature, surface water salinity, current speed, river discharge, phosphate and nitrate concentrations, and the tide level. The factors affecting the school sizes were the cloud cover and solar radiation (Table 2 and Table 3 (c) >. 4.1. Biological factors The biological factors affecting the larval anchovy fishery include the occurrence rate of Engraulis japonicus and fish body length (Table 3). The occurrence rate is positively related to the catches and school densities. This means that the catch increased significantly with an increase of the occurrence rate and school densities. Such a relationship is similar to that reported by Lee et al. ( 1990), Lee ( 1991) and Lee et al. ( 1994). In addition, the daily catch of larval anchovy was negatively related to the mean body length of the larvae (Table 3 (a) ) Lee ( 199 1) indicated that recruitment occurred with small larvae during the period from late March to the middle of April. However, in the periods before late March and after the middle of April, only one larval anchovy recruitment school occurred. Thus, following the growth of the larval anchovy, the catch of standing schools was gradually decreased. 4.2. Physical and chemical factors For the relationships between the larval anchovy fishery and the surface water temperature, Lee et al. ( 1990) reported that the catches dropped by almost 45% as a result of a rise in water temperature in 1988. During this year of high surface water temperatures, catches were greatly reduced and the genus Encrasicholina was dominant. During a year of low water temperatures, Engraulis japonicus became dominant and the catches increased (Lee et al., 1994). There is obviously a relationship between the abundance of anchovy larvae and the occurrence of dominant species in these fishing grounds which is strongly influenced by the surface water temperature. For surface water salinity and river discharge, Lee et al. (1990) pointed out that larval anchovy schools usually inhabit areas close to the mixing areas of ocean currents and river water. Funakoshi (1988) argued that ocean currents and Kuroshio waters tended to cause larval anchovy to inhabit in the coastal waters. Nojima and Nakamura (1988) found that when the waters which were uninhabitable to larval anchovy (i.e. Kuroshio) reached the coast, the larval anchovy schools tended to pack densely together. On the other hand, precipitation and river discharge are obviously closely related. Lee et al. ( 1994) reported that larval anchovy production was negatively correlated with precipitation and river discharge. In Japan, catches of larval anchovy were found to be inversely related to precipitation (Nojima and Nakamura, 1988; Mitani, 1990). The occurrence of heavy freshwater runoff into coastal waters at the time of typhoons and during the monsoon season was known to have an adverse effect on larval anchovy production (Mitani and Hasegawa, 1988) For tide level and current speed, Chao ( 1993) reported that when the convergence speed of the tide and/or current front was greater than 6 cm s - I. the abundance of anchovy larvae was small, and most of the schools inhabited the area of low convergence speed ( <4 cm sP ‘). In addition, Hwu (1994) thought that the school distribution of larval anchovy
M.A. Lee. K.T. Lee/Fisheries
46
05 a ._ E -_ E 2 “0 v E .z 2 Gi e
Research 26 (1996) 37-48
‘I
04
03
t+t 02
t
t+
t1 t
+
2 ,”
01
aI-
-rTTl-,
J
,
FMAMJ
It
I
I
I
I
I
J
A
S
0
N
I
D
Month Fig. 4. Monthly variation of mean solar radiation in the coastal waters of Fangliao, Taiwan, 1982-1992.
followed the direction of the current and tide. During the periods of northward current (spring tide) in the southwest waters of Taiwan, the school will aggregate to the north in the shallow water of the fishing grounds. During the periods of southward current (neap tide), the school will be distributed randomly on the grounds. Current speed and tide level are thus important factors affecting the aggregation and abundance of larval anchovy schools. For phosphate content and solar radiation, it is known that a massive production of zooplankton and phytoplankton from intensive photosynthesis results in a low phosphate content (Parsons et al., 1970; Cheng et al., 1989). In coastal waters of southwest Taiwan, solar radiation was between 0.15 and 0.4 cal cm-’ min- ’ (Fig. 4)) suggesting a negative relationship between nutrient content and photosynthesis rate. The increase in cloud cover in the region decreases solar radiation and thus increases the photosynthesis rate. This causes an increase in zooplankton and phytoplankton production (Paul, 1976). Cheng et al. ( 1989) also reported that an increase in cloud cover increases zooplankton and phytoplankton production, causing aggregation of Japanese sardine in the area. Apparently, the school density of larval anchovy is closely related to the abundance of plankton. As mentioned above, the school density and school size of larval anchovy may indicate the level of its aggregation, while the daily catches may indicate stock abundance in the aggregation. Based on the results of this study, mean body length, surface water temperature, salinity and food availability (plankton production) are the primary factors controlling the aggregation and abundance of larval anchovy that supports the larval anchovy fishery in coastal waters of Fangliao.
Acknowledgements This study was supported by the Council of Agricultural of the Executive Yuan, Republic of China (Program:AST81-FID-2.1 l-7). We would like to thank other colleagues in the
M.A. Lee, K.T. Lee /Fisheries
Research 26 (1996) 3748
47
Department of Fishery Science, National Taiwan Ocean University, for their valuable suggestions and comments, and Chin-Hsin Liao, Shih-Ching Chou and Pei-Chang Lee for their technical assistance.
