Poster abstracts and manuscripts from the Third International ...

Matsumura, Satsuki, Norihisa Baba, Takashi Domon, and Keiichi
Nasu
33
Change of Shape and Ghost Fishing Effect of Released Gillnet in
the Ocean
National Research Institute of Far Seas Fisheries, Fisheries
Agency Shizuoka, Japan
Lost or discharged fishing nets drift in the sea and continue to
catch fish, marine mammals and sea birds. This is called ghost
fishing. In order to deal with this problem, the Fisheries
Agency of Japan has conducted surveys since 1988 -on the adverse
effect of drifting nets on marine organisms. In the surveys that
have been conducted in the first two years, some findings were
obtained on the elapsed time pertaining to change in the
experimental drifting nets, the drifting of lost nets, the
configuration of nets, and the ghost fishing efficiencies.
Forty tans (2,000 meters) of monofilament gillnet with 115mm mesh
were used for the experiment mainly. The experiments on the time
elapsed from the beginning of drifting until the fishing
efficiency becomes zero have been done based on l) observations
on the number of organisms entangled in the lost nets, in
particular the number of fishes and the processes of
decomposition and dropout and on 2) a change of the fishing
efficiency of the lost nets with the passage of time.
The experimental drifting nets started forming an oblong mass
after 3 to 5 days of the deployment.. From the theoretical
equation, it was determined that the maximum length of the net
represented the fishing efficiency of the exponentially sharp
decrease with time.
On the other hand, the investigation of using bio-degradable
drift nets has been discussed. The net material is composed of
polyester made by some kinds of bacteria. A British company ICI
established a technology for mass-reduction of the polyester
marketed under the trade name "BIOPOL". A Japanese fishing net
company made a gillnet from this material. In the fishing
experiment, 3 tans of bio-degradable nets were set between 20
tans and 10 tans of standard nets. As a result, the fishing
efficiency of the bio-degradable nets was almost the same as
ordinal standard nets. Although, the net will be good for
decreasing debris whether at sea or on land, cost and strength
might reduce the practicality of using this material for
commercial fishing nets.