Effects of entrance design on catch Effects of entrance design on catch efficiency of arabesque greenling traps: a efficiency of arabesque greenling traps: a field experiment in Matsumae, Hokkaidofield experiment in Matsumae, Hokkaido花鯽魚籠具之入口設計在漁獲效率上的影響 :

於北海道松島野外實驗

Yong LI,1 Katsutaro YAMAMOTO,1* Tomonori HIRAISHI,1 Katsuaki NASHIMOTO2 AND Hiroyuki YOSHINO3

Reporter: 陳 湘 蕎

FISHERIES SCIENCE 2006.,72 :1147–1152

IntroductionIntroduction

Traps widely used in fisheries

simple structure convenient operation

factors

factors

factors

factors

trap entrance

trap entranceEntrance numberShapeSizeLocation.

Purpose

• The effects of trap entrance inclination angel and funnel length on the catch per trap.

• The body length distribution of fish caught in traps.

• And the mean body length of fish caught in traps.

IntroductionIntroduction

學名 :Pleurogrammus azonus

英名 :Arabesque greenling

中文名 : 鄂霍次克魚 、花鯽魚 ( 俗名 : 星斑六線魚或遠東六線魚 )

日文 : ホッケ (ho tsu ke)

Materials and methodsMaterials and methods

• Study time: 2002 June~JulyStudy time: 2002 June~July• Study sites: Study sites: Matsumae, Hokkaido, Japan• Temperature: surface temperature16.9 ~17.8 。 C• Depth: Depth: 128~140 m

Fig. 1 Location of the fishing experiment.

Materials and methodsMaterials and methods

Table 1Details of set time, hauling time, soak time, location, water depth and surface temperature during the five samplings in 2002.

Materials and methodsMaterials and methods

Commercial trap Experimental trap

73cm

87cm

30cm

• The traps were conical in shape• Top diameter 73 cm• Bottom diameter 87 cm• Height 30 cm.

•α: Inclination angle

•Lf :The entrance funnel length

•Bait: Sardines (approx. 200g)

Commercial trap

E4 trap

Materials and methodsMaterials and methods －－

Table 2 Dimensions of the trap entrances

Fish traps: 40 fish traps

Commercial traps 20Experimental traps 20(E1, E2, E3, E4 ；five traps of each type)

Results

Catch

Catch analysis of traps

Catch

Results• Total of trap hauls:200

• Total of fish:2200﹛Experimental traps:1017

Commercial traps:1183

Catch

CPUE and number of traps hauled

Ct, commercial trap; Ei, trap Ei (i = 1, 2, 3, 4); SD, standard deviation.

Table 3 Mean catch number per trap and number of traps hauled

Kruskal–Wallis test

Soak time 2 daysCPUE of traps

E1, E2, E3 and Commercial trap

Soak time 1 dayCPUE of traps

Trap E2 、 commercial trap 、 trap E1 ＞＞ trap E3.1.

Soak time 1 day CPUE

Table 3

Soak time 2 days CPUE

1. Commercial trap and trap E3

Trap E2 and trap E32.

difference

The overall mean CPUE was shown as trap E2>the commercial trap>trapE1>trap E3.

Kruskal–Wallis test

Significant differences

Soak time 1 dayCPUE of traps

Soak time 2 daysCPUE of traps

E1, E2, E3 and Commercial trap

Fig. 3 The relationship between the overall mean catch per trap (number) and entrance inclination angle.