References Bando, M., 1987. On the poor catch for Japanese anchovy in western Enshu Nada, Ise Bay and Mikawa Bay, 1987. Bull. Jpn. Sot. Fish. Oceanogr., 52(3): 266269. Chao. S.C., 1993. Studies on the short-term fluctuation of fishing condition of fish larvae and juveniles in the coastal waters adjacent to the Tanshui River Estuary, Taiwan. Master’s Dissertation, National Taiwan Ocean University. 72 pp. Chen, T.S., 1980. Study and investigation of bullard and anchovy fisheries in the coastal waters of Taiwan. Bull. Taiwan Fish. Res. Inst., 32: 219-233. Chen, T.S., 1987. Identification of engraulid larval fish. Bull. Taiwan Fish. Res. Inst., 42: 77-89. Chen, T.S. and Jean, C.T., 1982. Studies on larval fish and anchovy fisheries in the coastal waters of Taiwan: Relationship between larval fish, anchovy and mackerel, Jack. Bull. Taiwan Fish. Res. Inst., 34: 69-75. Cheng, L.J., Kishi, M.J. and Sugimoto, T., 1989. Multivariate analysis on the catch data of sardine and environmental data off Boso and Johban, Japan. Bull. Jpn. Sot. Fish. Oceanogr., 53(4): 372-377. FAO, 1983. Fisheries acoustics: A practical manual for aquatic biomass estimation. FAO Fish. Technol.. 240: l249. Fiedler, P.C.. Methot, R.D. and Hewitt, R.P., 1986. Effects of CalifomiaEl Nino 1982-84 on the northern anchovy. J. Mar. R.es.. 44: 317-338. Funakoshi, S.. 1988. Biological production mechanism of the Japanese anchovy and Japanese sardine shirasu in Suruga Bay and Enshu Nada. Bull. Jpn. Sot. Fish. Oceanogr., 52( 3): 240-243. Hwu, S.G., 11994. A preliminary study on the monthly fluctuation of fishing condition of larval anchovy in the coastal waters of southwestern Taiwan. Master’s Dissertation, National Taiwan Ocean University, 76 pp. Johnson, R.A. and Wichern, D.W., 1988. Applied Multivariate Statistical Analysis, Prentice Hall, London, 594 PP.
Koslow, J.A.. 1981. Feeding selectivity of schools of northern anchovy, Engruulis mnrdax, in the southern California Bight. Fish. Bull., 79( 1): 131-142. Lasker, R., 1078. The relation between oceanographic conditions and larval anchovy food in the California current: Identification of factors contributing to recruitment failure. Rapp. P.-V. Renu., Cons. Int. Explor. Mer, 177: 322-354. Lasker, R., I’98 I. Factors contributing to variable recruitment of the northern anchovy (Engrauliu mordux) in the Californi;a current: Contrasting years, 1975 through 1978. Rapp. P.-V. Renu., Cons. Int. Explor. Mer. 178: 375-388. Lasker, R., 1088. Studies on the northern anchovy: Biology, recruitment and fishery oceanography. Bull. Jpn. Sot. Fish. Oceanogr., 53( I): 88-94. Lee, K.T.. Lee. M.A. and Leu, S.R., 1987. Studies on quantification of echo sounder signals and comparison of the acoustic scattering characteristics of fishes with different body shape. J. Fish. Sot. Taiwan, 14(2): 53-66. Lee. K.T., Lszu. S.R.. Wu, L.J. and Wu, M.C., 1988a. The characteristics of construction and distribution of moontish schools in the coastal waters of southwestern Taiwan, Acta Oceanogr. Taiwanica, 20: 64-78. Lee. K.T., Sun, F.J., Liu, C.H. and Lee, M.A., 1988b. Studies on the estimation of the biomass of shirasu (Engrauhdae) by echograms shown in an echosounder. J. Fish. Sot. Taiwan, 15(2): 4S-54. Lee, M.A., I99 I. Fundamental studies on the hydroacoustic abundance assessment and fishing condition fluctuation of larval anchovy in the coastal waters of Fang-Liao. Ph.D. Dissertation, National Taiwan Ocean University. 214 pp. Lee, M.A., Lee, K.T., Sun, F.J., Shih, W.H. and Ou, H.C., 1989. Study on the relationship between acoustic backscattering strength and density of larval anchovies. J. Fish. Sot. Taiwan, 16(4): 217-230. Lee, M.A.. Lee, K.T. and Ou, H.C., 1990. The larval anchovy fishing ground formation in relation to osmotic pressure changes of the coastal waters along southern Taiwan. J. Fish. Sot. Taiwan, 17(4): 233-245.
