206 
Fishery Bulletin 117(3) 
(10%) indicates that either transmission of the parasite 
occurs on a small scale in northern regions of the CCS 
or a very small number of Pacific sardine <200 mm SL 
made the migration north. Moreover, the recovery of 
only 7 Pacific sardine infected with both L. gibbosus and 
M. ecaude and of only 3 Pacific sardine >200 mm SL in 
Northern California infected with L. gibbosus indicates 
that a complete migration to and from British Colum¬ 
bia, or even Washington and Oregon, for all migratory- 
size Pacific sardine did not occur during the years of our 
study. 
Other parasites recovered from Pacific sardine that 
contributed to differences among regions include the 
nematodes and the acanthocephalan that are both long- 
lived taxa. For example, Anisakis nematodes, which 
mature in cetaceans, accumulate as long-lived larvae in 
fish intermediate hosts and have been successfully used 
as biological tags for many fish populations (MacKen- 
zie, 2002; Mattiucci et al., 2008; Mattiucci and Nascetti, 
2008). In our study, there was also a greater abundance 
of Anisakis spp. in large Pacific sardine recovered off 
Central and Southern California, possibly because of a 
greater abundance of the definitive whale hosts in these 
regions of the CCS (Calambokidis and Barlow, 2004). 
Genetic identification of larval anisakids from a subset 
of Pacific sardine used in our study revealed a panmictic 
distribution of 3 populations of Anisakis spp., but these 
populations could not help inform stock structure or 
migration behavior of Pacific sardine in the CCS (Bald¬ 
win et ah, 2011). The acanthocephalan Rhadinorhyn- 
chus trachuri, also longer-lived than the trematodes, is 
known to be a parasite of offshore fish species (George- 
Nascimento, 2000; Jacobson et ah, 2012). Although less 
commonly recovered than the nematodes, it was recov¬ 
ered more often from the large Pacific sardine caught 
south of British Columbia. Its low abundance in large 
Pacific sardine from British Columbia indicates that 
fewer of these fish had been offshore compared with 
those from other regions, another line of evidence for res¬ 
idency in waters of British Columbia. 
The spatial distributions of parasites in marine fish spe¬ 
cies have often reflected large geographical patterns such 
as latitudinal gradients (Blaylock et ah, 1998; Gonzalez 
and Poulin, 2005; Gonzalez et ah, 2006). A combination 
of environmental gradients and dispersal limitation of 
hosts and different developmental stages of parasites 
contribute to the latitudinal distribution of marine par¬ 
asites (Oliva and Gonzalez, 2005; Gonzalez et ah, 2006; 
Gonzalez et ah, 2008; Timi et ah, 2010). For Pacific hal¬ 
ibut ( Hippoglossus stenolepis), a general north-south 
cline of parasite species distributions has been described 
from the Aleutian Islands, Alaska, to Northern Cali¬ 
fornia (Blaylock et ah, 1998). Separate stocks of Pacific 
halibut, with some overlapping migration patterns, were 
confirmed by using their parasite communities, but one 
continuous stock was identified south of the Queen Char¬ 
lotte Islands of British Columbia (Blaylock et ah, 2003). 
Similarly, in our study, the distributional patterns of par¬ 
asites showed high residency in British Columbia and an 
overlapping migration pattern for Pacific sardine south 
of British Columbia with a potential latitudinal gradient 
(Fig. 2A). 
In the eyes of fish collected off South Africa, where this 
species is known as the South African sardine, Weston 
et ah (2015) found a significant difference in the abundance 
of a “tetracotyle” type larval trematode, tentatively identi¬ 
fied as Cardiocephaloides sp. (Reed et ah, 2012), and that 
difference supports the existence of a putative western 
and a putative southern stock with some degree of mixing. 
After 6 years of continuous data on the prevalence of this 
larval trematode from the west and south coasts of South 
Africa, de Moor et ah (2017) fit a sardine stock assessment 
model directly to parasite prevalence-by-length data and 
found that this inclusion of parasitological data improved 
estimates of annual movement and mixing between these 
semi-discrete stocks. 
Migration north 
Following the early tagging studies (Clark and Janssen, 
1945), it has been assumed that Pacific sardine >200 mm 
SL, which are capable of migrating (Lo et ah, 2011), migrate 
north from Southern California in the spring when ocean 
conditions in the north are favorable. We found no signif¬ 
icant differences between the parasite communities of 
Pacific sardine <200 mm SL and those of Pacific sardine 
200-209 mm SL, indicating that there is not a clear cut off 
at 200 mm SL at which a Pacific sardine will migrate. A 
recent paper by McDaniel et ah (2016) that included size 
and age data for Pacific sardine from British Columbia, 
Oregon and Washington, and Central and Southern Cal¬ 
ifornia during 1981-2010 described a pattern of increas¬ 
ing age at length with distance from Southern California. 
They concluded that their results provide evidence that 
the migration of the northern subpopulation of the Pacific 
sardine to the northern reaches of their range in summer 
is age based, instead of length based. 
Sardine biomass and length data from surveys that 
combined data from acoustic and trawl sampling and 
were conducted in the spring and summer of 2008 
indicate that most, if not the entire, northern stock of 
Pacific sardine migrated from offshore waters of South¬ 
ern California to inshore waters of the PNW and Brit¬ 
ish Columbia (Demer et al., 2012). Unfortunately, we 
did not collect Pacific sardine from British Columbia in 
2008, but our results from other years do not support the 
conclusion that the entire stock migrates that far north. 
Although our parasite community analysis was sugges¬ 
tive of a statistically significant difference only between 
the Washington and Oregon region and the Central 
California region for Pacific sardine <210 mm SL (pair¬ 
wise PERMANOVA: P=0.06), the greater abundance of 
M. ecaude in Pacific sardine <210 mm SL in all California 
regions compared with that of the Pacific sardines from 
Washington and Oregon (Fig. 3) indicates that a propor¬ 
tion of Pacific sardine up to 210 mm SL may remain as 
residents in their natal regions. In addition, our samples 
of Pacific sardine >220 mm SL caught off Central and 