Trap E3

α=00

Trap E2α=270

Ct α=370

Trap E1 α=460

Trap E4 and the commercial trap

Mann–Whitney test

Soak time 1 dayCPUE of traps

Soak time 2 daysCPUE of traps

Table 3

Soak time 1 day CPUE

Trap E4 > Commercial trap

Table 3

Soak time 2 days CPUE

No significant difference

Trap E4 and the commercial trap

Soak time 1 dayCPUE of traps

Trap E4 > Commercial trap

Soak time 2 daysCPUE of traps

No significant difference

Mann–Whitney test

Bycatch species － 11 species

1. Octopus(章魚 )2. Hairy triton(法螺 )3. Hermit crab(寄居蟹 )4. Cod(鱈類 )5. Sculpins6. Fat greenling7. Yellow body rockfish8. Slime flounder9. White-edged rockfish10.Kurosoi rockfish11.Angry rockfish

Catch analysis of traps

Mean body length

Body length frequency distributions

Mean body length

E1, E2, E3 and commercial trap

No significant differencesSoak time of 1 day and 2days

Table 4 Mean body length (mm) of fish caught in each trap during the sampling period

Trap E4 and the commercial trap

Soak time of 1 day

Soak time of 2 days

No significant difference

Significant difference

Mean body length

Table 4 Mean body length (mm) of fish caught in each trap during the sampling period

Body length frequency distributions

ANOVA tests

E1, E2, E3 and commercial Soak time of 1 day or 2 days

No difference

Fig. 4 Size frequency distributions of the body length of fish in each 10-mm body length size class, caught using the experimental traps (E1, E2, and E3) and the commercialtrap (Ct).

E1, E2, E3 and Commercial trap

Soak time=1day

Soak time=2day

Body length frequency distributions

Trap E4 and the commercial trap

Fig. 5 Size frequency distributions of the body length of fish in each 10-mm body length size class, caught by the experimental trap (E4) and the commercial trap (Ct).

Soak time=1day

Soak time=2day

Not differ

Discussion

•Modification of the funnel design may significantly affect trap performance

Fig. 3 The relationship between the overall mean catch per trap (number) and entrance inclination angle.

•α increased, the overall mean CPUE first increased to a maximum, and then gradually decreased.

Max

•The catch efficiency of trap E2 was highest, followed by the commercial trap, E1, and E3.

•Trap E2 symmetrical funnel and the funnel opening is located in the middle of the trap.

•The symmetrical funnel can be considered to be easier for fish to enter the trap than the unsymmetrical funnel.

Trap type

α Swimming posture of fish

E3 0°The fish have to swim towards the bottom side and get through the funnel opening.

E1 46° The fish have to swim up and get through.Ct 37°

E2 27°The fish are able to swim through the funnel opening directly with no

need to adjust their swimming posture.

To inclination angle point of view……

•The trap E2 entrance is most effective in catching arabesque greenling, since it is easier for fish to enter the trap than other shaped entrances.

•The authors therefore recommend the application of a trap with an entrance similar to the symmetrical funnel.

To funnel length point of view……

Trap type Funnel length Overall mean CPUE

(1 day soak time)

Trap E4 8 cm 15.3

Commercial trap

22 cm 10.9

The results confirmed that the funnel length of trap entrance affects the catch of a trap.

The interior volume of trap affected the catchperformance……

► For a trap with shorter funnel length

Consequence of a lower probability of fish escaping

The catch efficiency was increased

According to the results of catch analysis……

• The inclination angle and funnel length of entrance had no effect on size selectivity of the trapno effect on size selectivity of the trap.

(soak time of 1 day)

Because the size of funnel opening of the experimental trap and commercial trap was about the same.

In conclusion……

When used in a commercial arabesque greenling trap fishery:

1)Trap E2 (α = 27°, Lf = 22 cm) produced higher catches than the commercial trap (α = 37°, Lf = 22 cm)

2)Trap E4 (α = 37°, Lf = 8 cm) caught more fish than the commercial trap over a 1-day soak time.

It is suggested……

It is suggested that the inclination angle of entrance of a commercial trap should be adjusted from 37° to approximately 27°.

Munro et al.

(1971)

single-funnel arrowhead double-funnel Z-traps

Luckhurst and Ward

(1987)

straight funnels horse-neck funnels

Matuda et al

(1984).

catch rates were affected by the diameter of the entrance ring

Furevik and Løkkeborg

(1994)

narrow entrances wider entrances

Other Studies

Thank you for your attention~