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Lee, M.A., Lee, K.T. and Chao, SC., 1993. Estimation of the biomass of larval anchovy along the coastal waters of Fangliao by a hydroacoustic method. J. Fish. Sot. Taiwan, 20( 2) : 105-l 12. Lee, M.A., Lee, K.T. and Shiah, G.Y., 1994. Seasonal changes in commercial catches of larval anchovy in the southwest coastal waters of Taiwan. J. Fish. Sot. Taiwan, 21( 1): 49-56. Liu, C.H., 1989. Studies on the factual distributional condition and fishing ground of Engraulid larval fish off the coastal waters of I-Lan Hsin. Master’s Dissertation, National Taiwan Ocean University, 71 pp. Methot, R.D., 1983. Seasonal variation in survival of larval anchovy, Engraulis moraizx, estimated from the age distribution of juveniles. Fish. Bull. US, 81: 741-750. Mitani, I., 1988. Food habits of Japanese anchovy in the shirasu fishing ground within Sagami Bay. Nippon Suisan Gakkaishi, 54( 1): 1859-1865. Mitani, I., 1990. Biological studies on the larvae of Japanese anchovy, Engraulis japonica Houttuyn, in Sagami Bay. Ph.D. Dissertation, University of Hokkaido, 213 pp. Mitani, 1. and Hasegawa, T., 1988. The shirasu fishing ground formations and sea surface salinity change in Sagami Bay. Bull. Jpn. Sot. Fish. Oceanogr., 52(4): 297-303. Murphy, G.T., 1974. Report of the fourth session of the panel of experts on stock assessment of Peruvian anchoveta. Inst. Mar. Peru, 2: 605-719. Nojima, M. and Nakamura, Y., 1988. Biological study on the shirasu in the adjacent waters to Satsunan sea region. Bull. Jpn. Sot. Fish. Oceanogr., 52(3): 248-252. Parrish, R.H., Nelson, C.S. and Bakun, A., 1981. Transport mechanism and reproductive success of fish in the California current. Biol. Oceanogr., 1: 175-203. Parsons, T.R., LeBrssur, R.J. and Barraclough, W.E., 1970. Levels of production in the pelagic environment of the strait of Georgia, British Columbia: A review. J. Fish. Res. Board Can., 27(7): 1251-1264. Paul, B., 1976. Marine Plankton Ecology. North-Holland, Amsterdam, 355 pp. Pieper, R.E. and Bargo, B.G., 1980. Acoustic measurements of a migrating layer of the Mexican lampfish, Triphofurus mexicanus, at 102 Kilohertz. Fish. Bull., 77(4): 935-942. Sun, F.J., 1988. Basic studies on the standing crop of Engraulid larval fish off the coastal waters of northeast Taiwan by an acoustic assessment method. Master’s Dissertation, National Taiwan Ocean University, 57 pp. Tzeng, W.N. and Wang, Y.Z., 1992. Structure, composition and seasonal dynamics of the larval and juvenile fish community in the mangrove estuary of Tanshui River. Taiwan Mar. Biol., 113: 481-490. Young, S.S., Chen, CC. and Chiu, T.S., 1992. Resource characteristics of young herring-like fish in the I-Lan Bay area: Fishing season, major species and size variation. J. Fish. Sot. Taiwan, 21(4): 263-271.
Fisheries Research 26 ( 1996) 3748
The larval anchovy (Engraulis japonicus) fishery in relation to the environmental factors in coastal waters of Fangliao, Taiwan M.A. Lee *, K.T. Lee Lkpnrtnwnt
oj’Fishery Science, National Taiwan Ocean University, Keelung. 20224, Taiwan, ROC
Accepted 20 May 1995
Abstract Daily commercial catches, school densities and school sizes of larval anchovy (EngruufisjuponiUS), and oc:eanographic and meteorological variables for the spring fishing season (January to June) from 1988 to 1990 were analyzed by multiple regression analysis to identify factors influencing the aggregation and abundance of larval anchovy in the coastal waters of Fangliao, Taiwan. The results suggest the important factors were school density, that related to the mean body length of the larvae, surface water temperature, that determined the occurrence of Engraulis japonicus, surface water salinity, that was affected by river discharge and spring and neap tides, and the phosphate content and solar radiation, that affected plankton production. Kevwords:
Anchovy fishery; Engraulis japonicus; Larval anchovy
1. Introduction Larval anchovy is fished for human food because of its high protein content and attractive taste (Sun, 1988; Lee, 1991). Anchovy is also utilized for fish meal (Lasker, 1988). A long fishing period, coastal fishing grounds and a significant exploitation proportion of the recruits are the main characteristics of this fishery (Lee et al., 1990)) which constitutes one of the most important fisheries in the coastal waters of Fangliao, Taiwan (Fig. 1) . Several types of gear have been used. These include trawlnet, light attracting lift net, beach seine and set net. Of these the trawlnet operated by a pair of trawlers, introduced in 1979, has been the most effective and dominant gear (Lee et al., 1994). According to the landing records of the Fangliao Fishermen’s Association, the annual catch of larval anchovy during * Corresponding
author.
016%7836/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDlO165-78X6(95)00412-2
M.A. Lee, K.T. Lee/Fisheries Research26 (I 996) 3748
38
Isobath
--.--_.SOm
-... ---
Fig.
-...
30m
--10m
I. Larval anchovy fishing ground (shaded area) in the coastal waters of Fangliao, Taiwan.
the period from 1980 to 1993 averaged 550 tons, with a cash value of NT$35 million (US$ 1.4 million). This accounted for about 20% of the total annual production of larval anchovy in Taiwan. The catches were primarily composed of the larvae (total length, 1.5-4 cm) of Engraulis japonicus, Encrasicholina punctifer, E. heteroloba and commercially unimportant species of the family Engraulidae. Larvae of other species from such genera as Scombridae, Carangidae, Leiognathidae and Elopidae were rare (about 5-10%) (Sun, 1988; Liu, 1989). Because of the economic importance of the fishery and concern for its possible effect on coastal resources, the stock abundance, biology and oceanography of larval anchovy have been studied intensively in Taiwan and other countries (Murphy, 1974; Lasker, 1978; Chen, 1980; Koslow, 1981; Lasker, 1981; Parrish et al., 1981; Chen and Jean, 1982; Methot, 1983; Fiedler et al., 1986; Bando, 1987; Lasker, 1988; Mitani, 1988; Cheng et al., 1989; Tzeng and Wang, 1992; Young et al., 1992; Lee et al., 1993; Lee et al., 1994). With respect to environmental factors affecting the fishery, Lee et al. ( 1990) indicated that in the coastal waters of southwest Taiwan, larval anchovy aggregated along the region of intermediate salinity (between 33.85 p.p.t. and 34.5 p.p.t.) between the flow axis of river discharge with low salinity and that of the offshore current with high salinity. In Sagami
M.A. Lee, K.T. Lee/Fisheries
Research 26 (1996) 37-48
39
Bay, Japan, the location of larval anchovy fishing grounds was also reported to be related to surface water salinity (Mitani and Hasegawa, 1988). Lasker ( 1988) noted the effects of storms and upwelling, and suggested that if newly hatched larvae did not find suitable food as soon as they were ready to eat then they would die. The present study analyses the daily data of commercial catches, school densities and school sizes of larval anchovy, and oceanographic and meteorological variables, by multiple regression analysis to identify factors controlling the abundance and aggregation of larval anchovy in coastal waters of Fangliao.
