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.
41
The figure is also shown that most of the fish was caught by gilled, instead of being snagged and wedged. For threadfins, no fish were caught by entangled.
Rengi 2002 who investigated the barred Spanish mackerels caught by drift gillnet in Bengkalis, Riau found that most of fish also caught by gilled. One of the
factors that probably caused this circumstance was the fish morphology compressed or non-compressed. Fishes that have a non-compressed body figure
were most caught by gilled.
y Snagged
Gilled Wedged
Figure 23. Captured condition of threadfins in percentage distribution
The same as Figure 22, Figure 23 is shown that most of threadfins caught by gilled. The largest percentage of fish being gilled was on the class range of 69-
75.9 cm, and 62-68.9 cm of total length. On both class ranges, the total of fish that were caught by gilled was 100 or all of the fish on the class range.
For the by-catch, the captured condition of fish was depends on the species. Two largest by-catch, stripped catfish eel and spotted catfish caught mostly by
gilled and wedged. Stripped catfish eel mostly caught by gilled and wedged while spotted catfish mostly caught by gilled. For the rest of by-catch i.e. great
barracuda, triple tail, barramundi, blue spotted snapper, silver pomfret, stingray, garfish and shark, the captured conditions was come on a variation. The variation
of captured condition depends on the species, but most fish caught by gilled and wedged. Shark was the only species caught by entangled.
42
5 DISCUSSIONS
5.1 Behaviour Study 5.1.1 Fish behaviour in relation to contrast colour net panel
White net, either new white net or old white, were higher in number of fish passing through the net panel comparing than black net. White net new and old
white also considered more significant affecting the number of fish passing through the net.
Tweddle and Bodington 1988 compared the effectiveness of black and white gillnets in Lake Malawi, Africa. They considered that white gillnets are
more effective than black. For the net in Lake Malawi, it was not the invisibility of a gillnet that makes it an efficient catcher of fish, but the nature of its visibility.
It seems that most Lake Malawi fish were more likely to attempt to force a passage through a curtain of white netting rather than black and hence are at
greater risk of getting tangle therein. This probably also happened to the fish in this experiment. Actually, since
fish were able to recognize both existence gillnet white and black. White netting was visible to the school of fish of Jack mackerels, but black net were more
visible. Visual cues found to play an important role in determining the responses of
fish to fishing gear and in particular, fish may prefer to pass through clear passages than darker meshes Glass et al., 1995. Glass and Wardle 1995
showed that fish tried to avoid entering a darkened cod-end black tunnel in a trawl net as they escaped through any available openings head of the tunnel, and
that the insertion of a black tunnel in a net enhanced the escapement of fish through clearer panels. Gray et al. 2000 showed that the low visibility of the
transparent panels of multi-monofilament netting and their contrast with the highly visible of black multifilament explain why sand whiting chose to escape
through the transparent panels. It could also explain why Japanese Jack mackerels avoid passing through the black net panel multi-monofilament.
From the result of the experiment, black net which represents of another gillnet instead of millennium gillnet nylon gillnet, was more visible. Nylon
gillnet has various dark colour, that includes dark blue and dark green. Fishes did the reaction behaviour when they recognized the existence net panel on their
swimming movement, they stop first, and tried to pass the net panel, either way they avoiding the net panel and just swimming in circling. Large mesh perimeter
and hanging ratio made the fish easily to pass the mesh. The result of this study demonstrates the natural behaviour of fish was to
keep clear the netting panel. To keep clear means to swim not too close with unknown object, in this case the net panel. This natural avoidance response is
emphasized by the fact that both netting panel could be recognized by fish. Jack mackerels as pelagic fish, is a typical of obligate schooling fishes.
After they passed through the mesh, they tend to return to its school. This fish was always tried to swim constantly, even though sometimes they seemed less active.
These responses were similar to the result to the herding and avoidance responses shown in the laboratory with school of mackerels Scomber scrombus
and haddock Melanogrammus aeglefinus as they passed into the area of funnel. This experiment was described in Glass et al. 1993, in order to study the
principles underlying mesh penetration. The millennium gillnet twine was diamond shaped mesh, as same as the
shape used in other types of gillnet. The experiment using different types of twine consequently gave different kinds of responses. The square mesh panel elicit the
strongest avoidance response. As the square mesh is split into its constituent horizontal and vertical components, the avoidance response is reduced, but
significant differences also apparent in the reactions of the fish to each component Glass et al., 1993.
White net old and new in each monofile, showed structures acting like vertically arranged mirror. Thus structures helping them less visible to predators
or fish target. Most fishing applications of monofilament lines involve a fish first seeing the material from relatively close up Wardle et al., 1991. In midwater, the
least visible lines are those with a colour which reduces the amount of green illumination as it passes into and out of the transparent material, resulting in a
better match with the background Wardle et. al., 1991. Suppose this was happen
44
