Squid Jigging and Trap-Net Fishing

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The effect of lunar cycle, tidal condition and wind direction on the catches Title and profitability of Japanese common squid Todarodes pacificus jigging and trap-net fishing

Masuda, Daisaku; Kai, Shuya; Yamamoto, Naotoshi; Matsushita, Yoshiki; Author(s) Suuronen, Petri

Citation Fisheries Science, 80(6), pp.1145-1157; 2014

Issue Date 2014-11

URL http://hdl.handle.net/10069/36069

This document is downloaded at: 2017-12-22T09:09:41Z

http://naosite.lb.nagasaki-u.ac.jp 1 The effect of lunar cycle, tidal condition and wind direction on the catches and

2 profitability of Japanese common squid Todarodes pacificus jigging and trap-net

3 fishing

5 DAISAKU MASUDA, SYUYA KAI, NAOTOSHI YAMAMOTO, YOSHIKI

6 MATSUSHITA, AND PETRI SUURONEN

8 D. Masuda

9 Tsushima Fisheries Extension Center, Nagasaki Prefecture Tsushima Development

10 Bureau, Tsushima, Nagasaki, 817-0342, Japan

11 Tel: 81-920-54-2084. Fax: 81-920-54-2613.

12 email: [email protected]

13 S. Kai

14 Nagasaki Prefectural Institute of Fisheries, Taira, Nagasaki, 851-2213, Japan

15 email: [email protected]

16 N. Yamamoto ･ Y. M atsushita

17 Graduate School of Fisheries Science and Environmental Studies, Nagasaki University,

18 Bunkyo Nagasaki, 852-8521, Japan

19 email: [email protected] ･ [email protected]

20 P. Suuronen

21 Fisheries and Aquaculture Department of Food and Agriculture Organization of the

22 United Nations (FAO), Rome, Italy

23 email: [email protected]

25 Abstract

27 Jigging with artificial lights (squid jigging) and deploying of large scale trap-net

28 (also known as a set-net in Japan), are the major methods to capture Japanese common

29 squid Todarodes pacificus in western Japan. Squid jigging is a highly selective fishing

30 method. However, it consumes large amount of energy for steaming to the fishing

31 ground and for lighting. In contrast, trap-net fishing requires substantially less energy

32 but its capture efficiency is strongly influenced by its stationary mode of capture.

33 The primary objective of this study was to analyze how various environmental and

34 biological factors such as the lunar cycle, tidal condition, wind direction and squid

35 abundance affect the capture efficiency of squid jigging and trap-net fishing. We

36 analyzed the effect of these factors on squid catch in five Fisheries Cooperative

37 Associations located on four islands in Nagasaki Prefecture, western Japan. Our

38 analysis shows that squid catch in jigging and trap-net fishing is mainly influenced by

39 the lunar cycle but also tide and wind direction play a marked role. In addition, squid

40 abundance significantly affects the catches in trap-net fishing. Recommendations are

41 made to improve the overall profitability of squid fishing by proper choice of the

42 capture method, location and season.

44 Key words: Japanese common squid Todarodes pacificus, Catch analysis, jigging, trap-

45 net, moon phase, tide, wind, abundance

47 Introduction

49 Squid fishing has attracted growing interest world-wide over the last two decades and

50 squid catches have increased steadily with marked year-to-year fluctuations [1].

51 Japanese common squid Todarodes pacificus, swordtip squid Photololigo edulis and

52 cuttlefish Sepia esculenta are the major targets in Japan. In 2011, they accounted for

53 8% of the total annual landings in weight of the Japanese capture fisheries [2]. Japanese

54 common squid is commercially the most important Decapoda in Japan and since 1998

55 its harvesting has been managed by a TAC (Total Allowable Catch) system [3].

56 Japanese common squid is classified into three populations with different spawning

57 seasons (summer, autumn and winter) [4]. The populations that spawn in autumn and

58 winter are the main target populations. These populations spawn around Kyushu Island

59 [5], and after hatching, migrate to the north for feeding and return to Kyushu to spawn

60 a year later. Mobile squid jigging fleet follows the year-around migration path of squid

61 whereas non-mobile trap-net fishing is seasonally and spatially more restricted.

