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Fishing debris accounted for 18.3% of the petrochemical debris;
gillnet floats alone comprised 15.0% of the total petrochemical
debris. Fishing net fragments (35 trawl net fragments, 27
gillnet
of the total petrochemical debris observed (Fig. 5).
fragments, 3 unknown net fragments) were minor components
As the
results of collecting the fishing net fragments, weight of two
fishing net fragments were more than several hundred kilograms.
They consisted of many kinds of trawl nets, gillnet, ropes, and
other strings, and those fragments were bound (Photo 1).
net fragments were mainly observed from June 24 to 30 in 1989
while cruising in the central North Pacific (Fig. 6).
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Density of marine debris
Fishing
Density (number/km 2 ) of marine debris was high in the center of
North Pacific (about 160°W line from 40°N to Hawaii, l.0/km 2 )
and off North America (0.6/km 2 ). It was low in the Bering Sea.
offshore area off Alaska, Kamchatka and Kurile Islands (under
0.2/km2). The highest densities of marine debris occurred in the
northeastern area off Hawaii (1.4/km 2 ) and the coastal area off
northern Japan (1.3/km 2 ). Distribution of plastic debris density
were similar to that of total debris density except off California
(Table 2).
Distribution characteristics of marine debris
Percentages of marine debris observed in the North Pacific and
Bering Sea are shown in Table 3. Percentage of wood and natural
log were higher than 14.4% in the Bering Sea, offshore area off
Alaska, Aleutian Islands, Kamchatka, and Kurile Islands except
high latitude (47°N line) of western North Pacific (53.1%). On
the other hand, percentage of petrochemical products were higher
than 82.1% off northern Japan, central North Pacific, and in the
north eastern area off Hawaii and low, less than 46.7%, off
California, Alaska Bay, Aleutian Islands, Bering Sea, off
Kamchatka, and Kurile Islands.
Discussion
Distribution of total density of marine debris in this study was
similar to results of Mio et al. and Day et al. Density of wood
and natural log were higher in the north area and lower in the
middle area of North Pacific. On the contrary, density of
petrochemical products was higher in the middle area and lower in
the north area of North Pacific. This result may be related to
human population and number of towns.
Matsumura et al. reported that marine debris in the North Pacific
may accumulate in the northeastern area off Hawaii. Density of
marine debris was highest off northern Japan and in the northeastern
area off Hawaii. This tendency was shown on change of
daily number of Styrofoam, vinyl, polyethylene, plastic observed
in 1989's survey (Fig. 7) and 1990's survey (Fig. 8).
Furthermore, many fishing net fragments were observed in the
northeastern area off Hawaii. Kuroshio extension flows to the
central North Pacific (Favorite et al. 1976) Matsumura et al.
indicated that a large gyre current exists in northeast area off
Hawaii. The northeastern area off Hawaii is recognized as an