Poster abstracts and manuscripts from the Third International ...

78
Materials and Methods
We conducted sighting surveys of marine debris from June 4 to
August 9 in 1989 and from June 2 to August 4 in 1990 in the North
Pacific and Bering Sea. In 1989, the research vessel cruised off
northern Japan, along the 40°N line from 160°E to 16O°W; thence
south along the 160°W line from 40°N to Hawaii; thence along 30°N
from 160°W to 130°W off California; thence to the Gulf of Alaska,
near shore off the Aleutian Islands, the Bering Sea, off
Kamchatka and Kurile Islands, and returned to Japan (Fig. 1). In
1990, vessel cruised almost the same track-as 1989 except along
about the 47°N line from 160°E to 130°W (Fig. 2).
Sightings were conducted by one or two persons from sunrise to
sunset from the flying bridge (pilot house in rain). Binoculars
were used only to confirm kind and number of debris. When
visibility was less than about 300 m; the survey was interrupted
but vessel continued to cruise. Cruising speed was about 10 knot
while sighting. Observers rotated every hour between the flying
bridge and pilot house.
When debris was observed, time, location, number, size, type of
debris, and distance from vessel to debris were recorded. Ship's
position, weather, wind direction, wind force, air temperature;
and surface water temperature were recorded every hour while
cruising. Types of debris were categorized as fishing net
fragments, other fishing debris except fishing net, plastic (nylon,
vinyl, polyethylene etc.), Styrofoam, glass goods; metal
goods, wood, natural log, and others. Debris was recorded as a
code (Mio and Takehama, 1987).
Sighting data were analyzed by sea regions, off northern Japan,
low (about 40°N line) and high (about 47°N line) in the western
North Pacific, central North Pacific (about 160°W line from 40°N
to Hawaii), low (about 30°N line) and, high (about 47°N line) in
the eastern North Pacific, off California, in the Gulf of Alaska,
near shore of Aleutian Islands and Bering Sea, and off Kamchatka
and Kurile Islands. Sighting width of observer (200 m) was
estimated by number of pieces of-debris per perpendicular
distance (Fig.3). Research area was calculated multiplying the
sighting width by research distance.
Results
Amount of marine debris
3,440 pieces of debris were observed in a total distance of
17,125.l km during the whole research periods. Number of pieces
of debris per l km research distance was 0.20 fragments through
the entire research period. The type of most abundant debris was
petrochemical products (nylon, Styrofoam, vinyl, polyethylene
goods etc.), which composed 76.2% of the total of 3,440 debris
sighted. Other. debris consisted of glass (3.2%), metal (1.3%),
wood (10.7%) and natural log (8.6%) (Table 1). Plastic debris in
petrochemical products except Styrofoam occupied 43% of the total
3,440 debris sighted and styrofoam was 20% (Fig. 4).