62 Squid jigging is the most common method for catching squid in East Asia. It uses

63 artificial light to attract squid in the nighttime and catches them by lures that are

64 attached to automated jigging machines. Fishermen are competing by using increasing

65 amount of lighting power to attract squid from further distances and consequently

66 electric output for lighting has escalated from a few kilowatts in 1960s to 300 kW in

67 1990s[6]. To reduce the effects of this competition, the Nagasaki Prefectural

68 government has limited the maximum power for lighting in coastal jigging boats of 5

69 to 30 GT. Similar regulations has also been provided by the Fisheries Adjustment

70 Commission for boats less than 5 GT that do not require a license for squid jigging.

71 Despite of these measures, squid jigging fishery has encountered financial difficulties

72 mainly due to the recent rise in fuel price [7-9].

73 Trap-net fishery, also known as set-net in Japan, uses large scale trap-nets set in

74 strictly licensed coastal locations. In general, trap-net fishing is an attracting capture

75 method due to its low energy use and minor impacts on habitats and environment [10].

76 Nonetheless, the initial investment costs for constructing a large scale trap-net are high

77 and it also requires relatively large amount of labor for its maintenance.

78 To provide the necessary knowledge-basis for promoting sustainable and profitable

79 utilization of squid resources around Kyushu, it is essential to know what are the

80 advantages and disadvantages, including the cost of operation, of these two different

81 fishing methods targeting the same stock.

82 The primary objective of this study was to improve our understanding how various

83 environmental factors such as the lunar cycle [11-15], tidal condition [14], wind

84 direction [14] and squid abundance [12-15], and their possible interactions, affect the

85 capture efficiency in squid jigging and trap-net fishing. This information is expected

86 to help optimizing the utilization of squid resources with these two gear types. We used

87 a Generalized Linear Model (GLM) analysis to study the relationship of various

88 environmental factors. We obtained the daily catch data of squid jigging and trap-net

89 fisheries in different islands during squid fishing seasons from 2009 to 2011 and

90 compared the trends of squid catches in both fisheries.

92 Materials and methods

94 Fishing data

96 Daily squid catch records during 2009-2011 were collected from five Fisheries

97 Cooperative Associations (FCAs) located on four islands in Nagasaki Prefecture

98 (Fig.1). In one FCA there were both squid jigging and trap-net fisheries whereas in Fig.1

99 others there was either trap-net or jigging fishery. We identified January and February

100 as a fishing season for Japanese common squid, whereas moderate catches with

101 annual fluctuations were recorded before and after the season (Fig.2). Along the three Fig.2

102 years of study the numbers of jigging boats and/or trap-nets in different FCAs varied

103 in the Table 1. Catch quantity for each fishery was provided in number of fish Table 1 104 containers (cases), each containing approximately 6 kg of Japanese common squid.

105 Fishing effort was provided by number of operating boats/trap-nets in the designated

106 day (Table 2). Table 2

107

108 Data analysis

109

110 To explore the effects and potential interactions of various factors, we performed

111 GLM analysis of expected catch amounts of Japanese common squid in squid jigging

112 and trap-net fisheries in the study area. The number of squid cases caught by fishing

113 sector i (i denotes one of six fisheries in this study), Ci was assumed to follow a

114 negative binomial distribution [12-15] with expected mean catch μi:

115 Ci ~ NB(μi, θi) (1)

116 where θi is a potential dispersion parameter to be estimated. Because our data set for

117 six fishing sectors (squid jigging fisheries in A and B, trap-net fisheries in A, C, D

118 and E) showed large dispersion (Table 2).

119 The expected mean catch μi is modeled with a log link function as,

120 log (μi) = ß0 + ß 1Moon + ß 2 Phase + ß 3 Tide + ß 4(Moon x Tide)

121 + ß 5Wind + ß 6N + log(Ei) (2)

122 where Moon is the ratio of the illuminating area of the moon at midnight. This ratio

123 varies between zero (new moon) and one (full moon) corresponding to the age of the

124 moon. Phase is a factor for the waxing and waning of the moon, expressing the time

125 period of appearance of the moon, i.e. the moon rises before midnight in the waxing

126 phase while it rises after midnight in the waning phase. We set a two-level categorical

127 variable (waxing; from new moon to full moon, waning; from full moon to new

128 moon). Tide is a factor expressing the tidal condition in the fishing ground. We set a

129 three-level categorical variable (fast, medium and slow) from the tide table. Moon x

130 Tide is the interaction between Moon and Tide. This factor may partially show

131 multicollinearity with Moon because the periodic cycle of the tide is approximately a

