Poster abstracts and manuscripts from the Third International ...

87
Characteristics of entangled fur seals
Of the 22 entangled fur seals, five were males (23%) and 17 were
females (77%) (Table 2). Males entangled in debris were 1, 2 and
5 years old. 2-year old males accounted for 60% of the total.
Females entangled in debris were from 2 to 23 years old. 2-to-4-
year olds accounted for 47% of total females. Two female seals
entangled in plastic packing bands were pregnant. Mean age of
both male and female fur seals entangled in debris was younger
than that of total seals collected for biological study under the
NPFSC (Fig. 4).
Discussion
Entanglement rate (0.06%) of fur seals including male and female
in the western North Pacific in this study was similar to that
(0.07%) in the eastern Bering Sea surveyed during 1984-1985 and
1988 (Baba et al.). Entanglement rate at sea in this study was
between entanglement rate on Robben Island (0.03-2.19%) and Commander
Islands (0.05-1.15%) (Kuzin). Although the entanglement
rate of fur seals at sea tends to be smaller than that on land,
it may be due to the small researched area and missed observation
of entangled seals at sea. Furthermore, entanglement rate of fur
seals at sea was low level in comparison with female entanglement
rate on St. Paul Island (0.15%, DeLong et al.) and juvenile male
entanglement rate at St. Paul Island (0.3-0.4%, Fowler), Robben
Island (0.83-4.20%) and Commander Islands (0.5202.46%) (Kuzin).
Discovery rate (0.32 seals/l,000 km) of entangled fur seals in
the western North Pacific in this study was about twice that
(0.14) in the eastern Bering Sea (Baba et al.). Fishing net
fragments are dominant in all debris entangled on fur seals, and
this tendency was similar to entanglements at Pribilof Islands,
Robben Island and Commander Islands (Fowler, Kuzin). It may be
because the number of fishing vessels in the western North
Pacific is greater than in the eastern Bering Sea.
Two of 22 entangled seals were decayed and drifted at sea. The
facts indicate that entangled fur seals-die at sea. Male seals
entangled in debris were 1 to 5 years old. Females were 2 to 23
years old. Many young seals under age 4 were entangled. Yoshida
et al. reported that young fur seals are apt to entangle more
than adult seals owing to curiosity of the floating materials.
Although fur seals of various ages may become entangled in marine
debris, I am afraid that entanglement of young fur seals affects
the population.
Acknowledgements
I thank Drs. Kazumoto Yoshida and Naoto Okumato for conducting
the pelagic survey and collecting the sighting data and samples
of fur seals. I thank the crew of the research vessel for their
cooperation in the fur seal research activity.