Jacobson et al.: Use of parasites to clarify migration of Sardinopssagax 
207 
Southern California in the spring had a greater abun¬ 
dance of the long-lived nematodes Hysterothylacium sp. 
and Anisakis spp. than those caught off Washington and 
Oregon and British Columbia in summer and fall. If the 
entire biomass of large Pacific sardine were migrating 
north, we would have expected to see the same abun¬ 
dance of these long-lived parasites throughout the CCS. 
Return migration south 
Lo et al. (2011) estimated different length-specific migra¬ 
tion rates in 2003-2005 between the PNW and California 
and estimated that close to 50% of Pacific sardine 200- 
210 mm SL and close to 100% of Pacific sardine >220 mm 
SL migrated back to California in the fall and winter of 
2003 and 2004. Similar to our conclusions, they questioned 
whether fish <200 mm SL remained as residents in the 
PNW because they had only weak evidence that some of 
these small fish returned to California. They concluded 
that not all Pacific sardine migrate and that some stay in 
the PNW and California (their study did not include Brit¬ 
ish Columbia). Our results indicate that a high proportion 
of Pacific sardine of all size classes remained in waters of 
Canada during the period of our study and that waters 
off Washington and Oregon could be an area of mixing 
between regions for large Pacific sardine but could also 
support local recruitment. 
In the McDaniel et al. (2016) study, Pacific sardine 
from British Columbia and from Oregon and Washing¬ 
ton collected from July through December were older 
than those from Central and Southern California. They 
did not have data from January through March, and age 
and length data from April through June were presented 
only for California catches, but the ages of the largest 
and oldest Pacific sardine from California at all seasons 
were still younger than those from Oregon and Wash¬ 
ington and from British Columbia. Although they state 
that their work assumed a single migrating population 
and that subpopulation structure could compromise their 
results of an age-based migration, they do not account 
for the difference in maximum ages between locations 
except for the unlikelihood of gear selectivity or different 
aging techniques. Our results indicate not only that they 
could indeed have documented age-based migration but 
also that their results could additionally reveal residency 
of fish in northern regions of the CCS, in contrast to the 
notion of a single migrating population. Similarly, Dorval 
et al. (2015) reported a reduction in the size distribution 
of Pacific sardine caught off California during 2005-2010 
compared with that in 1996-2004. The larger size classes 
(250 and 260 mm SL) present in the survey conducted 
in spring 2004 off California were not recorded again 
during the 2005-2010 survey (Dorval et al., 2015). They 
speculated that Pacific sardine >250 mm SL that did not 
return after a northern migration either remained in the 
north or were removed by fishing. These observations 
are not the first to suggest overwintering of Pacific sar¬ 
dine in northern regions of the CCS, as spawning had 
previously been reported in 1998 and 2004 in waters of 
Canada (McFarlane et al., 2005) and during 1994-1998 
and 2003-2004 in the PNW (Bentley et al., 1996; Emmett 
et al., 2004). 
Management implications 
Migration rates (the percentages of the population mov¬ 
ing into other regions) are an important factor for man¬ 
aging transboundary fish stocks like the northern stock 
of Pacific sardine. Schweigert et al. 5 estimated annual 
migration rates to British Columbia on the basis of dif¬ 
ferences in biomass of Pacific sardine caught during sur¬ 
veys conducted off the west coast of Vancouver Island and 
the total biomass estimate for the coast-wide population 
as presented by Hill et al. 6 in the annual U.S. sardine 
assessment. During the years of our study, Schweigert 
et al. 5 estimated an average migration rate of 27.2% in 
2006 and 34.7% in 2008. Their survey was not conducted 
in 2007, and in 2005 it was an incomplete survey from 
which they estimated a 13.2% annual migration rate. 
The significant differences among parasite communities 
of Pacific sardine from British Columbia and of those 
from all other regions indicate that the relatively large 
biomass (>200,000 metric tons, Schweigert et al. 5 ) found 
off the coast of Vancouver Island in those years consisted 
of a large proportion of Pacific sardine that remained as 
residents of British Columbia waters as well as migrants 
from the southern regions. 
The examination of allozymes among Pacific sar¬ 
dine from regions of Mexico and California (Hedgecock 
et al., 1989) and of mitochondrial DNA throughout the 
CCS (Lecomte et al., 2004) and among Mexican regions 
(Garcfa-Rodrlguez et al., 2011) provides evidence for no 
genetic stock structure in the CCS. However, although 
Lecomte et al. (2004) state that their mitochondrial DNA 
data support a basin modal for the Pacific sardine in which 
a species distribution contracts to a central optimal range 
during population crashes, they also state that on shorter 
time scales local recruitment may dominate. At this time, 
our parasite data from Pacific sardine cannot provide quan¬ 
titative information on migration rates, nor do they indi¬ 
cate distinct stock structure, but they do elucidate patterns 
of migration, residency, and periodic local recruitment and 
indicate that a greater variability in annual migratory 
behavior of Pacific sardine should be considered. A holis¬ 
tic inclusion of multidisciplinary approaches and tech¬ 
niques (as reviewed in Baldwin et al., 2012; Catalano et al., 
2014; Pita et al., 2016) that advances our understanding 
of economically and ecologically important species should 
improve management of Pacific sardine, even in the 
5 Schweigert, J., G. McFarlane, and V. Hodes. 2010. Pacific sar¬ 
dine (Sardinops sagax) biomass and migration rates in British 
Columbia. Dep. Fish. Oceans, Can. Sci. Advis. Seer. Res. Doc. 
2009/088,13 p. [Available from website.] 
6 Hill, K. T., E. Dorval, N. C. H. Lo, B. J. Macewicz, C. Show, and 
R. Felix-Uraga. 2008. Assessment of the Pacific sardine resource 
in 2008 for U.S. management in 2009,147 p. Agenda item G.2.b., 
Suppl. attach. 1. Pacific Fish. Manage. Counc., Portland, OR. 
[Available from website.] 
