58 
Fishery Bulletin 1 10(1 ) 
and non-CPS, with the following empirically derived 
ranges of S v differences: 
12 ^ S vl8 kHz - S u38 kHz < 20.5; 
p 70 kHz 
-17 < S 
-17 < S yl2 o kHz 
-14 < S^oo kHz “ S 1)38 kHz - ^ dB, 
&v38 kHz - 10 i 
&v38 kHz - I'll an ^ 
and a requirement that the maximum S v and the VMR 
at 38 kHz in the 5-m depth by 100-m distance cells 
exceeded -43 dB and —44.3 dB, respectively. For grid 
cells that did not meet all these criteria, their corre- 
sponding S v values in the noise-free echograms were set 
to -999 dB. The resulting “CPS echograms” were given 
thresholds below S ( ,=-60 dB, which corresponds to a 
density of approximately 2 fish per 100 m 3 in the case 
of 20-cm SL sardine (—0.1 kg per 20-cm sardine). The s v 
values were then integrated within each 5-m depth by 
100-m distance cell between an observational range of 
10 and 70 m depth, or, if the seabed was shallower, to 3 
m above the estimated dead zone (Demer et al., 2009b): 
70 
s A = 4/r(1852) 2 Jsn dz. (1) 
10 
The resulting s A values (m 2 nmi -2 ), attributed to CPS, 
were then apportioned to the epipelagic-fish species by 
using trawl data. Because most CPS schools reside at 
depth during day and ascend to the surface and dis- 
perse to feed during night (Mais, 1974; Table 1), only 
the s A values from the daytime portions of the surveys, 
the period between nautical twilights, were used to 
estimate the distributions and abundances of sardine 
and other CPS. 
Target strength estimation The daytime-s A values cor- 
responding to CPS (<S A cps ) were apportioned to the j 
species present by using the catch mixtures (Table 2) 
in the nearest (space and time) trawl samples (Nakken 
and Dommasnes 2 ): 
w xl0 ((TS - >/10) 
^"X^xlO^^o)^ 3 ’ (2) 
where w l - the proportion of the mass of the catch (kg) 
for the i-th species; and 
<TS t > = its length-weighted mean target strength 
(TS; dB re 1 m 2 kg -1 ). 
In other words, each <TS ; > is a mean TS weighted 
by the distribution of total length (TL) values for the 
sampled fish of that species. The 38 kHz-TS relation- 
ships employed were 
2 Nakken O., and A. Dommasnes. 1975. The application 
of an echo integration system in investigation of the stock 
strength of the Barents Sea capelin 1971-1974. ICES Coun- 
cil Meeting (C.M.) 1975/B:25, 20 p. 
