Presentation on theme: "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."— Presentation transcript:
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 FISHERIES SCIENCE 2006.,72 :1147–1152
Introduction Traps widely used in fisheries simple structure convenient operation factors trap entrance Entrance number Shape Size Location.
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~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 methods Table 1Details of set time, hauling time, soak time, location, water depth and surface temperature during the five samplings in 2002.
Materials 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)
Catch analysis of traps Mean body length Body length frequency distributions
Mean body length E1, E2, E3 and commercial trap No significant differences Soak 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 commercial trap (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 αSwimming 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 typeFunnel lengthOverall mean CPUE (1 day soak time) Trap E48 cm15.3 Commercial trap 22 cm10.9 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…… no effect on size selectivity of the trapThe 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 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 arrowheaddouble-funnel Z-traps Luckhurst and Ward (1987) straight funnelshorse-neck funnels Matuda et al (1984). catch rates were affected by the diameter of the entrance ring Furevik and Løkkeborg (1994) narrow entranceswider entrances Other Studies