Comparative Parasitology 67(2) 2000 - Peru State College

220 COMPARATIVE PARASITOLOGY, 67(2), JULY 2000
Table 3. Prevalence of Uncinaria lucasi in intestines of northern fur seal pups at necropsy in some
previous surveys on St. Paul Island, Alaska, U.S.A.
Reference Year of study
Lucas (1899)* 1897
Olsen (1954) 1952
Olsen (1954) 1953
Olscn (1956, 1958) 1955
Lyons and Olsen (1960) 1960
Rookery
Gorbatch
Kitovi
Lagoon
Lukanin
Northeast Point
Polovina
Reef
Tolstoi
Zapadni
Total
Unknown
Polovina
Kitovi
Polovina
Reef
Tolstoi
Vostochnif
Zapadni
Total
Little Polovina
Polovina
Reef
Vostochnit
Zapadni
Total
No. of pups
Examined Infected (%)
33
17
4
12
10
10
57
109
93
345
42
26
28
164
4
100
112
100
553
30
112
63
30
17
252
* These data apparently are for causes of death of pups due to U. lucasi rather than actual prevalence.
t A rookery on Northeast Point.
rain. The ground where fur seals now breed on
the 2 rookeries (Northeast Point and Reef) in the
present study is generally rocky. Previously,
when populations of fur seals were much higher,
breeding animals were more widely dispersed to
include sandy surfaces on these rookeries
(E.T.L., personal observation). Possibly the decline
in numbers of animals breeding on sandy
areas has contributed to the dramatic decrease in
prevalence of U. lucasi.
Table 4 summarizes literature on prevalences
of adult U. lucasi in northern fur seal pups in
some localities other than St. Paul Island. On the
Commander Islands (Bering Island and Medny
Island), Russia, and the Channel Islands (San
Miguel Island), California, U.S.A., the hookworm
prevalence is currently high, based on examinations
of relatively small numbers of dead
pups.
No definite cause has been determined for the
spectacular decline of hookworm infections in
northern fur seal pups on St. Paul Island. Per-
Copyright © 2011, The Helminthological Society of Washington
15 (45)
7 (41)
0(0)
7 (58)
7 (70)
6 (60)
12 (21)
52 (48)
38(41)
144 (42)
38 (90)
24 (92)
5 (18)
120 (73)
13 (27)
73 (73)
89 (79)
67 (67)
367 (66)
20 (67)
86 (77)
35 (56)
22 (73)
1 1 (65)
174 (69)
haps it is related to one or more unknown factors
in combination with a corresponding decline in
the herd. Numbers of fur seals in the 20th century
peaked in the 1950s and 1960s and began
to decline in the 1970s (Trites, 1992). Estimated
size of the fur seal population on the Pribilof
Islands (St. Paul Island and St. George Island)
was about 1.5 million in the 1960s (Baker, 1957;
Riley, 1961). This population is now estimated
at about 973,000 (York et al., 2000). The overall
population decreased about 40% in the last 40
years, but the number of pups born declined
much more; i.e., about 60% or from about
500,000 to 200,000 (York et al., 2000).
Although it is known that parasitic third-stage
larvae (L3) of U. lucasi can live for many years
in the tissues of northern fur seals, there is no
definite information on the time period or number
of lactations for clearance of these larvae
through the mammary system. In experimental
infections of the nematode Strongyloides ransomi
Schwartz and Alicata, 1930, in pigs, colos-