132 half of the lunar cycle. To include this factor in the analysis, however, is important

133 because it influences the distance that jigging boats drift when they attract squid and

134 the movement of squid aggregations. Wind is another factor that influences the

135 distance that jigging boats drift. We obtained the prevailing wind direction data at

136 Ashibe Observatory (Iki Island, Fig. 1) from the website of the Japanese

137 Meteorological Agency (http://www.data.jma.go.jp/obd/stats/etrn/index.php

138 “Accessed 2 June 2012”) and classified the wind direction by every 90 degrees (NE:

139 north-east-northeast, SE: east-south-southeast, SW: south-west-southwest, NW: west-

140 north-northwest). We used these wind direction classes as a four-level categorical

141 variable. We assumed the year-season differences in squid abundance and other

142 possible effects N. Therefore, we set a six-level categorical variable (Jan09, Feb09,

143 Jan10, Feb10, Jan11 and Feb11). These factors are summarized in Table 3. Table 3

144 Parameters ß0 to ß 6 are the intercept (constant) and the coefficients for Moon, Phase,

145 Tide, Moon x Tide, Wind and N, respectively. Fishing effort Ei, which is the number

146 of jigging boats or trap-nets operated in a day, is used as an offset variable.

147 Parameter estimation was performed by the maximum likelihood (glm.nb

148 function in the MASS package in R ver. 2.12.1, R Development Core Team). Based

149 on the initial model, the model selection was performed using AIC (Akaike’s

150 information criteria). The resultant model, the lowest AIC model was "optimum

151 model". Then, from the optimum model, the effect of explanatory variables was

152 evaluated based on the increments of AIC (ΔAIC) [16, 17] by removing variables one

153 by one from the optimum model.

154 To assess the catch amount which corresponds to daily fuel costs required to operate

155 squid fishing by jigging and trap-net, we explored the data of daily fuel costs from the

156 Report of statistical survey on fishery management 2009 [18]. This report shows the

157 following values: 9,322 Japanese yen (JPY)･ day-1･ trap-net-1 for a trap-net fishing and

158 9,514 - 31,844 JPY･ day-1･ boat-1 for squid jigging, depending on boat sizes (3 to 20

159 GRT). Squid prices were taken from the Annual statistics on marketing of fishery

160 products [19]. Because the annual average of squid price for the study years was 149

161 JPY･ kg-1, we assumed the average price of a fish container as 900 JPY･ case-1.

162

163 Results

164

165 Catch trends and the influence of moon age, tidal condition and wind direction

166

167 In total, 827,589 cases (about 4,965 tons) of Japanese common squid were caught during

168 the fishing seasons (January-February) in 2009-2011 (Fig. 3), which accounted for 59 % Fig. 3

169 of total catch in the study area in 2009-2011. Squid jigging in Iki and Tsushima Islands

170 (squid jigging fisheries in A and B) captured 77% of the total catch of six fisheries

171 during the fishing season. Total daily catch by the six fisheries varied between 0 and

172 18,624 cases (Fig. 4). Catches exceeding 10,000 cases were observed only for a few Fig. 4

173 days during the three study years.

174 In January 2009, squid was mainly captured in the northern part of the study area by

175 squid jigging fisheries in A and B. Trap-net A also captured squid in January, but it

176 peak was in early February. Then trap-nets in C, D and E captured in mid or late

177 February (Fig. 5). Thus, catch of squid begins from the north part of the study area and Fig. 5 178 trap-nets in the south part captured squid in the later period.

179 Catch tendency 2009 was similar for January in 2010, but small amount of squid

180 was captured in trap-nets in the south part (D and E) in February.

181 In 2011, total catch amount was larger than those in previous two years. Squid

182 jigging fisheries in A and B had captured squid until mid February and their peak

183 catches were in early February. Trap-net fisheries also maintained high catch levels

184 during January and February. Catch in trap-net in A became poor in late January, but

185 big hauls were again recorded for a few days in mid February. Trap-nets in C, D and E

186 continued catching squid with a peak in early February during the fishing season.

187 The daily catches on squid jigging fisheries in A and B show a clear pattern with

188 the age of the moon; catch was low in the full moon period and increased as the new

189 moon period approached (Fig. 6a). This trend was observed also in trap-net fisheries Fig. 6

190 in C, D and E. Trap-net catches in A exhibited the opposite pattern; more squid were

191 caught in the full moon period and less in the new moon period.

