Jacobson et al.: Use of parasites to clarify migration of Sardinops sagax 
205 
of P. merus in this size category made them cluster with the 
northern anchovy from Southern California, where P. merus 
had a 31.2% contribution to the parasite community. 
Discussion 
Regional comparisons 
The paradigm that when the northern stock of Pacific sar¬ 
dine is large and ocean conditions are favorable all Pacific 
sardine >200 mm SL, or some other length, migrate to 
northern waters and then all return to Central and South¬ 
ern California seasonally each year to spawn may no lon¬ 
ger be supported. We found that Pacific sardine were not 
uniformly infected with the same trophically transmitted 
parasite communities throughout the CCS, indicating 
that not all Pacific sardine of the northern subpopulation 
made the complete round-trip migration during the years 
studied. The parasite communities of all size categories of 
Pacific sardine collected off British Columbia were more 
similar to each other than to all sizes collected from any 
other region. The correct allocation in the CAP analysis of 
70-80% of these parasite communities to British Colum¬ 
bia indicates that, during the years studied, a large pro¬ 
portion of Pacific sardine in British Columbia remained as 
residents, not returning to Central or Southern California 
to spawn. Differences among parasite communities from 
the region off Washington and Oregon and the 3 regions 
in California were not statistically significant, although 
a north-south trend was apparent in the nonmetric MDS 
plot (Fig. 2A). 
Several taxa of parasites contributed to differences in 
the parasite communities among regions and size cat¬ 
egories of Pacific sardine. Among these, the trematode 
L. gibbosus was recovered primarily off British Colum¬ 
bia from all sizes of Pacific sardine and not from any 
sardines examined from Central and Southern Califor¬ 
nia. In contrast, the trematode M. ecaude was recovered 
in greatest abundances in small Pacific sardine from 
California regions and only from 5% of Pacific sardine 
collected in British Columbia. The parasite communi¬ 
ties recovered from California regions also had higher 
abundances of the nematode Hysterothylacium sp. than 
those collected off British Columbia. Distinct distribu¬ 
tional patterns of these parasites indicate that not all 
Pacific sardine of the northern stock make an annual 
roundtrip migration connecting the terminal regions of 
their habitat. 
Regional differences in the parasite communities of 
Pacific sardine are supported by observed regional differ¬ 
ences among parasite communities of northern anchovy. 
This other small, pelagic species generally harbors para¬ 
site species known to infect the Pacific sardine (Love and 
Moser, 1983), and, as a non-migratory species (Bakun, 
1996), northern anchovy should host parasite species pres¬ 
ent in a local geographical area. We found a significant 
difference among the parasite communities of all 3 north¬ 
ern anchovy collections, a finding that agrees with the 
distributions of parasites recovered from Pacific sardine. 
The parasite community of northern anchovy collected 
from Grays Harbor had high similarity to those of Pacific 
sardine from British Columbia and supported a restricted 
northern distribution of L. gibbosus in the CCS. The north¬ 
ern anchovy from Southern California (part of the central 
subpopulation of northern anchovy) had a higher preva¬ 
lence of Hysterothylacium sp., similar to the Pacific sar¬ 
dine collected there. 
Parasites as biological tags 
Parasite life span and life history are important con¬ 
siderations for selecting parasite taxa as biological tags 
(MacKenzie and Abaunza, 1998, 2014). The parasite 
communities of Pacific sardine in this study included 
both long-lived nematodes and shorter-lived trematodes. 
The maximum life span of the trematode L. gibbosus 
was reported to be 1-9 months in pink (Oncorhynchus 
gorbuscha) and chum (O. keta) salmon captured off cen¬ 
tral British Columbia (Margolis and Boyce, 1969). We 
recovered both mature and immature L. gibbosus in 
Pacific sardine off British Columbia from March through 
November, but we recovered none off Southern Califor¬ 
nia, not even among April samples that were thought 
to include returns from British Columbia. The complete 
absence of L. gibbosus in our samples of large Pacific sar¬ 
dine caught off Southern California could be interpreted 
3 ways: 1) our samples from Southern California were 
not representative of the Pacific sardine in the region at 
the time, 2) Pacific sardine did not return from British 
Columbia to Southern California, or 3) the life span of 
L. gibbosus is too short to be recovered after a return 
migration south. However, given that some of the 
L. gibbosus specimens recovered off British Columbia 
in November were still immature, their life span would 
have to be less than 5-6 months if this was the only 
reason for their absence from Pacific sardine caught in 
Southern California the following April. 
The other trematode that contributed to differences 
in parasite communities among regions was M. ecaude. 
Unfortunately, little information is available on the 
distribution and life history of this species in the CCS. 
However, we have confidence that this trematode and 
L. gibbosus have sufficiently long life spans to evalu¬ 
ate seasonal movements of their fish hosts. In the CCS, 
M. ecaude has been previously reported from Pacific sar¬ 
dine caught off Baja California, Mexico (Sanchez-Serrano 
and Caceres-Martinez, 2017), off Southern California 
(Montgomery, 1957; Kunnenkeri, 1962), and off south¬ 
ern Oregon (Jacobson et ah, 2012). These reports and 
our observations of the high abundance of this parasite 
in small Pacific sardine in Central and Southern Cal¬ 
ifornia compared to other regions and size classes of 
Pacific sardine suggest that the southern region of the 
CCS is likely the primary region of parasite transmis¬ 
sion. However, the recovery of M. ecaude from a small 
percentage of Pacific sardine <200 mm SL caught off 
British Columbia (9%) and off Washington and Oregon 
