effects of entrance design on catch efficiency of arabesque greenling traps: a field experiment in...
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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~