192 When daily catch is connected to the tidal current (Fig. 6b), catches on trap-net

193 fisheries in D and E (southern part of the study area) increased when the current was

194 slow. Other fisheries did not show clear catch tendencies against the tide. For the wind

195 detection, the daily catches on trap-net fisheries in C, D and E decreased when it was

196 the south wind (Fig. 6c).

197

198 GLM analysis

199

200 The GLM analysis detected the influence of Moon for both capture methods (ΔAIC

201 =10.77 to 26.21, Table 4) and Moon showed the largest effect except for squid Table 4

202 abundance (N) in any models based on ΔAIC results. The optimum models selected by

203 AIC are as follows.

204 Squid jigging A: log (μi) = ß0 + ß 1Moon + ß 2 Phase+ ß 5Wind +ß 6N+ log(Ei)

205 Squid jigging B: log (μi) = ß0+ ß 1Moon + ß 2 Phase + ß 5Wind+ log(Ei)

206 Trap-net A: log (μi) = ß0 + ß 1Moon + ß 2 Phase+ ß 5Wind +ß 6N+ log(Ei)

207 Trap-net C: log (μi) = ß0 + ß 1Moon + ß 2 Phase+ ß 5Wind+ß 6N + log(Ei)

208 Trap-net D: log (μi) = ß0 + ß 1Moon + ß 3 Tide + ß 5Wind+ß 6N + log(Ei)

209 Trap-net E: log (μi) =ß0 + ß 1Moon+ß 6N + log(Ei)

210 The influence of the year-season differences in squid abundance (N) was not

211 detected only in squid jigging fishery in B whereas it was detected in other fisheries.

212 Trap-net catches in E, which is located in the southern part of the study area, were

213 influenced only by Moon and N. The influence of N was larger in trap-nets in C, D and

214 E (ΔAIC =26.21 to 133.91) while its influence was moderate for squid jigging and

215 trap-net fisheries in A. Catches in Iki and Tsushima Islands (A, B and C), which are

216 located in the northern part of the study area, were influenced also by Phase and Wind.

217 The influence of Wind was larger in two squid jigging fisheries (ΔAIC =4.56 to 4.63).

218 The marginal influence of Tide was also only detected in the catch of trap-net in D

219 (ΔAIC =2.32), where also Moon, Wind and N affected. The interaction terms (Moon x

220 Tide) were not selected in any model.

221 A coefficient of Moon for trap-net in A shows a positive value while it is negative

222 for other trap-nets (Table 4), suggesting that the squid catches of these trap-nets

223 increases as the new moon approaches. For Phase, clear difference is observed between

224 trap-net and squid jigging. Catch of squid in squid jigging increased during the waxing

225 period (new moon to full moon), while this was the opposite in the trap-net fisheries.

226 We incorporated these coefficients into the optimum models for six fisheries and

227 estimated the expected daily catch amounts. Expected catch amounts tend to match

228 observed catch amounts, but the expected catch amounts of trap-net in E tended to be

229 underestimated when catch was large (Fig. 7). Fig. 7

230 We calculated the expected squid catch per unit effort (cases･ day-1･ boat-1 or

231 cases･ day-1･ trap-net-1) from the adopted models under the assumption that squid

232 abundance is constant at the Jan09 level. Expected catches ranged in 6-503 cases for

233 trap-net in A, 20-224 cases for squid jigging fishery in A, 46-1002 cases for trap-net in

234 C, 32-211 cases for squid jigging fishery in B, 15-539 cases for trap-net in D, and 50-

235 235 cases for trap-net in E.

236 We then examined how the above mentioned ranges of daily catch amount would

237 cover fuel costs for their capture in relation to Moon, the most influenced factor on Fig. 8

238 daily catch amount (Fig. 8). From the daily fuel cost and squid landing price values we

239 calculated that the average number of fish containers which would cover the fuel cost

240 required for daily operation were 11 cases for a trap-net and 11-36 cases for a squid

241 jigging boat. A trap-net operation does not cover the daily fuel cost when squid catch

242 was less than 11 cases. Such a low catch is expected in A during the waxing new moon

243 period when southern wind dominated. In other cases, trap-net catches covered the fuel

244 costs even in the most unfavorable conditions. Squid jigging fishery has risky period

245 around the full moon when the fuel cost exceeds landing value of squid catch. Squid

246 jigging fishery in A has a longer duration of unstable profitability than that of B

247 because expected squid catch was smaller.

