Poster abstracts and manuscripts from the Third International ...

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better understand the biological characteristics of entangled fur
seals.
Materials and Methods
I analyzed sighting and biological data on northern fur seals
collected by the pelagic research activities conducted under the
Interim Convention on Conservation of North Pacific Fur Seals.
(NPFSC, before 1984) and under the permit of Fisheries Agency,
Japanese Government (1985 and after) in the western North Pacific
and Okhotsk Sea from 1971 to 1987 and 1993. Research track is
shown in Figure 1.
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 species and number of animals. When
visibility dropped to less than about 300 m or beaufort scale
over 3, the survey was interrupted.
Entangled-fur seals were collected, the body lengths and weights
were measured and upper canines, stomachs, and reproductive
organs collected. The upper canines were frozen and stomachs and
reproductive organs were kept in 10% formalin. Age of fur seals
was determined from annual layers on dentine of canines
(Scheffer). Location of ship, weather, wind direction, wind
force, air temperature and water temperature etc., were observed
every hour during research.
Results
Entanglement rate of fur seals at sea
36,218 fur seals were observed in a total research distance of
69,164.l km in the western North Pacific and Okhotsk Sea during
1971-1987 and 1993. Of them, 22 fur seals were entangled. in,
marine debris. Discovery rate of entangled fur seals per year
were from 0.09 to 1.21 seals/l,000 km with a mean of 0.32
seals/l,000 km. Entanglement rates (number of entangled seals /
total observed seals) per year varied from 0.01% to 0.23% with a
mean of 0.06% during whole research periods (Table 1). Entanglement
rate increased from 1971 and attained the peak during
1975-1976 and decreased gradually to 1987. It increased again in
1993 (Fig. 2).
Kinds of entanglement debris
Of the 22 entangled fur seals, one was net-marked (without
debris) and 21 were actually entangled with debris. Of 21 seals
with debris, 17 were entangled in fishing net fragments (67%), 3
in plastic packing bands (14%) and 3 in cord (14%). Fishing net
fragments entangled on male seals accounted for 60% of total
males, and 70% of total females (Fig. 3). Size and weight of
debris were not always recorded-. Weights of two trawl net
fragments entangled on fur seals were 230 g and 500 g in air,
respectively. Whole length of one plastic packing band was 73 cm
(Table 2). One seal had a scar at the neck caused by fishing net
fragments.