FISHERIES SCIENCE 2006 72 1147 1152 Effects of
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FISHERIES SCIENCE 2006. , 72 : 1147– 1152 Effects of entrance design on catch efficiency of arabesque greenling traps: a field 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 NASHIMOTO 2 AND Hiroyuki YOSHINO 3 Reporter: 陳 湘 蕎
Introduction factors trap entrance Traps factors widely used in fisheries Entrance number Shape Size simple structure Location. convenient operation
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.
Materials and methods • • Study time: 2002 June~July Study sites: Matsumae, Hokkaido, Japan Temperature: surface temperature 16. 9 ~17. 8。C Depth: 128~140 m Fig. 1 Location of the fishing experiment.
Materials and methods Table 1 Details of set time, hauling time, soak time, location, water depth and surface temperature during the five samplings in 2002.
Materials and methods • 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. 200 g) 73 cm 30 cm 87 cm Commercial trap Experimental trap
Commercial trap E 4 trap
Materials and methods- Fish traps: 40 fish traps Commercial traps 20 Experimental traps 20(E 1, E 2, E 3, E 4; five traps of each type) Table 2 Dimensions of the trap entrances
Results Catch analysis of traps
Catch
Catch Results • Total of trap hauls: 200 � Experimental traps: 1017 • Total of fish: 2200 Commercial traps: 1183
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
E 1, E 2, E 3 and Commercial trap Kruskal–Wallis test Soak time 1 day CPUE of traps Soak time 2 days CPUE of traps
Soak time 1 day 1. Table 3 CPUE Trap E 2、commercial trap、 trap E 1 > trap E 3.
Soak time 2 days CPUE 1. Commercial trap and trap E 3 2. Trap E 2 and trap E 3 difference The overall mean CPUE was shown as trap E 2>the commercial trap>trap. E 1>trap E 3.
E 1, E 2, E 3 and Commercial trap Kruskal–Wallis test Soak time 1 day CPUE of traps Soak time 2 days CPUE of traps Significant differences
Trap E 2 α=270 Ct α=370 Trap E 3 Trap E 1 α=460 α=00 Fig. 3 The relationship between the overall mean catch per trap (number) and entrance inclination angle.
Trap E 4 and the commercial trap Mann– Whitney test Soak time 1 day CPUE of traps Soak time 2 days CPUE of traps
Soak time 1 day CPUE Trap E 4 > Commercial trap Table 3
Soak time 2 days CPUE No significant difference Table 3
Trap E 4 and the commercial trap Mann– Whitney test Soak time 1 day CPUE of traps Trap E 4 > Commercial trap Soak time 2 days CPUE of traps No significant difference
Bycatch species-11 species 1. Octopus(章魚) 2. Hairy triton(法螺) 3. Hermit crab(寄居蟹) 4. Cod(鱈類) 5. Sculpins 6. Fat greenling 7. Yellow body rockfish 8. Slime flounder 9. White-edged rockfish 10. Kurosoi rockfish 11. Angry rockfish
Catch analysis of traps Mean body length Body length frequency distributions
Mean body length Table 4 Mean body length (mm) of fish caught in each trap during the sampling period E 1, E 2, E 3 and commercial trap Soak time of 1 day and 2 days No significant differences
Mean body length Table 4 Mean body length (mm) of fish caught in each trap during the sampling period Trap E 4 and the commercial trap Soak time of 1 day No significant difference Soak time of 2 days Significant difference
Body length frequency distributions ANOVA tests E 1, E 2, E 3 and commercial Soak time of 1 day or 2 days No difference
E 1, E 2, E 3 and Commercial trap Soak time=1 day Soak time=2 day Fig. 4 Size frequency distributions of the body length of fish in each 10 -mm body length size class, caught using the experimental traps (E 1, E 2, and E 3) and the commercial trap (Ct).
Body length frequency distributions Trap E 4 and the commercial trap Soak time=1 day Not differ Soak time=2 day Fig. 5 Size frequency distributions of the body length of fish in each 10 -mm body length size class, caught by the experimental trap (E 4) and the commercial trap (Ct).
Discussion • Modification of the funnel design may significantly affect trap performance Max • α increased, the overall mean CPUE first increased to a maximum, and then gradually decreased. Fig. 3 The relationship between the overall mean catch per trap (number) and entrance inclination angle.
• The catch efficiency of trap E 2 was highest, followed by the commercial trap, E 1, and E 3. • Trap E 2 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.
To inclination angle point of view…… Trap α Swimming posture of fish type • The trap E 2 entrance is most effective in catching arabesque greenling, since it is easier for fish. The to enter trapto than othertowards shaped entrances. fishthe have swim the bottom side and get through the funnel 0° E 3 opening. • The authors therefore recommend the application of a trap with an entrance to the symmetrical funnel. E 1 similar 46° The fish have to swim up and get Ct E 2 37° 27° through. The fish are able to swim through the funnel opening directly with no need to adjust their swimming posture.
To funnel length point of view…… Trap type Funnel length Trap E 4 8 cm Overall mean CPUE (1 day soak time) 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 catch performance…… ► 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 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 E 2 (α = 27°, Lf = 22 cm) produced higher catches than the commercial trap (α = 37°, Lf = 22 cm) 2)Trap E 4 (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°.
Other Studies Munro et al. single-funnel arrowhead (1971) Luckhurst and Ward (1987) Matuda et al (1984). Furevik and Løkkeborg (1994) straight funnels double-funnel Z-traps horse-neck funnels catch rates were affected by the diameter of the entrance ring narrow entrances wider entrances
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