control. The control was the frequency of fish passing through the panel without a net.
In voluntary behaviour, the fish was less active than the conditioned behaviour. This probably because of none of stimulus is used to stimulate the fish
of not avoiding to pass through the net panel. The use of forcing panel to minimize the swimming area of fish in area B was very helpful to makes the fish
swim more active.
w w w
y ±
S E
Figure 15. Comparison among the fish passing through the net panel on conditioned behaviour
From Figure 15 above, the comparison of fish passing through the net panel on conditioned behaviour was not significant. The fish becoming more active than
if it was in voluntary because of the use of forcing panel. This made the frequency of passing in each of net panel of conditioned behaviour increasing, especially in
both white nets old white and new white. The frequency of passing in both white nets i.e. the old white net and new white net was higher than the black net, with
the highest frequency was in old white net. It showed that the fish was actually avoiding the contrast colour.
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4.2.1.1 Net colour transparency
From the result of TWO-WAY ANOVA α= 0.05, the net colour transparency between old white, new white and black painted has significant
difference.
Table 5. Signification level of comparison proportion among three types of net panel
Net colour Old white
Black painted New white
Old white 0.072
0.967 Black painted
0.049
New white Notes: significant in p0.05
Table 5 shown the signification level to compare the proportion among three types of net panel in voluntary behaviour. According of the signification level
between the three netting panel, it showed that the comparison between the new white and black painted was the most significant.
4.2.1.2 Fish behaviour in relation to netting panel
The behaviour of fish recorded on video tape were 1 Japanese Jack mackerels tend to swim in circling movement around and near the mesh panel
with their school; 2 After succeed passing the mesh and entering the other side of experimental tank, they tend to return to the previous side, and joined their
school; 3 Japanese jack mackerel was able to see net barrier on their swimming movement, but intend to pass; 4 Japanese jack mackerels was avoiding the black
panel.
4.2.2 Behaviour experiment using specific white net panels
From the result of the experiment, most of fish was to keep clear the mesh panel. According to Glass et al., 1993 keeping clear of mesh panel is considered
as the natural behaviour of fish. That would be the explanation, why it was very difficult to stimulate fish to enter the mesh in voluntary.
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As the result of the frame on frame analysis on mini DV, Japanese Jack mackerel did the reaction behaviour when they recognized the existence net panel
on their swimming movement, stop first, and tried to pass the net panel, either way they avoiding the net panel and just swimming in circling. The Jack
mackerels were not very active in voluntary unless they were given some stimulus, for example to herd their swimming movement, the treatment that was given as
conditioned behaviour on this experiment.
w w w
w y
y ±
S E
Figure 16. Comparison of fish passing through the net panel
The proportion of the frequency of passing in Figure 16 derived from the frequency of fish passing through each net panel divided into frequency of fish
passed through control. The control was the frequency of fish passing through the panel without a net.
The result of the experiment showed that the frequency of passing among white nets is not significant; it means that there is no effect of transparency among
three types of white nets. It makes that operating old white net or new white net considering similar in fish to pass. If this result will be implemented on the habit
of fishermen, the use of old white net considering fine to the fishermen in order to minimize the cost, as long as the web is less of damages and still in good
condition.
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w w w
w y
Figure 17. Proportion of fish passing through the net
Figure 17 showed that in 10 trials of this behavioural experiment, the frequency of fish passing was fluctuated. This was because of the natural
behaviour of this fish that sometimes very active but sometimes inactive. It was very difficult to maintain the fish in stable condition in each trial, even though
external factors that probably could influence the experimental result such as illumination, temperature, time of food giving are being controlled.
From this result, it can be derived that animal including also fishes, have their inactive period and active period of swimming, in this case the swimming of
passing through the net. This result only try to described the activity of fish during each trial, but from statistical test it can be inferred that if the net transparency of a
net panel less visible, then the more fish passing through it.
4.2.2.1 Mesh passing reaction of fish
As the result of observation on the conditioned behaviour, the behavioural reactions of fish when passed the netting panel were classified into two types of
behaviours, which are passed through netting panel with non-contact or contact. Contact behaviour is when the fishes passed through without any contact of their
body, while non contact is the opposites way.
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From the result of one way ANOVA on old white, new white and white dyed net panel showed that most fish could pass through the mesh without any
contact. Most fishes always try to keep clear on netting panel then try to pass through the netting panel. It means that non contact behaviour is significant
behaviour reaction in all of netting panel used on the experiment.
Figure 18. Contact and non-contact reaction of fish passing through old white net panel
Figure 18, 19, and 20 are proportion of fish passed through the netting panels old white, new white and white dyed. The value of proportion derives
from the frequency of fish passed the net with or without contact divided total number of fish passed through the net. From the three panels used on the
experiment, old white netting panel has the largest number proportion on non- contact reaction on passing. That is considering because most fish could be able to
pass this net without any contact, if it compares within the others. Figure 19. showed that most of fish could be able to pass the old white net
without any contact 12.032. It means that non-contact behaviour was dominant against contact behaviour. This happen because of the hanging ratio of
the netting panel 0.65 and the mesh perimeter that used in the experiment was bigger than in the real fishing operation hanging ratio around 0.4-0.45.