248

249 Discussion

250

251 This study indicates that the catch quantity of squid by squid jigging and large-scale

252 trap-net fisheries is heavily influenced by the lunar cycle. For squid jigging this

253 relationship has been reported earlier [11-15] but for trap-net fishing this is apparently

254 the first time this effect has been verified.

255 It is noteworthy that effect of lunar cycle was different in squid jigging and trap-net

256 fisheries, and the effect was influenced also by location. In the trap-net catches in A

257 (Tsushima Islands) were larger in the full moon period while in other areas trap-nets

258 and squid jiggings captured more squid in the new moon period. This difference is

259 likely due to the pattern and movement of squid aggregations and squid jigging boats.

260 In Tsushima Islands, squid jigging boats usually operate off the western coast of the

261 islands where also the trap-nets are set. On the other hand, in Iki island squid jigging

262 boats in B operate in northern or western waters of the island [12-15, 20] while the

263 trap-net fishery of C is located on the eastern coast of the island. Squid migrating in

264 the southwestern direction for spawning would be able to reach the eastern coast of Iki

265 Island without being captured by jigging boats. Thus, trap-net set in C have more

266 advantageous conditions for catching squid compared to trap-net in A. Trap-nets in D

267 and E captured more squid in the new moon period likely because no squid jigging

268 boats are operational near these islands.

269 The time when moon rose was another factor that impacted on catch amount. Catches

270 in squid jigging decreased when the moon appeared after midnight. Squid jigging boats

271 start the fishing operation just before sunset, and continue until sunrise [20]. At the

272 beginning of this operation, fishermen turn on all lamps to attract the dispersed squid

273 over a wider area to the boat, and then reduce the number of illuminating lamps to keep

274 the attracted squid in the upper water layer. This is because squid avoid strong light

275 [21, 22]. In the case of the waning period, the moon risen after midnight delivered light

276 and ambient illuminance in the water became relatively high in the later part of the

277 operation process. This high illuminance condition would weaken the effect of

278 reducing number of illuminating lamps which causes ascending behavior of attracted

279 squid. We therefore consider that this interference of light resulted in less catch amount.

280 Our results indicate the marked role of other key environmental factors such as wind

281 direction and tide. In squid jigging fisheries in A and B, catches significantly decreased

282 when wind blew from the northwest in Tsushima Islands and from the northeast in Iki

283 Island whereas northern winds (NW and NE) increased the catch amounts in trap-net

284 fishery. We assume that the influence of wind in squid jigging is a combination between

285 current and wind directions. Squid jigging boats drift with the tidal movement in order

286 to maximize their drifting distances to attract more squid. They usually plan to move

287 into the northern direction when lighting is started, and they drift in the opposite

288 direction when the tide turns. In the cases when a northern wind blows, the direction

289 of the current and wind are opposite and consequently boats are not able to drift over

290 a longer distance. We suspect that northern wind prevented the drifting of jigging boats

291 at the beginning of the operation which is an important phase to attract the dispersed

292 squid. It resulted in smaller catch of squid.

293 In conclusion, catches in squid jigging and trap-net fisheries in the four islands in

294 Nagasaki Prefecture are mainly influenced by the lunar cycle but also wind direction

295 affects in particular in the squid jigging fisheries and year-season differences in squid

296 abundance in the trap-net fisheries.

297 Trap-net fishery is in general associated with low fuel consumption [8]. On average,

298 boats used in the trap-net fishery consume approximately 40% of fuel when compared

299 to boats of the same sizes used in other coastal fisheries in Japan [8]. The low fuel

300 consumption means low CO2 emissions. The cumulative carbon dioxide emission per

301 unit of production value for the trap-net fishery is 0.5 ton-CO2/million JPY while it is

302 14.4 ton-CO2/million JPY for the squid jigging fishery [9]. Ninety-nine percent of the

303 CO2 emission in the squid jigging fishery is made from a direct fuel consumption in

304 daily operations and approximately 70% of fuel consumption is allocated for lighting

305 [10]. In trap-net fishery fuel is mainly used when setting up fishing gear and when

306 bringing the catch to the harbor. Squid jigging and trap-net fisheries have largely

307 opposite characteristics in terms of energy consumption.

