Zwolinski et al.: Distributions and abundances of Sardinops sagax and other pelagic fishes in the California Current Ecosystem 
117 
N Jack mackerel 
Figure 4 
Jack mackerel ( Trachurus symmetricus) biomass densities estimated by combining information from the acoustic and 
trawl samples. The northern and southern boundaries of the strata are shown (dashed lines). 
lowest and the population was more dispersed. Sardine 
were distributed within their potential habitat and were 
generally bounded by it (Fig. 3). In 2006, sardine may 
have extended slightly beyond the survey limits (Fig. 3), 
but there was little potential sardine habitat beyond the 
survey boundary. 
Sardine biomass declined monotonically by 80% be- 
tween 2006 and 2010 (Fig. 6). In 2006 and 2010, the 
confidence intervals of the acoustic-trawl estimates of 
sardine biomass encompassed the biomass from the as- 
sessment. The length distributions estimated from the 
acoustic-trawl data matched well the higher mode of 
those from the assessment, which were derived from the 
length distributions from the fisheries landings (Fig. 7). 
However, the acoustic-trawl length distributions lacked 
age-0 and age-1 fish, i.e., fish less than 15 cm SL, pres- 
ent in the results of the model assessment. Based on the 
acoustic-trawl length distributions, there was evidence 
that the cohorts present in 2006 were severely depleted 
by 2010, and there has not been another strong recruit- 
ment (Fig. 7). The instantaneous mortality rate of the 
sardine population, estimated from the spring acous- 
tic-trawl abundances and the summer 2008 estimate 
(Demer et al., 2012), was 0.56. 
Jack mackerel were the second most abundant CPS 
(Table 3). Their CV values ranged from 28.4% to 36.7%. 
Generally, the population of jack mackerel appears to 
have been encompassed in the survey area. In 2008, 
however, their densities were high near the southern 
limit (Fig. 4). During the study period, jack mackerel 
biomass either increased or remained stable in the 
survey area, but smaller confidence intervals and CV 
values are needed to be more certain of change (Fig. 6). 
Pacific mackerel, compared with sardine and jack 
mackerel, comprised a small fraction of the CPS bio- 
mass, and their CV values are high, resulting from 
their sparse and patchy distribution (Table 3). With 
low biomasses and high CV values, the trajectory of the 
stock size is uncertain (Fig. 6). 
The numbers of anchovy and herring in the catches 
were too low to allow reliable estimations of their bio- 
masses (Table 1; Fig. 1). Nevertheless, on the basis of 
the low number of catches with these species and the 
low acoustic backscatter in the vicinity of those catches, 
their biomasses were likely much lower than those of 
sardine, Pacific mackerel, and jack mackerel. 
Discussion 
Sardine were the most common and abundant CPS in the 
2006-10 trawl catches, and the acoustic— trawl estimates 