2. Materials and methods During the spring fishing seasons (January to June) from 1988 to 1990,39 hydroacoustic surveys were conducted, using the method described by Lee et al. ( 1993)) in coastal waters of southwestern Taiwan (Fig. 1) . For each survey an echosounder (Model he301, Honda Inc.) with a 200 kHz transducer (Lee et al., 1987) was deployed on the trawler ‘Hsin-linpo 226’ and towed at the side of the vessel at a speed of 1.5 m s- ’ at a depth of 1.5 m. The echosounder was set at 5 pings per second, a pulse duration of 0.6 ms, a beam angle ( - 3 dB ) of 12” and a bandwidth of 3 kHz. Each hydroacoustic survey lasted for 4 h. In addition, surface water temperature, salinity and current speed and direction were recorded by an SD201 multiparameter probe and an SD4 current meter. Surface water temperature was measured with a mercury thermometer, and salinity by a conductivity salinometer and standard seawater. One liter of seawater was collected and frozen for nitrate and phosphate analyses In the laboratory, the echo traces of larval anchovy schools on the echogram were selected, using the rnethod described by Lee et al. (1988a) and Sun (1988), for the measurements of vertical thickness (V) and horizontal extension width (H). The school size was estimated for each hydroacoustic survey by the formula S = ITH~V/~, as the shape of the school was defined as the cylinder described by Sun (1988). In addition, the echo signals on the magnetic tape obtained from the surveys were monitored on a synchroscope (Lee et al., 1987). Also. echo signals of larval anchovy schools were selected (Lee et al., 1988b), and their average backscattering strength (S,) and school density were measured by the method described by FAO (1983) and Lee et al. (1989). The school density (D) was estimated by the formula S, = S, + IOlogD (Pieper and Bargo, 1980)) where S, is the target strength. The S, value was estimated from the mean body length (BL) of the larvae using the formula S, = 26.421ogBL - 110.65 estimated by Lee et al. ( 1989). For each day of the hydroacoustic survey, commercial catches of larval anchovy were obtained from the Fishermen’s Association of Fangliao. Samples of scoops of the larvae were collected from the catches. The species composition of the sample was determined (Chen, 19X7), and body lengths of individual larvae in the sample were measured. The occurrence rate (O,.) of Engraulis japonicus was estimated by the following equation: 100 O’=“‘X(Mi+M,)
40
M.A. Lee, K.T. Lee/Fisheries
Research 26 (1996) 3748
where 4 is the abundance of Engraulis japonicus in the samples, and MOis the abundance of Encrasicholina punctiyer and E. heteroloba in the samples; these are the major species caught in this fishery. Meteorological data, including air temperature, wind speed, precipitation, solar radiation and atmospheric pressure, were obtained from the HengChun station of the Taiwan Central Weather Bureau. Daily discharges of the Linpein river in the vicinity of Fangliao were obtained from the Hsinpin station of the Taiwan Provincial Water Conservancy Bureau. The tide levels in the coastal waters of Fangliao were obtained from the Chinese Naval Hydrographic and Oceanographic Office. Multiple regression analysis (Johnson and Wichern, 1988) was used to relate the daily catches, school densities and school sizes of larval anchovy (dependent variables) to oceanographic and meteorological data (independent variables). The independent variables were surface water temperature, surface water salinity, current speed, phosphate and nitrate content, air temperature, atmospheric pressure, precipitation, river discharge, wind speed, solar radiation and cloud cover. In addition, the species composition and body length of the larvae were used as independent variables. All data were standardized by linear transformation using the formula (Xi -X) /SD to remove differences due to scaling. Xi is the observation of datum i, and X and SD are the mean and standard deviation of the data, respectively (Johnson and Wichern, 1988). The correlation coefficients of dependent and independent variables are obtained by using linear regression methods. If the coefficient between independent variables is high and attains the 1% significance level, the correlation coefficients between dependent and independent variables are compared with each other. The factor which affects the dependent variable with a high correlation coefficient is then chosen. Finally, by using the stepwise procedure of multiple regression analysis, the factor that affects the dependent variables is obtained. The dependent variable could generally be described by the joint probability density function of independent variables. This equation is
where Y is the dependent variable, a, is a constant value about zero and m is the number of independent variables. bi and Xi are the ith partial correlation coefficients and standardized value of independent variables among the joint probability density function, respectively.
