Capture Process Experiment Studies On Fish BehaviourIn Relation Net Transparency of Millennium Gillnet Operation In Bondet Waters, Cirebon
operation of 12 pieces gillnet and hauling process. For one day fishing trip, there were 2-3 times setting-hauling process, depends on the weather and current
condition. The catch number of millennium gillnet was dominated by threadfins
Polynemus spp. for 71.2871 of catch. While by-catch 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..
The millennium gillnet, mostly caught threadfins. The slim and long-shape figure and lack of spines on its body makes this fish caught mostly caught on its
gill or caught on its maximum body girth and not to be entangled. There are some theories of how fish encountered gillnet. Some observe that
if a fish encounters a gillnet, it stops its movement temporarily but in shallow water , if the net swing because of waves and tilts to the front, the fish follows the
net and, when the net swings back, the fish get its head caught in a mesh of the net. Nomura, 1991.
Captured conditions depend greatly on the length size and struggling effort. The small fish, which body girth, were slightly smaller than the mesh perimeter
could penetrate the mesh by their head and become finally snagged or gilled. Meanwhile, the medium or large fish whose body girth exceeds the mesh size
could result into the complicated entanglement in the net by their violent struggling. This was happening also by fish that caught in sweeping trammel net
Purbayanto et al., 1999. Struggling effort usually caused injuries on fish body. Purbayanto 1999
described six patterns of damaged body of the dead Japanese whiting Sillago japonica caught by sweeping trammel net in Tateyama Bay, Japan. The patterns
are: 1 minor scale loss on the upper parts of the fish head in front of dorsal fin; 2 scar injuries and minor scale loss around the circumference of the maximum
body girth; 3 scale loss on several parts of the fish body; 4 moderate scale loss
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on the fish body; 5 infections on the head and the fins being rotten; and 6 infections on the head, major fish body, and the fins being rotten.
Most threadfins caught in the experiment did not have any injuries on its body, but they have net-like shape mark caused by fish being gilled. Some fish
have minor scale loss on the upper parts of the fish head and scar injuries and minor scale loss around the circumference of the maximum body girth, the same
as first and second pattern of fish caught by sweeping trammel net. Since the fishes were in the good quality, with no injuries, most fishes sold
in the competitive price. Many of threadfins caught by this gillnet were export market oriented. They distributed this fish into Singapore and Malaysia.
The varieties of millennium gillnet target catch depends on the fish stock underwater and mostly influenced by fishing season. In west monsoon January-
February catch dominates by barred Spanish mackerel Scomberomorus spp. and frigate tuna Auxis thazard. This season concerning as the peak season of
millennium gillnet fishing. In east monsoon Juny-July sometimes barred Spanish mackerel and frigate tuna also get caught. In the monsoon betweens, the catch
dominated by threadfins. This explained why mostly gillnet catch in October- November was dominated by threadfins.
The multi-monofilament, the millennium gillnet material, has a very strong and flexible feature. Underwater, it could stretch and loose easily so then when the
fish entering the net, they easier to enter but difficult to escape. This material structure influencing the fish that caught by this gillnet. Probably because of this
reason, mostly fish caught without less of struggle and makes the fish has less injuries.
According of Stewart 1987 as cited by Ferno and Olsen 1994, the type of twine used in the net can, owing to differences in texture, influence the species
and the size range of fish caught. Comparative fishing experiments using twisted multifilament, monofilament and multi-mono nylon in loosely hung cod gillnets
produced very different size distributions of catches. The total of catch rates for the three net types were not very different, but as an example twisted
multifilament caught many smaller fish than monofilament. The most striking result of the investigations was the way that fish were caught in the three net types.
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Stewart 1987 as cited by Ferno and Olsen 1994 indicated that these results were due to differences in texture between the used gillnet. With
monofilament, which is hard and stiff, cod were mainly gilled, while with multifilament, which is soft, cod were mainly tangled. With multi-mono, the
proportion of tangled and gilled cod were somewhere in between. Even though, mostly targeted species of this experiment mostly caught by gilled, the reason of
the texture of the material influencing the captured condition was considering reasonable.
From the result of behaviour experiment and capture process experiment that was conducted, it was revealed that the fish used in behaviour experiment was
a pelagic fish while mostly catch were dominated by demersal fish. This is important to discuss regarding of different types of fish pelagic or demersal has
different characteristics. The most consequential problem is the difference characteristics of visual acuity between pelagic and demersal fishes. Demersal fish
has not good visual acuity. Geonita 2004 described that the visual acuity of red snapper Lutjanus malabaricus is around 0.08-0.13 for the fish length of 100-185
mm. This statement indicates that waters in dark condition without enough light penetration and bad visibility will reduce the visual acuity of a fish. For the
pelagic fishes, for example frigate tuna Euthynnus affinis, the visual acuity is around 0.14-0.19 for the fish length of 285-375 mm. The clear condition of waters
and larger of fish’s length make frigate tuna has good visual acuity. In this experiment, the visual acuity of fish did not investigate through
histological experiment. But the fact that the field experiment caught mostly demersal fishes is an unexpected result. At first, some interview from the local
fishermen explained that the millennium gillnet is operates to catch pelagic species, such as barred Spanish mackerels, frigate tunas, sharks, and other types of
mackerels. But from the result of experimental fishing, demersal fishes dominate the catch. It means that the local fishermen operates this type of gillnet not only to
catch pelagic species but also demersal species. This situation makes another research regarding the demersal fishes behaviour is also need to investigate. This
is important to implement in order to understand the demersal fishes behaviour in relation to millennium gillnet.
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6 CONCLUSIONS AND RECOMMENDATIONS