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Appendix 
The following is a primer on Pacific sardine in the Cali- 
fornia Current Ecosystem (CCE), relevant to acoustic- 
trawl surveys. 
Distribution 
There are two sardine stocks in the CCE, a “northern” 
and “southern” stock, distinguishable with the use of 
serological techniques (Vrooman, 1964), water tem- 
perature (Felix-Uraga et al., 2004; 2005), population 
dynamics, and spawning grounds (Smith, 2005). These 
two stocks do not overlap substantially and are man- 
aged separately. The northern stock is the principal 
target of U.S. and Canadian fisheries and is therefore 
the focus of the U.S. stock assessment and the surveys 
described here. 
During late winter through early spring, the northern 
stock aggregates to spawn in the coastal region between 
Ensenada, Baja California, and San Francisco, Califor- 
nia (Smith, 2005) — typically off the continental shelf 
where micro- and mesozooplankton abundance are at 
maximum abundance (Lynn, 2003). During late spring 
and summer, the stock migrates north to the coastal 
feeding grounds, older fish migrate farther north (Em- 
mett et al., 2005), and returns south offshore in the 
late fall (Zwolinski et al., 2011). Age-one sardine may 
not migrate and instead reside year-round in coastal 
waters where they were recruited (Emmett et al., 2005). 
As in other eastern-boundary currents (Barange et 
al., 2009), sardine in the CCE are highly mobile and 
adapted to the large ranges of temperatures and salini- 
ties associated with variable coastal upwelling. They 
are most prominent in the neritic and coastal regions, 
but seasonally exhibit excursions to 300 nmi offshore 
(Macewicz and Abramenkoff 3 ). Larger sardine tend to 
reside farther offshore. Sardine and other clupeoids re- 
3 Macewicz, B. J., and D. N. AbramenKoff. 1993. Collec- 
tion of jack mackerel, Trachurus symmetricus, off southern 
California during 1991 cooperative U.S.-U.S.S.R. cruise. 
SWFSC-NMFS Admin Rep. LJ 93-07, La Jolla, CA, 13 p. 
spond to oceanographic conditions, and, in the absence 
of predators and competitors, tend to aggregate near 
their prey in monospecific, epipelagic (ca. 0—70 m depth) 
schools (Robinson et al., 1995), comprising similar-size 
fish. Nevertheless, mixed-species schools are not uncom- 
mon (Freon and Misund, 1999; Gerlotto, 1993). 
Feeding 
Sardine can filter-feed on phytoplankton and small 
zooplankton (van der Lingen, 1994) ranging in size 
from tens of pm (Garrido et al., 2007) to a few mm 
(Emmett et ah, 2005). Although lacking teeth, they 
can also particulate-feed on larger prey, depending on 
their densities and types (Garrido et al., 2007; van der 
Lingen, 1994). However, because their gill rakers are 
not completely developed until they reach total lengths 
of approximately 100 mm (Scofield, 1932), small and 
large sardine generally feed on different prey. 
Spawning 
Sardine, like most CPS, are batch spawners and their 
eggs are fertilized in the water column (Blaxter and 
Hunter, 1982). Their fecundity is high, e.g., they spawn 
more than 300 eggs per gram of female mass (Lo 
et al., 2009), and each individual produces several 
egg batches throughout a usually extensive spawning 
season. 
Sardine spawning appears to coincide with times and 
locations with low upwelling, and associated seawater 
temperatures ranging from 13.5° to 16.5 °C (Zwolinski 
et ah, 2011). These areas and conditions provide ad- 
equate food supplies for adult sardine ( Aceves-Medina 
et al., 2009) and their larvae (Lynn, 2003) and are 
conducive to nearshore retention of their eggs and lar- 
vae (Parrish et al., 1981). The peak spawning occurs 
in spring, April and May, off southern California, but 
can occur from January until August, and in higher 
water temperatures. The extent of the spawning sea- 
son appears to be related to the food available to the 
adults, both before and during the spawning season 
(Somarakis et al., 2006; Aceves-Medina et al., 2009). 
Sardine spawning aggregations persist for a few 
hours and comprise actively spawning females and a 
larger proportion of actively spawning males in ad- 
vanced spawning conditions (Zwolinski et al., 2006; 
Ganias, 2008). Sardine eggs are positively buoyant 
and planktonic, but can take several hours to ascend 
to near the sea-surface. Sardine eggs hatch within 2-5 
days, depending on the seawater temperature (Lo et al., 
1986), and the larvae become juvenile sardine within 
two to three months (Lo et al., 1995). 
The success of a reproductive season appears to be 
related to the joint contribution of three physical pro- 
cesses: enrichment, concentration, and retention (Ba- 
kun, 1996). Enrichment refers to high primary pro- 
ductivity. Concentration of these phytoplankton and 
microzooplankton allows efficient consumption by the 
larvae. Retention by eddies and low currents keeps 