3. Results Table 1 shows the daily catches, school densities and school sizes of larval anchovy from the 39 hydroacoustic surveys, and associated meteorological and oceanographic data. Table 2 gives the matrix of correlation coefficients between the daily catches, school sizes and densities, and meteorological and oceanographic data. As shown in Table 2, the solar radiation and cloud cover, atmospheric pressure and wind speed, and phosphate and nitrate content of sea water have high correlations, with coefficients of - 0.862, 0.728 and 0.8 16, respectively. Also, the correlation coefficients of phosphate, nitrate, atmospheric
M.A. Lee, K.T. Lee/Fisheries Table 1 Biological and environmental January to June 1988-1990
Research 26 (1996) 37-48
data obtained for 39 hydroacoustic
41
surveys in the coastal waters of Fangliao, Taiwan,
Variables
Sample size
Mean
Standard deviation
Daily catches (Kg) School sizes (ml) School densities (individuals mm ‘) Phosphate content of seawater (mg I-‘) Nitrate content of seawater (gg I_ ’ ) Surface water temperature(“C) Surface water salinity (p.p.t.) Current speeli ( m s ’ ) River discharge of linpein hsi ( m3 s- ’ ) Air temperature (“C) Atmospheric pressure (mbar) Precipiation (mm) Wind speed ( m s_ ’ ) Solar radiation (cal m-’ min-‘) Cloud coverage Tide level (III) The occurrence rate of Engraulis japonicus (%) Mean body length (cm)
39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39
5730.8 4.6 1294.3 19.6 4.4 25.3 34.2 0.47 1.23 23.9 1011.3 10.76 2.94 3.17 6.12 1.45 72.33 2.45
5903.3 1.30 854.40 16.90 3.60 1.50 0.13 0.15 2.22 2.53 4.02 25.06 1.49 1.84 2.73 0.25 3 I .77 0.27
pressure, wind speed, solar radiation and cloud cover with the daily catches were - 0.128, - 0.2 16, -- 0.123, - 0.143, - 0.004 and - 0.033, respectively, suggesting that variables of phosphate content, atmospheric pressure and solar radiation were excluded in the multiple regression analysis of daily catches. Table 3 shows the results of multiple stepwise analysis for (a) daily catches, (b) school densities and (c) school sizes, and environmental variables. As shown in Table 3(a), school densities, tide level, nitrate content and the mean body length of the larvae are the major variables affecting the daily catch. The multiple regression equation, with a correlation coefficient of 0.89 1, can be expressed as follows: Y, = 0.579Y, - O.372X,s +0.247X,,
-0.206X,
where Y, is the daily catch, Yx is the school densities of larval anchovy, X,, is the mean body length of the larvae, X,, is the tide level and X, is the nitrate content of sea water. The partial correlation coefficients of the mean body length of the larvae and the nitrate content of sea water were - 0.372 and - 0.206, respectively. Fig. 2 shows the relationship between the 5day total catches and mean body lengths from February to May 1990. During the period from late March to the middle of April, the mean body lengths were smaller and the daily catches were higher as compared with those taken in the periods before late March and after the middle of April. On the other hand, the partial correlation coefficients of school densities and tide level to daily catches were 0.579 and 0.247, respectively. This implies that the daily catches increased significantly with an increase in school densities and tide level. The factors affecting the daily catches were similar to those affecting school densities. Table 3(b) shows the results of multiple regression analysis made between the school densities and the
- 0.456
- 0.255
- 0.075
+0.058
+0.471
+0.092
- 0.200
f0.158
- 0.003
+0.156
- 0.022
- 0.024
-0.160
- 0.287
+ 0.274
-0.162
- 0.682
+0.846*
- 0.079
+ 0.076
-0.217
-0.128
-0.216
- 0.420
-0.116
- 0.427
-0.194
- 0.203
-0.123
- 0.067
-0.143
- 0.004
- 0.033
+0.311
+ 0.280
- 0.559
-0.009
- 0.075
- 0.022
+ 0.060
-0.445
-0.131
- 0.360
+ 0.084
+ 0.394
+ l.c00
- 0.095
+1.000
Y,
f0.735’
Y2
- 0.003
+ l.ooQ
Y,
+0.071
+0.238
-0.069
-0.222
+0.181
+0.039
-0.139
io.049
-0.193
f0.094
f0.001
+0.058
- 0.052
f0.816’
+1.000
XI
-0.661
-0.014
- 0.222
+0.142
-0.161
+ 0.090
+ 0.092
+0.121
- 0.154
+0.011
+0.044
+0.162
+0.032
+ 1.000
XZ
+0.348
- 0.098
+ 0.276
+0.062
+0.016
- 0.266
+o.Ooo
- 0.333
f0.444
- 0.356
+0.187
+ 0.282
fl.000
X1
+ 0.262
- 0.653
+ 0.202
+0.285
-0.159
- 0.334
+0.117
-0.194
+0.260
+0.096
+ 0.295
+1.000
X,
+0.311
-0.159
+0.176
- 0.008
+ 0.092
- 0.109
- 0.079
-0.171
+0.278
+0.188
+1.OQO
XS
variables.
