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Fishery Bulletin 110(1) 
the larvae from being advected to open ocean where 
the food supply, and thus the probability of surviving, 
is low. Intense upwelling, although nurturing primary 
productivity, can result in suboptimal feeding conditions 
(Uehara et ah, 2005). A moderately stable water column 
is thus needed for concentration of the food and success- 
ful development of larvae (Lasker, 1981). Sardine re- 
cruitment improves during warm periods, characterized 
by an expansion of their habitat (; Lluch-Belda et ah, 
1991; Jacobson et al. 1 ), low-intensity coastal upwelling, 
and increased wind-stress-curl upwelling (Rykaczewski 
and Checkley, 2008). 
Sizes 
Sardine exhibit rapid growth and early maturation 
(Blaxter and Hunter, 1982), becoming mature during 
their first or second year of life. Increased length at 
maturity is associated with lower water temperature 
and higher latitude and population size. Sardine grow 
to standard lengths of 41 cm (Miller and Lea, 1972) and 
normally live for as many as 8 years (Butler et al., 1996). 
Physiology 
Sardine and anchovy are physostomous, possessing a 
swim bladder with a pneumatic duct to the stomach 
and an anal duct to the cloaca (Whitehead and Blaxter, 
1989). Like other clupeoids, sardine inflate their swim 
bladders by swallowing air at the surface and by forcing 
it from the stomach through the pneumatic duct into 
the swim bladder. These swim bladder features allow 
them to perform rapid vertical migrations, typically to 
the sea-surface to feed at night (Cutter Jr. and Demer, 
2008), and predominantly contribute to their high acous- 
tic backscatter (Foote, 1980). 