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Figure 19. Contact and non-contact reaction of fish passing through new white net panel
Figure 19 above showed that most of fish could be able to pass the new white net without any contact 8.999. It means that non-contact behaviour was
dominant against contact behaviour. This happen because of the hanging ratio of the netting panel 0.65 and the mesh perimeter that used in the experiment was
bigger than in the real fishing operation hanging ratio around 0.4-0.45.
Figure 20. Contact and non-contact reaction of fish passing through white dyed net panel
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Figure 20 showed that most of fish could be able to pass through the white dyed netting panel without any contact 7.185. It means that non-contact
behaviour was dominant against contact behaviour. This happen because of the hanging ratio of the netting panel 0.65 and the mesh perimeter that used in the
experiment was bigger than in the real fishing operation hanging ratio around 0.4-0.45.
The reason of using bigger hanging ratio in behaviour study is to avoid fishes got injured when they were passing the mesh, so the behaviour of passed
could be observed. In actual fishing operation, the fish suppose to get caught by the net, and then the hanging ratio and mesh perimeter considered being smaller.
4.2.2.2 Behaviour of fish in relation to net colour
Proportion of fish passed through different colour of mesh panels is shown in Figure 21. As we could see from the figure, old white net has the highest
proportion of fish passed through the mesh. Wardle et al. 1991 stated that the net colour appearance underwater was affected by many factors, at low intensities
gillnets made by fine twines chosen to be relatively invisible to the fish. If the luminance of an object matches the luminance of the background then the object
will see as invisible.
w w w
w y
Figure 21. Proportion of fish passed through the net colour
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With one way Anova, the significance of the influence of colour on the frequency of fish passed through the mesh showed no significance different. All
of the net panels are considered to have capability of facilitating fish to pass and the old white net panel is the highest. This means that fish was avoiding the more
visible white transparency.
4.3 Capture Process Experiment 4.3.1 Catch composition
The catch composition of millennium gillnet dominated by threadfins Polynemus spp. for 71.287 of catch. While by-catch were consists of striped
catfish eel Plotosus lineatus, spotted catfish Arius maculatus, great barracuda Sphyraena barracuda, triple tail Labotes surinamensis, barramundi Lates
calcarifer, blue spotted snapper Lutjanus rivulatus, silver pomfret Pampus argentus, stingray Dasyatis spp., garfish Hemirhampus spp. and shark
Charcarinus spp..
Table 6. Species composition in percentage and total length TL of fish caught by millennium gillnet
No English name
Scientific name TL cm
Number of catch
Catch
1 Threadfins Polynemus spp.
34-73 72 71.287
2 Striped catfish eel
Plotosus lineatus 32-82 11
10.891 3 Spotted
catfish Arius maculatus
44-53 7 6.931
4 Great barracuda
Sphyraena barracuda 89-94 2
1.980 5 Triple
tail Labotes surinamensis
45-57 2 1.980
6 Barramundi Lates calcarifer
63-72 2 1.980
7 Blue spotted snapper
Lutjanus rivulatus 30 1
0.990 8
Silver pomfret Pampus argentus
30 1 0.990
9 Rayfish Dasyatis spp.
180 1
0.990 10 Garfish
Hemirhampus spp. 78 1
0.990 11 Shark
Charcarinus spp. 58 1
0.990 Total
101 100
Note: demersal fish
From the Table 6, the catch of millennium gillnet came from various species, but it dominated by threadfins. Most of the catches also were demersal species,
even though actually the target catch of millennium gillnet was pelagic fishes.
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This was because fishermen operated the millennium gillnet in the shallow waters of Bondet Waters around 7-10 m of depth and the distance of fishing operation
just around 0-12 miles from the coastal zone. Since the body net was around 7.8 m of depth then the demersal species were caught by this gillnet.
If this gillnet were operated in deeper and further waters area, the catch were dominates by pelagic species, such as barred Spanish mackerel, frigate tuna,
sailing fish, etc as seen in Karangsong, Indramayu. In Indramayu, millennium gillnet is operated in industrial scale, not the artisanal fishery. They using larger
fishing boat around 20 GT and operates in the ocean and waters more than 12 miles. The period of fishing operation is also longer than in that of Bondet Waters.
Bondet fishermen operates gillnet in one day fishing, while Indramayu fishermen operates this net until a month of fishing.
4.3.2 Capture conditions
Figure 22 and Figure 23 shown that the threadfins were mostly caught in the millennium gillnet by gilled. The class range divided into 6 classes, the largest
frequency is on 48-54.9 cm with 24 fish.
S W
Figure 22. Captured condition of threadfins on class range cm
Figure 22 shown the captured condition of threadfins as the dominant catch of the millennium gillnet. From this figure, most of threadfins concentrated on the
class range of total length around 48 to 54.9 cm. This means that most of threadfins that caught by this gillnet was in the medium size.
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