308 Clearly there are specific advantages and disadvantages in squid jigging and trap-

309 net fisheries. Trap-net is a fuel-efficient fishing method, but the catch varies depending

310 on the conditions and squid abundance in the fishing ground. Squid jigging can flexibly

311 respond to changes in squid abundance and distribution; however, it consumes a

312 considerable amount of fuel.

313 There are periods when the income from the catches in the squid jigging and trap-

314 net fisheries clearly does not cover the fuel costs. These periods were full moon period

315 for the squid jigging in two FCAs (A and B) and new moon period for the trap-net in

316 A. In the case of squid jigging fisheries in A and B, when small catch is expected due

317 to the unfavorable environmental conditions, profitable operation can be achieved only

318 during the period of new moon to the waxing moon. Clearly, squid jigging is a fuel

319 intensive method and current fuel cost is high [8].

320 In order to operate and manage the squid jigging and trap-net fisheries in a

321 sustainable manner, non-profitable operations should be minimized. We observed non-

322 profitable operations in both fisheries. Managers and operators in squid jigging and

323 trap-net fisheries should be cost-consciousness. For example, jigging operators can

324 estimate a profit-line and judge whether to operate or not on the basis of moon age and

325 wind direction. This type of decision making is important under the present high fuel

326 price condition. In particular, larger squid jigging boats should reconsider their

327 operation style and strategy.

328

329 Acknowledgements

330 We are grateful to members of the five Fisheries Cooperative and researchers of

331 Nagasaki Prefectural Institute of Fisheries for their help in collecting data.

332

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398 【 Figures caption】

399

400 Fig.1 Locations of the Fisheries Cooperative Associations analyzed in the study. A

401 operates both squid jigging and trap-net fishing. B only operates squid jigging.

402 C, D and E only operate trap-net fishing

403 Fig.2 Catch amount of Japanese common squid in the squid jigging and Trap-net

404 fisheries in five Fisheries Cooperative Associations (A to E) in 2009-2011

405 Fig.3 Catch amount of Japanese common squid in the 6 fisheries in January-February

406 2009, 2010 and 2011

407 Fig.4 Variation in daily total catch of Japanese common squid in the 6 fisheries in

408 January-February 2009, 2010 and 2011

409 Fig.5 Variation in daily catch of Japanese common squid in the 6 fisheries in January-

410 February 2009, 2010 and 2011. Upper graph; catch of squid jigging sectors,

411 lower graph; catch of trap-net sectors

412 Fig.6 Variation of daily catch of Japanese common squid by the age of the moon (a),

413 Tide (b) and the wind direction(c)

414 Fig.7 Comparison of observed and expected catch amount of Japanese common squid

415 for the 6 fisheries. Expected catch amounts were calculated from optimum

416 models presented in Table 4

417 Fig.8 Relationship between expected catch amount and the ratio of the illuminating

418 area of the moon (Moon) for the six fisheries. Influences of other variables are

419 taken into account and are presented as a maximum (max) and a minimum

420 (min) lines. The dashed line is the number of cases corresponding to fuel costs

421 (note that this line is indicated by a range (a portion of a rectangular) for squid

422 jigging fishery due to the variation in boat sizes). A period of time that

423 expected minimum catch amount covers fuel cost is designated by a gray box

424 below the X-axis

425

426 Table 1 Five Fisheries Cooperative Associations in the study

427 ID Island position Number of trap-net Number of Squid jigging

428 A Tsushima East coast 5 56-64 429 B Iki North coast 67-83 C Iki East coast 2 430 D Hirado Northwest coast 1 431 E Goto North coast 2-3

432

433

434 Table 2 Catch data used in the study

ID Fishing Year* Number Fishing Total catch Average SD method of days (cases) (cases/day) (cases/day) Boat/trap A Squid jigging 2009 64 53 50721 957 1032 2010 56 50 40181 803 845 2011 61 55 43381 788 645 B 2009 83 41 132935 3242 1887 2010 67 46 178316 3876 3192 2011 75 41 191385 4667 3584 A Trap-net 2009 5 54 26145 484 514 2010 5 53 14331 270 358 2011 5 53 21584 407 540 C 2009 2 50 23072 461 570 2010 2 54 448 8 15 2011 2 51 40118 786 595 D 2009 1 50 4819 96 176 2010 1 52 2909 55 126 2011 1 53 8001 150 217 E 2009 3 49 13009 265 310 2010 2 49 12159 248 409 2011 2 51 24075 472 677 * Daily catch data between January and February were collected each year. 435

