Jacobson et al: Use of parasites to clarify migration of Sardinops sagax 
197 
or repeated spawning by migrants (Emmett et al., 2005; 
Lo et al., 2010). If the Pacific sardine commercially landed 
off British Columbia is from a portion of the northern sub¬ 
population that does not return to California to spawn in 
certain years, it could have management considerations 
for how quotas are determined for both Canada and the 
United States. 
The results of tagging studies conducted between 1936 
and 1942, during the peak of the California fishery, indi¬ 
cate that Pacific sardine routinely migrated from spawn¬ 
ing grounds off San Diego, California, to feeding grounds 
off the PNW and Vancouver Island (Hart, 1943; Clark and 
Janssen, 1945). In recent years, without a sufficient bio¬ 
mass or a reduction fishery to collect tags, repeating large- 
scale tagging studies has not been feasible. Financial costs 
of such studies have been prohibitive because thousands of 
tagged fish are needed to increase the probability of recov¬ 
ery of tagged individuals (Jacobsen and Hansen, 2005). 
The recent use of techniques to examine potential stock 
discrimination and migration patterns of the northern 
stock, such as genetics (Hedgecock et al., 1989; Lecomte 
et al., 2004), size composition (Lo et al., 2011), otolith mor¬ 
phometries (Javor et al., 2011; Javor, 2013), and stable oxy¬ 
gen isotopic signatures (Javor and Dorval, 2014), have had 
mixed results. No genetic differences have been identified 
between the Pacific sardine captured in any region of the 
CCS (Hedgecock et al., 1989; Lecomte et al., 2004). Lo et al. 
(2011) used biomass estimates of different size classes to 
estimate migration of different size classes between the 
PNW and California in 2003-2005. Otolith morphomet¬ 
ries differentiated age-1 Pacific sardine collected from 
Monterey, California, from those collected off San Diego in 
2006-2007 (Javor et al., 2011). Stable oxygen isotopic signa¬ 
tures of otoliths showed some north-south trends for juve¬ 
nile Pacific sardine but no regional differentiation among 
otoliths of adult Pacific sardine (Javor and Dorval, 2014). 
One method that has successfully identified or con¬ 
firmed migration patterns and stocks of marine fish 
species worldwide is the use of parasite species as biolog¬ 
ical tags (Thomas et al., 1996; MacKenzie and Abaunza, 
1998; MacKenzie, 2002). Many parasite taxa can serve 
as biological tags because a fish can become infected 
with a parasite only within that parasite’s endemic area 
(where all conditions for transmission exist). The pres¬ 
ence of a parasite in a fish host caught outside of that 
parasite’s endemic area, therefore, indicates that the fish 
host had previously been in the parasite’s endemic area. 
Parasites of fish can be acquired by direct transmission 
or through trophic transmission, meaning the consump¬ 
tion of infected prey including crustaceans and other 
fish. Once in a fish host, parasites can be relatively long 
lived, remaining in or on the host from months to years, 
depending on the host-parasite association (Rohde, 
1984). The technique of using parasites has limitations, 
such as time-consuming examination of hosts for internal 
parasites, a potential need for molecular techniques for 
correct identification, and a lack of adequate information 
on a parasite’s ecology and biology (reviewed in MacKen¬ 
zie and Abaunza, 1998, 2014). Despite these limitations, 
this technique has often been used by scientific and fish¬ 
eries agencies (Pita et al., 2016), and by 2014 more than 
290 peer-reviewed manuscripts had been published on 
the topic (Timi and MacKenzie, 2015). 
The objective of our research was to determine if para¬ 
sites infecting the northern stock of Pacific sardine could 
be used to identify migration patterns of the northern 
stock of Pacific sardine within the CCS. Our approach 
included comparing 1) the parasite communities of Pacific 
sardine collected from 5 regions along the west coast of 
North America and 2) the parasite communities of Pacific 
sardine to those of the central and northern subpopula¬ 
tions of non-migratory northern anchovy (Engraulis mor- 
dax), which are infected with many of the same parasite 
species (Love and Moser, 1983; Zorica et al., 2015). The 
parasites of northern anchovy could help confirm distribu¬ 
tions of parasites recovered from migratory Pacific sardine 
in the northern CCS. 
Materials and methods 
Fish samples 
From March through November 2005-2008, 1388 Pacific 
sardine were opportunistically collected by research and 
commercial fishing personnel in the CCS, between Van¬ 
couver Island (32° to 51°N) and Southern California 
(119-128°W) (Fig. 1). Pacific sardine from British Colum¬ 
bia were caught with a modified Cantrawl 2 (Cantrawl 
Nets Ltd., Richmond, Canada), a model 240-rope trawl (for 
details, see Morris et al. 3 ). All other Pacific sardine and 
northern anchovy (except for northern anchovy collected 
off Southern California with a seine net) were caught 
using a Nordic 264-rope trawl (for details, see Baldwin 
et al., 2008). Fish collected for this study were immedi¬ 
ately frozen onboard the vessel and later stored at -80°C 
in the laboratory until processed for parasites. 
Pacific sardine ranged in size from 100.6 to 285.7 mm 
fresh standard length (SL). Of 1388 collected specimens, 
562 fish were classified as non-migrants (<200 mm SL) and 
826 fish were classified as migrants (>200 mm SL) (Table 1). 
Following Lo et al. (2011), Pacific sardine <200 mm SL are 
non-migratory. Therefore, we hypothesized that parasite 
communities in this size category of Pacific sardine would 
differ among regions of the CCS. In contrast, migratory¬ 
sized Pacific sardine (>200 mm SL) would have similar 
parasite communities throughout the CCS, if the entire 
population of the northern stock was migrating annually 
from Southern or Central California to British Columbia 
and then returning to California to spawn. 
2 Mention of trade names or commercial companies is for identi¬ 
fication purposes only and does not imply endorsement by the 
National Marine Fisheries Service, NOAA. 
3 Morris, J. F. T., M. Trudel, M. E. Thiess, T. B. Zubowski, H. R. 
Maclean, J. M. R. Curtis, and L. Felli. 2009. CCGS W.E. Ricker 
Gulf of Alaska salmon survey, June 20-July 5, 2007. Dep. Fish. 
Oceans, Can. Data Rep. Fish. Aquat. Sci. 1221,178 p. [Available 
from website.] 