+ 0.090
- 0.056
-0.138
-0.005
to.021
- 0.033
+0.142
- 0.089
f0.026
+1.OQo
X6
f0.213
- 0.301
+0.572
-0.170
+ 0.323
- 0.503
-0.133
-0.616
+1.000
Xl
+ 0.057
-0.167
- 0.681
- 0.258
+0.120
+ 0.728’
- 0.038
+1.OfKJ
X,
-0.063
-0.059
-0.237
+0.442
-0.532
-0.061
+ l.OOll
X9
+0.030
+0.061
-0.661
-0.158
f0.062
fl.000
Xl0
+0.148
-0.069
+0.182
-0.862’
f1.000
X,,
-0.165
+0.005
-0.134
+I.000
X,2
-0.051
-0.026
+ l.ooo
XI3
-0.461
+ 1.000
XM
+ I.@30
XIS
YI. daily commercia1 catch; YI, school size; Y,, school density of larva1 anchovy; X,, phosphate content of sea water; X,, nitrate content of sea water; X,, surface water temperature; X4, surface water salinity; X5, mean C~~enf sped; X,, discharge of the Linpein river; X,. air temperature; X,, atmospheric pressure; X,, precipitation; X,,,, wind speed; X, ,, solar radiation; X1*. cloud cover; X,,, tide level; X1.,.occurrence rate of Engraulis juponicus; X Ls, mean body length of larvae. * p < 0.01
Variables
Correlation coefficients between dependent (Y,, Y?, Y,) and independent (X,-X,,)
Table 2
M.A. Lee, K.T. Lee/Fisheries Research26 (1996) 37-48 Table 3 Multiple regression stepwise analysis to determine the component (b) the school densities and (c) the school sizes of larval anchovy
43
effects on (a) the daily commercial
catches,
(a) Daily catches steps %
I 2 3 4
Y,
XI,
XI,
xz
13,
b>
b,
J,,
-0.001 +0.737 I + 0.545
- 0.00 -0.001 -0.001
- 0.402 -0.381 -0.372
+0.292 +0.247
-0.206
x,5
X,
XI,
X,
&
X,
(10
b,
bz
bl
bs
b,
b,
+ 0.000 + 0.000 +0.000 + 0.000 + 0.000 + 0.000 + 0.000
- 0.477 - 0.362 -0.193
+0.558 +0.579
R’
F
Degrees of freedom
0.5416 0.6663 0.6539 0.7940
43.73 35.94 35.74 32.76
(1.37) (2,36) (3,35) (4,34)
R?
F
Degrees of freedom
0.2274 0.3231 0.4177 0.3920 0.4670 0.5348 0.5755
10.89 8.59 8.37
( 1.37)
(2,36) (3,35) 11.60 (2,36) 10.22 (3,35) 9.77 (4.34) 8.95 (5,33)
R’
F
Degreesof freedom
0.7168
93.66
(1.37)
(b) School densities Steps
I
2 3 4 5 6 I
- 0.330 -0.355 -0.414 -0.521 -0.624 -0.578
+0.34s +0.431 + 0.404 +0.631 +0.636
- 0.295 -0.355 -0.301
+0.368 +0.418
-0.219
(c) School sizes
steps
I
Xi?
“0
b,
0.000
0.845
oceanographic and meteorological variables in the present experiment. The partial correlation coefficients of the occurrence rate of Engraulis juponicus (X,,) and surface water salinity (X,,), surface water temperature (X,), discharge of the Linpein river (X,) and current speed (X,) were 0.636, 0.418, - 0.578, - 0.301 and - 0.219, respectively. This implies that the school densities and catches of larval anchovy increased significantly with an increase in the occurrence rate of Engraulis japonicus and surface water salinity, but decreased with a rise in river discharge (Fig. 3), surface water temperature and current speed. Table 3(c) shows that cloud coverage is the major factor affecting the school sizes of larval anchovy. This correlation coefficient of 0.845 implies that the school sizes were correlated with the cloud coverage and solar radiation (Table 2). 4. Discussions and conclusions The results of this study suggest that daily catches and school densities of larval anchovy are affected by biological factors such as the occurrence rate of Engraulis juponicus and
44
M.A. Lee, K.T. Lee/Fisheries
Research 26 (1996) 3748
30
3.5
25 3.0 m z ,o
20 C _c 15
25 3
c 0 ;
a m”
10 20 5
0
1.5 February
March
April
May
Date Fig. 2. Five-day catches (open bars) and mean body length (continuous waters of Fangliao, Taiwan, February to May 1990.
line) of Iarval anchovy
in the coastal
Month Fig. 3. Monthly mean variation of catches and river discharge of the Linpein hsi in the coastal waters of Fangliao, Taiwan. The solid circles and vertical lines represent the mean and range of observation variables, respectively.
M.A. Lee, K.T. Lee/Fisheries
Research
26 (1996) 3748
45
the body length of the larvae, and by physical and chemical factors including surface water temperature, surface water salinity, current speed, river discharge, phosphate and nitrate concentrations, and the tide level. The factors affecting the school sizes were the cloud cover and solar radiation (Table 2 and Table 3 (c) >. 4.1. Biological factors The biological factors affecting the larval anchovy fishery include the occurrence rate of Engraulis japonicus and fish body length (Table 3). The occurrence rate is positively related to the catches and school densities. This means that the catch increased significantly with an increase of the occurrence rate and school densities. Such a relationship is similar to that reported by Lee et al. ( 1990), Lee ( 1991) and Lee et al. ( 1994). In addition, the daily catch of larval anchovy was negatively related to the mean body length of the larvae (Table 3 (a) ) Lee ( 199 1) indicated that recruitment occurred with small larvae during the period from late March to the middle of April. However, in the periods before late March and after the middle of April, only one larval anchovy recruitment school occurred. Thus, following the growth of the larval anchovy, the catch of standing schools was gradually decreased. 4.2. Physical and chemical factors For the relationships between the larval anchovy fishery and the surface water temperature, Lee et al. ( 1990) reported that the catches dropped by almost 45% as a result of a rise in water temperature in 1988. During this year of high surface water temperatures, catches were greatly reduced and the genus Encrasicholina was dominant. During a year of low water temperatures, Engraulis japonicus became dominant and the catches increased (Lee et al., 1994). There is obviously a relationship between the abundance of anchovy larvae and the occurrence of dominant species in these fishing grounds which is strongly influenced by the surface water temperature. For surface water salinity and river discharge, Lee et al. (1990) pointed out that larval anchovy schools usually inhabit areas close to the mixing areas of ocean currents and river water. Funakoshi (1988) argued that ocean currents and Kuroshio waters tended to cause larval anchovy to inhabit in the coastal waters. Nojima and Nakamura (1988) found that when the waters which were uninhabitable to larval anchovy (i.e. Kuroshio) reached the coast, the larval anchovy schools tended to pack densely together. On the other hand, precipitation and river discharge are obviously closely related. Lee et al. ( 1994) reported that larval anchovy production was negatively correlated with precipitation and river discharge. In Japan, catches of larval anchovy were found to be inversely related to precipitation (Nojima and Nakamura, 1988; Mitani, 1990). The occurrence of heavy freshwater runoff into coastal waters at the time of typhoons and during the monsoon season was known to have an adverse effect on larval anchovy production (Mitani and Hasegawa, 1988) For tide level and current speed, Chao ( 1993) reported that when the convergence speed of the tide and/or current front was greater than 6 cm s - I. the abundance of anchovy larvae was small, and most of the schools inhabited the area of low convergence speed ( <4 cm sP ‘). In addition, Hwu (1994) thought that the school distribution of larval anchovy
M.A. Lee. K.T. Lee/Fisheries
46
05 a ._ E -_ E 2 “0 v E .z 2 Gi e
Research 26 (1996) 37-48
‘I
04
03
t+t 02
t
t+
t1 t
+
2 ,”
01
aI-
-rTTl-,
J
,
FMAMJ
It
I
I
I
I
I
J
A
S
0
N
I
D
Month Fig. 4. Monthly variation of mean solar radiation in the coastal waters of Fangliao, Taiwan, 1982-1992.