436

437

438 Table 3 Explanatory variables in the initial generalized linear model (GLM) with a

439 negative binomial distribution

440 Explanatory variables Category 441 Moon Continuous variable, (0 to 1) (ratio of the illuminating area of the moon) 442 Phase (waxing and waning of the moon) waxing, waning 443 Tide (speed of tidal current in the fishing ground) fast, medium, slow Wind (wind direction) NE(N-ENE), SE(E-SSE), 444 SW(S-WSW), NW(W-NNW) 445 E (fishing effort, number of boats or traps per day) Offset variable(0 to 83) N (month-year difference in squid abundance) Jan09, Feb09, Jan10, Feb10, 446 Jan11, Feb11 447

448

449

Table 4 Parameters and output for the selected optimum generalized linear models

Explanatory variable Squid jigging A Squid jigging B Trap-net A Trap-net C Trap-net D Trap-net E Estimate (SE) P Estimate (SE) P Estimate (SE) P Estimate (SE) P Estimate (SE) P Estimate (SE) P

β0 (Intercept) 4.81 (0.28) <0.01 4.67 (0.16) <0.01 2.84 (0.46) <0.01 5.67 (0.48) <0.01 4.78 (0.49) <0.01 5.46 (0.28) <0.01

β1 (Moon) ΔAIC = 26.21 ΔAIC = 21.86 ΔAIC = 25.08 ΔAIC = 10.77 ΔAIC = 25.93 ΔAIC = 21.02 -1.22 (0.20) <0.01 -0.77 (0.15) <0.01 1.91 (0.33) <0.01 -1.24 (0.32) <0.01 -2.06 (0.32) <0.01 -1.54 (0.29) <0.01

β2 (Phase: relative to ‘waning’) ΔAIC = 6.81 ΔAIC = 14.57 ΔAIC = 6.65 ΔAIC = 4.33 0.44 (0.14) <0.01 0.46 (0.10) 0.01 -0.78 (0.24) <0.01 -0.57 (0.22) 0.01 / / β3 (Tide: relative to ‘fast’) ΔAIC = 2.32 medium / / / / 0.04 (0.28) 0.88 / slow / / / / 0.65 (0.28) 0.02 /

β5 (Wind: relative to ‘SE’) ΔAIC = 4.56 ΔAIC = 4.63 ΔAIC = 2.55 ΔAIC = 0.23 ΔAIC = 0.10 NE -0.27 (0.25) 0.29 -0.43 (0.17) 0.01 1.25 (0.43) <0.01 1.01 (0.43) 0.02 0.47 (0.41) 0.26 / NW -0.61 (0.22) <0.01 -0.00 (0.14) 0.98 1.25 (0.39) <0.01 0.88 (0.39) 0.02 0.86 (0.37) 0.02 / SW 0.17 (0.40) 0.68 0.21 (0.27) 0.42 1.03 (0.69) 0.13 1.25 (0.66) 0.06 -0.13 (0.70) 0.85 /

β6(N relative to ‘Feb09’) ΔAIC = 2.96 ΔAIC = 3.09 ΔAIC = 133.91 ΔAIC = 27.63 ΔAIC = 26.21 Jan09 -0.53 (0.24) 0.02 / 0.33 (0.41) 0.41 -0.93 (0.38) 0.02 -1.27 (0.40) <0.01 -0.63 (0.35) 0.07 Jan10 -0.40 (0.25) 0.12 / -0.62 (0.41) 0.14 -4.01 (0.40) <0.01 -0.91 (0.40) <0.02 0.32 (0.34) 0.35 Feb10 -0.09 (0.24) 0.72 / -0.24 (0.41) 0.56 -5.15 (0.40) <0.01 -1.36 (0.39) <0.01 -1.81 (0.35) <0.01 Jan11 -0.74 (0.25) <0.01 / 0.31 (0.42) 0.47 0.01 (0.39) 0.99 -0.79 (0.41) 0.05 0.83 (0.34) 0.02 Feb11 -0.04 (0.23) 0.88 / -0.96 (0.40) 0.02 0.71 (0.40) 0.07 0.75 (0.37) 0.04 0.47 (0.34) 0.17 ΔAIC indicates the increment in AIC if the explanatory variable is removed from the optimum models