followed the direction of the current and tide. During the periods of northward current (spring tide) in the southwest waters of Taiwan, the school will aggregate to the north in the shallow water of the fishing grounds. During the periods of southward current (neap tide), the school will be distributed randomly on the grounds. Current speed and tide level are thus important factors affecting the aggregation and abundance of larval anchovy schools. For phosphate content and solar radiation, it is known that a massive production of zooplankton and phytoplankton from intensive photosynthesis results in a low phosphate content (Parsons et al., 1970; Cheng et al., 1989). In coastal waters of southwest Taiwan, solar radiation was between 0.15 and 0.4 cal cm-’ min- ’ (Fig. 4)) suggesting a negative relationship between nutrient content and photosynthesis rate. The increase in cloud cover in the region decreases solar radiation and thus increases the photosynthesis rate. This causes an increase in zooplankton and phytoplankton production (Paul, 1976). Cheng et al. ( 1989) also reported that an increase in cloud cover increases zooplankton and phytoplankton production, causing aggregation of Japanese sardine in the area. Apparently, the school density of larval anchovy is closely related to the abundance of plankton. As mentioned above, the school density and school size of larval anchovy may indicate the level of its aggregation, while the daily catches may indicate stock abundance in the aggregation. Based on the results of this study, mean body length, surface water temperature, salinity and food availability (plankton production) are the primary factors controlling the aggregation and abundance of larval anchovy that supports the larval anchovy fishery in coastal waters of Fangliao.
Acknowledgements This study was supported by the Council of Agricultural of the Executive Yuan, Republic of China (Program:AST81-FID-2.1 l-7). We would like to thank other colleagues in the
M.A. Lee, K.T. Lee /Fisheries
Research 26 (1996) 3748
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Department of Fishery Science, National Taiwan Ocean University, for their valuable suggestions and comments, and Chin-Hsin Liao, Shih-Ching Chou and Pei-Chang Lee for their technical assistance.
References Bando, M., 1987. On the poor catch for Japanese anchovy in western Enshu Nada, Ise Bay and Mikawa Bay, 1987. Bull. Jpn. Sot. Fish. Oceanogr., 52(3): 266269. Chao. S.C., 1993. Studies on the short-term fluctuation of fishing condition of fish larvae and juveniles in the coastal waters adjacent to the Tanshui River Estuary, Taiwan. Master’s Dissertation, National Taiwan Ocean University. 72 pp. Chen, T.S., 1980. Study and investigation of bullard and anchovy fisheries in the coastal waters of Taiwan. Bull. Taiwan Fish. Res. Inst., 32: 219-233. Chen, T.S., 1987. Identification of engraulid larval fish. Bull. Taiwan Fish. Res. Inst., 42: 77-89. Chen, T.S. and Jean, C.T., 1982. Studies on larval fish and anchovy fisheries in the coastal waters of Taiwan: Relationship between larval fish, anchovy and mackerel, Jack. Bull. Taiwan Fish. Res. Inst., 34: 69-75. Cheng, L.J., Kishi, M.J. and Sugimoto, T., 1989. Multivariate analysis on the catch data of sardine and environmental data off Boso and Johban, Japan. Bull. Jpn. Sot. Fish. Oceanogr., 53(4): 372-377. FAO, 1983. Fisheries acoustics: A practical manual for aquatic biomass estimation. FAO Fish. Technol.. 240: l249. Fiedler, P.C.. Methot, R.D. and Hewitt, R.P., 1986. Effects of CalifomiaEl Nino 1982-84 on the northern anchovy. J. Mar. R.es.. 44: 317-338. Funakoshi, S.. 1988. Biological production mechanism of the Japanese anchovy and Japanese sardine shirasu in Suruga Bay and Enshu Nada. Bull. Jpn. Sot. Fish. Oceanogr., 52( 3): 240-243. Hwu, S.G., 11994. A preliminary study on the monthly fluctuation of fishing condition of larval anchovy in the coastal waters of southwestern Taiwan. Master’s Dissertation, National Taiwan Ocean University, 76 pp. Johnson, R.A. and Wichern, D.W., 1988. Applied Multivariate Statistical Analysis, Prentice Hall, London, 594 PP.