Nagasaki

Japan A

Tsushima Islands

N34 B C

Iki Island D

E N33 Goto - retto Islands

E129 E130

2 Fig.1 Masuda et al.

4 Fig.2 Masuda et al.

5 25

Trap-net E Trap-net D

Trap-net C

Squid jigging A Trap-net A

Squid jigging B

7 827,589 cases (approx. 4,965 t)

8 Fig.3 Masuda et al.

2009 12000 Total 10000

8000

6000

4000

2000

0 01/01 01/11 01/21 01/31 02/10 02/20 10 2010 16000 Total 14000

12000

10000

8000

6000

4000

2000

0 01/01 01/11 01/21 01/31 02/10 02/20 11 2011 20000 Total 18000 16000 14000 12000 10000 8000 6000 4000 2000 0 01/01 01/11 01/21 01/31 02/10 02/20 12

13 Fig. 4 Masuda et al.

2009 2010 2011 20000 20000 20000 Squid jigging B 18000 Squid jigging B 18000 Squid jigging B 18000 Squid jigging A Squid jigging A Squid jigging A 16000 16000 16000 14000 14000 14000 12000 12000 12000 10000 10000 10000 8000 8000 8000 6000 6000 6000 4000 4000 4000 2000 2000 2000 0 0 0 01/01 01/11 01/21 01/31 02/10 02/20 01/01 01/11 01/21 01/31 02/10 02/20 01/01 01/11 01/21 01/31 02/10 02/20

5000 Trap-net E 5000 Trap-net E 5000 Trap-net E Trap-net D Trap-net D 4500 4500 Trap-net D 4500 Trap-net C Trap-net C Trap-net C 4000 4000 4000 Trap-net A Trap-net A Trap-net A Catch amount amount Catch (cases) 3500 3500 3500 3000 3000 3000 2500 2500 2500 2000 2000 2000 1500 1500 1500 1000 1000 1000 500 500 500 0 0 0 01/01 01/11 01/21 01/31 02/10 02/20 01/01 01/11 01/21 01/31 02/10 02/20 01/01 01/11 01/21 01/31 02/10 02/20 14 15 Fig. 5 Masuda et al.

Squid jigging A Squid jigging B n=33 n=48 n=30 n=47 n=27 n=41 n=20 n=40

Trap-net A Trap-net C n=33 n=46 n=31 n=50 n=29 n=47 n=31 n=48 catch amount (cases )

Trap-net D Trap-net E n=30 n=47 n=30 n=48 n=30 n=45 n=30 n=44

28th 4th 13th 19th 28th 4th 13th 19th to 3rd to 12th to 18th to 27th to 3rd to 12th to 18th to 27th The age of the moon 16 17 Fig. 6a Masuda et al.

Squid jigging A Squid jigging B n=41 n=60 n=57 n=32 n=48 n=48

Trap-net A Trap-net C n=44 n=61 n=55 n=40 n=60 n=55 (cases )

catch amount Trap-net D Trap-net E n=41 n=58 n=56 n=39 n=58 n=52

fast medium slow fast medium slow Tide 19

20 Fig. 6b Masuda et al.

c Squid jigging A Squid jigging B n=20 n=31 n=101 n=6 n=20 n=25 n=77 n=6

Trap-net A Trap-net C n=20 n=32 n=102 n=6 n=18 n=30 n=101 n=6 (cases )

catch amount Trap-net D Trap-net E n=19 n=34 n=97 n=5 n=20 n=33 n=92 n=4

SE NE NW SW SE NE NW SW The wind direction 22 23 Fig. 6c Masuda et al.

Squid jigging A Squid jigging B )

(cases Trap-net A Trap-net C amount

Trap-net D Trap-net E expected catch

catch amount (cases) 25

26 Fig. 7 Masuda et al.

28 1000 Squid jigging A max 1000 Squid jigging B max min 29 min fuel fuel 30 100 100 31 32 10 10 Expected catch (casese) 33 Expected catch (cases) 1 1 34 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

35 The ratio of the illuminating area of the moon 36 Trap-net A Trap-net C 1000 10000 37 max max min min fuel fuel 38 1000 100 39 100 40 10 10 41

Expected catch (cases) Expected catch (cases)

42 1 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 43

1000 Trap-net D 1000 Trap-net E 44 max max min min fuel 45 fuel 100 100 46 47 10 10 48 Expected catch (cases) Expected catch (cases)

49 1 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 50 The ratio of the illuminating area of the moon 51

52 Fig. 8 Masuda et al.