Koslow, J.A.. 1981. Feeding selectivity of schools of northern anchovy, Engruulis mnrdax, in the southern California Bight. Fish. Bull., 79( 1): 131-142. Lasker, R., 1078. The relation between oceanographic conditions and larval anchovy food in the California current: Identification of factors contributing to recruitment failure. Rapp. P.-V. Renu., Cons. Int. Explor. Mer, 177: 322-354. Lasker, R., I’98 I. Factors contributing to variable recruitment of the northern anchovy (Engrauliu mordux) in the Californi;a current: Contrasting years, 1975 through 1978. Rapp. P.-V. Renu., Cons. Int. Explor. Mer. 178: 375-388. Lasker, R., 1088. Studies on the northern anchovy: Biology, recruitment and fishery oceanography. Bull. Jpn. Sot. Fish. Oceanogr., 53( I): 88-94. Lee, K.T.. Lee. M.A. and Leu, S.R., 1987. Studies on quantification of echo sounder signals and comparison of the acoustic scattering characteristics of fishes with different body shape. J. Fish. Sot. Taiwan, 14(2): 53-66. Lee. K.T., Lszu. S.R.. Wu, L.J. and Wu, M.C., 1988a. The characteristics of construction and distribution of moontish schools in the coastal waters of southwestern Taiwan, Acta Oceanogr. Taiwanica, 20: 64-78. Lee. K.T., Sun, F.J., Liu, C.H. and Lee, M.A., 1988b. Studies on the estimation of the biomass of shirasu (Engrauhdae) by echograms shown in an echosounder. J. Fish. Sot. Taiwan, 15(2): 4S-54. Lee, M.A., I99 I. Fundamental studies on the hydroacoustic abundance assessment and fishing condition fluctuation of larval anchovy in the coastal waters of Fang-Liao. Ph.D. Dissertation, National Taiwan Ocean University. 214 pp. Lee, M.A., Lee, K.T., Sun, F.J., Shih, W.H. and Ou, H.C., 1989. Study on the relationship between acoustic backscattering strength and density of larval anchovies. J. Fish. Sot. Taiwan, 16(4): 217-230. Lee, M.A.. Lee, K.T. and Ou, H.C., 1990. The larval anchovy fishing ground formation in relation to osmotic pressure changes of the coastal waters along southern Taiwan. J. Fish. Sot. Taiwan, 17(4): 233-245.
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Research 26 (1996) 3748
Lee, M.A., Lee, K.T. and Chao, SC., 1993. Estimation of the biomass of larval anchovy along the coastal waters of Fangliao by a hydroacoustic method. J. Fish. Sot. Taiwan, 20( 2) : 105-l 12. Lee, M.A., Lee, K.T. and Shiah, G.Y., 1994. Seasonal changes in commercial catches of larval anchovy in the southwest coastal waters of Taiwan. J. Fish. Sot. Taiwan, 21( 1): 49-56. Liu, C.H., 1989. Studies on the factual distributional condition and fishing ground of Engraulid larval fish off the coastal waters of I-Lan Hsin. Master’s Dissertation, National Taiwan Ocean University, 71 pp. Methot, R.D., 1983. Seasonal variation in survival of larval anchovy, Engraulis moraizx, estimated from the age distribution of juveniles. Fish. Bull. US, 81: 741-750. Mitani, I., 1988. Food habits of Japanese anchovy in the shirasu fishing ground within Sagami Bay. Nippon Suisan Gakkaishi, 54( 1): 1859-1865. Mitani, I., 1990. Biological studies on the larvae of Japanese anchovy, Engraulis japonica Houttuyn, in Sagami Bay. Ph.D. Dissertation, University of Hokkaido, 213 pp. Mitani, 1. and Hasegawa, T., 1988. The shirasu fishing ground formations and sea surface salinity change in Sagami Bay. Bull. Jpn. Sot. Fish. Oceanogr., 52(4): 297-303. Murphy, G.T., 1974. Report of the fourth session of the panel of experts on stock assessment of Peruvian anchoveta. Inst. Mar. Peru, 2: 605-719. Nojima, M. and Nakamura, Y., 1988. Biological study on the shirasu in the adjacent waters to Satsunan sea region. Bull. Jpn. Sot. Fish. Oceanogr., 52(3): 248-252. Parrish, R.H., Nelson, C.S. and Bakun, A., 1981. Transport mechanism and reproductive success of fish in the California current. Biol. Oceanogr., 1: 175-203. Parsons, T.R., LeBrssur, R.J. and Barraclough, W.E., 1970. Levels of production in the pelagic environment of the strait of Georgia, British Columbia: A review. J. Fish. Res. Board Can., 27(7): 1251-1264. Paul, B., 1976. Marine Plankton Ecology. North-Holland, Amsterdam, 355 pp. Pieper, R.E. and Bargo, B.G., 1980. Acoustic measurements of a migrating layer of the Mexican lampfish, Triphofurus mexicanus, at 102 Kilohertz. Fish. Bull., 77(4): 935-942. Sun, F.J., 1988. Basic studies on the standing crop of Engraulid larval fish off the coastal waters of northeast Taiwan by an acoustic assessment method. Master’s Dissertation, National Taiwan Ocean University, 57 pp. Tzeng, W.N. and Wang, Y.Z., 1992. Structure, composition and seasonal dynamics of the larval and juvenile fish community in the mangrove estuary of Tanshui River. Taiwan Mar. Biol., 113: 481-490. Young, S.S., Chen, CC. and Chiu, T.S., 1992. Resource characteristics of young herring-like fish in the I-Lan Bay area: Fishing season, major species and size variation. J. Fish. Sot. Taiwan, 21(4): 263-271.